Incidence Of R. felis Infection In Australians May Be Under-Reported

The incidence of human infection with Rickettsia felis (R. felis) in Australia may have been
underestimated in the past because of the similarity between clinical presentations of R. felis
and Rickettsia typhi (R. typhi), according to a case study published in the latest Medical
Journal of Australia.


Human infection with this bacteria has been reported in most parts of the world. Dr Stephen
Graves (PhD), Director of Microbiology at the Hunter Area Pathology Service in Newcastle,
NSW, Dr John Stenos (PhD), Supervising Scientist at the Australian Reckettsial Reference
Laboratory, Geelong Hospital, Victoria, and co-authors describe the first reported cases of
probable human R. felis infection in Australia. The cases involve two adults and three
children in Victoria who contracted a rickettsial disease after exposure to fleas from kittens.


Serological tests showed rising typhus-group rickettsial antibody titres in three of the patients
and high titres in the other two patients. Serological testing on one of the kittens also showed
the presence of typhus-group rickettsial antibodies.


DNA samples from the serum of one of the patients and the cat, and from pooled and crushed
fleas collected from the group of cats that the kittens had been associated with, showed that
the fleas, but not the patient's or cat's serum, were positive for rickettsial DNA. Sequencing
of the DNA showed closest phylogenetic similarity to R. felis, and R. typhi was not detected
in the cat fleas.


Dr Graves said the analyses provided the first molecular evidence of R. felis in cat fleas in
Victoria.


"While genetically a member of the spotted-fever rickettsia group, R. felis behaves clinically
and serologically like a typhus-group rickettsia," he said.


"The human cases reported in this study were only identified serologically, and as the clinical
presentations of R. typhi and R. felis are similar, R. typhi cannot be completely ruled out.
However, given the molecular data from the cat fleas, R. felis is the more likely causative
agent.


"In the past, the incidence of R. felis infection in patients with raised typhus group antibody
levels may have been underestimated, with the causative agent probably reported as R. typhi
when it may have been R. felis - a confusion that has been seen in other studies."


The Medical Journal of Australia is a publication of the Australian Medical Association.


Source:

Medical Journal of Australia