Human immunodeficiency virus (HIV) infection together with acquired immunodeficiency syndrome (AIDS) caused by HIV are important public health problems in Canada. It has been estimated that among the approximately 49,800 people living with HIV infection at the end of 1999, 4,190 were newly infected in 1999. Between 1981 and 1999, a total of 16,913 AIDS cases were reported in Canada1. HIV infection causes a broad spectrum of disease and has a varied clinical course, from mild, flu-like symptoms to AIDS, which is life threatening and the end stage of HIV infection.
HIV is transmitted through sexual contact, sharing of HIV contaminated needles and/or syringes, transfusion of blood components, and nosocomial exposure to HIV contaminated blood or bodily fluids, and can be passed vertically from a mother to her infant.
An HIV antibody test for serologic screening of blood donors was implemented in 1985 in Canada. Since then, the risk of transmission of HIV through blood transfusion has been reduced substantially, from approximately 1 in 16,000 in 1985 to 1 in more than 1 million donations at present2,3. Factors that can contribute to HIV transmission through blood transfusion include the window period (i.e. a short viraemic period in which the donor is infected with HIV at a very early stage and often tested negative in a donor screening test), HIV-antibody negative chronic carriers, HIV mutant infection, and laboratory error. The primary source of Transfusion Transmitted HIV infection, however, is donations collected during the window period. Laboratory technologies such as HIV-1 p24 antigen test and HIV nucleic acid amplification testing (HIV NAT) have significantly reduced the window period, from 42 days by HIV antibody assays in the 1980s to 16 days by HIV-1 p24 antigen test and 13 days by HIV NAT3. The risk of HIV transmission through blood transfusion was estimated to be 1 in 752,000 donations between 1987 and 19964. This risk has been estimated to be 1 in 1.3 million donations following the implementation of HIV-1 p24 testing, and 1 in 1.6 million donations following the implementation of HIV NAT on a pool of 24 samples3.
Infection with human T-lymphotropic viruses type I and II (HTLV-I/II) had been associated with adult T-cell leukemia, lymphoma, and tropical spastic paraparesis. However, infection with HTLV-I and HTLV-II is mostly asymptomatic, and only about 5% of people with the infection develop significant clinical outcomes. While HTLV-I infection is relatively common in certain geographic areas, such as Japan and Caribbean countries, HTLV-II infection is prevalent in specific populations, such as North American aboriginals and injection drug users.
The viruses are transmitted mainly through sexual contact with an infected individual. Vertical transmission from mother to infant occurs primarily through breastfeeding. The viruses can also be transmitted through transfusion of blood components and plasma derivatives. The risk of Transfusion Transmitted HTLV-I/II infection has been reduced significantly since the implementation of blood donor serologic testing for antibodies to HTLV-I and HTLV-II in 19885. In Canada, the risk of transmission of HTLV-I/II through blood transfusion is estimated to be 1 in 1,316,000 units of donation during 1987-19964.
Caused by hepatitis A virus (HAV), hepatitis A is an important vaccine preventable infectious disease in Canada. In 1997, a total of 1,904 hepatitis A cases were reported to Health Canada6. The fecal-oral route is the most common mode of HAV transmission, which occurs either through personal contact or through ingestion of contaminated food or water. Hepatitis A outbreaks have been strongly associated with drinking HAV-contaminated water. Individuals who have household or sexual contact with infected people are at increased risk of acquiring hepatitis A. Travellers to hepatitis A endemic countries are also at risk.
Approximately 70% of infected adults and 30% of infected young children present with clinical symptoms such as fever, malaise, and jaundice. The acute disease usually lasts for several weeks, and there are no chronic carriers of HAV. In Canada, hepatitis A vaccine is currently recommended for individuals who are at increased risk7.
