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Volume 35 • ACS-7
November 2009

Recommendations Regarding the Management of Bat Exposures to Prevent Human Rabies

Preamble

The National Advisory Committee on Immunization (NACI) provides the Public Health Agency of Canada with ongoing and timely medical, scientific, and public health advice relating to immunization. The Public Health Agency of Canada acknowledges that the advice and recommendations set out in this statement are based upon the best current available scientific knowledge and is disseminating this document for information purposes. People administering the vaccine should also be aware of the contents of the relevant product monograph(s). Recommendations for use and other information set out herein may differ from that set out in the product monograph(s) of the Canadian manufacturer(s) of the vaccine(s). Manufacturer(s) have sought approval of the vaccine(s) and provided evidence as to its safety and efficacy only when it is used in accordance with the product monographs. NACI members and liaison members conduct themselves within the context of the Public Health Agency of Canada's Policy on Conflict of Interest, including yearly declaration of potential conflict of interest.

Change in Recommendations Regarding Bat Exposures

This statement outlines a change to the recommendations for rabies post-exposure management of bat exposures. Since publication of the fifth edition of the Canadian Immunization Guide in 1998, NACI has recommended rabies post-exposure prophylaxis (RPEP) for persons sleeping unattended in a room where a bat is present and the possibility of a bite cannot be excluded(1), unless the bat tests negative for rabies. This recommendation was subsequently expanded to include persons in the same room as a bat who could not report that a bite had occurred, such as a child or cognitively impaired person(2,3). In practice, bats in adjacent rooms were also often considered to be potential exposure situations.

The 1998 Canadian recommendation was originally based on case reports from the United States where a bat strain of rabies virus was isolated from people without obvious reported bat exposures. It was suggested that rabies may have developed as a result of unrecognized exposures while the person was sleeping, since bat teeth are so fine that bites could have gone unnoticed. Because of the possibility of unrecognized exposures, in 1995, the Centers for Disease Control and Prevention (CDC) advised consideration of post-exposure prophylaxis for “persons potentially exposed to bats even where a history of physical contact cannot be elicited(4) and later “in situations in which a bat is physically present and the person(s) cannot exclude the possibility of a bite(5).

Researchers have since reviewed this approach and determined that when there is no obvious contact with a bat, the risk of rabies is extremely rare. Furthermore, there are considerable resource implications to implementing this strategy. Based on the review, which is outlined below, NACI is now recommending intervention only when both of the following conditions apply:

  • There has been direct contact with a bat;  and
  • A bite, scratch, or saliva exposure into a wound or mucous membrane cannot be ruled out.

Recommendation Grade A - There is good evidence to recommend

Direct contact is defined as the bat touching or landing on a person. NACI no longer recommends RPEP when there is no contact involved. Any direct contact of a bat with skin or mucous membranes is considered a reason for intervention unless a bite, scratch, or saliva exposure into a wound or mucous membrane can be ruled out. In an adult, a bat landing on clothing would be considered reason for an intervention only if a bite, scratch, or saliva exposure into a wound or mucous membrane could not be ruled out. In a child, any direct contact with a bat should be considered a reason for an intervention, including contact through clothes, as a history to rule out a bite, scratch, or mucous membrane exposure may not be reliable. When a bat is found in the room with a child or an adult who is unable to give a reliable history, assessment of direct contact can be difficult. Factors indicating that direct contact may have occurred include the individual waking up crying or upset while the bat was in the room, or observation of an obvious bite or scratch mark.

Intervention is defined as testing the bat for rabies, if it is available, and/or RPEP as indicated.

This statement will review the rationale for this change in recommendation and provide details regarding the recommended approach to the management of bat exposures. This statement deals with common exposures to bats and does not address the issue of spelunkers who are exposed to bats in caves.

Methodology

In developing the recommendations in this statement, NACI reviewed published and unpublished data and consulted with bat biologists and a medical ethicist.

Bats and Rabies

Bats in Canada and the United States are insectivorous, meaning they eat insects. They do not feed on the blood of animals, as do vampire bats found in Central and South America. Bat species in North America can be classified as “colonial” or “solitary”. Colonial bats congregate in groups in protected areas such as caves, under bridges, or in buildings, and are therefore in proximity to humans. Solitary bats live on their own in wooded areas and are often found in trees or shrubs. As well, some species of bats are migratory while others hibernate over the winter.

Any species of bat can be infected with the rabies virus. Species of bats in which rabies is found in Canada include but are not limited to the big brown, little brown, silver-haired, hoary, red, California, and long-eared bats(6,7). Both the big brown bat and little brown bat are colonial species that can live in colonies of 100 or more bats. They live in caves or human dwellings where they hibernate over the winter(7). The number of big brown bats and their proximity to humans is likely what makes the big brown bat the most commonly reported rabid species in Canada. The silver-haired and hoary bats are solitary, tree-dwelling species and tend to have less human contact(8).

