Flea

Abstract: Exposure to cats infected with Yersinia pestis is a recently recognized risk for human plague in the US. Twenty-three cases of cat-associated human plague (5 of which were fatal) occurred in 8 western states from 1977 through 1998, which represent 7.7% of the total 297 cases reported in that period. Bites, scratches, or other contact with infectious materials while handling infected cats resulted in 17 cases of bubonic plague, 1 case of primary septicemic plague, and 5 cases of primary pneumonic plague. The 5 fatal cases were associated with misdiagnosis or delays in seeking treatment, which resulted in overwhelming infection and various manifestations of the systemic inflammatory response syndrome. Unlike infections acquired by flea bites, the occurrence of cat-associated human plague did not increase significantly during summer months. Plague epizootics in rodents also were observed less frequently at exposure sites for cases of cat-associated human plague than at exposure sites for other cases. The risk of cat-associated human plague is likely to increase as residential development continues in areas where plague foci exist in the western US. Enhanced awareness is needed for prompt diagnosis and treatment. Plague is a bacterial zoonosis caused by infection with Yersinia pestis, a gram-negative coccobacillus. Active foci exist in wild rodent and flea populations in many regions of the world, including the western US (where the disease probably was first introduced in 1899‐1900 by rat- and flea-infested ships) [1‐3]. To date, surveillance programs have identified evidence of Y. pestis infection in mammal or flea samples collected from 17 western states (K.L.G., Plague Section, Centers for Disease Control and Prevention [CDC], unpublished data). A total of 297 human cases of plague were identified in 13 of these states from 1977 through 1998.

Abstract: We assayed the ability of cat fleas to become infected with Bartonella henselae , using an artificial feeding device. Fleas fed a concentration of 1 X 105 cfu/ml in blood were examined using immunofluorescent antibody assay and polymerase chain reaction. Bacteria were present in the gut at 3 h, and persisted up to 9 d after infection. Qualitatively, the density of B. henselae was greater in the flea gut at 9 d, indicating that replication was occurring in the gut. B. henselae also was detected in the feces of infected fleas 9 d after infection, and produced viable colonies upon inoculation onto heart infusion agar/rabbit blood plates. Our results indicate that fleas can maintain infection with B. henselae , and may play a role in the transmission of this bacterium from infected cats to humans.

Abstract: All fleas used in this study were collected in the field and except for Pulex irritans were cultured in the laboratory. The ten species studied were Xenopsylla cheopis, Nosopsyllus fasciatus, Orchopeas sexdentatus sexdentatus, Opisodasys-nesiotus, Megabothris abantis, Malaraeus telchinum, Diamanus montanus, Echidnophaga gallinacea, Pulex irritans and Oropsylla idahoensis . All fleas transmitted in individual feeding studies with the exception of the latter two species, which transmitted en masse . Echidnophaga gallinacea could not be fed periodically as were the other fleas because of its tick-like feeding habits. Consequently, the vector efficiency obtained for this species is not strictly comparable to that found for the other species. The transmission data obtained from individual flea feeding studies was analysed statistically to estimate the expected number of transmissions per flea of each species. These values are obtained as intervals which have a 90% probability of containing the true value. The true vector efficiency of Xenopsylla cheopis was found to be 0·660 ± 0·234 (expected transmissions per flea), that of Nosopsyllus fasciatus to be 0·213 ± 0·157, and that of Orchopeas sexdentatus sexdentatus to be 0·170 ± 0·138. Opisodasys nesiotus, Megabothris abantis, Malaraeus telchinum and Diamanus montanus transmitted very inefficiently. Experimental evidence was obtained that different strains of a species of flea may differ markedly in their biological vector capacity. In contrast to results obtained in this study, Wheeler & Douglas found Diamanus montanus to be an exceptionally good vector; in their studies it proved to be an even more efficient vector than Xenopsylla cheopis . The strain of Diamanus montanus employed by them came from an area widely separated from that in which the strain used in the present studies was originally collected. Since many blocked fleas did not transmit it is probable that the experimentally determined vector efficiencies are lower than they would be in nature, where the blocked flea has constant access to a host and hence greater opportunity to feed. Attempts to determine the number of organisms regurgitated by a blocked flea during its attempt to feed did not prove entirely satisfactory, but gave an indication that the number may be at times from 11,000 to 24,000 organisms. The technique consisted of feeding a blocked flea on the shaved abdomen of a mouse (later on the ear), then immediately doing a biopsy on the area around and including the bite wound. This biopsy material was then finely ground and plated on a sensitive bacteriological medium. Some mice upon which biopsies were performed nevertheless contracted plague and died. This must lead to the conclusion that an infective flea may deposit organisms directly into the capillaries and that the primary stage of infection resulting from a flea bite is frequently bacteraemia.