Wild and Domestic Pig Interactions at the Wildlife-Livestock Interface of Murchison Falls National Park, Uganda, and the Potential Association with African Swine Fever Outbreaks

Abstract

Bushpigs (BPs) (Potamochoerus larvatus) and warthogs (WHs) (Phacochoerus africanus), which are widely distributed in Eastern Africa, are likely to cohabitate in the same environment with domestic pigs (DPs), facilitating the transmission of shared pathogens. However, potential interactions between BP, WH, and DP, and the resulting potential circulation of infectious diseases have rarely been investigated in Africa to date. In order to understand the dynamics of such interactions and the potential influence of human behavior and husbandry practices on them, individual interviews (n = 233) and participatory rural appraisals (n = 11) were carried out among Ugandan pig farmers at the edge of Murchison Falls National Park, northern Uganda. In addition, as an example of possible implications of wild and DP interactions, non-linear multivariate analysis (multiple correspondence analyses) was used to investigate the potential association between the aforementioned factors (interactions and human behavior and practices) and farmer reported African swine fever (ASF) outbreaks. No direct interactions between wild pigs (WPs) and DP were reported in our study area. However, indirect interactions were described by 83 (35.6%) of the participants and were identified to be more common at water sources during the dry season. Equally, eight (3.4%) farmers declared exposing their DP to raw hunting leftovers of WPs. The exploratory analysis performed suggested possible associations between the farmer reported ASF outbreaks and indirect interactions, free-range housing systems, dry season, and having a WH burrow less than 3 km from the household. Our study was useful to gather local knowledge and to identify knowledge gaps about potential interactions between wild and DP in this area. This information could be useful to facilitate the design of future observational studies to better understand the potential transmission of pathogens between wild and DPs.

Keywords: African swine fever; Uganda; bushpig; interactions; interface; warthog.

Figure 1

Spatial distribution of 233 pig owning households individually interviewed in southern Nwoya district, Uganda, near Murchison Falls National Park, 2015.

Figure 2

Monthly evaluation of three variables collected during individual interviews with 233 pig owning household in Nwoya District, Uganda, in 2015. Lines represent the type of housing system used (Fr, free range; Co, confined; Teth, tethered); dots represent the number of wild pig sightings (BP, bushpig; WH, warthog); and bar charts represent the number of ASF outbreaks (ASFob, ASF outbreaks) during the dry and wet seasons.

Figure 3

Spatial distribution of 233 pig owning households individually interviewed in southern Nwoya district, Uganda, near Murchison Falls National Park, 2015 and kernel density estimation of bushpig sightings distribution as reported by the interviewers.

Figure 4

Spatial distribution of 233 pig owning households individually interviewed in southern Nwoya district, Uganda, near Murchison Falls National Park, 2015 and kernel density estimation of warthog sightings distribution as reported by the interviewers.

Figure 5

Biplot of individuals and variable categories with confidence ellipses. Labels for variable categories are displayed: watersource (private/natural_or_both); iif = indirect interaction (iif_Yes/iif_No); season = season of the ASF outbreak (dry/wet/no; “no” refers to no ASF outbreaks reported by the respondent); waterdist = HH distance from the pig’s water source (more_500 m/less_500 m); ASF = ASF outbreak (ASF_Yes/ASF_No); burrowdist = HH distance from a WH burrow (less than 3 km/more than 3 km); and hunter = respondent being a hunter (hunter_Yes/hunter_No).

Figure 6

Associations between ASF occurrence and several categorical variables depicted by a multiple correspondence analysis, from data collected during individual interviews carried out in pig owning household in Nwoya District, Uganda. Coordinates of the categorical variables [namely, being a hunter, having indirect interactions with either warthog (WH) or bushpig, having a WH burrow less than 3 km from the HH, and season of ASF occurrence] are indicated by squares. Individuals with ASF occurrence is indicated by orange triangles, whereas those with ASF absence are indicated by green dots. Ellipses represent point concentrations. ASF.outbreak (ASF_Yes/ASF_No); Distance.to.Burrow = HH distance from a WH burrow (less than 3 km/more than 3 km); Being.Hunter = respondent being a hunter (hunter_Yes/hunter_No); Indirect.interaction (ii_Yes/ii_No); Season = season of the ASF outbreak (dry/wet/no; “no” refers to no ASF outbreaks reported by the respondent); Water.Distance = HH distance from the pig’s water source (more_500 m/less_500 m); and Water.Source (private/natural_or_both).

Figure 7

Divisive hierarchical clustering analysis of categorical variables from data collected during individual interviews carried out in pig owning household in Nwoya District, Uganda, 2015. Cluster one (black) and cluster two (red) (please refer to the online colored version) divide the data in HH without and with ASF occurrence, respectively.