Encounters with colonial bats are most common in the second half of the summer when the young are learning to fly(9). Colonial bats with rabies rarely exhibit furious behaviour; they generally exhibit symptoms of exhaustion, weakness, and paralysis when rabid. This serves to protect the colony and the virus, because if the rabid bat behaved aggressively and the virus was efficiently transmitted, the whole colony would die, eliminating the virus from circulation(10). The big brown bat, a common colonial bat in Canada, has not been associated with a single case of human rabies in the past 15 years(11).

In contrast, solitary bats, such as the silver-haired bat, develop furious rabies and actively attack other bats or other animals(10). The rabies virus variant associated with the silver-haired bat is of note since it is the strain responsible for 15 of the 21 human deaths due to bat-associated rabies in the United States between 1980 and 1997(8). Two of the three Canadian cases from 1990 to 2007 may have also been due to the rabies virus variant associated with the silver-haired bat(12 ,13). It is hypothesized that the silver-haired bat rabies virus variant may have enhanced pathogenicity, including being more effective in replicating at the inoculation site(14). The silver-haired bat’s aggressive behaviour when rabid may also facilitate transmission.

Since the 1980s, the development of monoclonal antibody technology and nucleotide sequencing has allowed bat strains of rabies to be characterized(7,15). Based on these testing methodologies, there are multiple strains or variants of bat rabies viruses. One strain tends to have a principal bat species host; however, multiple strains can be found within one species of bat and the same strain can be found across several species of bats(16). As an example, the silver-haired bat rabies virus had been identified primarily in the silver-haired bat and more recently in the eastern pipistrelle, although it can be found in other species such as the big brown bat as well(17).

The prevalence of rabies in wild bats is generally unknown, although older studies from the 1960s suggest a prevalence between <1% and 4.1%(18,19). Among routinely tested species, the number of positive bats is higher in colonial bats because they are more likely to be submitted for testing; however, the proportion of tested bats with positive test results is higher for solitary bats since it is relatively rare for humans to encounter healthy solitary bats(18). Studies of the prevalence of rabies in bats submitted for testing are prone to bias because it is more likely that an ill rabid bat will be captured and tested than a healthy bat.

The Canadian Food Inspection Agency (CFIA) conducts rabies testing on submitted animals, including bats. This testing is carried out mainly when there is a possible exposure involving a human or animal, or for special studies. In 2006, the CFIA tested 2,150 bats, of which 72 (3.3%) were positive(6). The distribution of tests and positivity rates by province/territory is shown in Table 1. It should be noted that some of the rates are influenced by the small number of bats submitted for testing.

Table 1: Distribution of bat tests and positivity rates, by province/territory, 2006
Province/territory Number tested Number positive Positivity rate (%)
Northwest Territories 0 0 0
Yukon 0 0 0
Nunavut 0 0 0
British Columbia 181 11 6
Alberta 26 4 15
Saskatchewan 26 4 15
Manitoba 4 3 75
Ontario 1,329 42 3
Quebec 519 8 2
New Brunswick 26 0 0
Nova Scotia 25 0 0
Prince Edward Island 13 0 0
Newfoundland 0 0 0
CANADA 2,150 72 3

 

A study of Canadian rabies virus tests, mainly from 1987 to 1998, noted that rabid bats in Canada exhibit marked regional variation(7). Higher numbers of rabid bats were reported in Ontario and Western provinces (Alberta and British Columbia), fewer positive bats were reported from the Prairie provinces (Saskatchewan and Manitoba), and only occasional reports were made in Eastern regions (New Brunswick, Nova Scotia, Quebec, and Prince Edward Island). Reports of rabies-positive bats in recent years reveal significantly higher numbers of rabid bats in Ontario, with British Columbia and Quebec having lower numbers, and most other provinces/territories having very few, if any, positive bats(20). The number of rabid bats could be influenced by a variety of factors, including the human population sizes of the provinces/ territories (which influences the number of bats submitted for testing), the type of bats present in a particular area and the prevalence of rabies in the bat population.

Table 2: Bats tested for Rabies in Canada, 2007
Bat species Total number tested Total number positive (%)
Big brown bat 1,887 70 (4%)
Little brown bat 430 7 (2%)
Yuma bat 73 3 (4%)
Northern long-eared bat 21 0 (0%)
California bat 16 1 (6%)
Long-eared bat 18 4 (22%)
Silver-haired bat 10 0 (0%)
Keen’s bat 9 0 (0%)
Others* 9 1 (11%)
Bat species not identified 17 0 (0%)
Total 2,490 86

* includes eastern pipistrelle bat, hoary bat, red bat, western big-eared bat, western small-foot bat.

 

Table 2 indicates the species of bats submitted for testing to the CFIA in 2007 and the percentage positive by species(21). It can be noted that most of the bats tested are big brown bats (1,887 of the 2,490, or 76% of the total), but strains isolated from human rabies are most often associated with solitary bats such as the silver-haired and eastern pipistrelle, which represent 0.48% (12 of the 2,490) of tested animals. Of the big brown bats, approximately 4% were rabid, while none of the specimens from the silver-haired bats or eastern pipistrelle bats were rabid in 2007. It should be noted that bat testing is done based on specimens submitted. Although every effort is made to ensure accuracy, determining the species of bat submitted can be difficult, potentially leading to misclassification(21).

