| dc.description.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 EnzymeLinked
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-InfectedRecovered
(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 <
0.001). The seroprevalence of FMD was also higher in zone 1 than zones 2 and 3 (χ2 = 116.1,
df = 2, p < 0.001). In decreasing order, the overall seroprevalences of FMDV serotypes A,
SAT 2, O and SAT 1 were 26.3% (95% CI; 23.5-29.2), 21.4% (95% CI; 18.8-24.0), 21.2%
(95% CI; 18.7-23.9) and 13.1% (95% CI; 11.1-15.3), respectively. The distribution of these
serotypes differed significantly between zones (p < 0.05) except for SAT 2 serotype (χ2 =
0.90, df = 2, p = 0.639). Both serotypes A and O were more prevalent in zones 1 and 2 than
zone 3 (low interface area) while serotype SAT 1, was higher in zone 3 compared to other
zones. The results of multivariable analyses identified animal sex (female) and zones (high
interface area) as significant predictors (p < 0.05) of animal-level seropositivity
of Brucella spp. while for Leptospira spp., important predictors of animal-level seropositivity
were animal sex (female), zones (moderate interface area) and herds utilizing a communal
grazing reserve. For FMD, animal sex (female), raising of cattle in zones with moderate and
high wildlife-livestock interactions; mixing of cattle from multiple herds at watering points
and pastoral husbandry practices were all identified as significant predictors of animal-level
seropositivity. The results of the vaccination scenario analyses against FMD indicated that
both cattle and sheep hosts should be vaccinated in the Maasai Mara ecosystem for vaccination
campaigns to have the desired effect on this disease. Reactive vaccination of cattle alone, for
example, with 100% coverage reduced the cumulative incidence of FMD by 4.23% and 0.04%
in cattle and sheep populations, respectively, while when both host species were targeted, the
cumulative incidence of FMD decreased by 4.43% and 2.15% in cattle and sheep hosts,
respectively. The results also showed that reactive mass vaccination can substantially reduce
the cumulative incidence of FMD if implemented immediately at the onset of the outbreak
and with high coverage to compensate for the low vaccine efficacy. The cumulative incidence
of FMD, for example, reduced by 3.18% and 1.61% in cattle and sheep populations,
respectively, at day 1 of reactive mass vaccination with 75% coverage compared to 0.009%
(cattle) and 0.005% (sheep) at day 15 with the same coverage. Overall, pre-emptive mass
vaccination was found to be more effective in reducing FMD cumulative incidence than
reactive vaccination even when the former was implemented at low coverage. At a low
coverage of 25% in both cattle and sheep hosts, pre-emptive vaccination reduced the
cumulative incidence of FMD by 75.5% and 10.3% in cattle and sheep populations
respectively, when implemented 5 days before the outbreak. This study provides information
on disease priorities that occur in the surveyed zones in the Mara ecosystem and which the
locals must consider when accessing key ecosystem services such as water and pasture. The
seroprevalences of Brucella spp., Leptospira spp. and FMD in cattle were higher in areas with
moderate to high wildlife-livestock interactions than those with rare interactions. The
observed differences in the seroprevalences of the targeted pathogens between zones can be
considered while instituting routine disease control programs. | en_US |
