Pathogens of Vertebrate Animals as Invasive Species: Insights from South Africa

Abstract

The study of disease organisms as invasive alien species has not received a great deal of attention in the field of invasion science. Introduced pathogens can have profound effects on living organisms, the ecosystems that they inhabit, and the economies that the ecosystems support. In this chapter, we use case studies of introduced diseases of domestic and wild animals (canine rabies, bovine tuberculosis, and rinderpest) and humans (smallpox, measles and human immunodeficiency virus, HIV) to illustrate the kinds of effects that these pathogens can have. The most dramatic impact to date was that of rinderpest, which caused the death of millions of cattle, and practically annihilated certain forms of wildlife from large parts of southern Africa. This in turn impacted severely on the region's economy, and resulted in large-scale changes to the structure and dynamics of ecosystems. Rinderpest has been eradicated globally, but both canine rabies and bovine tuberculosis remain, and ongoing vigilance and management will be required to contain them. Of the human diseases, smallpox has also been eradicated globally, but the effect of the disease, introduced by European colonists, was devastating. In the early 1700s, a large proportion (up to 90% in some communities) of the indigenous Khoekhoe people died, destroying their culture and way of life, and leaving the few survivors to be recruited as farm labourers. HIV, first detected in South Africa in 1982 has also had substantial impacts and antiretroviral treatment alone currently costs the government ZAR 66.4 billion annually. We also include West Nile Virus and African Swine Fever as examples of diseases that originated in Africa, and that may yet become globally destructive. We predict that new diseases will emerge as humans continue to expand their range into wild areas, and as trade volumes increase.

Biological Invasions in South Africa: An Overview

“…3-11) deals with the current situation. The first chapters focus on specific taxa-terrestrial plants (Richardson et al 2020b), aquatic plants (Hill et al 2020a), terrestrial vertebrates (Measey et al 2020a), terrestrial invertebrates (Janion-Scheepers and Griffiths 2020), and pathogens that affect mammals, including humans (van Helden et al 2020). The ecology of diseases, such as those covered by van Helden et al (2020), has not yet been integrated within the invasion science agenda in South Africa.…”

A review of the impacts of biological invasions in South Africa

“…This virus laid waste to cattle and wildlife populations across southern and eastern Africa, with severe ecological and economic consequences. It is estimated that 2.5 million cattle died in South Africa alone, with up to 95% mortality in some districts (van Helden et al 2020). Bovine tuberculosis (caused by the alien bacterium Mycobacterium bovis, which was introduced with cattle from Europe) has infected many wild mammals, including herbivores and carnivores.…”

“…The long-term effects on wild mammal populations are not well understood, but in the case of threatened species such as lions (Panthera leo) the effects of the disease may be compounded by other threatening factors such as habitat loss, poaching and feline immunodeficiency virus. This could have devastating consequences for the survival of lions in the wild (van Helden et al 2020). In a more recent development, the polyphagous shothole borer (Euwallacea fornicatus) and its fungal symbiont (the pathogen Fusarium euwallaceae) are known to have infected and killed individuals of at least 80 tree species, 35 of them native species (Paap et al 2018; Department of Agriculture, Forestry and Fisheries 2020).…”

Terrestrial Vertebrate Invasions in South Africa

“…Painted Reed Frogs were detected in Villiersdorp, Western Cape in 1997 and in Cape Town in 2004 (Davies et al 2013). A subsequent genetic study showed that these animals consisted of individuals that were extending their range from the Eastern Cape, and translocated animals from Mpumalanga, with the first records around 1995 (Tolley et al 2008). Davies et al (2013) explained how Painted Reed Frogs have been able to overcome their historical range limits by using a combination of human-mediated jump dispersal and artificial impoundments.…”

“…However, most recently, is the arrival of 'domestic exotics' (Guo and Ricklefs 2010), species that have part of their native and introduced range within South Africa. Studies to date (Telford et al 2019;Tolley et al 2008) suggest that all invasions originate from populations within the country.…”