Current Advice on Parasite Control:
- Flea-borne Rickettsiosis
Rickettsia typhi (murine typhus, endemic typhus)
Overview of Life Cycle
- Cats and people are thought to become infected with Rickettsia typhi and Rickettsia felis by infected fleas.
- Rickettsia typhi is maintained in a natural cycle involving rodent or opossum reservoir hosts and flea vectors; flea vectors for R. typhi include Xenopsylla cheopis, the Oriental rat flea, and Ctenocephalides felis, the cat flea.
- Occasionally, R. typhi will spill over from peridomestic wild vertebrates into dogs and cats, particularly when premises are infested with C. felis.
- Ctenocephalides felis is the only currently defined biological vector for R. felis but the bacteria has been identified in many different flea species as well as ticks and mites.
- A number of R. felis-infected mammals have been described, including opossums, rodents, dogs, and cats.
- Rickettsia typhi and R. felis are minute coccobacilli, measuring approximately 1-2 µm by 0.3-0.5 µm, and are widely disseminated throughout the flea vector.
- Rickettsia typhi is in the typhus group of Rickettsia spp., while R. felis is considered in the transitional group. Both are related to but distinct from spotted fever group Rickettsia spp.
- Infections with R. typhi and R. felis are considered to be largely asymptomatic.
- Experimental infection of cats with R. felis results in seroconversion between 2-4 months post infection, but no overt disease.
- Although associated with cats, R. felis infection has been reported in a number of different mammals
- Infection with R. typhi results in fever, headache, myalgia, confusion, and a diffuse rash.
- Severity of disease due to R. typhi is greater in the elderly and in patients with immunosuppressive conditions.
- Infection with R. felis has been associated with fever, rash, myalgia, and an eschar at the site of a flea bite.
- Neurologic complications have been reported in patients infected with both R. typhi and R. felis.
- Diagnosis of both agents is complicated by the variable presentation of disease.
Incidence and Prevalence
- In an endemic area, 40% of opossums and 90% of cats sampled were seropositive to R. typhi.
- Cat fleas (Ctenocephalides felis) collected from opossums from an endemic area showed an infectivity rate of 0.8% for R. typhi and 3.8% for R. felis.
- Studies have shown that as many as 62.4% of fleas collected from cats contain R. felis DNA, and serologic surveys report documented feline exposure to R. felis from 3.9-11.1%.
- Reported cases of R. typhi in the US are usually from southern California, central and southcentral Texas, and Hawaii.
- Careful epidemiological studies have shown that R. typhi and R. felis co-infections exist in the same maintenance cycles in the same areas.
Host Associations â Transmission between hosts
- Rickettsia typhi is thought to be primarily transmitted by scratching infected flea feces (also known as ‘flea dirt’ or frass) into a flea bite wound. Some transmission also occurs directly by flea feeding.
- It is suspected that wildlife hosts, especially opossums, may play an important role in maintaining the rickettsial infections and infecting fleas.
- Fleas are infected with R. felis when feeding on an infected host.
- Both R. typhi and R. felis can be maintained in cat flea populations by transovarial transmission.
- Infection with R. felis can be maintained vertically in cat flea populations through both transovarial and transstadial transmission for several generations without requiring an infectious vertebrate blood meal for the fleas.
Prepatent Period and Environmental Factors
- Rickettsia typhi is ingested in a blood meal and enters the midgut epithelial cells of the flea. The bacteria then replicate and spread throughout the midgut.
- It takes ten days after ingestion of R. typhi for a flea to then transmit it to a host through infected feces.
- Little is known about transmission dynamics of R. felis in natural maintenance cycles.
- Rodents, opossums, and other peridomestic wildlife harboring cat fleas are thought to increase the risk of infection to people.
- Human cases of R. typhi have been associated with seropositive pet cats and opossums.
- Rickettsemia associated with R. typhi and R. felis infections may quickly drop to undetectable levels.
- Due to cross reactivity among the Rickettsia species, multiple serologic tests may be required to confirm diagnosis of R. typhi or R. felis infections.
- In people, the onset of symptoms for a flea-borne rickettsiosis can be seen up to a week before antibodies can be detected in the patient.
- Polymerase chain reaction (PCR) can also be used to identify infection with R. typhi or R. felis so long as the rickettsial bacteria are present in circulation at adequate levels for detection.
- Rickettsia typhi and R. felis are ultrastructuraly and serologically indistinguishable from one another and from other Rickettsia spp., such as R. prowazekii.
- Standard protocols are not available for antibiotic treatments of cats or dogs infected with R. typhi or R. felis.
- People with clinical disease due to R. typhi are treated with tetracycline, doxycycline, or fluoroquinolone antibiotics.
- People with disease that is thought to be due to infection have been treated with doxycycline, rifampin, and fluoroquinolone antibiotics.
Control and Prevention
The key to prevention of flea-borne rickettsiosis in both dogs and people is to limit exposure to potentially infected fleas.
- The CAPC recommends administration of preventive flea products as soon after birth as possible (consistent with label claims) for the life of the pet. However, because substantial geographic differences occur in flea prevalence and seasonality, prevention programs should be tailored to needs of the individual pet.
- Year round flea control is particularly important to prevent establishment of home infestations with Ctenocephalides felis, the most common flea found on dogs and cats and a confirmed vector of R. typhi and R. felis in North America.
- Routine use of flea control containing both an adulticide and an insect growth regulator or insect development inhibitor, which will help prevent establishment of an environmental infestation, should be administered to every animal, every month, all year long.
- The environmental burden of immature fleas can be further reduced by thoroughly and regularly vacuuming floors, carpets, and furniture, and by regularly washing animal bedding. Only 5% of the total flea infestation is comprised of the adult fleas on the pets; the other 95% are immature life stages in carpet, upholstery, and bedding.
- Premise sprays can also be used in conjunction with the above control regimen
- Flea infestations can be very difficult to eradicate and it may require several months of sustained effort to bring an infestation under control.
- Vaccines are not available to protect pets or people from infection with R. felis or R. typhi.
- The key to prevention of flea-borne rickettsiosis in both dogs and people is to limit exposure to potentially infected fleas.
Public Health Considerations
- The vector fleas and preventive strategies (flea control) are similar for pets and people.
- While subclinical in animals, R. typhi and R. felis infections can be associated with clinical disease in people, including fever, rash, myalgia, and neurologic complications.
- Azad AF, Radulovic S, Higgins JA, Noden BH, Troyer JM. "Flea-Borne Rickettsioses: Ecological Considerations." Emerging Infectious Diseases 3, no. 3 (1997): 319-27.
- Bitam I, Dittmar K, Parola P, Whiting MF, Raoult D. "Fleas and Flea-Borne Diseases." International Journal of Infectious Diseases 14 (2010): e667-e676.
- Little SE, Starkey L. "Conquering Fleas: Preventing Infestations and Limiting Disease Transmission." Today's Veterinary Practice, 2012, 33-38.
- Reif KE, Macaluso KR. "Ecology of Rickettsia Felis: A Review." Journal of Medical Entomology 46, no. 4 (2009): 723-36.