with fragmentation of landscape, a risk factor for disease outbreaks, although in the
context of disease, we would venture to say we have little understanding of the
effects of landscape heterogeneity and general principles of invasion ecology (FAO
2013; White et al. 2018). This is unfortunate, since climate change and landscape
heterogeneity can have a vast impact on the epidemiology of disease. Increased
temperatures may cause an increase, or even possibly a decrease in some cases, in
the number of diseases and an expansion in range of vectors and pathogens, while
indirectly, land use and biodiversity are changed by the changing climatic conditions. Recently there has been an expansion in cases of diseases such as Zika,
dengue, and yellow fever, which is a movement of these agents from wild to more
urban environments (Ali et al. 2017; Hamrick et al. 2017). Some disease agents that
are vector-borne develop faster within the mosquito at higher temperatures. In the
host, increases in temperature cause a higher degree of physiological stress, decreasing immunity and therefore increasing the risk of disease. Additionally, a drying
climate causes more farmers to switch to irrigating their crops, creating new habitats
for vectors in previously unsuitable areas. Health professionals should, therefore, be
aware of the effects of climate change in their areas and the previously undetected
diseases that may emerge as a result. Climate change may facilitate range expansion
within a country or expansion into a new country. This can be driven by the
increased movement of people and their animals because of political and climate
change, which is a threat for introduction of new diseases (Vorou et al. 2007). The
watch–word here is geopolitical instability.
An example of a viral disease that poses a likely threat to South Africa is peste des
petits ruminants (PPR) (Baazizi et al. 2017), which has been expanding its geographic range since it was identified in West Africa in the 1940s (Gargadennec and
Lalanne 1942) (Fig. 10.5). It is currently the focus of a global eradication strategy.
PPR resembles rinderpest, but infects sheep and goats instead of cattle, causing
damage to the respiratory and gastro-intestinal mucosa and resulting in up to 90%
mortality from diarrhoea and dehydration or secondary bacterial pneumonia (FAO
2015). The effect of PPR on wildlife, particularly smaller ruminants, is currently
unclear. PPR has resulted in high mortalities in Asian wildlife, including Ovis
orientalis (Wild Sheep), Capra aegagrus (Goat) and Gazella subgutturosa (Blacktailed Gazelle) in Iran (Marashi et al. 2017) and several wildlife species kept in
captivity (Munir 2014). Should PPR successfully invade South Africa, the possibility exists that it could cause a wide-scale outbreak affecting either or both domestic
livestock and wildlife. It is also possible that the disease could establish itself in a
wildlife reservoir, from where it could repeatedly spill over to domestic livestock,
although this situation has not been observed in infected countries. The threat of PPR
is exacerbated by climate change. As regions become drier, farming practices move
from the keeping of cattle to sheep and goats, which are more adaptable in drought
situations (Rust and Rust 2013). PPR, therefore, has a higher population of susceptible hosts available, and can have a more substantial impact on animal populations
and food security in regions which are already experiencing climate change or
ecosystem damage. Vaccines are being developed and will hopefully be effective
against this problem.
10 Pathogens of Vertebrate Animals as Invasive Species: Insights from South Africa
267
context of disease, we would venture to say we have little understanding of the
effects of landscape heterogeneity and general principles of invasion ecology (FAO
2013; White et al. 2018). This is unfortunate, since climate change and landscape
heterogeneity can have a vast impact on the epidemiology of disease. Increased
temperatures may cause an increase, or even possibly a decrease in some cases, in
the number of diseases and an expansion in range of vectors and pathogens, while
indirectly, land use and biodiversity are changed by the changing climatic conditions. Recently there has been an expansion in cases of diseases such as Zika,
dengue, and yellow fever, which is a movement of these agents from wild to more
urban environments (Ali et al. 2017; Hamrick et al. 2017). Some disease agents that
are vector-borne develop faster within the mosquito at higher temperatures. In the
host, increases in temperature cause a higher degree of physiological stress, decreasing immunity and therefore increasing the risk of disease. Additionally, a drying
climate causes more farmers to switch to irrigating their crops, creating new habitats
for vectors in previously unsuitable areas. Health professionals should, therefore, be
aware of the effects of climate change in their areas and the previously undetected
diseases that may emerge as a result. Climate change may facilitate range expansion
within a country or expansion into a new country. This can be driven by the
increased movement of people and their animals because of political and climate
change, which is a threat for introduction of new diseases (Vorou et al. 2007). The
watch–word here is geopolitical instability.
An example of a viral disease that poses a likely threat to South Africa is peste des
petits ruminants (PPR) (Baazizi et al. 2017), which has been expanding its geographic range since it was identified in West Africa in the 1940s (Gargadennec and
Lalanne 1942) (Fig. 10.5). It is currently the focus of a global eradication strategy.
PPR resembles rinderpest, but infects sheep and goats instead of cattle, causing
damage to the respiratory and gastro-intestinal mucosa and resulting in up to 90%
mortality from diarrhoea and dehydration or secondary bacterial pneumonia (FAO
2015). The effect of PPR on wildlife, particularly smaller ruminants, is currently
unclear. PPR has resulted in high mortalities in Asian wildlife, including Ovis
orientalis (Wild Sheep), Capra aegagrus (Goat) and Gazella subgutturosa (Blacktailed Gazelle) in Iran (Marashi et al. 2017) and several wildlife species kept in
captivity (Munir 2014). Should PPR successfully invade South Africa, the possibility exists that it could cause a wide-scale outbreak affecting either or both domestic
livestock and wildlife. It is also possible that the disease could establish itself in a
wildlife reservoir, from where it could repeatedly spill over to domestic livestock,
although this situation has not been observed in infected countries. The threat of PPR
is exacerbated by climate change. As regions become drier, farming practices move
from the keeping of cattle to sheep and goats, which are more adaptable in drought
situations (Rust and Rust 2013). PPR, therefore, has a higher population of susceptible hosts available, and can have a more substantial impact on animal populations
and food security in regions which are already experiencing climate change or
ecosystem damage. Vaccines are being developed and will hopefully be effective
against this problem.
10 Pathogens of Vertebrate Animals as Invasive Species: Insights from South Africa
267