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), accordingto 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."
Journal of Australia
is a publication of the Australian Medical