A study on the seasonal variations in the population structure of Haemonchus contortus and Trichostronglyus colubriformis was conducted for a period of 12 months in a typical large scale sheep farm on improved pasture in Peninsular Malaysia which has a wet tropical climate. Successive groups of helminth-free tracer lambs were grazed for 4 weeks together with naturally infected sheep and were necropised for worm counts 2 weeks after their removal from the pasture. The monthly populations of H. contortus fluctuated slightly except in May and August during which more worms were found in the tracer animals. The numbers of T. colubriformis were comparatively high from October to December 1992 and again in March 1993, low during April and June 1992. Small numbers of hypobiotic larvae of H. contortus were detected in the tracer animals. Development and survival of infective larvae of H. contortus and T. colubriformis on pasture were investigated by spreading faeces containing eggs on grass plots in October 1993, February and May 1994. Development of the eggs to the infective larvae occurred within one week and their survival times were 7 weeks in the 3 experiments. The potential for control by rotational grazing is discussed.
In 3 urban areas in Selangor, Peninsular Malaysia between 1973 and 1981, blood from 4084 dogs was examined for haematozoa. The following frequencies were found: Babesia gibsoni 17.7%; microfilariae of Dirofilaria immitis 9.6%; Hepatozoon canis 1.2%; B. canis 1.1%; Ehrlichia canis 0.2%; Trypanosoma evansi 0.1%. A detailed examination of B. gibsoni infections and microfilariasis due to D. immitis with regards to monthly distribution, breed frequency, sex and age, revealed that pedigree and non-pedigree dogs were equally susceptible to Babesia and microfilariae infections.