In a review of Quebec’s public health follow-up of bat encounters over a two-year period (from October 2004 to September 2006), bats were submitted for virologic testing in 34% of the 957 reported bat exposure events and the submitted bats tested positive 5% of the time(22). When there was known direct contact with the bat, the positivity rate was higher (10%) compared with a positivity rate of 3% when the bat was present in the household with no known direct contact. Similarly, a study in Colorado(8) of bats submitted for testing between 1977 and 1996 found 30% positivity rates among the 233 tested bats that had bitten a person, compared to 14% positivity among the 4,237 tested bats that had not bitten a person. Overall, 15% of the 4,470 bats that were tested were determined to be rabid. In contrast, in the CFIA study of 2,150 bat submissions from 2006, the positivity rates were lower in bats submitted for testing that had had known direct human contact (45 of 1,567 submissions, or 2.9%) compared with bats submitted that had had no known human contact (27 of 440, or 6.1%)(6).

Spillover of bat rabies into non-bat species is rare but does occur. Other animals that have rarely been found to be infected with bat rabies in Canada include one or more foxes, cows, horses, squirrels, skunks, dogs, and cats(7,23,6). In 2007, a hamster that was being cared for in a classroom tested positive for rabies after bats were noted in the school. This virus was not typed, so its definitive strain of rabies is unknown(21). No human cases of bat-strains of rabies have been known to be transmitted from exposure to other animals.

Review of literature related to bats and bat encounters

Canadian researchers have conducted a series of studies to identify the following:

  • the incidence of human bat-related rabies;
  • the frequency and types of bat exposures;
  • the proportion of eligible persons reached by the previously recommended interventions;
  • the number needed to treat to prevent one case associated with particular types of encounter with bats; and
  • the resources required to prevent a case of human rabies.

These studies and their findings are described below. As well, the section includes information on the safety of rabies immune globulin and rabies vaccines.

Incidence of bat-related rabies in humans

De Serres et al. reviewed all human case reports of bat rabies from January 1950 to September 2007 in the United States and Canada as published in the Morbidity and Mortality Weekly Report and Canada Communicable Disease Report(15). Excluding five transplant-related cases, 56 bat-related rabies cases were identified, which translates to a rate of bat-related rabies in humans of 3.9 cases per billion person-years. Of the 56 human cases, 6 occurred in Canada. Rates were similar in Canada and the United States.

Prior to the late 1970s, bat-related human rabies was diagnosed based on a history of bat exposure, which in some instances was difficult to obtain since the diagnosis was made post-mortem. Since the 1980s, anti-nucleocapsid monoclonal antibody and nucleotide sequencing detection methods have been able to identify the strain of rabies in human cases, so human recall is not necessary to make the diagnosis of bat-related rabies. From 1990 to September 2007, when the diagnosis of bat-related rabies was more reliable, 36 bat-related human cases were identified in the United States and Canada resulting in an incidence rate of 6.7 cases per billion person-years. Two of the 36 cases involved children less than 10 years of age. One involved a bat found in the bedroom of a 4-year-old child, with no obvious marks on the child. The other involved a 9-year-old from Quebec who was staying in a cabin where two bats were found. He noted a mark on his arm about three days later (described below)(13).

Of the 36 bat-related human cases from 1990 to September 2007, the types of exposures reported were as follows:

  • Direct contact with the bat – 19 (52.8%)
    • With recognized bite – 10 (27.8%)
    • Without recognized bite – 9 (25%)
  • History of household exposure – 6 (16.7%)
  • No history of exposure – 11 (30.5%)(15)

Of the 17 cases with no direct contact with the bat, only 2 (11.8%) would have qualified for post-exposure prophylaxis based on the expanded criteria first suggested in 1995 where post-exposure prophylaxis is recommended when a bat is found in the room of a sleeping person(15). Based on these data, it can be estimated that, even with no intervention, a case of human rabies related to bedroom exposure to a bat is expected to occur in Canada once every 84 years(25).

In Canada between 1990 and 2007, there have been only three reported human cases of bat rabies as follows:

  • 9-year-old boy from Quebec (2000)(13) — Two bats were found and removed from the cabin where he slept, one of which was observed to have difficulty flying. There were also noises in the cabin from what was thought to be a colony of bats in the roof or attic. The boy did not report a bite but about three days later he reported a lesion 2 cm in diameter with a central laceration on his upper arm. The strain of rabies that was identified has been associated with the silver-haired and eastern pipistrelle bats.
  • 52-year-old male from British Columbia (2003)(26) — He had no previous reported exposure but was an avid outdoorsman and reported to relatives that he had been around bats in abandoned cabins in British Columbia in the previous year. The virus strain isolated from this individual was a variant associated with the Myotis species of bats, the most common of which is the little brown bat.
  • 73-year-old male from Alberta (2007)(12) — While sleeping, he was bitten by a bat, which he killed and discarded. The strain of rabies was a variant that has been associated with silver-haired bats.

The reported number of human rabies cases in Canada between 1990 and 2007 indicate that bat-related human rabies is very rare, with a human bat-related case expected once every five years.

