Experimental chemotherapy of dermatobiosis in laboratory animals
Chaia, G.; Borja, G.E.; Chiari, L.; dos Santos, C.N.; Abreu, R.T.
Revista do Instituto de Medicina Tropical de Sao Paulo 17(5): 298-306
1975
ISSN/ISBN: 0036-4665 PMID: 1198005 Document Number: 95543
Experiments on the chemical control of Dermatobia hominis (L. jr.) were facilitated by the maintenance of the insect through its whole life-cycle under laboratory conditions and the insect through its whole life-cycle under laboratory conditions and the successful infestation of small animals. Fallen larvae were collected from a slaughter-house and from experimentally infested cattle kept in an animal house and were stored at 28 deg C and 70-95% R.H. until pupation. Puparia were half buried in shallow sand in a container inside a nylon-gauze cage. The adults were transferred to another cage to mate. Pupation rates were 83.6 and 88% and adult emergence rates 63.4% and 71%.Experimental groups of 1-10, 11-20, 21-30 and 31-40 adults of D. hominis and 200 of Musca domestica L. were set up in cages measuring 45 X 30 X 30 cm in the humid chamber. The mean number of house-flies on which eggs were laid increased with the proportion of Dermatobia from 9.9 to 39.2. The flies bearing eggs were transferred to a smaller cage in the humid chamber and mechanically killed after 6-8 days. Eggs that dropped were held on the palm of the hand, and larvae that hatched within 30-45 s were collected and transferred to the skin of an anaesthetised experimental animal with a small brush. The percentage hatch was 48.2. The 340 rats and 30 hamsters used received 4 larvae each, 30 mice 2 larvae each and 2 calves 1500 larvae each. All the rats, hamsters and mice became infected, but there were death rates of 33.3% in hamsters and 76% in mice, whereas in rats there was a negligible death rate of 0.8%. Nearly 900 larvae dropped from one calf and 387 from the other, mostly during the fifth and sixth weeks after infestation.Of the infested rats, 63 were treated percutaneously on the 15th day of infestation with single doses of trichlorphon (Dipterex) at 50, 100, 150 or 300 mg/kg, and 39 by mouth at 50, 150 or 300 mg, to determine the effect on D. hominis in rats of this compound which is known to control it in cattle. The highest rate gave complete kill of larvae by both routes. The lower dosages gave kills ranging from 25 to 100%. These results suggest that the rat is a suitable host for tests of insecticides against D. hominis, especially for the preliminary screening of new compounds.