Rugutt, Moses Kipngeno Arap (1999) Epidemiology and control of ruminant helminths in the ...

369 Pages·2012·13.05 MB·English

Rugutt, Moses Kipngeno Arap (1999) Epidemiology and control of
ruminant helminths in the Kericho Highlands of Kenya.

PhD thesis

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EPIDEMIOLOGY AND CONTROL OF RUMINANT
HELMINTHS IN THE KERICHO HIGHLANDS OF
KENYA
MOSES KIPNGENO ARAP RUGUTT
BVM (Nairobi), M.Sc (Edinburgh)
Athesis submitted in fulfilment of the requirements for the degree of Doctor of
Philosophy in the Departmentof Veterinary Clinical studies, Faculty of
Veterinary Medicine.
University of Glasgow
April 1999
Abstract
The studies reported inthis thesis have been conducted in a high potential area of
the country where no previous studies had been undertaken. The two majorcomponents
of the research were anepidemiology study and an intervention study, both of which
were conducted on farms in the peri-urban area of Kericho. An initial background study
was conductedto collect data from the local VeterinaryInvestigation Laboratory, from
extension staffin aparticipatoryrapid appraisal (PRA) study and a cross-sectional socio
economic survey was undertaken with local farmers. These provided some
understanding of the problems caused byhelminths and the approaches taken to control
them, together with socioeconomic data relating to the keeping oflivestock in the area.
Disease appeared to be a major constraint affecting ruminant productivity, with
nematodoses appearing to be the most important helminth disease in the area particularly
in small ruminants. In the cross-sectional survey, more than 60 % of farmers reported
that they administered anthelmintics therapeutically and over 30 % gave routine
treatments. On average, cattle were reported as being given up to 1.5treatments per
year, sheep justover 1.1and goats 0.9 treatments per annum. In general, extension
workers recommend that animals are wormed every 3 -4 months, however this practice
was not adopted by the farmers because of the expense involved.
The epidemiology study conducted on 27 smallholderfarms over a 22 month
period obtained data on the prevalence of a)helminth ova in cattle, goat and sheep
faeces b) helminth larvae on herbage and c)the different nematode species acquired by
introduced Dorpertracer lambs which grazed on communal land. Grazing ruminants in
Kericho appear to be exposed to infection with gastrointestinal nematodes throughout
the year, there was no evidence of a marked seasonal influence on the availability of
infective larvae on pasture. The two commonest genera Trjchostrongylus and
Haemonchus are both well adapted to the three ruminant species that are commonly
grazed together.
II
Haemochus contortus was the predominant species in pasture samples and
accountedfor up to 88 %of the total worm populations recovered from the susceptible
Dorper lambs used as tracers. However, Haemonchus contortus was not the
predominant genera in the worm burdens recovered from locally purchased adult sheep
where Trichostrongylus species predominated, T.axei accounting for about 66 % and
T.colubriformis for 27 %of the average burden of local ewes. There was no indication
that arrested development played a keyrole in the population dynamics ofnematodes in
the area although retarded populations of T. axei were found in both local and tracer
sheep.
There was a marked similarity inthe pattern of egg counts seen in goats and
sheep in the epidemiology study and the faecal egg counts of lambs and kids mirrored
those of adult goats and sheep. This apparent regulatory capacity may be due to innate
resistance and/or the rapid acquisition of effective immunity. Calves passed significantly
more eggs than adultcattle passing on average over five times as many extraeggs as
adults.
The intervention study in which calves were treated on the basis of age confirmed
the crucial role ofacquired immunity in infrapopulation regulation. The faecal egg
counts of treated calves aged between 6-9 months and 9-12 months were 50 % and 37.5
% lower than control counts respectively. These differences were attributable to the
acquisition of immunity that reduced the impact of reinfection in the treated animals. A
similar effect was not apparent in the small ruminants that were treated in May, August
and November. Further studies arerequired to determine whetherit would also be
beneficial to treat young small ruminants on the basis of age.
A study of anthelmintic resistance on the small scale farms and 5 larger
farms in the district was conducted according to the WAAVP guidelines. The quality of
locally available anthelmintics was also assessed as part of this study. The use of adult
goats which tend to have overdispersedpopulations appeared to have influenced the
outcome of the trial since resistance was not confirmed but merely suspected.
Levamisole resistance was suspected on 3 of the large scale farms and the smallholder
farms, whereas resistance against ivermectin was suspected on three large scale farms
III
and benzimidazole resistance was suspected on one of the larger properties. Suppressive
anthelmintic regimes and intensive treatment regimes do not appear to be a sustainable
option for the control of nematodes in the region given the extent ofsuspected
anthelmintic resistance on the large and small scale farms in the study area.
