Infectious causes of small ruminant mortality in Kenya: A review

Small Ruminant Research 29 Ž1998. 1–11

Infectious causes of small ruminant mortality in Kenya: A review E.J. Peeler ) , S.W. Wanyangu National Veterinary Research Centre, Kenyan Agriculture Research Institute, P.O. Box 32, Kikuyu, Kenya Accepted 2 October 1997

Abstract Small ruminant production systems in Kenya are briefly described. The types of study reporting small ruminant mortality rates, and the large range of values found, are documented and discussed. It was noted that reports from arid and semiarid areas greatly outweigh the number of reports from higher rainfall areas and that more data on mortality before weaning than at any other age are available. Indeed there was only sufficient evidence to draw conclusions regarding pre-weaning mortality rates from arid and semiarid areas, which appear to vary, between locations and from year to year, from 10 to 30% in lambs and from 20 to 30% in kids. Differences in mortality between sheep and goats, and singles compared to twins are discussed. The following infectious causes of mortality were reported in the literature reviewed: tick-borne diseases, including Nairobi sheep disease and heartwater, trypanosomiasis, fasciolosis, pneumonia, capripox, helminthosis, coccidiosis and enterotoxaemia. This review of the literature indicates that the majority of recorded small ruminant deaths are disease-related and that respiratory and intestinal diseases are the most important infectious causes. The quality and value of the available data, the design of on farm studies and the general requirements for animal health and production information in planning livestock development are discussed. Based on the deficiencies in current knowledge, recommendations for future research are made. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Sheep; Goat; Mortality; Disease; Kenya

1. Introduction Livestock management and climatic conditions vary greatly in Kenya, influencing rates and infectious causes of mortality. This review uses two broad production system categories: mixed livestock, arable, smallholder production in agro-climatic zones ŽACZ. 1–4 ŽPratt and Gwynne, 1977., where average annual rainfall is between 700 and 2000 mm and )

Corresponding author. University of Bristol, School of Veterinary Science, Langford House, Langford, Bristol B518 TDU, UK.

pastoral production which predominates in ACZ 5–7, average annual rainfall of 200–700 mm, where arable agriculture is neither widespread or appropriate Žsee Fig. 1.. Peeler and Omore Ž1997. used data from the Ministry of Agriculture, Livestock Development and Marketing ŽMALDM. ŽAnonymous, 1993. to arrive at the following estimates of livestock populations by system: 2.7 million sheep and 3.7 million goats in smallholder production systems ŽACZ 1–4. and 6.0 million sheep and 4.3 million goats in pastoral systems ŽACZ 5–7.. Indigenous breeds of sheep and

00921-4488r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 9 2 1 - 4 4 8 8 Ž 9 7 . 0 0 1 2 0 - X

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E.J. Peeler, S.W. Wanyangur Small Ruminant Research 29 (1998) 1–11

Fig. 1.

goats, i.e., the Red Maasai and black-headed Persian breeds of sheep and Small East African ŽSEA. and Galla breeds of goat, predominate in both systems.

However, the Dorper breed of sheep is becoming popular and small numbers of exotic dairy goats are kept by smallholders.

E.J. Peeler, S.W. Wanyangur Small Ruminant Research 29 (1998) 1–11

Infectious diseases affect the productivity of small ruminants in many ways. However, from an examination of the available information, there appears to

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be very little quantitative information on the impact of disease on any production parameter except mortality. Thus, this paper confines itself to reviewing

Fig. 2.

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E.J. Peeler, S.W. Wanyangur Small Ruminant Research 29 (1998) 1–11

the importance of infectious disease in causing mortality, while recognising that the impact on other aspects of production are often significant, and aims to assess the current state of knowledge and future research priorities. 2. Materials and methods Most of the reports reviewed have appeared in refereed journals and were identified through searching abstract databases. MALDM annual reports were consulted and other reports have come to the authors’ attention through contact with livestock development projects in Kenya. The library at the University of Nairobi was searched for theses with relevant data. The location of the study sites referred to in this paper are indicated on Fig. 2. In the reports reviewed, mortality rates have been calculated by a number of methods. For the purposes of comparison, the authors have expressed mortality as risk rates ŽMartin et al., 1987., using, whenever possible, the number of animals at the outset of the period of observation as the denominator and the number dying during the period as the numerator. The period of observation is one year unless otherwise stated. 3. Mortality rates 3.1. Pastoral production Herren Ž1991. studied Maasai livestock production in Laikipia district while Bekure et al. Ž1991., Peacock Ž1984., Wilson et al. Ž1985. and Maina Ž1996. worked with the Maasai in Kajiado district. In all these studies, regular visits were made to record production events. They noted variable levels of mortality but all, except Wilson et al. Ž1985., recorded higher pre-weaning mortality in goats Žsee Table 1.. Peacock Ž1984. found that for both sheep and goats, twins and offspring born in the dry season had a higher mortality Žgoats had a higher level of twinning, 1.3 compared to 1.02 in sheep.. Carles et al. Ž1987. made daily recordings of mortality over a 3-yr period in two pastoral areas in northern Kenya, Marsabit and Isiolo districts. In Isiolo, mortality was highest during the first 3 weeks of life Ž30%. while in Marsabit it was minimal Ž3%.

