controlling their natural predators. In addition, overgrazing by domestic livestock
combined with above-average rainfall had resulted in severe bush encroachment that
favoured kudu, as they are browsers. Water provision in the form of windmills and
farm dams in a traditionally arid country where water is limited are also important in
kudu population dynamics and dispersal. Kudu are social animals, often browsing
close together, grooming each other and grouping together and dispersing with the
seasons. A rabid kudu produces large quantities of saliva, and due to their habits of
feeding from thorn trees, kudu often have injuries in their mouths: an easy route of
entry for the rabies virus. The combination of these factors resulted in rabies causing
very high mortalities in the kudu population. Several smaller outbreaks of rabies in
Namibian kudu have occurred in the years following the initial large outbreak.
Molecular analysis of these rabies viruses shows that kudu are capable of
maintaining epidemiological cycles of rabies within their species; this is an interesting example of how a pathogen adapts to and becomes endemic in a population
(Mansfield et al. 2006).
The high burden of rabies virus during the outbreak in kudu resulted in spillover
of rabies back to carnivores, including bat-eared foxes, jackals and lions in Etosha
National Park in Namibia (Berry 1993). Large carnivores in Hwange and Kruger
National Park in Zimbabwe and South Africa, respectively, have never been affected
by rabies in the same manner when outbreaks occurred adjacent to these parks. A
possible explanation for this is the higher carnivore species diversity in the latter two
parks, which prevents the population of any one carnivore species from becoming
particularly high. Due to its arid environment, Etosha National Park has a lower
species diversity and therefore less intraspecific competition, which may facilitate
rabies spread within infected species (Foggin 1988; Swanepoel 1995).
Rabies spillover in South Africa has also added a significant threat to an already
endangered species. The IUCN estimates the total worldwide population of African
Wild Dogs (Lycaon pictus) to be 6600 adults, and declining (Woodroffe and SilleroZubiri 2012). Current threats to wild dogs include habitat fragmentation and subsequent competition with other predators and conflict with humans (Woodroffe and
Sillero-Zubiri 2012). In 1997, just 2 years after their reintroduction into the area, an
outbreak of canid-biotype rabies decimated a pack of African wild dogs in Madikwe
Game Reserve. Of the pack of 27, only three survived (Hofmeyr et al. 2000). A
second outbreak in 2000 killed 10 of 12 pups, but the five adults in the pack survived
thanks to individual rabies vaccination that had been given to the wild dogs in the
park after the first outbreak (Hofmeyr et al. 2004). Similarly, in the Bale Mountains
of Ethiopia, the endangered Canis simensis (Ethiopian Wolf) is under severe threat
from rabies circulating in sympatric domestic dogs (Randall et al. 2004; Aguirre
2009).
The example of rabies in South Africa shows how a new strain of a previously
existing disease can have radically different effects when introduced to a new area
with a diverse potential host spectrum. It also shows that for a disease to become
established and invasive requires more than just introduction, especially if control
measures are used. In the case of rabies, repeated introductions were required before
the disease established itself in wild South African canids and became endemic. This
256
L. van Helden et al.
combined with above-average rainfall had resulted in severe bush encroachment that
favoured kudu, as they are browsers. Water provision in the form of windmills and
farm dams in a traditionally arid country where water is limited are also important in
kudu population dynamics and dispersal. Kudu are social animals, often browsing
close together, grooming each other and grouping together and dispersing with the
seasons. A rabid kudu produces large quantities of saliva, and due to their habits of
feeding from thorn trees, kudu often have injuries in their mouths: an easy route of
entry for the rabies virus. The combination of these factors resulted in rabies causing
very high mortalities in the kudu population. Several smaller outbreaks of rabies in
Namibian kudu have occurred in the years following the initial large outbreak.
Molecular analysis of these rabies viruses shows that kudu are capable of
maintaining epidemiological cycles of rabies within their species; this is an interesting example of how a pathogen adapts to and becomes endemic in a population
(Mansfield et al. 2006).
The high burden of rabies virus during the outbreak in kudu resulted in spillover
of rabies back to carnivores, including bat-eared foxes, jackals and lions in Etosha
National Park in Namibia (Berry 1993). Large carnivores in Hwange and Kruger
National Park in Zimbabwe and South Africa, respectively, have never been affected
by rabies in the same manner when outbreaks occurred adjacent to these parks. A
possible explanation for this is the higher carnivore species diversity in the latter two
parks, which prevents the population of any one carnivore species from becoming
particularly high. Due to its arid environment, Etosha National Park has a lower
species diversity and therefore less intraspecific competition, which may facilitate
rabies spread within infected species (Foggin 1988; Swanepoel 1995).
Rabies spillover in South Africa has also added a significant threat to an already
endangered species. The IUCN estimates the total worldwide population of African
Wild Dogs (Lycaon pictus) to be 6600 adults, and declining (Woodroffe and SilleroZubiri 2012). Current threats to wild dogs include habitat fragmentation and subsequent competition with other predators and conflict with humans (Woodroffe and
Sillero-Zubiri 2012). In 1997, just 2 years after their reintroduction into the area, an
outbreak of canid-biotype rabies decimated a pack of African wild dogs in Madikwe
Game Reserve. Of the pack of 27, only three survived (Hofmeyr et al. 2000). A
second outbreak in 2000 killed 10 of 12 pups, but the five adults in the pack survived
thanks to individual rabies vaccination that had been given to the wild dogs in the
park after the first outbreak (Hofmeyr et al. 2004). Similarly, in the Bale Mountains
of Ethiopia, the endangered Canis simensis (Ethiopian Wolf) is under severe threat
from rabies circulating in sympatric domestic dogs (Randall et al. 2004; Aguirre
2009).
The example of rabies in South Africa shows how a new strain of a previously
existing disease can have radically different effects when introduced to a new area
with a diverse potential host spectrum. It also shows that for a disease to become
established and invasive requires more than just introduction, especially if control
measures are used. In the case of rabies, repeated introductions were required before
the disease established itself in wild South African canids and became endemic. This
256
L. van Helden et al.