Frequency and type of bat exposures

To estimate the frequency of bat exposures in 2006, a random digit dial phone survey was conducted in Quebec between January 15 and March 30, 2007(27). Household members with bat exposures were interviewed individually. Parents (with the assistance of the child) responded for children less than 14 years of age who had been exposed to a bat.

A large proportion of households (63% of the valid phone numbers) participated in the survey. The 14,453 households that agreed to participate resulted in 36,445 individuals completing the survey. A total of 156 people reported exposure to or the presence of a bat in the house as follows:

  • no one reported being bitten by a bat;
  • 4 individuals reported direct contact with the bat with no bite (one individual reported that this occurred twice in 2006);
  • 34 individuals reported a bat in the bedroom;
  • 41 reported a bat in another room that had access to the bedroom; and
  • 77 reported other indoor exposures.

The above information was extrapolated to the population of Quebec (population 7.6 million) to determine the frequency of the various types of bat exposures and an estimate of the number of individuals in Quebec exposed in 2006. These results are summarized in Table 3.

Table 3: Estimate of the proportion of the population of Quebec with bat exposures,* 2006
Type of contact Number of exposed individuals from survey Estimated proportion of population with annual exposure Estimated number of individuals exposed per year in Quebec
Direct contact, no bite 4 1 in 10,000 751
Household exposure with no known contact 152 43 in 10,000 32,640
  • Bedroom
34 10 in 10,000 7,548
  • Another room with bedroom access
41 12 in 10,000 8,869
  • Other household exposure
77 21 in 10,000 16,223

*based on a telephone survey of 36,445 persons

 

Proportion of eligible persons reached by the previously recommended interventions

Canadian researchers retrospectively reviewed all investigations by Quebec public health units of human encounters with bats between October 1, 2004, and September 30, 2006(22). During the two-year study period, 957 bat encounters were reported involving 1,933 individuals. Of the 1,875 individuals with sufficiently detailed records, 8% had direct contact with a bat and a bite was known to have occurred, 6% had direct contact with a bat but no bite was reported, 23% had a bat in their bedroom where they slept, 42% reported a bat in another room, 8% had a bat in an unspecified room, and 13% had other non-specific encounters that are not considered indications for RPEP. Of the 1,081 individuals who received RPEP, 20% had had direct contact with a bat with or without a bite, 30% had found a bat in their bedroom, 48% had found a bat in another room or unspecified room, and 3% had had non-specific encounters.

Combining the information regarding the number of individuals with a reported bat exposure in Quebec in 2006(22) and the estimated frequency of bat encounters from the same year derived from the random digit dial telephone survey described above, the researchers were able to estimate the percentage of all exposures that were reported and followed-up by public health(27).This analysis concluded that only a small proportion of those exposed to a bat reported these exposures to public health: 7% of all people with direct bat contacts with no bite; 3% of all instances where the bat was found in the bedroom with no known contact; and 4% of all instances where the bat was found in the bedroom or another room with bedroom access with no known contact.

Of those who participated in the Quebec telephone survey(27), 79 people would have been eligible for post-exposure follow-up and/or prophylaxis based on the recommendations that existed at the time of the survey. The exposure histories for these individuals included 4 people with direct contact, 34 people with bedroom exposure, and 41 people with a bat in another room with access to the bedroom. Only 2 (2.5%) sought and received RPEP; these individuals were from the latter group.

Number needed to treat to prevent one case associated with particular types of encounter with bats

Based on the incidence of human rabies cases and the rates of bat exposures for various categories, the researchers were able to determine a “number needed to treat” to prevent a case of human rabies for the various categories of exposures. The treatment in this instance consists of testing the bat for rabies and/or administering RPEP. It was determined that to prevent one case of rabies from the presence of a bat in the bedroom, approximately 2,670,000 people needed to be treated. Using a conservative estimate that assumes that all cases of rabies with no direct contact are in fact bedroom or similar types of exposures where rabies could be prevented, 314,000 people would need to be treated to prevent one case of human bat-related rabies(27). These results are summarized in Table 4.

Table 4: Number needed to treat for various categories of exposure
  Categories of Exposure
Direct contact Household contact without direct contact
Without bite Known bedroom Assuming all human cases with household contact were bedroom or similar types of exposures that warranted follow-up and/or RPEP
Number of human rabies cases between 1990 and 1997 in the U.S. and Canada 9 2 17
Incidence (per million person-years) 1 in 601 million 1 in 2,706 million 1 in 318 million
% exposed in the population ~1 in 10,000 ~10 in 10,000 ~10 in 10,000
Number needed to treat 59,000 2,668,000 314,000

 

Resources required to prevent a case of human rabies

To determine the resources required to prevent a case of human rabies, the researchers determined the professional time required to manage each type of exposure, along with the cost of RPEP and virological analysis of the bat(22,27). They determined that to prevent one case of human rabies due to bedroom exposure required 2,463 professionals (doctors, nurses, and veterinarians) devoting all of their time to the follow-up and management of bat exposures. In addition, at $1,000 per course of RPEP and $250 per virological analysis, it would cost approximately $2 billion for rabies immune globulin, rabies vaccine, and the cost of virological tests of the bats to prevent one human case of rabies from bedroom exposures. Using more conservative estimates that assume that all cases of rabies with no direct contact are in fact bedroom or similar types of exposures where rabies could be prevented under previous recommendations, at least 293 professionals were required to dedicate all of their time to prevent one case of human rabies, and the total cost for rabies vaccines, rabies immune globulin, and virological testing was $228 million.