The transmission of HAV through blood transfusion has not been established; however, transmission of HAV through infusion of blood products has been reported among patients with hemophilia8. Since pooled plasma from multiple donors is used for preparing blood products, and since the solvent-detergent method for viral inactivation is ineffective against HAV, the risk of transmission of HAV through the use of blood products, though extremely small, may still exist. Currently, blood units are not routinely tested for antibodies to HAV. It has been suggested that recipients of clotting factors receive vaccine against HAV to prevent Transfusion Transmitted hepatitis A9.
Caused by hepatitis B virus (HBV), hepatitis B is also an important vaccine preventable disease in Canada. In 1997, a total of 1,043 hepatitis B cases were reported to Health Canada6. Acute HBV infection is often asymptomatic in infants and young children (90%); however, about 40% of adults present with clinical manifestations such as loss of appetite, nausea and vomiting, stomach pain, fatigue, and jaundice. On the other hand, the risk of subsequent chronic HBV infection decreases with age. About 90% of infants and 1% to 5% of adults develop chronic HBV infection, which is associated with the development of cirrhosis and hepatocellular carcinoma. The prevalence of chronic HBV infection, which is measured by a positive hepatitis B surface antigen (HBsAg) test, is estimated to be 0.5% to 1.0% in the Canadian population.
HBV is transmitted cutaneously through injection drug use, through exposure to contaminated blood or bodily fluids, sexually through heterosexual or male homosexual activities, vertically from mother to infant, and horizontally among household contacts. In Canada, injection drug use and risky heterosexual activities are the major risk factors associated with HBV transmission10. HBV infection can be effectively prevented through immunization programs, which are widely available for infants and preadolescents7.
The risk of transmission of HBV through blood transfusion is minimal because of the donor serologic test for HBsAg. It has been estimated that the risk was 1 in 89,000 donations and came primarily from donations collected during the window period4. In recent years, with the emergence of HBsAg escape mutants, the investigation of their implications for blood safety has become an important research priority. HBsAg escape mutants may not be detected by the current HBsAg assays used for blood donors, and the routine HBV vaccine may not protect the infection induced by the mutants; therefore, these pathogens pose a potential risk to the safety of blood transfusion11.
Caused by hepatitis C virus (HCV), hepatitis C has been recognized as an increasingly important infectious disease in Canada. It has been estimated that the prevalence of infection with HCV is about 0.8% among Canadians. Approximately 90% of individuals infected with HCV are either asymptomatic or have only mild symptoms. However, about 80% of acute infections progress to chronic infection, and almost half of those chronically infected individuals eventually develop cirrhosis or hepatocellular carcinoma after a few decades.
HCV is transmitted through several routes, including injection drug use, nosocomial exposure to contaminated blood or bodily fluids, blood transfusion, sexual activities, and from mother to infant. In Canada, HCV is primarily transmitted through sharing of needles among injection drug users10. Currently, no vaccine against HCV is available. Prevention of HCV infection relies on public health education and programs aimed at reducing high-risk behaviours, such as initiating injection drug use and sharing needles.
The risk of HCV transmission through blood transfusion was reduced remarkably after the implementation of blood donor serologic testing for HCV in 1990. The risk was estimated to be 1 in 225,000 donations between 1987 and 1996 based on an incidence window period mode14. The window period yielded with HCV nucleic acid amplification testing (HCV NAT) is shorter than that from the HCV antibody test. In Canada, the implementation of HCV NAT on pools of 24 samples in 1999 further reduced the risk of HCV transmission through transfusion12.
Hepatitis E is an acute infection caused by hepatitis E virus (HEV) and is endemic in parts of Asia and Africa. Most cases reported in Canada occur in travellers to the endemic areas. The clinical presentation of hepatitis E is similar to that of hepatitis A, and there are no chronic carriers of HEV. While HEV infection is generally subclinical or rarely results in significant outcomes, the infection in pregnant women may cause severe complications and result in death. HEV is transmitted primarily through the fecal-oral route, either directly through close personal contact or indirectly through ingestion of contaminated food or water. Outbreaks of hepatitis E occur frequently as a result of drinking HEV-contaminated water.
