Mosquito vector monitoring at Liberty Print E-mail
News - Rubrieke
Tuesday, 24 November 2015 22:19
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The Zoonoses Research Unit, Department Medical Virology, University of Pretoria did a demonstration of their insect vector monitoring programme at Liberty Stables in Mooiplaats in October. A visiting delegation from the US-Centers for Disease Control and Prevention and Department of Health and Human Services (HHS) of the USA attended the demonstration.

The delegates included representatives from the US Department of Health and Human Services, including dr Holly Wong, principal deputy assistant secretary for Global Affairs, and Dawn O’Connell, deputy chief of staff to the secretary. Also present were representatives of the Centers for Disease Control and Prevention (CDC)-South Africa office, dr Nancy Knight (country director), deputy director, Division of Global Health Protection, ms Stephanie Griswold and the One Health director, prof Marietjie Venter.

Prof Venter, also affiliated with the Zoonoses Research Unit (ZRU) and Professor Leo Braack, ecologist in the ZRU and head of the Vector Cluster in the Centre for Sustainable Malaria Control, are collaborating in a programme to investigate certain insect-transmitted viruses that can infect animals and humans.

The research approach has been to use horses, livestock and wildlife species with neurological signs to identify areas where these viruses are circulating as an early warning for human cases.

Mosquitoes and other insects are monitored at monthly intervals at a number of key sites where cases had been detected in the past in animals to see which mosquitoes are carrying viruses. Liberty Stables has been one of the key vector monitoring sites for the Pretoria East region in the past three years.

A programme of monitoring horses with neurological disease was initiated in 2006. Through this programme cases of West Nile virus (WNV) have been detected throughout the country as well as a number of other less well-known viruses such as Middelburg and Shunivirus, all of these able to cause severe and fatal disease in horses and certain livestock and wildlife species.

The mosquito trap

Severe cases of WNV may also occur in humans, although the frequency is lower than in horses, but the consequences may include meningitis, paralysis and even death. These viruses circulate in mosquitoes in late summer and autumn but also potentially in the Culicoides biting midges, which transmit the African horse sickness virus (AHSV). They are detected at the same time as AHSV cases.

Typical signs of WNV in horses include stumbling, front and or hind leg paralysis, facial tremors and inability to rise. Prof Venter helped to diagnose WNV in a horse at Liberty Stables in 2008 as well as various other cases in horses in Pretoria East including cases of WNV, Middleburg and Shunivirus.

The horse at Liberty survived the infection, but was severely sick at the time, needing hospitalization at Onderstepoort where he was cared for in a sling due to complete paralysis. Today he is competing at elementary medium dressage again, thanks to the perseverance, love and care of his owner, prof Juanita Jamneck, and extensive veterinary care.

From left to right: Holly Wong, principal deputy assistant secretary for Global Affairs, US Department of Health and Human Services (HHS); Dawn O’Connell, deputy chief of staff to the secretary, HHS; Melanie Boyer, manager of communications, Office of Global Affairs, HHS; Austin Demby, director and HHS deputy principal, Office of Global Affairs, HHS; dr Nancy Knight, US Centers for Disease Control and Prevention (CDC) South Africa country director; Steven Smith, health attaché and regional representative for Southern Africa, HHS; Stephanie Griswold, CDC South Africa Global Disease Detection deputy director, prof Marietjie Venter, One Health director; and Juanita Jamneck from Liberty Stables. Back: Piage Prangley-Maine on horseback

The ZRU started monthly mosquito monitoring sites on a number of horse farms and wildlife reserves in 2011 where neurological cases had been detected in animals, one of which is Liberty Stables.

During the visit prof Venter explained the value of the programme for detecting and responding to potential emerging and reemerging zoonotic viruses in Africa that have the ability to cause large outbreaks locally and spread internationally.

Cases of neurological disease in horses, wildlife and livestock are an early warning of a rise in virus activity in mosquitoes. Horses in particular are highly sensitive, although wildlife species such as rhinoceros also become paralyzed and die of these viruses.

By monitoring mosquito vectors, an increase of viruses in the area can be seen and vector control can be implemented. Prof Braack and PhD student, Todd Johnson, demonstrated to the delegation how mosquitoes are collected and sampled for virus screening.

Veterinarians are reminded to send suspected cases for testing to the ZRU at the University of Pretoria Medical School. This unit has a high level containment laboratory (Biosafety level three) that is approved by the Department of Agriculture, Forestry and Fisheries for handling and diagnosing zoonotic viruses and is accredited for testing them.

A vaccine for WNV is now available in the country as a result of the surveillance programme in horses.

A vaccine trial conducted by the ZRU showed that the vaccine used in the northern hemisphere can provide complete protection against South African strains. It is recommended that horse owners vaccinate their horses before the summer to provide protection against WNV. No vaccine is available to the other viruses at this stage, but using mosquito repellents that contain DEET and pyrethroids, such as cypermethrin, as well as stabling during the night can provide protection against mosquitoes and biting midges.

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