Distribution and ecology of Ornithodoros moubata porcinus Walton (Acarina) in animal burrows in East Africa

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Abstract
In a survey of animal burrows in nine East African game areas or ranches 112621 specimens of Ornithodoros moubata pordnus Walton, vector of African Swine Fever Virus (ASFV), were collected from 172 burrows (out of 442 examined) in six areas. Burrows were usually located in open ground, in patches of scrub thicket and frequently in termite mounds; often the burrows had been excavated originally by antbear. Ticks were obtained by means of a lure, by chipping samples from the burrow walls and by taking soil samples from the burrow floors. Tick populations ranged from a few individuals to 250000 per burrow, second- and third-stage nymphae accounting for over 70% of the total population. Generally, ticks were found near the entrances of burrows on the floor, or on the roofs if the burrows had been unoccupied for some time, the latter position appearing to be a hunger response. Factors favouring large tick populations were neutral soils, high relative humidity, optimal temperature to be found at 3000–5000 ft above sea level, vegetation surrounding the burrow and the presence of burrow-inhabiting animals. Above 5000 ft O. m. porcinus was less common, and above 6150 ft none was found. Blood-meal identifications have shown warthog to be the primary host; other hosts included antbear, porcupine and hyaena. In areas with a particularly favourable environment the ticks can remain quiescent for long periods; in less favourable areas the continued maintenance of colonies is dependent upon the frequency with which ticks can feed on a suitable host. Some predation of adult ticks occurs but losses due to bush fires are not important. Heavy infestations of ticks may contribute to the mortality of young warthogs. The survey confirms experimental evidence that ASFV is well adapted to maintenance in the vector population.