Although transmission of HEV through blood transfusion has not been established in North America, it is possible that the virus has been transmitted through blood transfusion in hepatitis E endemic areas13. If such a risk in Canada exists, it is extremely small because of the short viremic period and the lack of chronic carriers of HEV. Currently, blood units are not tested for serologic markers of HEV infection. The solvent-detergent method and heat method for viral inactivation are used to reduce the amount of HEV in pooled plasma. However, these inactivation methods cannot completely eliminate HEV contamination in the plasma.
The acute infection of hepatitis G (HGV) or GB virus C (GBV-C) is mostly asymptomatic. This virus also causes chronic infection and viremia, nevertheless, it has not been identified as a causative agent for any form of hepatitis14. Co-infection with HBV and HCV is common, but it seems that the co-infection does not change either the clinical course or the severity of HBV and HCV infection.
HGV/GBV-C is primarily transmitted through blood transfusion, but it can also be spread by organ transplantation, hemodialysis, sexual activity, and injection drug use, as well as through vertical transmission from mother to fetus. The prevalence of HGV/GBV-C infection measured by HGV RNA is about 1.1% among Canadian blood donors15. Currently, no screening assays have been approved to test blood donors for serologic markers of HGV/GBV-C infection.
Infection with cytomegalovirus (CMV) is common and often lasts for a lifetime. The prevalence of CMV antibodies increases with age, and approximately 50% to 80% of the adult population are infected with the virus. The acute infection is usually asymptomatic, particularly in immunocompetent individuals. However, CMV infection may result in severe outcomes in immunocompromised or immunodeficient individuals. These include bone marrow transplant or solid organ transplant recipients, HIV infected patients, cancer patients, premature infants and pregnant women.
CMV can be spread through sexual contact with infected individuals. It can also be passed from mother to infant in utero as well as from cervical secretions at birth and during breast-feeding. In addition, CMV can be transmitted effectively through blood transfusion, and organ and bone marrow transplantation.
The prevalence of CMV antibodies among blood donors ranges between 35% and 50%. Prevention of Transfusion Transmitted CMV infection in the high-risk recipients is critical. It has been reported that pre-storage leukodepletion of blood components may be as effective as the use of CMV-seronegative blood components16. In Canada, CMV-seronegative blood components are available for high-risk recipients, and a universal program of leukodepletion of cellular blood components has been implemented since 199917.
Epstein-Barr virus (EBV) infection is common in the general population. It is usually asymptomatic in children, although in adults the infection often results in clinical symptoms such as fever and sore throat. EBV has been associated with the development of Burkitt's lymphoma, nasopharyngeal carcinoma, and B-cell lymphoma in immunosuppressed individuals.
Transmitted primarily through person-to-person contact via saliva, EBV can also be spread through blood transfusion. The prevalence of antibodies to EBV among blood donors is as high as 90%, therefore, it is not practical to screen and eliminate all seropositive blood units through donor serologic screening tests. On the other hand, leukodepletion may be an effective way to reduce EBV transmission through blood transfusion17.
Human parvovirus B19 (HPV-B19) has been identified as the causative agent for fifth disease. Infection with HPV-B19 is common and mostly asymptomatic or presents as mild symptoms such as fever. However, severe complications may occur in certain high-risk groups. HPV-B19 infection occurring during pregnancy may result in fetal anemia and/or fetal death. HPV-B19 infection may cause transient aplastic crisis (TAC) in immunodeficient patients with hemolytic anemia and chronic bone marrow failure.
HPV-B19 is transmitted through contact with respiratory tract secretions and vertically from mother to fetus. This virus has been transmitted to patients with hemophilia through infusion of clotting factors (factor VIII and factor IX)18. The prevalence of antibodies to HBV-B19 among blood donors seems to be very low. Currently, blood units are not routinely screened for serologic markers of HPV-B19 infection, and the viral inactivation methods are ineffective against HPV-B1919. Therefore, a very low risk of HPV-B19 transmission through blood transfusion, in particular through the infusion of blood products, may exist. It has also been suggested that high-risk individuals receive anti-HPV-B19 negative blood components in order to prevent/reduce severe complications associated with HPV-B19 infection.
