What scientists know about microscopic invaders that cause disease in South Africa

This book chapter summarises the latest information on diseases such as rinderpest, rabies, measles and HIV, all caused by invasive microorganisms (viruses, bacteria and other small creatures that are considered a non-native species, meaning that they are not naturally found in a particular environment). These diseases all affect animals and people in South Africa, and outbreaks ultimately hurt the country’s economy.

In a field of research called ‘invasive science’, scientists study organisms that thrive and cause harm after being introduced into new environments where they are not normally found. Most research has focussed on large “invasive species” like plants and animals, but microscopic invaders that cause disease are as important.

In this chapter, the authors discussed some animal and human diseases in South Africa that are caused by those introduced microorganisms.

They said the most dangerous was the ‘rinderpest’ disease, detected in South Africa in 1896. Rinderpest was caused by a virus and affected cattle and buffaloes. The same virus caused measles in people. Many rural people faced hunger after the 1896 outbreak, but the disease has now been eradicated through vaccination.

The authors said between 1772 and 1861, many dogs in South Africa had rabies, even though people did not know what disease this was. By 1893, it was known that rabies was caused by a virus, so the government decided to kill affected dogs and vaccinate those not affected. However, this did not eradicate the disease and it still affected many wild animals like duikers, lions, wild dogs, jackals and foxes.

The authors said in 1928, 2 children were bitten by a Yellow Mongoose and died of rabies. Since then, rabies became common in South Africa.

They said in 1954, many South Africans were also affected by measles. When this chapter was being written, measles was killing about 400 children each day. They said measles was common where people and cattle were in close contact.

The authors also mentioned a disease called bovine tuberculosis (BTB), caused by bacteria. BTB killed cattle, buffalo, warthogs, cheetahs, leopards, kudus, baboons and lions. They said BTB disease was first reported in a South African national park in 1996. The government controlled the disease by killing the infected buffaloes.

The authors said another virus, introduced into South Africa by travellers from Europe, caused a disease called ‘smallpox’ in people. The disease killed over 90% of the local Khoekhoe people. At the end of the disease outbreak, the Khoekhoe culture had been virtually destroyed.

The authors also reported on the human immunodeficiency virus (HIV) that caused the AIDS disease outbreak. Scientists still think the virus was originally transferred to humans from animals, in a process called zoonosis. The virus was first detected in South Africa in 1982. They said, as of 2019, HIV had no vaccine or cure.

They concluded the chapter by talking about the West Nile Virus and African Swine Fever, which they said originated from Africa and spread to Europe and America. 

The West Nile virus was transmitted by mosquitoes and killed mostly birds, but also affected horses and people. 

They said animals like warthogs and bush pigs transmitted the African swine fever disease. The disease affected pigs, and greatly affected pig businesses.

The authors said they only discussed diseases caused by bacteria and viruses, so this chapter is not a complete account of all invasive microorganisms.

The authors were 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

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