The problems ofanthelmintic resistance inthe imidazothiazole family will
almost certainlyhave been exacerbatedby the numbers ofpoor quality drugs on the
market. Only 2 ofthe 9 levamisole containing drugs purchased locallyfulfilled the
expected quality criteria.
The average daily weight gains of calves, kids and lambs were relatively low in
this study which is not surprising considering the relatively poor nutritional environment,
tendency for overgrazing and background of disease in the locality. Socio-economic
factors may also contribute to these low growth rates since emphasis is given to the
numbers of animals rather than their performance.
Improving disease control is simply one of the many changes that are required in
order to improve the productivity and quality oflocal livestock and thus create additional
income for the smallholderfarmers. Given the limited resources that are available these
much neededchanges can only be brought about through an integratedprogram which
involves not only researchers and extension workers but also seeks to promote actively
farmer education regarding these issues.
iv
This thesis is dedicated to Obot Cheptoo, Cheptoo, Kipngetich and
Cheruiyot.
v
Declaration
The work described in this thesis was undertaken by me as part of a wider study of the
National Agricultural Research Programme at the National Veterinary Research Centre
Muguga, Kenya. I declare that the experimental designs, execution and interpretation of
the data are my own unless stated otherwise. All contribution made by otherpeople are
fully acknowledged in the text.
Moses Kipngen
April 1999.
VI
Acknowledgements
The study in Kenya lasted a duration of38 months during which many people
directly or indirectlycontributed to the overall outcome. First and foremost I must thank
my supervisors FrankJackson, Moredun Research Institute, (MRI), Prof.Quintin
McKellar (firsthalfofthe study), Prof. J. L. Duncan (second half) and DrR.L. Coop
(MRI) who contributed immenselyto the overall design ofthe HelminthologyProject at
theNational VeterinaryResearch Center(NVRC)-Muguga, Kenya ofwhich this study
was part of. Many thanks to Dr. R. K. Bain and othercolleagues for critical review as
the study progressed. The inputofthe Socio-economic Division in NVRC, for the
design ofthe cross-sectional surveyquestionnaires and analysis which enabledfarms to
be selected for intervention study is appreciated.
The field component went on well without any majorproblem. Thanks to the
extension staffespecially the District Veterinary Officer (DVO) for the support during
selection ofthe study site and throughout the entire period. The support ofKericho
Veterinary Investigation Laboratory (VIL) staffwas foremost appreciated as they availed
laboratory room for sampleprocessing. Thecooperation and support ofHelminthology
laboratorytechnical staffunder the supervision ofMr. W. Chepkwony is acknowledged,
as that ofthe animal attendants and the drivers. Ofcourse without the farmers this work
would not have been a success, thanks to the 75 small-scale farmers and 5 large estates
who participated in the study, in particular, FarmerNumber29 who availed spaceto
construct a pen to house the tracers. In Swahili language we sayAHSANTESANAA.
The support ofthe TeaResearch Institute in Kericho for provision ofweather
data is acknowledged.
The U.K part of the study was essentially analysis ofdata and writing up at the
MRI, Edinburgh. Iam greatly indebted to the Scientific Director, Prof. Q. McKellarfor
the use ofexcellentfacilities especiallythe library, photography and graphics. Thanks a
lot to those who assisted in these sections. Secondly, my supervisorDr. Jackson for
critically reading the manuscript and the support and encouragement from the
Parasitology group. Thirdly, on analysis ofdata. This was in two components, one was
effectively handled by Glasgow University Veterinary School; Division ofVeterinary
Vll
Informatics and Epidemiology and the second component in MRIunder Dr. Ian
McKendrick and Ms Cathy Hau. I must single for praise Cathy who conscientiously
went through all the data for the entire study period.
My employer, Kenya Agricultural Research Institute (KARl) supported the study
by provision of support staffand facilities. Secondly the Department for International
Development (DFID) of United Kingdom with the government of Kenyawho provided
financial supportunderthe auspices of National Agricultural Research Programme
(NARP)-amulti-donor agricultural project which also funded the U.K study period.
Last but not the least, I must thank myentire family-especially my wife for the
support throughout the duration of the study.
Those who may not have been mentioned take heart as I appreciated your input
and may God bless you all.
viii
Table ofContents
Title .i
Abstract .ii
Dedication v
Declaration vi
Acknowledgements vii
Table of Contents .ix
List of Figures xvii
List of Tables xxi
List of Plates xxv
Abbreviations xxvi
CHAPTERl
General Introduction
1.1Introduction 2
1.2Studies in Kenya 3
1.2.1 Nematodes 4
1.2.2 Trematodes 10
1.3Studies on different agroclimatic zones in other tropical and subtropical
countries 12
1.4Description of the study area-Kericho 14
1.5Nematodoses 15
1.5.1 The Life cycle 16
1.5.2 The Ecology ofInfective Trichostrongylid Larvae 20
1.5.3 Pathogenesis and Clinical Signs : 22
1.5.3.1 Haemonchosis 22
1.5.3.2 Trichostrongylosis/Cooperiasis 23
1.5.3.3 Oesophagostomiasis 23
IX