Project Leaders: Dr Chantel de Beer &
Dr Nonkululeko Raseasala
The Diptera family, Glossinidae, consists of only one genus, namely Glossina or tsetse flies. Although the distribution of these blood sucking flies are restricted to the African continent, they have on occasion been recorded in south-west Arabia as well as in Gizar in Saudi Arabia. David Bruce, working in Zululand in 1895, was the first to make the connection that these flies transmit a pathogenic trypanosomes that causes nagana in livestock. In 1909 he also demonstrated the role of
Glossina palpalis, in the transition of human trypanosomosis.
Economic development in Africa is greatly impeded by disease and tsetse flies play a major role in this. Agricultural utilization of the tsetse and trypanosome infected areas remains challenging. The human population of Africa is expanding and agricultural development, especially livestock, is extremely important. Livestock not only play a role as food source and draught power but also have great monetary and cultural value. It is thus important to control diseases of livestock, amongst with trypanosomosis plays a major role.
The tsetse population present in Zululand, north-west KwaZulu-Natal, South Africa represented the most southern distribution of tsetse flies in Africa. It is alleged that this fly population (including South Africa, Swaziland and southern Mozambique) is isolated from the rest of Africa. If this population is truly geographically isolated it may have major implications for tsetse eradication not only in the infected arae, but also from the rest of the continent.
The historical destruction of the tsetse flies G. m. morsitans in the most northerly parts of South Africa, and G. pallidipes, G. brevipalpis and
G. austeni in Zululand (after Fuller 1923 and Du Toit 1954).
Of the four tsetse species, Glossina morsitans morsitans, G. pallidipes, G brevipalpis and
G. austeni historically encountered in South Africa,
G. m. morsitans was the only species present in the most northerly parts, Limpopo Province, of South Africa. The other three species were restricted to Zululand. The first record of tsetse flies in the northern parts of South Africa dated back to 1872. Between 1872 and 1888 the northern distribution gradually decreased and finally, in 1897, as a result of the rinderpest epizootic (1896-1897) which led to a great reduction in cattle and antelope numbers, G. m. morsitans disappeared from the region. Of the three remaining species (G. pallidipes, G brevipalpis, and
G. austeni in Zululand),
G. pallidipes, was the most abundant and considered the most important vector.
G. austeni were confined to relative small areas and were not considered as important vectors for nagana.
The most commonly found tsetse transmitted trypanosomes in Zululand were
Trypanosoma brucei, T. congolense and T. vivax. From 1900 to 1946 numerous outbreaks of nagana was reported, and the most severe nagana outbreaks were reported in Zululand. In 1945 DDT become available in South Africa and by 1954
G. pallidipes was eradicated from the region.
Agricultural development in Zululand since 1955 onwards includes the establishment of commercial pine and eucalyptus plantations, which together with the increase in human and livestock populations let to bush clearing and only sporadic cases of trypanosomes were recorded. In 1990, however, a severe outbreak of nagana led to the implementation of emergency control measures and the re-entry of South Africa into the field of tsetse and trypanosomes research.
After the outbreak in 1990 in the area, dipping compounds was changed from Amitraz, used for tick control and does not kills flies, to pyrethroid cyhalothrin for two years. The adapted dipping system, together with the use of drugs, successfully controlled the disease. Disease control by means of dipping and drug treatment is very expensive and it soon became evident that a long term solution to the nagana problem will have to include the sustainable control of the vector.
To facilitate research on the vector the ARC-OVR established a tsetse research station at Hellsgate Military Base on Lake St Lucia In 1992. In 2006 this research station was relocated at Kuleni.
In 1996 a survey guideline was compiled and a 16 000 km2 area was surveyed using XT sticky traps to determine the extent of G brevipalpis and
G. austeni distribution in Zululand. Research on trap development led to the development of the H-trap which is especially aimed at the collection of the two species found in Zululand.
The historical distribution of the tsetse fliesG. pallidipes, G. brevipalpis and
G. austeni (after Du Toit 1954)
XT sticky traps used to determine
G. austenidistribution in Zululand in the 1990 survey.
H-trap developed by the ARC-OVR for trappingG. brevipalpis and
G. austeni in South Africa.
One of the control options investigated for the eradication on tsetse flies South Africa was the use of an area-wide integrated pest management (AW-IPM) approach, which included the sterile insect technique (SIT). The possibility of the use of SIT led to the involvement of the International Atomic Energy Agency (IAEA) in tsetse and Trypanosomes research in South Africa. The IAEA funded the investigation into the feasibility that an AW-IPM in South Africa and a number of documents were created:
Feasibility Study: The creation of a tsetse-free zone in the republic of South Africa and in the southern part of the republic of Mozambique (ARC-OVR)
Situation analysis of the feasibility and desirability for tsetse fly eradication in Kwazulu Natal South Africa (G.D. Parker, 2003)
Feasibility and Desirability of Tsetse Fly Eradication: Situation analysis of the environmental impact of tsetse intervention operations in South Africa (Ian Grant, 2003)
An examination of the costs and benefits of tsetse control in Kwazulu-Natal including the provision of a public relations campaign.(J D Knight, 2006)
A Strategy for an Area-Wide Control Campaign with an SIT Component to Establish a Tsetse- (G. austeni and G. brevipalpis) Free South Africa (Kappmeier et. al 2007).
The involvement of the IAEA further led to the establishment of colonies of
G. austeni and
G. brevipalpis at the ARC-OVR. These colonies were established from seed material provided by the IAEA. Research at the ARC-OVR has been directed towards the development and improvement of blood collection procedures to ensure the supply of a quality product, comparable to fresh blood, for the maintenance of viable colonies. As part of the research the role Salivary Gland Hypertrophy Virus (SGHV) could play in the sub-optimal production of these colonies was investigated. Although no obvious salivary gland hypertrophy could be seen in flies of different ages it remains to be seen what the results of GpSGHV-specifc PCR testing will be.
Research done on
Trypanosomosis since 2005 include topics such as:
The Epidemiology of animal trypanosomosis in KwaZulu-Natal
Vectorial competence studies on colony material indicated G. austeni to play a more important role than G. brevilpalis in the transmission of trypanosomes in livestock.
To understand the biology of mixed infections of different Trypanosoma congolense genotypes within tsetse flies, experiments were undertaken using colony flies to observe the possible production of recombinant trypanosomes, when different genotypes of Trypanosoma congolense are given in either equally mixed ratios or in varying ratios.