Vaccine Safety

Although rabies immune globulin and rabies vaccine are both safe and effective products, as with all medications they should be used only where the benefit-risk analysis clearly indicates that they are warranted, as they do carry small risks as outlined below.

Rabies immune globulin: Rabies immune globulin is a blood product prepared from pooled venous plasma from individuals immunized with rabies vaccine. Testing of the donors and manufacturing processes significantly reduce the risk of transmission of blood-borne infections. Although it has never been known to cause any blood-borne infections, it should not be used unnecessarily. Anaphylactic reactions have rarely been reported after injection of human immune globulin preparations(28).

Human diploid cell vaccine (HDCV): Local reactions such as pain, erythema, swelling, and itching at the injection site may occur in 30% to 74% of recipients with Imovax® Rabies vaccine; mild systemic reactions such as headache, nausea, abdominal pain, muscle aches, and dizziness may occur in about 5% to 40%. Systemic allergic reactions characterized by generalized urticaria and accompanied in some cases by arthralgia, angioedema, fever, nausea, and vomiting have been reported. These reactions are uncommon in people receiving primary immunization but have occurred in up to 7% of those receiving a booster dose, with onset after 2 to 21 days. Such reactions have been shown to follow the development of IgE antibodies to beta propiolactone-altered human serum albumin in Imovax® Rabies vaccine. Immediate anaphylactic reactions have occurred in 1 in 10,000 people given HDCV. Neurologic complications are rare, but three cases of neurologic illness resembling Guillain-Barré syndrome, which resolved without sequelae within 12 weeks, were reported in the early 1980s(3) .

Purified chick embryo cell vaccine (PCECV): Local reactions commonly reported (i.e., > 10% of recipients) with RabAvert® consist of pain, tenderness, and induration at the injection site, which lasted for 2 to 3 days. Other local reactions, including erythema, itching, and swelling, have also been reported. Systemic reactions are generally less common (i.e., 1% to 10% of recipients) and may consist of malaise, myalgia, arthralgia, headache, and fever. Lymphadenopathy, nausea, and rash have been reported occasionally. Temporally associated neurologic and anaphylactic events have been very rarely reported following the administration of RabAvert® (3) .

A study was conducted to determine the adverse events related to Rabavert® reported through the Vaccine Adverse Event Reporting System (VAERS) in the United States from October 20, 1997, to December 2005(29). During this time period, approximately 1.1 million doses of vaccine were distributed in the United States. There were a total of 336 reported adverse events during this time, of which 24 were reported as serious, requiring hospitalization in 20 cases. Thirteen of the serious events were neurologic in nature, but there was no particular pattern among the events to suggest a plausible relation to vaccine. Of the reported events, 96 necessitated an emergency room visit. The data indicated 20 reports of anaphylaxis (14 probable and 6 possible), all of which were non-fatal, although one occurred while driving.

Summary of the Rationale for the Change in Recommendations Related to Bat Encounters

The following summarizes the rationale for recommending that intervention related to bat exposures occur only when there has been direct contact with a bat and a bite, scratch, or saliva exposure into a wound or mucous membrane cannot be ruled out.

  • Human rabies from bats is very rare. Even with no management, a human case of bat-related rabies is expected only once every 5 years in Canada. This is despite the fact that rabies in captured, tested bats is fairly common.
  • Approximately half of the very rare bat-related human rabies cases are due to direct contact with the bat.
  • Recommendations for post-exposure management when a bat is found in the room with an individual who could not report an exposure, such as a sleeping person, have been in place in Canada since 1998(1). Studies from Quebec indicate that these occurrences are fairly common, occurring in ~10 out of 10,000 population, and that these occurrences are reported less than 5% of the time(27). Therefore, very low human rabies rates in Canada cannot be attributed to post-exposure management guidelines recommended previously.
  • Using conservative parameters, it is estimated that 314,000 individuals need to receive follow-up to prevent one human rabies case when a bat is found in a room with a person who cannot report an exposure and no direct contact has been reported(27). This is a very resource-intensive activity with very limited benefit.
  • Although rabies immune globulin and rabies vaccine are safe and effective, adverse events do occur. When the benefit of the intervention is very small, as in the case of RPEP for situations where a bat is found in the bedroom or other room in the house with no direct contact, the risk of the intervention becomes relatively more important.

Based on the above, NACI no longer recommends vaccination when there is no direct contact with a bat. (Recommendation Grade D – Fair evidence against immunization).

NACI recommends vaccination when there is direct contact and a bite, scratch, or mucous membrane exposure cannot be ruled out (Recommendation Grade A – Good evidence for immunization). The literature to support these recommendations is summarized in Table 8.

