| dc.description.abstract | Helminthiasis is recognised as a major production and health constraint of small
ruminants in Africa, including Kenya. Among the helminthosis, haemonchosis has been
recognised as a serious and persistent constraint in Kenya despite it's well known
biology. This is mainly due to the significant influences of micro-climatic and
management factors on it's epidemiology. The influences of these factors in specific
regions have resulted in highly variable patterns of this disease in different agro-climatic
zones of Kenya which in turn have made it difficult to formulate a common and
effective management approach of combating it.
In general, the level of haemonchosis has been determined by assessmg the
faecal egg counts (fee) assuming that these correlate well to the total worm burden.
However this is not always true since fee are influenced by various factors, for example
fecundity of the worms, ingesta volume, age of the worms and host resistapce, yet many
tactical and strategic management programmes are based on the total egg counts.
The objective of this study was to establish the epidemiology of helminthiasis
with special reference to Haemonchus contortus in Muguga, a cool temperate, semij
humid to semi-arid area of Kenya with a view of recommending a cost-effective
management approach based on the risks exposed to sheep. The study set out to asses
the risk posed according to the level of third stage infective larvae (L3) available on
pasture and how this level was influenced by climatic factors. A series of experimental
plots were seeded with infected sheep faeces and monitored weekly for their ability to
yield Haemonchus contortus L3 and their magnitudes and persistence over time. A
parallel experiment monitored L3 recovered from a paddock naturally grazed by infected
sheep. Faecal egg counts and total worm counts were monitored from a group of these
sheep. Daily maximum, rmmmum and grass temperatures, rainfall, sunshine hours,
evaporation and relative humidity were recorded for the duration of the study.
Over the study period, absolute L3 recoveries ranged from 0.06-48.05%.
Survival of L, on herbage varied between 5-22 weeks and persistence in faeces for 3-22
weeks. The eggs were viable for 10.5-19.0 weeks. A repeated measures analysis of
variance showed that the magnitude of L3 recovered significantly differed (p=0.001)
with the seasons, with the time (p=O.OOl) following deposition of faeces on pasture and
was significantly affected (p = 0.035) by temperature. Optimal development of eggs to
L) required at least 50 mm of rainfall, 11-21°C and a sunshine index (n/N) of less than
0.6. These conclusions were also supported by Life Table analysis. High rainfall
increased survival of L) but decreased their magnitudes. Sunshine decreased both the
magnitude and survival of larvae while the prevailing temperatures (11-21°C) were
conducive for both development and survival of Lj.
Faecal egg counts correlated with rainfall and patterns of infection on pasture.
Packed cell volume (peV) remained within the physiological normal range. Total worm
counts observed in this study were an indication of pasture infestation. This study found
out that Haemonchus contortus was the most important helminth during the warm wet
periods, while Trichostrongylus colubriformis was the common helminth during the dry
cool periods. Larval inhibition (L4) was most significant (33%)during the cold season.
In Muguga L3 could not survive in appreciable amounts over the cold and hot
dry seasons. These seasons occurred in between the two rainy seasons. However, L3
developed from eggs deposited towards the end of the dry periods. These periods were
therefore important in maintaining infection from one rainy season to the next. Whereas
the measured weather parameters were related to development and survival of larvae,
they did not account for all the differences observed between the seasons.
Based on the results of this study. three anthelminthic treatments are
recommended. A single strategic treatment could be given at the end of each rainy
season to expel [he parasites at the beginning of the adverse hot-dry and cold-dry
seasons. These would result in sanitation of the pastures. A third tactical treatment given
in the middle of the long rainy season would reduce pasture contamination during this
period when conditions are highly favourable for L3 development. | en |