for the same period. The difference was attributed to contrasting systems of neonatal management. A cross-sectional survey conducted in Isiolo district ŽAnonymous, 1992. estimated that, in an average year, annual mortality was 15–20% for adult sheep and goats and 20–25% for lambs and kids. Njanja Ž1991. recorded small ruminant production from a single herd in Turkana district over 3 yr. Annual adult mortality rates varied from 0 to 25% for sheep, 13 to 33% for goats, while the average pre-weaning mortality was 5% for lambs and 11% for kids. There are four reports of pre-weaning mortality from research stations in semiarid areas ŽACZ 4–5.. Angwenyi and Bebe Ž1989., Gachuiri et al. Ž1986. and Gatongi Ž1995. studied SEA goats and all reported pre-weaning mortality between 17 and 19%. Angwenyi and Bebe Ž1989. noted a variation in pre-weaning mortality of 7.6–26.3% over a period of 4 yr. Work by Skea et al. Ž1990. with Galla goats in Meru district indicated the low level of mortality Ž3%. that is achievable with good management and a high level of inputs in a semiarid environment. 3.2. Smallholder production There are fewer reports of mortality rates from smallholder systems. Siamba and Semenye Ž1989. monitored pre-weaning mortality in cross-bred exotic kids in Kakamega and Siaya districts and found that 21% of singles and 46% of twins died Žage was not given.. Wachira and Shavulimo Ž1986. monitored the health of 320 SEA and SEA cross-bred exotic goats in Kisumu and Kakamega districts. Sixty two goats died during 1 yr of monitoring, an annual mortality rate of 19%. Stotz Ž1983. in an analysis of smallholder livestock production in Kenya used mortality rates, based on information from researchers and extension workers, of 10 and 6% for weaned and adult sheep and goats and 17 and 15% for suckling lambs and kids Žweaning at 6 months.. 4. Infectious causes of mortality 4.1. Pastoral production 4.1.1. Tick-borne diseases Bekure et al. Ž1991. noted tick-borne disease as the most common cause of adult mortality in sheep

Author

Angwenyi and Bebe Ž1989., District Baringo Bekure et al. Ž1991., Kajiado Carles et al. Ž1987., Marasbit Carles et al. Ž1987., Isiolo Gachuiri et al. Ž1986., Isiolo b Gatongi Ž1995., Nakurub Herren Ž1991., Laikipia Njanja Ž1991., Turkana

Sample size—no. animals monitored Duration of study Žbirths. wyrx Ždates.

Pre-weaning mortality risk rates w%x

Lambs

Kids

Lambs

Ž501.

665 Ž741.

b

150 Ž331. 205 94

Ž140. 150 Ž276. 457 145

Maina Ž1996., Kajiado Peacock Ž1984., Kajiado Skea et al. Ž1990., Merub

Ž120.

Ž200.

Wilson et al. Ž1985., Kajiado

Ž703.

a b

Mortality rate including prenatal deaths. Research station.

897 Ž1009.

4 Ž1985–1988. 2 Ž1981–1983.

18

2 Ž1991–1993. 1 3

17 29 5 Ž7 a .

2 Ž1992–1994. 2 5

23 10

32

Weaning age wdaysx

Kids 19 34 24 15 18 17 39 11 Ž24 a . 34 29 3 28

120 150 150 160 150 180 140 Žmales. 224 Žfemales. 130 120 Žmales. 150 Žfemales.