Recommendations Regarding Bat Testing

No direct contact with the bat: If there has been no direct contact with the bat as defined in this statement, the bat should not be captured for testing. Attempting to capture the bat puts the individual at risk of coming into direct contact with the bat, which potentially exposes them to rabies. If the bat is inadvertently tested and comes back positive, the determination of the need for RPEP should depend on whether direct contact with the bat occurred and not the rabies status of the bat.

To get the bat out of the house in circumstances where there has been no direct contact, the area with the bat should be closed off from the rest of the house. People and pets should be kept away from the area. The doors or windows in the area with the bat should be opened to the exterior, allowing the bat to escape(30).

Direct contact with the bat: If there has been direct contact with the bat as defined in this statement, it is best to call a trained animal control or wildlife professional to capture the bat, if possible. Capturing the bat and testing it will mean that RPEP is not needed if the results come back negative. Extreme care should be taken to ensure that there is no further exposure to the bat if it is captured.

If attempting to capture the bat, the person should always wear thick leather gloves and place the bat in a closed secure container(30). Once the bat has been captured, the local public health department should be contacted. They will arrange with the CFIA to send the bat for rabies testing.

Rabies testing of animals is done using a fluorescent antibody test, which is the gold standard recommended by the World Health Organization. It has a reported sensitivity of 98% to 100%(31). If the test is negative and there was human exposure to the bat, additional testing is done using the rabies tissue culture inoculation test(6).

Recommendations for Post-Exposure Prophylaxis for Bat Exposures

Immediate washing and flushing of the wound with soap and water is imperative and is probably the most effective procedure in the prevention of rabies. Tetanus vaccination should be updated if required.

For people who have not previously received rabies vaccine for pre-exposure or post-exposure prophylaxis, rabies immune globulin (RabIg) is recommended for post-exposure prophylaxis along with rabies vaccine. If possible, the full dose of RabIg should be thoroughly infiltrated into the wound and surrounding area. If this is not anatomically feasible, any remaining volume of RabIg should be injected, using a separate needle and syringe, intramuscularly at a site distant from vaccine administration. If the site of the wound is unknown, the entire dose should be administered intramuscularly.

For previously unimmunized individuals, five doses of 1.0 mL of human diploid cell vaccine or purified chick embryo cell vaccine are indicated, the first dose (on day 0) should be given as soon as possible after exposure, with additional doses given on days 3, 7, 14 and 28 after the first dose. Vaccine should be administered intramuscularly into the deltoid muscle or the anterolateral upper thigh in infants but never in the gluteal region, as this may result in decreased effectiveness. Rabies vaccine should not be given in the same syringe or at the same site as RabIg.

Individuals who have received pre-exposure or post-exposure rabies vaccine in the past require only two doses of vaccine given on days 0 and 3 and do not require RabIg. Consult the most recent version of the Canadian Immunization Guide and applicable erratum for more details(3).

NACI recommends that RPEP be initiated immediately when there is a known bat bite, scratch, or saliva exposure in a wound or mucous membrane. This is particularly important when exposure involves the face, neck, or hands, or when the behaviour of the bat is clearly abnormal, such as when it hangs on tenaciously or when the bat has attacked the person. If the bat is available for testing, RPEP can be discontinued if the bat is found not to be rabid. In some instances where the exposure is less certain, such as when the bat touches the individual while in flight, the clinician may feel it is safe to delay RPEP if the bat is available for testing. If RPEP is indicated based on the NACI recommendations, it should never be delayed beyond 48 hours while waiting for bat testing results.

This recommendation is based on expert opinion.

Recommendations for Pre-exposure Prophylaxis for Bat Exposures

People who are likely to encounter bats as part of their work, such as animal control or wildlife professionals, should receive pre-exposure rabies vaccination. Pre-exposure vaccinations are provided using human diploid cell vaccine or purified chick embryo cell vaccine on days 0, 7, and 21 or 28. Consult the most updated version of the Canadian Immunization Guide regarding the use of intramuscular versus intradermal administration(3). Serologic testing is recommended after use of intradermal vaccination and at 6-month to 2-year intervals with ongoing exposure, regardless of the route of vaccination.

Recommendations for Preventing Bat Exposures

Bats can crawl through openings as small as 1.5 cm by 2.0 cm. Common points for bats to enter houses include chimney tops; the area around the chimney; through vents, open doors, windows or broken screens; or under doors, siding, eaves, or loose roof shingles.

To prevent bats from entering a house, ensure that all screens are intact and secure and that doors close tightly, including doors in the attic. Chimneys should be capped and any openings into the house that are larger than a dime should be caulked or netted as appropriate. Fill electrical and plumbing holes with stainless steel wool or caulking.

If bats are roosting in a house, the homeowner should consult with an animal control or wildlife professional. The bats must leave the building before entrances can be sealed to prevent re-entry. This cannot be done from May to August when the young bats that cannot fly are present in the roost. Bat proofing is best done in the winter when the bats have left the roost, and is best done by a professional.

