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On Culicoides as a Vector of Onchocerca gibsoni (Cleland & Johnston, 1910)
Published online by Cambridge University Press: 05 June 2009
Extract
The problem of the vector of Onchoccrca gibsoni was investigated in Kuala Lumpur, F.M.S., where the parasite is endemic and a high percentage of cattle is infected.
For reasons which are outlined, the experimental work was confined to species of Culicoides and Lasiohelea of which 18, possibly more, species were found on cattle, some of them being found to bite cattle in very large numbers daily.
The distribution of the microfilariae of 0. gibsoni in the skin of live cattle was found to be very irregular, even within small areas of skin. In transverse sections of skin the microfilariae appear to have a maximum concentration just under the epidermis at a depth of ·05 to ·2 mm.
0·52% of 1,523 Culicoides pungens, which were dissected soon after an infective blood meal, were found to have picked up the microfilariae. 0·96% of 1,670 of this species, dissected some days after an infective blood meal, were found to have developing or mature filarial larvae in the thorax or head. 0·35% of 3,734 of this species, were found to be naturally infected with filarial larvae in the thorax or head. The difference between the experimental infection rate and the natural infection rate is shown statistically to be significant and it is concluded that C. pungens is an intermediate host of O. gibsoni.
Culicoides oxystoma, C. shortti and C. orientalis were also dissected in large numbers and were found to pick up the microfilariae of O. gibsoni; in each of these species the experimental infection rate exceeded the natural infection rate, but the difference in none of these is significant. It is concluded however, from the results obtained and from the morphological similarity of the mature larvae found in these species with that in C. pungens, that these species are also intermediate hosts of O. gibsoni.
C. peregrinus and C. buckleyi are suspected but not proven intermediate hosts. C. anophelis and/or C. anophelisv. flavcscens and Lasiohelea stimulans were found to pick up the microfilariae but only partial development was found in them. C. sumatrae and C. raripalpis also picked up the microfilariae but no development was found in them. The remaining species worked with were entirely negative. In view, however, of the very minute percentage of infection which occurs in Culicoides spp. and the large numbers which must be dissected to obtain positive results, the negative results given by these less common species are not necessarily conclusive.
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- Copyright © Cambridge University Press 1938
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