A theoretical strategic snthelmintic control programme for haemonchosis in Kenya

Abstract

A study was carried out to analyse for the periods of the year with climatic conditions suitable for prolonged survival on pasture and hence increased chances of transmission of Haemonchus Contortus L)larvae to livestock, in seven different Agro-climatic Zones of Kenya. Data on mean total monthly rainfall, mean maximum and mean minimum monthly temperatures covering a span of over 30 years from 81 sites were analysed using Superscale 5 spread sheet programme. Zones 1:8, 111:5 and III: 1 had the potential to support the survival of larvae on pasture for most of the year except in January and February. Depending on altitude, Zones 11:3 and 111:6 bad, in addition, December as an unsuitable month to support the survival of larvae on pasture. All zones between 1:7 - 11:4 and 111:5 showed the potential to support the survival of larvae on pasture throughout the year. All other Agro-climatic Zones between 111:4 and VII: 1 showed seasonality in the likelihood to support the survival of larvae on pasture because of reduced availability of moisture. All months of the year, except August and September in Zone V:4 1ocated in the highlands (1,850 metres above sea level) were able to support the survival of larvae on pasture. Areas located at around l,5oo m above sea level in this zone had in addition the periods May-June as unsuitable for larval survival on pasture. In Zones 111:4, IV:5, V:5, V:3 and V:l, the months with potential to support the survival of larvae on pasture coincided with short rainy (November/December) and long rainy (March - May) seasons, and with the months preceding the long rainy season (January/February). The period between June and September was found to be unsuitable for the survival of larvae on pasture because it was the cold dry period in these regions. In ones 111:3, 1V:3, 1V:6, V:2 and VI:l, the months which supported the maximal survival of larvae on pasture coincided entirely with the rainy seasons. The hotter regions of Zone VII: l, with mean monthly maximum temperature in excess of 34°C and with hardly any rainfall, however, did not appear to support the survival of larvae on pasture. Based on the results of these analyses, a strategic anthelmintic control programme was suggested for Kenya and other East African regions with similar climatic potentials. In the wetter zones (1:8 - 111:5), it was proposed that an effective strategic anthelmintic control programme could be one in which all grazing livestock were treated twice during the period of short rains (November-December), at 3-week intervals (the pre-patent period of H. contonus), and again just before the onset of the long rainy season (late February). In the drier zones (111:4 - VI:l) effective strategic anthelmintic control of haemonosis could be achieved by treating all livestock immediately after the long rains (May-June) and after the short rains (January/February).