Children should be advised never to touch a bat and to promptly report any direct contact with a bat to an adult. Domestic pets should be kept up-to-date with their rabies vaccinations.

Table 5: Levels of evidence based on research design

I
Evidence from randomized controlled trial(s)
II-1
Evidence from controlled trial(s) without randomization
II-2
Evidence from cohort or case-control analytic studies, preferably from more than one centre or research group using clinical outcome measures of vaccine efficacy
II-3
Evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled experiments (such as the results of the introduction of penicillin treatment in the 1940s) could also be regarded as this type of evidence.
III
Opinions of respected authorities, based on clinical experience, descriptive studies, and case reports, or reports of expert committees.

 

Table 6: Quality (internal validity) rating

Good
A study (including meta-analyses or systematic reviews) that meets all design- specific criteria* well.
Fair
A study (including meta-analyses or systematic reviews) that does not meet (or it is not clear that it meets) at least one design-specific criterion* but has no known “fatal flaw.
Poor
A study (including meta-analysis or systematic reviews) that has at least one design-specific* “fatal flaw.

 

* General design-specific criteria are outlined in Harris et al.(32)

Table 7: NACI recommendations for immunization

A
NACI concludes that there is good evidenceto recommend immunization.
B
NACI concludes that there is fair evidenceto recommend immunization.
C
NACI concludes that the existing evidence is conflicting and does not allow making a recommendation for or against immunization; however, other factors may influence decision-making.
D
NACI concludes that there is fair evidence to recommend against immunization.
E
NACI concludes that there is good evidence to recommend against immunization.
I
NACI concludes that there is insufficient evidence (in either quantity and/or quality) to make a recommendation; however, other factors may influence decision-making.

 


Table 8: Summary of evidence used to support rabies prophylaxis for individuals with direct contact with a bat
Study Study type/ description Number of participants Outcome measure Level of evidence Quality
De Serres et al. 2008(15) Literature review of published human rabies cases from 1950 to 2007 61 cases:
  • 5 transplant-related cases excluded
  • 56 analyzed
  • includes 36 cases from 1990 to 2007 when diagnosis of bat-related human rabies more specific due to improved technology 
Case of bat-related human rabies in North America III Good
  • extensive search of available literature
Huot et al. 2008(22) Retrospective cohort review of bat encounters reported to public health authorities in Quebec from October 1, 2004, to September 30, 2006 957 bat encounters involving 1,933 individuals:
  • sufficient information available on 1,875 individuals

Type of exposure to bats

Management of reported cases

Professional and monetary resources required to manage the various types of bat exposures

II-2 Good
De Serres et al. 2009(27) Random digit dialling telephone survey in early 2007 regarding household bat exposure in 2006 36,445 individuals from 14,453 households; representing 63% of households with valid telephone numbers

Type of exposure to bats to determine frequency of exposures in the population

Management of exposure

Under-reporting of cases

Number needed to treat

Professional and monetary resources required to manage the various types of bat exposures

III Fair
  • relied on recall of exposure

 