E.J. Peeler, S.W. Wanyangur Small Ruminant Research 29 (1998) 1–11

Table 1 Pre-weaning mortality in sheep and goats in arid and semiarid areas

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E.J. Peeler, S.W. Wanyangur Small Ruminant Research 29 (1998) 1–11

and goats in Kajiado district during 1983 ŽTable 2.. The most important tick-borne disease was Nairobi sheep disease ŽNSD., a viral infection transmitted by the tick Rhiphicephalus appendiculatus. The disease can result in mortality of 66–75% of the entire flock ŽDavies, 1987.. Heartwater or cowdriosis, a rickettsial infection caused by Cowdria ruminantium has been shown to be endemic in sheep from most agro-climatic zones in Kenya ŽNgumi and Wafula, 1995; Ngumi et al., 1997.. However, there are no records of losses in the literature. 4.1.2. Trypanosomiasis Carles Ž1986. demonstrated that indigenous sheep and goats can be naturally infected with trypanosomes in Ngurunit, Marsabit district, but found no evidence that the infection caused mortality or a decrease in productivity. However, Griffin and Allonby Ž1979., working in Kitui district, demonstrated high levels of trypanosomiasis in exotic and exotic cross breeds of sheep and goats resulting in mortality and decreased growth rates. 4.1.3. Helminthosis and other causes of diarrhoea Bekure et al. Ž1991. considered that diarrhoea in growing small ruminants was caused by coccidiosis, enterotoxaemia and enteric colibacillosis. A similar finding was made by Angwenyi and Bebe Ž1989., who attributed 23% of pre-weaning kid mortality to coccidiosis, 12% to enterotoxaemia, 17% to helminthosis and 31% to pneumonia. Allonby Ž1975. considered that significant neonatal mortality was due to undiagnosed septicaemia, and that clostridial infections were responsible for sudden deaths in weaners. Enterotoxaemia was reported as a major cause of loss of sheep in Kajiado ŽAudi et al., 1995. and Samburu districts ŽKariuki et al., 1995.. Carles Ž1980, 1986. in Marsabit district found that the majority of goat deaths were due to CCPP, though other important causes of death in sheep and goats w ere coenurosis and helm inthosis. Haemonchus contortus was the major species of strongyle found and is generally considered to be the most important helminth infection of small ruminants in Kenya. Galla kid mortality on a research station in Meru district doubled to 7%, and weaning weights dropped considerably due to a heavy H.

contortus challenge in 1 yr ŽSkea et al., 1990.. Very high sheep and goat mortality at the end of a long dry season in 1991 in Isiolo district was attributed primarily to haemonchosis ŽAnonymous, 1992.. 4.1.4. Respiratory infections The only reported pneumonic agents of sheep in Kenya Pasteurella haemolytica, which Bekure et al. Ž1991. identified as a cause of pneumonia in lambs, and the retrovirus suspected as the cause of ovine pulmonary adenomatosis ŽShompole, D., personal communication, 1977.. Herren Ž1991. found that CCPP caused 36% of all goat mortalities, and another 8% of losses were attributed to other lung diseases Žonly 3% of sheep losses were due to lung diseases.. Gachuiri et al. Ž1986. reported that 17.5% of all adult goat deaths on a research station in Isiolo district were due to CCPP during the drought year of 1984 Ž30% of mortalities were due to starvation.. Goat mortality due to CCPP has also been reported in Tana River district ŽSemenye and Chabari, 1980.. Outbreaks of CCPP are regularly reported from arid areas of Rift Valley and Coast provinces all of North–Eastern and Eastern provinces, except Meru district, ŽAnonymous, 1991.. 4.1.5. Carpripox Davies Ž1976. noted that primary reports of capripox invariably originated from the northern and eastern parts of the pastoral areas, and outbreaks in other areas have followed movement of livestock. He investigated field outbreaks and showed that in some parts of the pastoral areas, the disease was endemic Ž82% sero-positivity.. Outbreaks in these areas occurred with a morbidity of 5–10% and a low mortality, 3–5%, with mainly young animals dying, especially at times of drought. In flocks and herds with no immunity, morbidity can reach 60% ŽDavies, 1976.; one such outbreak which occurred in Rift Valley province resulted in mortality, ranging between flocks, from 2 to 30% ŽDavies, 1981.. 4.1.6. Rift Valley feÕer Major epidemics of Rift Valley fever occur every 5–20 yr in Kenya causing abortion in sheep, goats and cattle and high mortality in new-born lambs ŽDavies, 1987.. The main presenting sign is abortion.

Author

District

Sheep Most important cause

Pastoral production Angwenyi and Bebe Ž1989. Bekure et al. Ž1991. Carles Ž1980. Carles Ž1986. Gachuiri et al. Ž1986. Herren Ž1991. Maina Ž1996. Smallholder production Mucuthi et al. Ž1992. Njeru Ž1991. Shavulimo et al. Ž1986. Wachira and Shavulimo Ž1986. Young Ž1987. a

Pre-weaning mortality.

