Epidemiology Of Foot And Mouth Disease, Brucellosis And Leptospirosis At The Livestockwildlife Interface Area In Maasai Mara, Kenya

ABSTRACT

Intact ecosystems can regulate the transmission of infectious diseases by maintaining the

diversity of species in equilibrium. However, human driven land use change is a major driver

of environmental change and can affect the emergence and the transmission dynamics of

infectious diseases. This study investigated how land use change, and hence the extent of

wildlife-livestock interactions affect the transmission dynamics of infectious diseases in the

Maasai Mara ecosystem in Kenya, using foot and mouth disease virus (FMDV), Brucella spp.

and Leptospira spp. as case study pathogens. Three ecological zones were selected along

transect from the Maasai Mara National Reserve (MMNR) to settled areas with different landuse

types and varying resulting levels of wildlife-livestock interactions. Areas surrounding the

MMNR and wildlife conservancies represented zone 1 (areas with intensive wildlife-livestock

interactions) while areas between 20-40 km away from the MMNR constituted zone 2 with

moderate wildlife-livestock interactions. Zone 3 was represented by areas more than 40 km

away from the MMNR where wildlife-livestock interactions are low. A participatory

epidemiological study was first conducted to determine peoples’ perceptions on prevalence,

seasonality, and impacts on livestock production of infectious diseases of concern to

pastoralists in the defined zones. For this objective, four villages were purposively selected in

zone 1 and another two in zone 2. Data were collected in focus group discussions (FGDs)

using participatory epidemiological methods and with each group having 8-13 participants. A

cross-sectional study was also conducted to determine the seroprevalences of Brucella spp.,

Leptospira spp. and foot and mouth disease (FMD) among cattle herds raised in the area. Five

villages were purposefully selected; two in zone 1, another two in zone 2 and one in zone 3.

A total of 1,170 cattle sera were collected from 390 herds distributed across the zones and

tested for antibodies against Brucella abortus, Leptospira interrogans serovar hardjo and

non-structural 3ABC proteins (NSPs) of FMDV using commercially available Enzyme-

Linked Immunosorbent Assay (ELISA) kits. All sera samples were further tested for serotypespecific

antibodies of FMDV using Solid Phase Competitive ELISA (SPCE) kits (IZSLER,

Italy). The specific FMDV serotypes targeted included, A, O, South African Territory [SAT]

1 and SAT 2, known to be endemic in Kenya. Data on putative risk factors for transmission

of the targeted pathogens were collected for each sampled herd using a household

questionnaire. A compartmental baseline model with Susceptible-Exposed-Infected-

Recovered (SEIR) epidemiological classes was also developed to simulate the theoretical

transmission of FMDV between cattle and sheep hosts. Thereafter, a series of deterministic

SEIR models were fitted using the baseline model framework to evaluate the effects of

reactive and pre-emptive vaccination strategies in reducing the cumulative incidence of FMD.

The results of the participatory study showed that groups associated wildlife presence with

malignant catarrhal fever (MCF), FMD, East coast fever (ECF), African animal

trypanosomiasis (AAT), and anthrax, but they did not identify such linkages with goat pox,

bovine ephemeral fever (BEF), salmonellosis and bovine cerebral theileriosis (BCT). When

data from all sites were combined for impact matrix scoring, MCF, anthrax, FMD, contagious

bovine pleuropneumonia (CBPP), ECF and AAT, in decreasing order, were considered to

cause the highest economic losses in livestock production. A Kruskal–Wallis test revealed a

significant difference in FMD annual prevalence between cattle age groups (p < 0.001) and

was the highest in animals > 4 years (median score of 32.5, range; 10-50). FMD had the

highest impact on milk production, but in relation to its treatment costs, it was ranked second

to CBPP. The overall apparent animal-level seroprevalences of Leptospira spp., Brucella spp.

and FMD were 23.5% (95% CI; 21.1-26.0), 36.9% (95% CI; 34.1-39.8) and 83.8% (95% CI;

81.5–86.2), respectively. Zones 1 and 2 (closer to the MMNR) had significantly higher

seroprevalence of Leptospira spp. than zone 3 (χ2 = 7.0, df = 2, p = 0.029), while for Brucella

spp., the seroprevalence was higher in zone 1 than in zones 2 and 3 (χ2 = 25.1, df = 2, p