Paralysing virus attacks warthogs

What can monitoring mosquitoes and other blood-feeding insects in national parks tell you about diseases in humans? Dr Leo Braack of the Zoonoses Research Unit at the University of Pretoria believes “quite a lot”.

Arboviral or insect-borne viral diseases are caused by a wide variety of viruses that cycle between a mammal or bird host and an insect vector (disease transmitter).

They require multiplication in insects such as mosquitoes, sandflies, ticks, or biting midges before being able to be transmitted to a suitable vertebrate host, usually wild animals.

“What makes these viruses so successful is their ability to mutate quickly, making them very adaptable to local conditions, hosts and vectors that may be present,” says Braack, an entomologist with a long history of studying these disease vectors.

More than 130 arboviruses are known to cause human disease, and are responsible for some of the most explosive epidemics of emerging infectious diseases over the past decade.

From April to August 2010 and then again in 2011, a strange paralytic syndrome befell warthogs on the plains of Marakele National Park. Roughly 40 of them died and another 30 were detected showing mild paralysis and incoordination. The syndrome appeared to be limited to warthogs, although a similar neurological disease was later seen in jackals and blue wildebeest.

The course of the disease was protracted and affected warthogs progressed from initial incoordination, to eventual complete paralysis and death. Many of these animals needed to be euthanased. At the same time a similar paralysis syndrome was seen in white rhinoceros and disease-free buffalo in farms surrounding Marakele.

Dr Marietjie Venter of the Zoonoses Research Unit-University of Pretoria was able to isolate various arboviruses in the brains and spinal cords of affected animals.
The Marakele cases are believed to have been due to a distinct Shuni virus outbreak.

Due to the complex viral life cycle and interlinking factors, understanding the factors that drove the outbreak is not easy, but proactive disease vector surveillance will go a long way to improving our predictive abilities to when and why these diseases emerge.

Studying the biology of the insect vectors, their seasonality and adaptability in a systematic vector- surveillance programme will provide some clues as to possible vector dynamics that are driving disease emergence.

Partnering with the Zoonoses Research Unit, SANParks has launched a surveillance programme in the greater Marakele area that is designed to monitor virus activity in vectors. It is hoped this will not only provide a system for mapping disease distribution, but also provide information needed to assess risk and identify vector species for targeted control.