Investigation of fleas as vectors in the transmission of plague during a quiescent period in North-Eastern, Tanzania

Yersinia pestis, the etiologic agent of plague, is normally transmitted to animals by infective flea-bites. Fleas associated with rodents, cats, dogs and other small mammals are considered important for the maintenance and transmission of the bacterium. Therefore, a study was undertaken to investigate the presence of Y. pestis in fleas of North-Eastern Tanzania during a quiescent period. House rodents were trapped with box traps while field and forest rodents were trapped with Sherman live traps. Fleas were collected from rodents by brushing the animal using shoe-shiner brush. House dwelling fleas were trapped with light traps while fleas from cats, dogs, goats and pigs were collected by rubbing their fur with ether soaked cotton wool and brushing as for rodents. All collected fleas were identified to genus level and subjected to polymerase chain reaction (PCR) test for Y. pestis DNA. Chi square test was used for comparison of proportions and statistical significance and p value of less than 0.05 was considered statistically significant. A total of 340 rodents, the majority of which Mastomys natalensis (32.6%), Rattus rattus (26.7%), Lophuromys flavopunctatus (16.6%) and Praomys delectorum (16.3%) were captured. A total of 805 fleas (Xenopsylla spp., Dinopsyllus spp., Ctenophthalmus spp. and Echidnophaga gallinacea) were collected from rodents with an overall flea index of 2.4 fleas/rodent. Fleas from domestic animals were mostly Ctenocephalides spp. (>90%). A total of 270 house dwellings fleas with an overall index of 3.6 fleas per house were collected. Pulex irritans, Xenopsylla spp., Tunga penetrans, E. gallinacea and Ctenophthalmus spp. were dominant. All fleas were negative for Y. pestis DNA. This study has demonstrated a high flea abundance and high density indicating a high susceptibility of the study area to plague if and when other conditions are favorable, hence effective flea and rodent control measures should be put in place. The non-detection of Y. pestis in all fleas collected from rodents, domestic animals and domestic dwellings in the current study suggests that the ectoparasites do not normally harbor the bacterium during periods of quiescence. The findings of the present study further suggest that fleas should be tested for Y. pestis DNA during the active phase of plague outbreaks for confirmation of infection and during inter-epidemic periods to confirm disease quiescence or detect infection activity.