Bartonella Species and Trombiculid Mites of Rats from the Mekong Delta of Vietnam

A survey of Bartonella spp. from 275 rats purchased in food markets ( n =150) and trapped in different ecosystems (rice field, forest, and animal farms) ( n =125) was carried out during October, 2012–March, 2013, in the Mekong Delta of Vietnam. The overall Bartonella spp. prevalence detected by culture and PCR in blood was 14.9% (10.7–19.1%), the highest corresponding to Rattus tanezumi (49.2%), followed by Rattus norvegicus (20.7%). Trapped rats were also investigated for the presence and type of chiggers (larvae of trombiculid mites), and Bartonella spp. were investigated on chigger pools collected from each rat by RT-PCR. A total of five Bartonella spp. were identified in rats, three of which ( B. elizabethae , B. rattimassiliensis , and B. tribocorum ) are known zoonotic pathogens. Among trapped rats, factors independently associated with increased prevalence of Bartonella spp. included: (1) Rat species ( R. tanezumi ); (2) the number of Trombiculini–Blankaartia and Schoengastiini–Ascoschoengastia mites found on rats; and (3) the habitat of the rat ( i.e ., forest/fields vs. animal farms). The prevalence of Bartonella infection among chiggers from Bartonella spp.–positive R. tanezumi rats was 5/25 (25%), compared with 1/27 (3.7%) among Bartonella spp.–negative R. tanezumi rats (relative risk [RR]=5.4, 95% confidence interval [CI] 0.68–43.09). The finding of Bartonella spp.–positive chiggers on Bartonella spp.–negative rats is strongly suggestive of a transovarial transmission cycle. Rats are ubiquitous in areas of human activity and farms in the Mekong Delta; in addition, trapping and trading of rats for food is common. To correctly assess the human risks due to rat trapping, marketing, and carcass dressing, further studies are needed to establish the routes of transmission and cycle of infection. The widespread presence of these zoonotic pathogens in rats and the abundance of human—rat interactions suggest that surveillance efforts should be enhanced to detect any human cases of Bartonella infection that may arise.