process is still happening, as repeated contacts with a new species may be leading to
the virus establishing itself in new maintenance hosts, as was seen in the Namibian
kudu. Rabies spillover to vulnerable populations, such as those of lions and African
wild dogs, provides a good example of indirect species competition by one species
acting as a disease reservoir for another. Lastly, rabies provides an example of the
indirect damage to wildlife by the previous control measures implemented by
humans to control the disease.
10.2.2 Bovine Tuberculosis
Bovine tuberculosis (BTB) caused by Mycobacterium bovis, has existed in European
cattle for centuries. It is a chronic, slow-progressing disease that can affect most
mammals, causing emaciation and eventual death (Morris et al. 1994; Rodwell et al.
2001a; De Vos et al. 2001). Transmission between individuals occurs as a result of
contact with infected body fluids, usually through aerosol inhalation. It spread from
the Netherlands and the UK to many parts of the world that were colonised,
including South Africa, to which European breeds of cattle were brought in the
late eighteenth century (Huchzermeyer et al. 1994). BTB was first recorded in cattle
in South Africa in 1880 (Hutcheon 1880) and has existed ever since in livestock at a
prevalence kept low by state testing and eradication schemes. Sporadic cases of BTB
in wildlife were recorded since 1928 (Renwick et al. 2007), but the disease did not
appear to be established in any wildlife populations until it was detected in Syncerus
caffer (African Buffalo) in Hluhluwe-iMfolozi Park (HiP) in 1986 (Michel et al.
2006) and the southern part of Kruger National Park (KNP) in 1990 (Bengis et al.
1996; de Garine-Wichatitsky et al. 2010; DAFF 2013). In both cases, the source of
infection is believed to be from the interaction between buffalo and infected cattle
surrounding the parks. In the 1950s and 1960s, buffalo were frequently observed
grazing together with cattle adjacent to the KNP, and at least two cattle farms in the
area were confirmed to be infected with BTB (Renwick et al. 2007). In addition, at
that time several cattle on these farms died of Corridor disease (Theileriosis) which is
a buffalo-associated disease, illustrating contact between these species. The infection
of buffalo is therefore believed to have occurred at this time.
BTB has since been detected in buffalo herds throughout the KNP, and buffalo
are recognised as the primary maintenance host of the disease in this ecosystem.
Other wildlife species such as Greater Kudu (Fig. 10.3), Warthogs, Cheetahs,
Leopards, Black and White Rhinoceros, Chacma Baboons and Lions have all been
diagnosed with clinical BTB (Renwick et al. 2007; Miller et al. 2017) with speculation that kudu, lions and warthogs have the potential to be maintenance hosts of the
disease as well. As in the case of rabies, the social nature of certain species facilitates
establishment and transmission of BTB in a population due to close contact. Because
BTB is a chronic disease, infected animals have the potential to remain in their herds
for months to years and infect others for long periods before succumbing to the
disease. Social support systems also enable sick animals to survive for longer and
10 Pathogens of Vertebrate Animals as Invasive Species: Insights from South Africa
257
the virus establishing itself in new maintenance hosts, as was seen in the Namibian
kudu. Rabies spillover to vulnerable populations, such as those of lions and African
wild dogs, provides a good example of indirect species competition by one species
acting as a disease reservoir for another. Lastly, rabies provides an example of the
indirect damage to wildlife by the previous control measures implemented by
humans to control the disease.
10.2.2 Bovine Tuberculosis
Bovine tuberculosis (BTB) caused by Mycobacterium bovis, has existed in European
cattle for centuries. It is a chronic, slow-progressing disease that can affect most
mammals, causing emaciation and eventual death (Morris et al. 1994; Rodwell et al.
2001a; De Vos et al. 2001). Transmission between individuals occurs as a result of
contact with infected body fluids, usually through aerosol inhalation. It spread from
the Netherlands and the UK to many parts of the world that were colonised,
including South Africa, to which European breeds of cattle were brought in the
late eighteenth century (Huchzermeyer et al. 1994). BTB was first recorded in cattle
in South Africa in 1880 (Hutcheon 1880) and has existed ever since in livestock at a
prevalence kept low by state testing and eradication schemes. Sporadic cases of BTB
in wildlife were recorded since 1928 (Renwick et al. 2007), but the disease did not
appear to be established in any wildlife populations until it was detected in Syncerus
caffer (African Buffalo) in Hluhluwe-iMfolozi Park (HiP) in 1986 (Michel et al.
2006) and the southern part of Kruger National Park (KNP) in 1990 (Bengis et al.
1996; de Garine-Wichatitsky et al. 2010; DAFF 2013). In both cases, the source of
infection is believed to be from the interaction between buffalo and infected cattle
surrounding the parks. In the 1950s and 1960s, buffalo were frequently observed
grazing together with cattle adjacent to the KNP, and at least two cattle farms in the
area were confirmed to be infected with BTB (Renwick et al. 2007). In addition, at
that time several cattle on these farms died of Corridor disease (Theileriosis) which is
a buffalo-associated disease, illustrating contact between these species. The infection
of buffalo is therefore believed to have occurred at this time.
BTB has since been detected in buffalo herds throughout the KNP, and buffalo
are recognised as the primary maintenance host of the disease in this ecosystem.
Other wildlife species such as Greater Kudu (Fig. 10.3), Warthogs, Cheetahs,
Leopards, Black and White Rhinoceros, Chacma Baboons and Lions have all been
diagnosed with clinical BTB (Renwick et al. 2007; Miller et al. 2017) with speculation that kudu, lions and warthogs have the potential to be maintenance hosts of the
disease as well. As in the case of rabies, the social nature of certain species facilitates
establishment and transmission of BTB in a population due to close contact. Because
BTB is a chronic disease, infected animals have the potential to remain in their herds
for months to years and infect others for long periods before succumbing to the
disease. Social support systems also enable sick animals to survive for longer and
10 Pathogens of Vertebrate Animals as Invasive Species: Insights from South Africa
257