Human herpesvirus 6 (HHV-6) has been described as the causative agent of the sixth disease. This disease features high and persistent fever and affects primarily children between 3 months and 3 years of age. Most children become seropositive by the third year of life. HHV-6 infection in adults is generally asymptomatic, nevertheless, significant symptoms may occur in immunocompromised individuals such as HIV infected patients and transplant recipients, and can result in severe outcomes. Transmission of the virus occurs primarily via person-to-person contact of secretions of infected individuals.
Recently, HHV-6 has been described as a potential threat to transfusion safety because of its persistent infection and the high prevalence of antibodies to HHV-6 among blood donors. However, little is known about its clinical significance in blood recipients. Currently, blood units are not routinely screened for HHV-6 serologic markers20.
Human herpesvirus 8 (HHV-8) is a newly discovered virus that has been associated with Kaposi's sarcoma, in particular in immunocompromised individuals such as patients with HIV. Little is known about the epidemiology and mode of transmission of this virus. HHV-8 may be transmitted through sexual contact and close personal contact, and vertically from mother to fetus. Transmission of HHV-8 through blood transfusion has not been established, although the virus has been transmitted through organ/bone marrow transplantation21. Serologic screening for HHV-8 in blood donors is not implemented because of the low prevalence among donors and the lack of evidence of transmissibility by transfusion22.
TT virus (TTV) is also a newly identified virus. Infection with TTV is common throughout the general population, particularly in recipients who have received multiple transfusions and in injection drug users. TTV has not been associated with any hepatitis or other clinical disease23. The virus is transmitted through blood transfusion, and the prevalence of TTV infection among donors may range from 2% to 60%24. Nevertheless, blood units are not routinely screened for serologic markers of TTV infection.
SEN virus (SEN-V) was discovered in 1999. Again, little is known about its epidemiology, mode of transmission, and pathogenicity. The prevalence of antibodies to SEN-V is higher among individuals infected with HIV, HBV or HCV than in the general population. Infection with SEN-V is mostly asymptomatic, and it has not been associated with any form of hepatitis. Co-infection with HCV does not influence the clinical course or the severity of HCV infection.
SEN-V is transmitted through blood transfusion and injection drug use. However, it is not known whether the virus can also be transmitted through sexual contact or nosocomial exposure25. The prevalence of SEN-V infection among blood donors is about 2%, and approximately 30% of recipients who received SEN-V seropositive blood through transfusion seroconverted26. Currently, there are no specific measures to prevent SEN-V transmission through blood transfusion.
Creutzfeldt-Jakob Disease (CJD) is a form of the human transmissible spongiform encephalopathies (TSEs) and is characterized by mental deterioration, cerebellar dysfunctions, involuntary movements, and psychiatric alterations. CJD is a rare disease and occurs at a rate of approximately 1 per million population annually. In 2000, about 31 cases of CJD were reported to Health Canada through the CJD Surveillance System (CJD-SS) (HCAID - personal communication, 2001).
The risk of transmission of CJD through blood transfusion has not been established, but it cannot be completely ruled out. The disease has a long incubation period, and studies and surveillance programs have not lasted long enough or included sufficient numbers of cases to conclude that CJD is transmitted through blood transfusion27. Further, the transmissibility of CJD cannot be supported by lookback investigations and studies on CJD mortality trends28,29.
Variant Creutzfeldt-Jakob Disease (vCJD) is thought to be the human form of bovine spongiform encephalopathy (BSE) and was first described in 1996. Unlike CJD, vCJD primarily affects people under 50 years of age and is likely to be transmitted by eating contaminated meats from BSE-infected cattle. The major risk for acquiring vCJD is residence in the UK, Ireland, and France. It has been speculated that the transmissibility of vCJD through blood may be greater than that of classic CJD30.
Recently there has been one case of BSE and one of vCJD in Canada.
