Volume 22, Number 5—May 2016
Exposure to Bat-Associated Bartonella spp. among Humans and Other Animals, Ghana
To the Editor: Human contact with wildlife is a leading cause of disease spillover. Bats, in particular, host numerous zoonotic pathogens, from henipaviruses to lyssaviruses (1). In Ghana, the straw-colored fruit bat (Eidolon helvum) frequently and closely interacts with humans through roosting in urban areas and human harvesting of bushmeat. Large colonies live in Accra, the capital city, and >128,000 bats, on average, are hunted for food yearly in southern Ghana alone (2). Serologic evidence of human infection with novel paramyxoviruses from E. helvum bats (3) supports concerns regarding this contact. In addition, Kosoy et al. (4) isolated several new strains of Bartonella that were found in >30% of E. helvum bats, whereas Billeter et al. found Bartonella in 66% of their ectoparasites (5), with Bartonella transmissibility to other species unknown. This prevalence causes concern because many Bartonella species are zoonotic and cause substantial human disease (6). Previous studies of febrile patients in Thailand have shown prevalence rates of <25% for antibodies against zoonotic Bartonella species (7). Serologic studies have been conducted in Europe and in the United States, but few studies have examined such prevalence in Africa among patients and in the general population (8).
To address these concerns, we conducted a prevalence study in Ghana, West Africa, for evidence of bat-associated Bartonella infection in humans and other common animal species. We sampled humans who had close contact with fruit bats and also sampled domestic animals that lived around the bat colonies.
We obtained serum samples from 335 volunteers from Accra and the Volta region who had close contact with E. helvum bats and also sampled 70 domestic animals that lived underneath bat colonies (5 cats, 23 chickens, 7 cows, 6 dogs, 21 goats, 8 sheep) in Accra. We used 3 testing approaches: culture, PCR, and indirect immunofluorescent assays for serologic testing. We tested serum specimens for antibodies against B. henselae, B. quintana, B. clarridgeiae, B. vinsonii vinsonii, B. elizabethae, and Bartonella strain E1–105, which had been isolated from E. helvum bats (6).
All culture results for human and domestic animal samples were negative for Bartonella species. One human serum sample was positive for B. clarridgeiae by PCR, which was confirmed by repeat testing. No other human samples were consistently positive by PCR. Of 70 animal blood clots and 62 serum samples tested by using PCR, 1 serum sample from a cat tested positive for B. henselae. One human serum sample was positive by immunofluorescent assay for antibodies against B. henselae at titers of 1:128, another had reactivity to B. henselae at 1:64, and 1 sample was reactive at 1:32. Five human serum samples were reactive to B. quintana at titers of 1:32.
The absence of evidence of any human exposure to bat-associated Bartonella suggests that the species isolated from E. helvum bats never or rarely infects humans in Ghana. If Nycteribiidae bat flies serve as the vector for Bartonella transmission between bats as hypothesized, then the high host specificity of these vectors (8) could explain why little infection is spilling over to other species. However, no experimental studies have confirmed that bat flies are competent vectors of bat-associated Bartonella species or that these ectoparasites only bite bats. These facts must be confirmed because bat flies are occasionally found on other animals and whether the parasites can successfully use these animals as hosts is unknown (9). Although further studies are needed to clarify the dynamics of Bartonella species infection in E. helvum bats, as well as the species’ zoonotic potential, the current risk of spillover of this bat-associated Bartonella species appears low in West Africa. This fact may be useful in directing limited public health resources.
The seroprevalence to B. henselae in healthy human participants in this study was <1%. The low levels of seropositivity to B. henselae and B. quintana are consistent with those found in the only other study on Bartonella in humans in sub-Saharan Africa: a survey of 155 subjects in the Democratic Republic of Congo showed 1% seroprevalence of B. henselae and <1% seroprevalence of B. quintana (8).
The results of study in the Democratic Republic of Congo and this study contrast with some studies in Asia and Europe, which show higher rates of human exposure to Bartonella species. For example, a study of febrile patients in Thailand found serologic evidence of exposure to Bartonella infection in 25% of patients (7).
Laudisoit et al. (8) were, to our knowledge, the first to report evidence of Bartonella infection in humans in Africa. Our study contributes to this nascent effort of understanding Bartonella on the continent. Because a substantial proportion of Bartonella prevalence studies have been done on hospital patients, our study provides a survey of the general population to help determine background infection rates and illuminate the complex risks posed by this zoonosis.
The research for this article was carried out during fieldwork in southern Ghana; at the 37 Military Hospital in Accra; at the University of Cambridge, Cambridge, UK; and at the Centers for Disease Control and Prevention, Fort Collins, Colorado, USA.
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1Current affiliation: Colorado Hospital Association, Greenwood Village, Colorado, USA.