A serological survey of anthrax in domestic dogs in Zimbabwe: a potential tool for anthrax surveillance

Abstract

Anthrax is an important disease caused by the bacterium Bacillus anthracis affecting both domestic and wild animals at the wildlife/livestock interface, defined here as a physical space in which wild and domestic species overlap in range and potentially interact. In endemic regions, sporadic anthrax outbreaks occur, causing significant deaths of both wildlife and livestock and sporadically, humans. However, it may also occur as isolated outbreaks with a few animals affected. Such isolated anthrax outbreaks maybe missed. High seroprevalence among carnivores suggests either regular non-fatal exposure to the pathogen circulating in a given environment, or contact with missed cases through consumption of anthrax carcases. To investigate the relevance of this potential indicator, a cross-sectional study was conducted to determine anthrax seroprevalence in domestic dogs (Canis lupus familiaris) from selected interface and non-interface areas of Zimbabwe with known history of anthrax outbreaks. Based on past anthrax outbreaks in the respective areas, the sites were further classified as high or low risk areas for anthrax outbreaks. Sera were collected from domestic dogs (n = 186) and tested for antibodies against B. anthracis protective antigens (PA) using an ELISA test. The overall seroprevalence was 51.6% (96/186; 95% CI 44.2-59.0). Sites from the non-interface areas recorded a significantly (P < 0.001) higher (72.1%) anthrax seroprevalence compared with those from the wildlife -livestock interface (41.5%). The results demonstrated a strong association (χ2 = 14.3; OR = 3.2, 1.6 < OR < 6.2, P < 0.001) between anthrax seropositivity and interface type. Low-risk sites (42.5%) had a significantly (P = 0.044) lower seroprevalence compared with high-risk sites (58.5%) but still demonstrated high seroprevalence for areas where anthrax was last reported more than 20 years back. Dogs from Tsholotsho South were more than 90-times (OR = 96.5, 13.5 < OR < 690.8) more likely to be seropositive compared with those from Hwange. The study demonstrated the potential to use domestic dogs as indicators of anthrax in the study areas to survey anthrax circulation in supposed low-risk areas and calls for a redefinition of both low and high risk areas for anthrax in Zimbabwe based on an improved surveillance.

A serological survey of Bacillus anthracis reveals widespread exposure to the pathogen in free-range and captive lions in Zimbabwe.

“…The duration of antibody reactivity to anthrax has been found to be much longer in surviving carnivores, and indefinite in humans (Bower et al, 2019;WHO, 2008;Turnbull et al, 1992). These attributes make carnivores ideal sentinel animals for the surveillance of anthrax in the multi-host system at the interface (Hampson et al, 2011;Mukarati et al, 2018). Indeed in Namibia, results of serological reactions toB.…”

“…Despite anthrax being considered endemic in some parts of Zimbabwe (Chikerema, Pfukenyi, Matope, & Bhebhe, 2012;Mukarati et al, 2018), the epidemiology in wildlife is poorly understood due to suboptimal surveillance and outbreak investigations. Over the past 20 years to 2018, no overt anthrax outbreaks have been reported in wildlife in Hwange National Park (HNP) despite sporadic outbreaks of the disease in livestock in adjacent communal areas of Tsholotsho District to the South-East of the park (Mukarati et al, 2018). In this study, we gathered serum from 114 wild carnivores collected across high and low risk zones in Zimbabwe in order to explore the patterns of anthrax seropositivity in lions.…”

The pattern of anthrax at the wildlife-livestock-human interface in Zimbabwe

“…The study sites were selected to represent well defined porous wildlife-livestock-human interface and non-interface areas of Zimbabwe as previously identified [ 22 ] ( Fig 1 ). The wildlife-livestock-human interface (interface) was defined as an area with a potential overlap between sympatric wildlife, livestock and human populations, either through a direct physical sharing of the same space at the same time or an indirect sharing through sequential contacts with soil, forage and water [ 21 ].…”

“…Four porous interface sites were selected: two close to Gonarezhou NP, Malipati and Chizvirizvi in Chiredzi district and another two adjacent to Hwange NP, Ngamo in Tsholotsho district and Hwange in Hwange district ( Fig 1 , Table 1 ). Three non-interface sites, at least 15km from a NP or a protected area were also chosen namely, Chomupani in Chiredzi, Magunje in Hurungwe and Tsholotsho South in Tsholotsho districts, as described in a previous study [ 22 ]. Some of the selected study sites had a history of anthrax outbreaks in livestock and in some cases wildlife as well, according to information made available by the Epidemiology and Disease Control Unit, Department of Veterinary Services (DVS), Ministry of Lands, Agriculture, Water, Climate & Rural Resettlement, Zimbabwe.…”

“…The selection of the final respondents in the study sites was based on voluntary oral consent and the method was already described in detail in Mukarati et al . (2018) [ 22 ]. Briefly, on average each site is made up of about 30 villages and each village has 30 households, giving an average of 900 households per site and 6300 households across the seven sites.…”