Faculty of Veterinary Science
Department of Veterinary Tropical Diseases
Selected Highlights from Research Findings
The identities have been recorded of 558 ticks feeding on 194 humans in South Africa and collected over a period of 40 years. The ticks belonged to 20 species in 6 genera. Those most frequently encountered were the bont tick Amblyomma hebraeum, the yellow dog tick Haemaphysalis leachi, a bont-legged tick Hyalomma marginatum rufipes, another bont-legged tick H. truncatum, the brown ear tick Rhipicephalus appendiculatus, R. gertruda ( no common name) and the glossy brown tick R. simus. With the exception of H. leachi of which the adults feed on domestic and wild carnivores, the adults of all the other ticks feed on cattle and large wild herbivores. With the exception of the larvae of R. appendiculatus, the incidents of these ticks feeding on humans correlated well with their seasonal occurrences on preferred hosts. This means the ticks were generally present on the humans during the same seasons of the year that they were present on their normal cattle, herbivore or carnivore hosts. With the exception of the bont-legged ticks, the yellow dog tick, the glossy brown tick and R. gertruda, all of whose adult stages feed on humans, it was mainly the larvae of the other tick species that fed on humans.
Ticks were collected at monthly intervals, for 14 consecutive months, from the clothing of a game-guard providing protection for field-workers engaged in the collection, by means of flannel strips, of free-living ticks from the vegetation of four localities in the southern region of the Kruger National Park. In addition, with the exception of three months when the particular worker was absent, ticks that fed on one of the field-workers were collected over the same 14-month period. A total of 54 429 free-living ticks belonging to 14 species and 6 genera were collected from the vegetation at the four localities during this time and 3 751 ticks belonging to 11 species and 6 genera from the clothing of the game-guard. The larvae of A. hebraeum and the blue tick Boophilus decoloratus were the most numerous of the immature ticks, and H. leachi and R. simus of the adults on both the vegetation and the guard's clothing. Ticks fed on the field-worker on 6 occasions and 14 were collected, all of which were A. hebraeum larvae. This means that although there were at least 54 429 ticks out in the particular environment of the Kruger Park where we were collecting ticks, only 3 751 climbed onto the clothing of the game-guard and only 14 of them bit him. Thus, compared to the number of ticks present in the environment, the chances of being bitten are slight.
Contact person: Prof IG Horak.
In South Africa, as in all the important sheep producing countries of the world, resistance of internal parasites (worms) of sheep and goats to worm remedies has reached such high levels that it is posing a threat to sustainable production. In order to counter this problem a South African team developed the FAMACHA© system — a novel approach to worm control/ management. The system is based on clinical evaluation of anaemia by comparing the colour of the ocular mucous membranes to a colour chart we designed, depicting eyes of sheep with various degrees of anaemia. This enables treatment of only those individual animals in a flock that are unable to manage unaided. The effect is that selection for drug resistance is reduced to a large extent. After preliminary testing during 2001, it has now been confirmed — possibly a first for any clinical method of evaluation — that the FAMACHA© values of sheep under duress from worm infection are highly heritable. There is also considerable interest from abroad and the method is being disseminated widely internationally: this year, on invitation, it is being presented in Brazil to interested persons from Brazil, Argentine, Mexico, Cuba and Ethiopia. In October we published an invited review of the research on the FAMACHA© method in France, in a special issue of Veterinary Research.
In Suid-Afrika, soos in al die belangrike skaapproduserende lande van die wêreld, het weerstand van interne parasiete (wurms) van skape en bokke teen wurmmiddels sulke hoë vlakke bereik dat volhoubare produksie bedreig word. Ten einde hierdie probleem die hoof te bied, het 'n Suid-Afrikaanse span 'n nuwe benadering tot wurmbeheer/ bestuur ontwikkel. Die sisteem is gebaseer op kliniese evaluering van anemie, deur vergelyking van die kleur van die oogslymvliese van kleinvee teenoor 'n kleurkaart wat ons ontwerp het, en wat die oë van skape met verskillende grade van bloedarmoede uitbeeld. Hierdie maak individuele dosering van skape moontlik, wat nie sonder behandeling die mas teen heersende wurmdaging kan opkom nie. Die effek is dat seleksie vir wurmweerstand teen middels tot 'n groot mate verminder word. Na voorlopige toetsing in 2001 is dit nou bevestig dat — moontlik 'n eerste vir enige metode van kliniese evaluering — die FAMACHA© waardes van skape onder toestande van hoë blootstelling aan wurmbesmetting hoogs oorerflik is. Buitelandse belangstelling is groot, en die metode word tans internasionaal baie wyd bevorder en ook reeds toegepas: vanjaar op uitnodiging in Brasilië aan belangstellendes uit Brasilië, Argentinië, Meksiko, Kuba en Ethiopië. In Oktober het ons ook op uitnodiging 'n oorsig oor die FAMACHA© metode in 'n spesiale uitgawe van Veterinary Research in Frankryk gepubliseer.