In Canada, precautionary measures against the theoretical risk of vCJD transmission through transfusion have been implemented. In addition, a universal program of pre-storage leukodepletion implemented in 1999 may play an important role in further reducing the theoretical risk.
For blood deferral information please refer to the following websites:
Transfusion Transmitted bacterial reaction has been identified as the most common and severe infectious complication associated with transfusion. Approximately 57% of all Transfusion Transmitted infections and 16% of transfusion-related deaths have been associated with bacterial contamination. It has been estimated that 1 in 38,500 units of red cells, 1 in 3,300 units of random donor platelets, and 1 in 2,000 units of apheresis platelets are contaminated with bacteria32. Blood components may be contaminated with bacteria throughout many stages of preparation, including blood collection, processing, pooling, and transfusion. Bacteria may enter into blood components through several sources: donors' bacteremia, exposure to donor skin bacteria by venipuncture, and contaminated bags and environment in blood banks or hospitals.
The bacteria implicated in bacterial reactions associated with red cells are typically gram-negative bacilli such as Yersinia enterocolitica and Pseudomonas fluorescens. In contrast, bacteria implicated in reactions associated with platelets are mostly gram-positive species such as Staphylococcus and Streptococcus species. The clinical severity of Transfusion Transmitted bacterial reactions depends largely on the type and load of bacteria involved as well as the recipient's condition. While gram-negative agents usually produce endotoxins and cause severe reactions, gram-positive agents often cause minor reactions. The load of bacteria is determined by the storage time. Platelet units that are stored over 3 days and red cell units that are stored over 21 days are strongly associated with an increased risk of bacterial reactions. In addition, age and underlying diseases in recipients may also play an important role in determining the severity of a bacterial reaction.
Measures have been implemented to prevent and reduce bacterial contamination and its associated transfusion reactions. In Canada, blood donors are carefully screened by questions related to bacterial infections. Phlebotomy sites on donors' skin are carefully prepared using an improved skin disinfected method33. All red blood cell units and platelet units are leukodepleted to further remove bacteria from blood components17. Since it is impossible to eliminate bacteria from blood components, it is important to recognize early clinical symptoms associated with bacterial reactions in order to reduce the morbidity and mortality. A surveillance system plays an important role in monitoring such trends, and in developing and evaluating measures aimed at prevention of bacterial contamination.
For blood deferral information please refer to the following websites:
On the basis of degree of infectivity and progression, infection with Treponema pallidum - the agent of syphilis - can be classified into different clinical stages, including primary, secondary, early latent, late latent, and tertiary. Primary syphilis is characterized by a painless genital ulcer; about one-third of untreated primary cases will progress to secondary syphilis. Secondary syphilis features a symmetrical maculopapular rash involving the palms and soles; about one-third of untreated secondary cases will progress to latent infection. In general, latent syphilis is asymptomatic, and one-third of untreated latent cases will progress to tertiary syphilis. Tertiary syphilis usually involves the heart and central nervous system (CNS) and may result in cardiovascular and neuropsychiatric disorders and blindness. Infection during pregnancy may lead to miscarriage, stillbirth, prematurity, and congenital syphilis. In addition, syphilis increases the risk of acquiring HIV infection, and tertiary syphilis in HIV infected individuals is difficult to treat.
Syphilis is transmitted primarily through sexual contact with an infected individual who is in the primary, secondary or early latent stage of the disease. T. pallidum can also be transmitted from mother to fetus and from an infected donor to a recipient through unscreened blood or direct blood transfusion.
Transmission of syphilis by blood transfusion has become extremely rare after implementation of the serologic test for antibodies to T. pallidum - the first infectious disease marker tested in blood donors. In Canada, the risk of Transfusion Transmitted syphilis was estimated to be 6 in 1 million donations during the period of 1990-19964. Currently, all blood units are continually screened for serologic markers of syphilis.
