African horse sickness (AHS) was reported in the south-western Khomas Region,
central Namibia (22° 24.063´ S, 17° 01.791´ E; 23° 32.617´ S, 15° 53.870´ E), contrary to
expectations that the arid conditions in the area would limit its occurrence. This prompted
investigation into the occurrence of AHS in horses, a possible reservoir animal, the
Hartmann’s mountain zebra (Equus zebra. hartmannae) and the occurrence of
the Culicoides midge vector (Diptera: Ceratopogonidae) of the disease in the area.
Questionnaires were used to explore the geographic characteristics of the study area, the
occurrence of an expected AHS virus reservoir animal, E. z. hartmannae and AHS in horses
in the study area. According to the questionnaire, rainfall patterns seem to follow topography
of the area, where the north-east formed the higher rainfall (420 mm/a) high-ground and the
south-western formed the lower rainfall (120 mm/a) pediment zone in the south-west. Cases
of AHS occurred mostly in mid-rainfall zones. E. z. hartmannae were present throughout the
area. They migrated from the southwest towards the north-eastern high-grounds during
droughts, presumably along ephemeral river beds.
E. z. hartmannae were sampled for blood and tissues and analysed for evidence of African
Horse Sickness Virus (AHSV) infection by indirect ELISA, RT-PCR and virus isolation
techniques. All useable samples tested positive for anti-AHSV antibodies. Viral RNA was
demonstrated in 26% of all the zebra sampled. No viable viruses were isolated from these
samples, however further research is required, as difficult sampling conditions may have
yielded false-negatives.
From 6 July to 21 September 2009, Culicoides midges were collected during the dry winter
season in suction UV-light traps installed at five selected sites along a rainfall gradient. In 38
collections, a total of 9091 Culicoides individuals, representing 25 species were collected.
The dominance of the proven vector of AHSV, Culicoides imicola Kieffer, varied in
dominance from 94% near Windhoek with high altitude and relatively higher annual rainfall,
to 12% at the site situated farthest southwest, with the lowest altitude and annual rainfall.
From what was observed of the occurrence of AHS in horses, E. z. hartmannae and the
distribution and abundance of the AHSV vector (Culicoides spp.), it was concluded that AHS
can be maintained in the south-western Khomas Region even in the lowest mean annual
rainfall zones. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/9508 |
| Date | January 2011 |
| Creators | Becker, Elbe |
| Publisher | North-West University |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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