Gastrointestinal nematode infection in small ruminants in Ethiopia: A systematic review and meta-analysis
Graphical abstract
The review provides pooled prevalence estimates of GI nematode infestation in small ruminants in Ethiopia.
Introduction
Infections with gastrointestinal (GI) nematodes severely affect small ruminant health and compromise their productivity and reproductive performances (Baker, 2001, Suarez et al., 2009) and can be a major cause of economic losses in small ruminant production (Coop and Kyriazakis 2001). The clinical disease development or pathologies causing death or sickness in animals are effected through the parasites’ feeding activities or physical presence, migration and associated host immune response. Abomasal hypertrophy, blood and protein loss, damage to the intestinal wall and other related tissues are some of the mechanisms by which the host suffers (Taylor et al., 2007). Consequent to such pathologies, animals manifest anorexia, diarrhea, submandibular edema, emaciation and anemia (Soulsby, 1982, Urquhart et al., 1996).
High burden of infections with nematodes may lead to death; and under field conditions, most infections are usually mixed consisting of different species of nematodes. Indeed, the impact of nematode infections on the animal not only depends on the burden of infection but also the physiological and immunological status of the host. For instance growing lambs and peri-parturient ewes are most susceptible to infection by nematodes (Bishop and Stear, 2001).
In Ethiopia, the reported coproscopical and postmortem prevalence of small ruminant GI nematode infections range from 15.7% to 100% (Sissay et al., 2007a, Aga et al., 2013, Aragaw and Gebreegziabher, 2014). Such infections were due to diverse nematode genera both in sheep and goats. These include Haemonchus, Trichostrongylus, Oesophagostomum, and others (Tembely et al., 1997, Asha and Wossene, 2007, Bitew et al., 2011, Shankute et al., 2013, Mohammed et al., 2014). Owing to its importance a large number of surveys and experimental trials were performed on helminthes, particularly nematode in small ruminants (Abebe and Esayas, 2001, Asha and Wossene, 2007, Sissay et al., 2007a, Sissay et al., 2007b, Abebe et al., 2010, Mohammed et al., 2014). Consequently, researchers have agreed that nematodes infections are among the most devastating diseases of small ruminants with huge economic significance. However, as the reports were based on different set-ups, including various study designs, study areas, sample sizes, diagnostic methods, small stock species, parasites involved, management systems or other factors, high variability is expected. Hence there is a need to capture the overall status of nematodes infection in small ruminants in Ethiopia so that veterinary clinicians, researchers and livestock policy experts of the country can use the finding to set out the way forward. Therefore this study aimed at (i) producing a pooled prevalence estimate of GI nematode infection in small ruminants at country level, and (ii) identifying the relevant predictors that could possibly dictate the observed variation between reports and (iii) highlighting the information gap on nematode infection studies in small ruminants.
Section snippets
Study protocol
The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline was followed in the review process (Moher et al., 2009). A protocol that addresses the study outcomes of interest, review questions, inclusion and exclusion criteria, data source, preliminary article assessment criteria, assessment criteria for articles screened eligible, and a data extraction form were developed. The data extraction form was pre-tested and modified to suit the purpose of the study.
Literature search strategy
The
Literature search
During the literature search period that lasted from December 15, 2014 to June 15, 2015, 78 published and grey literatures were retrieved for GI nematodes. Of these, only 24 reports met the inclusion criteria (Fig. 1). The data set was composed of 50 observations at species, region, agro-ecology and type of diagnostic test level (Table 1). One of the reports for GI nematode was a MSc dissertation, while the rest were published articles in peer-reviewed journals. The earliest valid report was
Discussion
In this systematic review 24 studies were used to retrieve 50 animal level reports. The pooled overall prevalence estimate of GI nematode infection in small ruminants was very high (75.8%). In the subsequent analysis for variation between studies, i.e. the inverse variance index (I2 = 97.8%) revealed the presence of significant level of true heterogeneity between reports. Since the studies involved the major agro-ecologies of the country and considered a range of study populations from different
Conflict of interest
None.
Acknowledgements
This review was funded through the CGIAR research program on Livestock and Fish. Authors would like to acknowledge the International Center for the Agricultural Research in Dry Areas (ICARDA) and International Livestock Research Institute (ILRI) for facilitating this review. Drs Barbara Rischkowsky, Berhanu Admassu, Takele Abayneh, Hailu Degefu and Tsegaw Fentie are greatly acknowledged for all sorts of technical and logistical support they provided.
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