NAME: Rickettsia rickettsii
SYNONYM OR CROSS REFERENCE: Rocky Mountain Spotted Fever (RMSF), Brazilian Spotted Fever, Tobia Fever, fiebre maculosa, fiebre manchada, New World Spotted Fever, Tick- borne typhus fever, Sao Paulo Fever
CHARACTERISTICS: Rickettsia rickettsii is an obligate intracellular alpha proteobacteria that belongs to the Rickettsiacae family(1,2,3). It is a small (0.2-0.5 µm by 0.2-0.3 µm) pleomorphic, gram-negative coccobacillus which multiplies by binary fission and has both DNA and RNA(1,2,3).
PATHOGENICITY/TOXICITY: RMSF is a potentially fatal tick-borne disease normally causing moderate to severe illness(1). It can appear as an abrupt onset of fever (typically higher than 38.9 ºC), malaise, headache, anorexia, nausea, vomiting, abdominal pain, photophobia, diarrhoea and neck stiffness(1,3). The characteristic maculopapular rash usually appears 2-5 days after the other symptoms, starting on wrists and ankles before progressing to the rest of the body(1). 95% of children and 80% of adults have the rash; however, absence of the rash is more common in fatal cases and cases involving the elderly or African-Americans(1). The rash is due to the infection of host vascular endothelial cells and is a multisystem vasculitis that can lead to necrotic or gangrenous lesions in severe cases(1,3). Mucosal ulcers, postinflammatory hyperpigmentation, jaundice, cough, pneumonia, acute renal failure, lymphadenopathy, hepatomegaly, splenomegaly, conjunctivitis, peripheral, periorbal and optic disk oedema, arterial occlusion, retinal vein engorgement, retinal haemorrhage and retinal sheathing are some of the complications that can be caused by RMSF(1,3). After the skin, the CNS is the most affected system and people over 15 are at higher risk of developing CNS complications(3). 40% of all patients reported neurological abnormalities such as meningismus, seizures, altered mental states, temporary deafness, lethargy and amnesia(1,3). The symptoms can last 2 weeks although some patients have neurological sequelae lasting up to one year after disease onset. 20% of untreated cases are fatal compared to 5% of treated cases(1). Mortality rates are higher for patients over the age of 60(1). The symptoms of RMSF can be confused with meningococcemia, various viral infections and other tick-borne diseases(1,3).
EPIDEMIOLOGY: The disease is restricted to the Americas where it is common in the United States of America, Western Canada, Mexico, Panama, Costa Rica, Argentina, Brazil, Colombia and Bolivia(1,2,3). It is the most common tick-borne disease in the USA where 250-1200 cases are reported each year(1). 90-93% of the cases reported in the USA occurred between April and October with most of them occurring in rural and suburban areas(1,3). The highest infection rates were among children between 5-9, Caucasians and men(3). Infections are more common in tick-infested areas(1).
INFECTIOUS DOSE: The precise infectious dose for R.rickettsii is unknown; however rickettsiales generally have a very low infectious dose. The bite of a single tick is sufficient to cause RMSF in humans(1,3). Dogs that were innoculated with approximately 3000 vero cells infected with RMSF or infected with 10 ticks all developed clinical symptoms of the disease(5).
MODE OF TRANSMISSION: RMSF is usually spread by the bite of an infectious tick where the bacterium changes from a dormant avirulent state to a pathogenic state(1). The tick normally needs to be attached for a 4-6 hour period in order to transmit the disease to humans(1). Rickettsia rickettsii can also be spread through contact with the tick's infected saliva, blood, bodily fluids or feces(1,2,6). Human-to-human transmission has not been confirmed but aerosols are a potential source of infection(4,7).
RESERVOIR: The disease in maintained by transovarial and transstadial passages in ticks where it is then spread to humans, dogs, rodents and other mammals(1,2). Small mammals can serve as amplifying hosts by maintaining the bacteria in their blood (they are infective for a maximum of 8 days) and then passing it to a tick during a blood meal(8).
ZOONOSIS: The disease is spread from ticks to humans through the bite, or contact with tick feces or internal contents(1,1,2). Mammals (such as dogs) can also spread the ticks to humans, thus spreading the RMSF infection(2,4).
VECTORS: Several tick species are responsible for the spread of this disease(1). Dermacentor variabilis is most prevalent in the United States of America, Demacentor andersoni in the Rocky Mountains and in Canada, Rhipicephalus sanguineus in Mexico, Amblyomma cajennense in Central and South America and Amblyomma aureolatum in Brazil(1).
