Ricketsia felis is a worldwide emerging arthropod-borne pathogen. It was described as a human pathogen in 1991.1 Then, the detection of R. felis in laboratory-reared colonies of cat fleas, Ctenocephalides felis, drove scientists to the conclusion that this bacterium is hosted and transmitted by fleas.1 Numerous detections of R. felis in fleas collected from wild and domestic animals all around the world confirmed this hypothesis. The disease associated with R. felis has been named as “flea-borne spotted fever.”2 Multiple laboratory experiments confirmed that R. felis may be transmitted by cat fleas.3 However, until 2010, R. felis cases were very rarely reported. The disease has become increasingly more recognized in the tropical countries of Africa4 and Asia1 after simultaneous reports of high prevalence of R. felis infection in Kenya4 and in Senegal5 had been published. It was reported that fleas collected in an R. felis–endemic region in Senegal did not contain this bacterium6; this may suggest that another transmission mechanism exists. Moreover, it appears that the epidemiologies of malaria and R. felis infection in Senegal are very similar.5
These observations led us to the hypothesis that R. felis may be transmitted by mosquitoes in tropical countries.7–9 We have reported the correlation between mosquito-transmitted malaria and R. felis infection regarding geographic distribution, seasonality, asymptomatic infections, and a potential vector.5 Ricketsia felis has been also detected in wild Anopheles and in Aedes.8 Later, the ability of Anopheles mosquitoes to acquire and transmit R. felis to susceptible hosts was proven in an experimental model.7–9 Here, we report additional evidence of the connecting epidemiologies of both diseases. Dielmo and Ndiop are two villages in the Sine-Saloum region of Senegal situated 5 km from each other, with a total population about 800 persons and where the point-of-care laboratory was installed in 201110 to perform rapid detection of both pathogens. This laboratory serves two village dispensaries where all cases of acute febrile diseases are reported. The diagnosis is performed by using quantitative polymerase chain reaction and rapid diagnostic immunochromatographic tests. We analyzed the total monthly number of cases of malaria and R. felis infection in both villages for the period from August 2013 to October 2016, including the episode of malaria rebound in 2013.11 Over the study period, 236 and 28 human cases of malaria and R. felis, respectively, were identified. Figure 1 illustrates the dynamics of monthly number of cases of these infections. Both curves show the same peaks and declines. Using the R software (R Project, Auckland, New Zealand), we performed a Pearson correlation test to determine if there was a correlation between the cases of malaria and that of R. felis throughout the study period. Intriguingly, we identified a strong and significant correlation between the appearance and disappearance of the two diseases (correlation coefficient equal to 0.6, P value < 10−3).
Long-lasting insecticide-treated nets (LLIN) marked a real breakthrough in malaria prevention, resulting in a significant decline in morbidity and mortality. It seems that the renewal of LLIN in 2013 helped to stop malaria10 and R. felis infection rebound in Dielmo. As the growing number of cases of R. felis infection dropped to zero at the same time, it seems that this effective tool to reduce malaria burden may also decrease the number of acute R. felis infection cases. The strong significant correlation between the number of cases of R. felis infection and that of malaria further reinforces the hypothesis that most cases of R. felis infection in tropical areas may be transmitted by mosquitoes, in particular Anopheles spp.
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Richards AL, Jiang J, Omulo S, Dare R, Abdirahman K, Ali A, Sharif SK, Feikin DR, Breiman RF, Njenga MK, 2010. Human infection with Rickettsia felis, Kenya. Emerg Infect Dis 16: 1081–1086.
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Dieme C, Bechah Y, Socolovschi C, Audoly G, Berenger JM, Faye O, Raoult D, Parola P, 2015. Transmission potential of Rickettsia felis infection by Anopheles gambiae mosquitoes. Proc Natl Acad Sci USA 112: 8088–8093.
Sokhna C, Mediannikov O, Fenollar F, Bassene H, Diatta G, Tall A, Trape JF, Drancourt M, Raoult D, 2013. Point-of-care laboratory of pathogen diagnosis in rural Senegal. PLoS Negl Trop Dis 7: e1999.
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