Walia Special Edition on the Bale Mountains (2011) - Zoologische ...

Moreover, whereas domestic animals may be treated with anthelminthics to control parasite burdens
and their effect, wild species may be affected by increased loads. It is however impossible from this
preliminary work, to draw further conclusions on the (bi)directionality of parasite transmission,
which species might be involved, or which species might be most affected in and around the BMNP.
Nevertheless this result is valuable in demonstrating that such transmission could present a real rather
than purely hypothetical risk. Moreover, whilst mountain nyala are predominantly browsers, they
do feed on grass, particularly in the early wet season at exactly the time when helminth larvae may
emerge after a period of dormancy. and although widespread mortality is very unlikely, sublethal
effects of helminthes can have effects at both individual and population level and thus should be
considered in the future.
Third, this study has demonstrated that contact between wildlife and domestic animals
on the Gaysay grassland was and is both possible and probable. However, the risk of disease
transmission between these groups varies with both host and pathogen ecology, particularly by the
degree of separation of the two groups of host. The general avoidance behaviour of the two groups
of hosts is an important factor that will lower the chance of direct pathogen transmission. Wild
and domestic species did appear generally to avoid each other and rarely grazed sympatrically.
However, some mixed species groups were observed and the same land was used by the groups
at different times. Pathogen species and the mode of transmission also affects the risk of disease
transmission; pathogens with indirect transmission routes through the environment, wind, fomites
or vectors, or with intermediate stages such as helminths, are much more likely to be transmitted that
those requiring direct contact. In any scenario, an outbreak of an aerosolly transmitted and highly
pathogenic agent, such as CBPP would pose a grave risk to susceptible wildlife species. Fortunately
in recent years, extensive vaccination campaigns in domestic livestock have controlled many of the
most devastating viral infections, for example rinderpest is now thought to have been eradicated,
thus reducing the likelihood of such an event.
There is also evidence from this study that human activities disturb wild ungulates in this
area. A huge number of livestock and people cross the Gaysay grasslands on a weekly basis. Wild
ungulates clearly kept away from the road to avoid this disturbance, thus the continual increase in
people and livestock traffic in the park is of concern from a disturbance perspectives and well as
increasing the potential for disease transmission. The number of people and livestock using the
main bridge has apparently already increased since the mid 1980s, when Hillman (1986) recorded
an average of 1676 people and 1531 livestock crossing this bridge on market days, compared to
1882 people (12% increase) people and 1946 livestock (27% increase) in 1999-2000. It is possible
that transit rates have increased even more in the decade since this study was carried out and the
near completion of upgrade and asphalting of the major trunk road through the Gaysay grasslands is
likely to increase vehicle traffic in the further.
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 278