DRUG SUSCEPTIBILITY: Tetracyclines and chloramphenicol are the only drugs that are confirmed as being effective against an infection by Rickettsia rickettsii(1). The most effective and recognized antibiotic used to treat RMSF is doxycycline(1,3).
SUSCEPTIBILITY TO DISINFECTANTS: Gram-negative bacteria are susceptible to 1% sodium hypochlorite, 4% formaldehyde, 2% glutaraldehyde, 70% ethanol, 2% peracetic acid, 3- 6% hydrogen peroxide and 0.16% iodine(4).
PHYSICAL INACTIVATION: Rickettsia rickettsii is susceptible to moist heat (121 ºC for at least 15 minutes) and dry heat (170 ºC for at least 1 hour)(9).
SURVEILLANCE: Monitor for symptoms. The presence of the pathogen can be confirmed using a variety of laboratory techniques(11). Immunofluorescent assays (IFAs) and ELISAs can be used to identify antibodies to the bacteria; however, sera must be tested at least 7 days after the appearance of symptoms in order to detect seroconversion because IgG antibodies do not appear until a minimum of 7 days after the onset of the disease(3). A four-fold increase in titres of paired samples or a convalescent titre greater 1/64 is considered diagnostic(1). The bacteria can be visualized using Giemsa and Gimenez staining methods. Immunohistochemical staining of skin biopsies can be useful in patients presenting with rash(1,2,3). Immunohistochemical staining is the most useful method to diagnose RMSF in severe cases(12). PCR of blood, biopsy tissues and ticks is possible although this technique is not sensitive enough to be commonly used to diagnose RMSF and most diagnoses of the disease are retrospective(1,3).
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Appropriate antibiotic therapy (i.e. doxycycline) should be initiated at the onset of RMSF-like symptoms without waiting for laboratory confirmation of the diagnosis(11,13). 100 mg of doxycycline should be taken twice a day for 5-7 days and until the patient is afebrile for at least 2-3 days(1,3). For children weighing less than 45 kg, a 2.2 mg/ kg twice daily dose of doxycycline is recommended for 5 to 7 days(1,3).
PROPHYLAXIS: The administration of the appropriate antibiotic treatment before any signs of clinical illness is not recommended(2).
LABORATORY-ACQUIRED INFECTIONS: 63 laboratory-acquired infections have been reported as of date with 11 deaths(11). The 11 fatal cases were associated with manipulating infected eggs, tissue cultures or ticks, and the respiratory route, mucous membrane contact, needle puncture wounds or cuts were involved(13). 9 cases were reported in the same lab over a 6 year period, all caused by infectious aerosols(7).
SOURCES/SPECIMENS: Tissues and blood from ticks or infected animals(1).
SPECIAL HAZARDS: None
RISK GROUP CLASSIFICATION: Risk group 3(14).
CONTAINMENT REQUIREMENTS: Containment Level 3 facilities, equipment, and operational practices for work involving infected or potentially infected material, including necropsy of infected animals, arthropods, inoculation, incubation and harvesting of embryonated eggs or tissue cultures.
PROTECTIVE CLOTHING: Personnel entering the laboratory should remove street clothing and jewellery, and change into dedicated laboratory clothing and shoes, or don full coverage protective clothing (i.e., completely covering all street clothing). Additional protection may be worn over laboratory clothing when infectious materials are directly handled, such as solid-front gowns with tight fitting wrists, gloves, and respiratory protection. Eye protection must be used where there is a known or potential risk of exposure to splashes(15).
OTHER PRECAUTIONS: All activities with infectious material should be conducted in a biological safety cabinet (BSC) or other appropriate primary containment device in combination with personal protective equipment. Centrifugation of infected materials must be carried out in closed containers placed in sealed safety cups, or in rotors that are loaded or unloaded in a biological safety cabinet. The use of needles, syringes, and other sharp objects should be strictly limited. Open wounds, cuts, scratches, and grazes should be covered with waterproof dressings. Additional precautions should be considered with work involving animals or large scale activities(15).
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up (30 min)(15).
DISPOSAL: Decontaminate all wastes before disposal by incineration or steam sterilization(15).
STORAGE: The infectious agent should be stored in a sealed and identified container in a level 3 containment laboratory(15).
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: July 2010
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2010