Malaria is an important parasitic infectious disease worldwide. It has been estimated that about 300-500 million people are infected, and over 1 million people die from this disease each year. Malaria is endemic in subtropical and tropical areas such as Central and South America, Africa, and Southeast Asia. About 400 to 1,000 cases of malaria were reported in Canada each year between 1990 and 1997, and most of these cases were associated with international travel to malaria endemic areas6. Human malaria is caused by four species of Plasmodium, including P. falciparum, P. vivax, P. ovale and P. malariae. Malaria caused by P. falciparum often results in severe complications and/or death. On the other hand, malaria caused by other Plasmodium species usually results in non-life-threatening symptoms.
The parasites are transmitted to a human by the bite of an infected female Anopheles mosquito. The parasites can also be transmitted from an infected mother to her fetus and from an asymptomatic donor to a recipient. Transfusion Transmitted malaria (TTM) is rare, but it is a potential severe complication in blood recipients. Three cases of TTM have been reported in Canada. The donor deferral policy remains the most efficient way to prevent and reduce the occurrence of TTM in Canada.
For blood deferral information please refer to the following websites:
Caused by a protozoan parasite - Trypanosoma cruzi - Chagas' disease has become an increasingly important infectious disease in Central and South America and some regions of Mexico. It has been estimated that 16 to 18 million people are infected, and 100 million people are at risk of T. cruzi infection. Chagas' disease is not endemic in Canada, and the incidence cannot be obtained because the disease is not a national notifiable disease.
Acute infection with T. cruzi is often mild and self limiting, although asymptomatic chronic infection may last for a lifetime and can be characterized by detectable antibodies to T. cruzi. Approximately 36% of acutely infected individuals develop clinical manifestations that result in cardiac (27%), intestinal (6%), and peripheral nervous (3%) complications after one or two decades35. T. cruzi is transmitted from an infected vector to a person through feces deposited on the skin at the time of biting. The agent can also be transmitted vertically from mother to infant and through blood transfusion and organ transplantation.
Transfusion Transmitted Chagas' disease has been reported in endemic areas for almost 40 years. In recent years, however, several cases of Transfusion Transmitted Chagas' disease have also been reported in the US and Canada. The risk of T. cruzi transmission through transfusion is very low and depends on several factors, including the prevalence of asymptomatic parasitemia in blood donors and the immunologic status of recipients. Donors who were born or have lived in endemic areas for more than 1 year are more likely to be positive for T. cruzi antibodies. The majority of patients diagnosed with Transfusion Transmitted Chagas' disease in North America have been found to be immunosuppressed36. Screening methods, such as inquiry about travel history and testing for serologic markers, are neither sensitive nor specific enough to effectively identify asymptomatic blood donors. Leukodepletion may reduce the risk of Transfusion Transmitted Chagas' disease in Canada.
Toxoplasmosis is a zoonosis caused by Toxoplasma gondii, a parasite that is hosted in cats and dogs and has three forms - trophozoites, cysts and oocysts. The annual incidence rate of toxoplasmosis has been estimated to range from 1% to 5%, resulting in approximately 500 million people infected worldwide37. The acute infection is either asymptomatic or yields mild symptoms such as malaise, fever, and cutaneous rashes. However, severe complications such as meningoencephalitis and myocarditis may occur in immunocompromised individuals and result in disabilities and/or deaths. The seroprevalence of antibodies to T. gondii increases with age and varies from 8% to 60%, according to geographic region.
T. gondii is transmitted through several routes: ingestion of T. gondii oocysts, eating undercooked contaminated pork or beef, direct contamination of open wounds, and vertical transmission from mother to infant. In addition, the agent has been reported to be transmitted through blood transfusion and organ transplantation38. Nevertheless, the risk of T. gondii transmission through blood transfusion is extremely low, and serologic testing of antibodies to T. gondii in blood donors appears to be unnecessary. It has been suggested that people who are at increased risk of toxoplasmosis, such as immunosuppressed individuals and pregnant women, receive T. gondii antibody-negative blood components for transfusion. The universal program of leukodepletion that is currently carried out in Canada may reduce the risk of Transfusion Transmitted toxoplasmosis.