Contact person: Dr JA van Wyk.
Only a limited number of publications dealing with bovine viral diarrhoea (BVD) virus infections in cattle in southern Africa have appeared. Our project dealt with the isolation and characterization of BVD viruses from cattle in South Africa. The results indicated that the newly recognized type II BVD virus present in North America and Japan is not present in South Africa. Phylogenetic comparison with strains isolated in other countries pointed to the fact that the current generation of imported commercial vaccines should protect cattle adequately against local strains of BVD.
Contact person: Prof M van Vuuren.
Serogroup-spesific enzyme linked immunosorbant assays (ELISA) for the detection of equine encephalosis virus (EEV) antigen and antibody were designed, developed and validated.
The international movement of horses for trade, competition and breeding has increased markedly during the last decade. Because most of these animals are now transported by air, the risk of them either incubating or carrying exotic agents has also increased. A project was undertaken to develop sensitive and specific assays for the detection of EEV antigen and antibodies. Serogroup-specific enzyme linked immunosorbent assays (ELISA) were designed, developed and validated. Such assays are important to study the epidemiology of EEV and also to differentiate between EEV and African horse sickness virus (AHSV) infections in equids. Both of these viruses are transmitted by the same insect vectors and in some cases horses infected with either virus may exhibit similar clinical signs. This could result in a misdiagnosis and a subsequent delay in the implementation of appropriate control measures.
The assays will be made available and used to determine the geographic and species distribution of EEV in Africa and elsewhere, to study the epidemiology of EEV in vertebrate and invertebrate hosts, to rapidly differentiate between EE and AHS viruses, to rapidly test sera from animals destined for international trade and to study EE- and AHS virus/antibody interactions in equids.
These assays were shown to be reliable, sensitive and specific and will prove invaluable in epidemiological studies of EEV infections, including the study of vertebrate and invertebrate host interactions, vector susceptibility and competence, sero-surveillance, virus transmission, and geographic and species distribution.
Contact person: Dr JE Crafford.
Foot-and-mouth disease (FMD) virus is a highly contagious disease of cloven-hoofed animals and camelids. The most susceptible animals are pigs, cattle, sheep and goats but the virus can affect up to 70 species of domestic and wild animals. Due to the rapid spread of the disease, as well as control and eradication costs, it is one of the most devastating socio-economic diseases of livestock. The epidemiology of FMD has been investigated largely in Europe, the Middle East, Asia and southern Africa and little is known about it in East and West Africa. This virus is a major threat to the livestock industry and although strict prevention measures are employed in most countries of the world, the implementation of FMD virus control programmes in Africa is a difficult task. In Africa, farmers commonly use intensive or nomadic livestock systems that facilitate the spread of infectious diseases, such as FMD.
To obtain a better understanding of the epidemiology of FMD viruses in East and West Africa and to assist in the implementation of control programmes in these regions, research on the molecular epidemiology of FMD was undertaken. Ms Oumou Sangare, a PhD student in the Department of Veterinary Tropical Diseases (DVTD) and originally from Mali, analysed the Type O viruses from West Africa and found three major lineages in this area with no distinct lineage confined to a specific country. This indicates that virus isolates in different countries were part of the same epidemic and emphasizes the lack of control of animal movement in the region. Isolates from both Type O and SAT 2 FMD viruses from East Africa have been characterized by Dr Mesfin Sahle, a PhD student (DVTD) from Ethiopia. These research results have given us a better understanding of the epidemiology of the disease in these countries and will assist in the implementation of appropriate control measures in the region.
Contact person: Prof EH Venter.
|