Goat Second most important cause

Most important cause

Second most important cause

Baringo Žresearch station. Kajiado ŽMaasai. Marsabit ŽSambururRendille. Marsabit ŽSambururRendille. Isiolo Žresearch station. Laikipia ŽMaasairNdorobo. Kajiado ŽMaasai.

pneumonia coccidiosisa tick-borne disease Žesp. NSD. tick-borne disease Žesp. NSD. coenurosis pneumonia coenurosis pneumonia ŽCCPP. pneumonia pneumonia pneumonia intestinal disease tick-related Ždisease or anaemia. pneumonia ŽCCPP. intestinal disease helminthosis copper deficiency copper deficiency helminthosis

Laikipia Machakos

pneumonia pneumonia

Kisumu Meru

diarrhoea Žhelminthosis.

pneumonia ŽCCPP. pneumonia ŽCCPP. pneumonia pneumonia pneumonia

helminthosis

E.J. Peeler, S.W. Wanyangur Small Ruminant Research 29 (1998) 1–11

Table 2 Infectious causes of mortality in small ruminants

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E.J. Peeler, S.W. Wanyangur Small Ruminant Research 29 (1998) 1–11

4.2. Smallholder production 4.2.1. Tick-borne diseases NSD is of less importance in high potential areas but was confirmed in a flock kept at a research station in Kiambu district ŽBain, R., personal communication, 1993., and in a commercial flock of Dorper sheep in Thika district ŽCarles, A., personal communication, 1993.. 4.2.2. Trypanosomiasis Kanyari et al. Ž1983. studied trypanosomiasis in Kwale district, Coast Province, and found prevalence rates, greater than 40% in Galla goats and Toggenbergs and 12% in SEA goats. Case fatality rates were 37% and 10% for Galla goats and SEA goats, respectively. Trypanosomiasis is present in smallholder production systems of Western and Nyanza provinces, but there are no reports of disease in small ruminants. 4.2.3. Respiratory infections Njeru Ž1991. and Mucuthi et al. Ž1992. surveyed smallholder farmers in Machakos and Laikipia district, respectively. Pneumonia was reported to be an important cause of mortality in both areas, CCPP being most common diagnosis of the disease in goats. Disease-related mortality was the constraint to small ruminant production most frequently mentioned by respondent farmers Ž54%. in Laikipia district. In the high rainfall provinces of Western and Nyanza, pneumonia has also been reported as the major cause of death and disease in goats ŽShavulimo et al., 1986; Wachira and Shavulimo, 1986.. Pneumonia mainly affected kids before weaning. 4.2.4. Helminthosis and other causes of diarrhoea Wachira and Shavulimo Ž1986. found that helminthosis was the second most important cause of mortality, after pneumonia, in cross-bred exotic goats in Kisumu district. Smallholders in Meru district reported that 36% of all sheep that died suffered diarrhoea, however no goat mortality was associated with diarrhoea ŽYoung, 1987.. In Kenya, fasciolosis is caused by Fasciola gigantica ŽPreston and Castelino, 1977. and less commonly by F. hepatica ŽBrown, undated.. Cheruiyot

Ž1987., using meat inspection records from 1978 to 1982, discovered that 4.4% of sheep and 3% of goat liver condemnation was due to fasciolosis. The geographic distribution of the disease was similar to cattle—the highest level in Nyanza province and the lowest in the Coast province. Acute fasciolosis is common in F. gigantica infections in small ruminants, and even light infections are known to prove fatal ŽHammond and Sewell, 1990..

5. Conclusions and recommendations 5.1. Limitations of the aÕailable data and recommendations for study designs The majority of studies reviewed are observational prospective studies conducted in the field over a number of years ŽBekure et al., 1991; Carles, 1986; Herren, 1991. or studies on similar duration conducted on research stations, ŽAngwenyi and Bebe, 1989; Gatongi, 1995; Gachuiri et al., 1986; Skea et al., 1990.. Research on field stations will yield accurate data since events are closely observed and frequently recorded, however, it is not possible to extrapolate such results to the field. Other studies reviewed have assessed rates and causes of mortality from cross-sectional questionnaire studies ŽAnonymous, 1992; Young, 1987; Njeru, 1991; Mucuthi et al., 1992. or from participatory approaches ŽAudi et al., 1995; Kariuki et al., 1995., a methodology discussed in detail by Cately and Aden Ž1996.. These studies are obviously much quicker and cheaper to conduct than prospective studies, however, they suffer from a number of drawbacks. The researcher is entirely reliant on both the livestock owner’s recall of events and his diagnosis of mortality. It is recognised that while livestock owners may accurately recall the death of adult stock, neonatal mortality is often forgotten. All three types of study have a role depending on quality and reliability of the data required. In reviewing the published literature reporting mortality and morbidity, some problems were encountered in comparing information from different sources, notably: Ø the method of calculation of mortality and morbidity rates is often not given.