Caused by Leishmania donovani, leishmaniasis affects approximately 12 million people in tropical and subtropical areas. The acute infection is often subclinical, although chronic infection may result in anemia and lymphadenopathy.
Transmitted primarily by the bite of an infected vector - the sandfly, L. donovani can also be transmitted through blood transfusion and cause clinical disease in newborns or immunosuppressed recipients37. Currently, Transfusion Transmitted leishmaniasis has not been reported in Canada or the US38. Given the very low risk, no recommendations have been made to test antibodies to L. donovani in Canadian blood donors on a routine basis.
Caused by Babesia microti, babesiosis is a zoonotic disease endemic in the coastal areas of Massachusetts and New York States. Babesiosis occurs primarily during the period from May to August. In immunocompetent individuals the acute infection is either subclinical or results in some unspecific mild symptoms such as fever and headache. However, severe outcomes may occur in older patients, infants, and splenectomized or immunocompromised individuals.
In general, B. microti is transmitted to humans through the bite of deer ticks - Ixodes scapularis; however, it can also be transmitted through blood transfusion to recipients from asymptomatic and parasitemic donors. Approximately 25 cases of Transfusion Transmitted babesiosis, including one recent case in Ontario, have been reported in North American since 198042.
The risk of transmission of B. microti through blood transfusion is very low and varies according to geographic region. The risk is higher in babesiosis endemic than nonendemic regions. The majority of the 25 reported cases occurred in immunocompromised recipients. Currently, there are no effective methods of donor screening and testing. Because of the extremely small risk in Canada, blood donors are not routinely asked about a history of travel to babesiosis endemic areas or a history of tick bites, and blood units are not routinely tested for evidence of B. microti infection.
Rocky Mountain Spotted Fever (RMSF) is a severe tick-borne disease caused by Rickettsia rickettsii. The disease is endemic in most parts of the United States, in particular the south eastern and south central states. Although RMSF cases have been reported in Canada, the incidence cannot be obtained since RMSF is not a national notifiable disease. RMSF is characterized by the sudden onset of moderate to high fever, which normally persists for 2-3 weeks if untreated. Other typical symptoms include headache, myalgia, and petechial rash, and early RMSF may be confused with meningitis. Diagnosis of RMSF is confirmed by a serologic test for specific antigens. Serious complications such as cerebral edema and non-cardiogenic pulmonary edema may occur. The case fatality ratio can be as high as 20% to 30% for untreated patients and 3% to 4% for treated patients.
RMSF is transmitted mainly through the bites of infected ticks. The American dog tick in the east and the Rocky Mountain wood tick in the west are the principal vectors for R. rickettsii transmission. This agent has also been transmitted through blood transfusion43. However, Transfusion Transmitted RMSF has never been reported in Canada. Currently, no specific questions or assays are used for screening and testing of serologic markers of R. rickettsii in blood donors.
Human ehrlichiosis has been recognized as an emerging tick-borne infectious disease since 1986. There are three forms of ehrlichiosis: human monocytic ehrlichiosis (HME) caused by Ehrlichia chaffeensis; human granulocytic ehrlichiosis (HGE) caused by E. phagocytophila; and an undefined human ehrlichiosis caused by E. ewingii. As ehrlichiosis is not a national notifiable disease in Canada, the incidence is largely unknown. In the USA, the highest incidence rates of HME have been reported from southern and south central regions, and the highest incidence rates of HGE from north eastern and upper mid-western areas.
HME and HGE share many clinical symptoms, including fever, headache, myalgia and rash. Although most cases of ehrlichiosis are mild, complications such as respiratory distress syndrome and renal failure occur in about 10% to 20% of patients. The case fatality ratios can be as high as 5% for HME and 10% for HGE44.
The agents are transmitted primarily through bites of infected ticks. In addition, ehrlichiosis, in particular HGE, may be transmitted through blood transfusion from an asymptomatic donor to a recipient. However, such a mode of transmission has not been established because of the limited knowledge and information on ehrlichiosis. Currently, there are no effective screening questions or serologic tests available to identify infected blood donors.
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