References

  • (1) National Advisory Committee on Immunization. Canadian Immunization Guide. 5th ed. 1998. p. 151.
  • (2) National Advisory Committee on Immunization. Canadian Immunization Guide. 6th ed. 2002. p. 194.
  • (3) National Advisory Committee on Immunization. Canadian Immunization Guide. 7th ed. 2006. p. 285-298.
  • (4) Centers for Disease Control and Prevention (CDC). Human Rabies, Alabama, Tennessee and Texas, 1994. MMWR — Morbidity & Mortality Weekly Report 1995; 44(14):269-272.
  • (5) Centers for Disease Control and Prevention (CDC). Human Rabies, Washington, 1995. MMWR — Morbidity & Mortality Weekly Report 1995; 44(34):625-627.
  • (6) Fehlner-Gardiner C, Muldoon F, Nadin-Davis S, et al. Laboratory diagnosis of rabies in Canada for calendar year 2006. Canadian Veterinary Journal 2008; 49(4):359-361.
  • (7) Nadin-Davis SA, Huang W, Armstrong J, et al. Antigenic and genetic divergence of rabies viruses from bat species indigenous to Canada. Virus Research 2001; 74(1-2):139-156.
  • (8) Pape WJ, Fitzsimmons TD, Hoffman RE. Risk for rabies transmission from encounters with bats, Colorado, 1977-1996. Emerging Infectious Diseases 1999; 5(3):433-437.
  • (9) Kuzmin I, Rupprecht C. Bat Rabies. In: Jackson A, Wunner W, editors. Rabies. 2 ed. London, England: Elsevier and Academic Press; 2007. p. 269.
  • (10) Kuzmin I, Rupprecht C. Bat Rabies. In: Jackson A, Wunner W, editors. Rabies. London, England: Elsevier and Academic Press; 2007. p. 276.
  • (11) Tuttle M. Bat Conservation International Living in Harmony. (Accessed April 1, 2009).
  • (12) Centers for Disease Control and Prevention (CDC). Human rabies—Alberta, Canada, 2007. MMWR — Morbidity & Mortality Weekly Report 2008; 57(8):197-200.
  • (13) Turgeon N, Tucci M, Deshaies D, et al. Human Rabies in Montreal, Quebec — October 2000. Canada Communicable Disease Report 2000; 26(24): 209-10.
  • (14) Kuzmin I, Rupprecht C. Bat Rabies. In: Jackson A, Wunner W, editors. Rabies. London, England: Elsevier and Academic Press; 2007. p. 272.
  • (15) De Serres G, Dallaire F, Cote M, et al. Bat rabies in the United States and Canada from 1950 through 2007: Human cases with and without bat contact. Clinical Infectious Diseases 2008; 46(9):1329-1337.
  • (16) Brass D. Insectivorous Bats and Rabies in Canada. Rabies in Bats, Natural History and Public Health Implications. Ridgefield, Connecticut: Livia Press; 1994. p. 191-192, 209-211.
  • (17) Kuzmin I, Rupprecht C. Bat Rabies. In: Jackson A, Wunner W, editors. Rabies. 2 ed. London, England: Elsevier and Academic Press; 2007. p. 277.
  • (18) Brass D. Prevalence and distribution of rabies in insectivorous bats. Rabies in Bats, Natural History and Public Health Implications. Livia Press, Ridgefield, Connecticut; 1994. p. 143.
  • (19) Kuzmin I, Rupprecht C. Bat Rabies. In: Jackson A, Wunner W, editors. Rabies. 2 ed. London, England: Elsevier and Academic Press, 2007. p. 267.
  • (20) Canadian Food Inspection Agency. Positive Rabies in Canada. (Accessed February 1, 2009).
  • (21) Personal communication. Wandeler A. October 10, 2008.
  • (22) Huot C, De Serres G, Duval B, et al. The cost of preventing rabies at any cost: Post-exposure prophylaxis for occult bat contact. Vaccine 2008; 26(35):4446-4450.
  • (23) Brass D. Insectivorous Bats and Rabies in Canada. Rabies in Bats, Natural History and Public Health Implications. Ridgefield, Connecticut: Livia Press; 1994. p. 208.
  • (24) British Columbia Centers for Disease Control. Rabies. (Accessed February 1, 2009).
  • (25) De Serres, G. Rabies Post-exposure prophylaxis after bat exposure. Presentation to NACI. February 2008.
  • (26) Parker F, McKay D, Hawes C, et al. Human Rabies, British Columbia — January 2003. Canada Communicable Disease Report 2003;29(16):137-8.
  • (27) De Serres G., Skowronski DM, Mimault P, et al. Bats in the bedroom, bats in the belfry: Re-analysis of the rationale for rabies post-exposure prophylaxis. Clinical Infectious Diseases 2009;48;1493-99.
  • (28) sanofi pasteur. Imogam Rabies Pasteurized Product Monograph.[PDF] (Accessed February 1, 2009).
  • (29) Dobardzic A, Izurieta H, Woo EJ, et al. Safety review of the purified chick embryo cell rabies vaccine: Data from the Vaccine Adverse Event Reporting System (VAERS), 1997-2005. Vaccine 2007; 25(21):4244-4251.
  • (30) Centers for Disease Control and Prevention (CDC). Bats and Rabies. (Accessed February 1, 2009).
  • (31) OIE. Manual of Diagnostics and Vaccines for Terrestrial Animals.[PDF] (Accessed March 31, 2009).
  • (32) Harris R, Helfand M, Woolf S, et al. Current methods of the US Preventive Services Task Force: A review of the process. American Journal of Preventive Medicine 2001; 20:21-35.

Members: Dr. J. Langley (Chairperson), Dr. B. Warshawsky (Vice-Chairperson), Dr. S. Virani (Executive Secretary), Dr. Natasha Crowcroft, Ms. A. Hanrahan, Dr. Bonnie Henry, Dr. K. Laupland, Dr. D. Kumar, Dr. A. McGeer, Dr. S. McNeil, Dr. C. Quach-Thahn, Dr. B. Seifert, Dr. D. Skowronski, Dr. B. Tan.

Liaison Representatives: Dr. B. Bell (CDC), Dr. P. Orr (AMMI Canada), Ms. S. Pelletier (CHICA), Ms. K. Pielak (CNCI), Dr. P. Plourde (CATMAT), Dr. S. Rechner (CFPC), Dr. M. Salvadori (CPS), Dr. C. Cooper (CAIRE), Dr. N. Sicard (CPHA), Dr. V. Senikas (SOGC).

Ex-Officio Representatives: Dr. S. Desai (CIRID – Vaccine Preventable Diseases),
Dr. P. Varughese (CIRID), Dr. R. Ramsingh (FNIHB), Dr. F. Hindieh (BGTD).

Acknowledgements

This statement was prepared by Drs. Bryna Warshawsky and Shalini Desai and approved by NACI and the Public Health Agency of Canada. NACI gratefully acknowledges the work of Drs. Robert Barclay, Mark Brigham, Paul Faure, Dean Middleton, Ross Upshur, Jackie Badcock, Alex Wandeler, and Christine Fehlner-Gardiner for their contribution to the development of the statement.