E.J. Peeler, S.W. Wanyangur Small Ruminant Research 29 (1998) 1–11

Ø mortality and morbidity are expressed as risk rates but the period of recording is not stated Že.g., age definition of lamb or kid not given.. Ø diseases are quoted as causing a proportion of total deaths Žproportional mortality rates. but the overall mortality rate is not given. Ø neonatal mortality is not defined Žinclusion of abortion, stillbirths and deaths within 24 h.. Failure to include the information listed above may be due to omission by the authors or gaps in data collection. There is a case to be made for researchers to more clearly define the parameters they report and to give the methods used to calculate mortality and morbidity rates. In addition if the researcher wishes to compare pre-weaning mortality between species or breeds season of birth, parity of dam and twinning needs to be recorded. The prospective studies reviewed attributed approximately 50% of deaths ŽMaina, 1996; Carles et al., 1987. to a definite cause. This figure could be improved if study designs incorporated the following: careful recording of the age of death of young stock, from which likely causes of death can be inferred, and increased use of post mortem and laboratory investigations. Many of the on farm studies reviewed do not discuss how closely the results of the study correspond to the real situation in the population of interest, i.e., target population, which is often not defined. Non-probability, i.e., convenience or purposive, sampling methods were usually used rather than random sampling, making it impossible to determine the accuracy of the data. In addition convenience or purposive sampling can often lead to bias. 5.2. Influence of agro-climatic zone and management In both smallholder and pastoral production systems intestinal and respiratory conditions appear to be the main cause of mortality, while in the latter system coenurosis and tick-borne disease are important in some locations. The weight of evidence from the literature reviewed suggests that the majority of small ruminant deaths are caused by infectious disease. In pastoral systems, starvation during periods of drought ŽGachuiri et al., 1986. and predation ŽMaina, 1996. are the major non-infectious causes of death, resulting in higher levels of mortality, espe-

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cially pre-weaning, compared to smallholder systems. 5.3. Research and policy recommendations Causes of pneumonia in sheep are not well elucidated, however, pasteurellosis may well be important and sheep pulmonary adenomatosis is known to exist. The most likely causes of caprine pneumonia are pasteurellosis and CCPP in smallholder and pastoral systems, respectively. In growing animals, coccidiosis and enterotoxaemia, and in all age groups, helminthosis, are the important intestinal diseases. Helminthosis is likely to be important every year in high potential areas, but in arid and semiarid areas levels of infection are only sufficient to cause significant mortality in years of high rainfall. As Lebbie and de Leeuw Ž1994. pointed out, health and productivity monitoring is required from national to farm level ‘for improved and sustainable livestock production’. At a national level, knowledge of disease prevalence and the impact of disease on production is required for both planning of disease control programmes and animal health research. The high levels of pre-weaning mortality, especially in pastoral systems Ž10–30% and 20–30% in lambs and kids, respectively. indicates considerable scope for animal health interventions to improve levels of production. This review would indicate that pneumonia and helminthosis should be the focus of small ruminant disease control programmes. However, it should also be noted that studies in the same district have reached different conclusions regarding the important causes of mortality. This is an indication of the variation in disease morbidity both temporally and spatially which needs to be considered when designing intervention strategies. While the major causes of mortality are known, their prevalence, geographic distribution and importance as causes of mortality are not well documented. The relative importance of the aetiological agents causing diarrhoea and pneumonia and the losses they cause are not known. The incidence and geographic distribution of capripox, CCPP, fasciolosis and tick-borne diseases and their impact on mortality require assessment. The importance of trypanosomiasis in small ruminants has been little studied outside of Coast province.

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E.J. Peeler, S.W. Wanyangur Small Ruminant Research 29 (1998) 1–11

Ideally, production system-based studies should be undertaken over prolonged periods to quantify the impact of disease on all aspects of production and to assess the importance of disease in the context of other constraints to production. Data required to assess the economic importance of disease, and thus to plan sustainable integrated animal health programmes would then be generated.

Acknowledgements We would like to thank all those who kindly brought to our attention important sources of information that we had overlooked. This paper is published with the kind permission of the Director of the Kenya Agricultural Research Institute. The work was supported by the Department for International Development Žformerly the Overseas Development Administration..

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