INTRODUCTION
Toxocara vitulorum is an intestinal ascarid parasite of cattle and water buffaloes (Bubalus bubalis). Although the parasite may occur worldwide, it is of particular economic importance in tropical and subtropical regions, mainly due to lacking or inefficient control [1]. T. vitulorum causes morbidity and mortality in calves, which typically become infected early post-partum by ingesting larvae excreted in the colostrum and milk [2]. After a prepatent period of 3-4 weeks, the ingested larvae have matured to adult worms in the calf’s duodenum that produce a large number of eggs, during a patent period of about 4 weeks. At the age of 8 weeks, most infected calves are able to clear the parasite due to strengthened and acquired immunity [3].
Cambodia, a Southeast Asian country, has a tropical climate characterized by distinct rainy and dry seasons. Agriculture is the major work sector in Cambodia, and within this sector, livestock is the third largest subsector, behind crop production and fisheries [4]. Cattle (mainly Bos indicus) and water buffaloes (Bubalus bubalis) provide draught power, manure used as fertilizer or biogas, and increasingly, animal protein and income from trade [5]. Nevertheless, the ruminant sector is characterized by smallholder farmers rearing limited numbers of animals in traditional production systems. As a result, the animals are highly susceptible to endemic diseases, including T. vitulorum and other gastrointestinal parasites [6], resulting in substandard agricultural output.
The aim of this study was to investigate the prevalence and associated risk factors of T. vitulorum infection in buffalo and cattle calves in Cambodia.
MATERIALS AND METHODS
Study design
The study was conducted in 3 provinces, i.e., Pursat, Kampong Chnnang, and Kampong Cham, located in central Cambodia from June till October 2011. In each province, 6 communes were randomly selected and local farmers were asked for their cooperation. Fecal samples were collected from calves between the age of 1 and 15 weeks. The age of the animals was registered as either ≤28 days, 28-56 days, or >56 days.
Fecal examination
Each fecal sample was examined for the presence of eggs of T. vitulorum and strongyle eggs and Eimeria spp. oocysts by the McMaster technique with a sensitivity of 50 eggs per gram of feces (EPG) [7]. The consistency of the fecal sample was scored as being either normal, or soft, or watery.
Statistical analysis
T. vitulorum prevalence and corresponding exact 95% confidence intervals (CI) were calculated for the entire sample and for the different provinces, species, age groups, fecal consistencies, and co-infection categories. Additionally, the results of the T. vitulorum fecal egg counts were summarized by their arithmetic mean and SD.
Association of T. vitulorum prevalence with species, age group, fecal consistency, and co-infection category was assessed with a generalized linear mixed model for binary data, using adaptive Gaussian quadrature with 25 quadrature points. Commune was included as a random effect. A final multivariable model was obtained through a backwards selection procedure, at a significance level for removal of 5%. The analysis was performed in R 3.0.2 using the lme4 package [8,9].
RESULTS
A total of 517 animals were subjected in this study. Of these, 64 were found to excrete T. vitulorum eggs in their feces (12.4%; 95% exact CI: 9.7-15.5). The mean fecal egg count was 2,798 EPG (SD=16,351; range=0-224,400). Table 1 shows descriptive statistics by the province, species, age group, fecal consistency, and co-infection category.
The final multivariable generalized linear mixed model showed a higher odds of T. vitulorum infection for buffalo versus cattle, for animals aged 4-8 weeks versus younger and older ones, and for animals with strongyle infection (Table 2). There was no association with fecal consistency.
DISCUSSION
To our knowledge, this is the first report on T. vitulorum infections in buffalo and cattle calves from Cambodia. Prevalence estimates of T. vitulorum in neighboring countries also appear to be rare. Compared to those countries, the prevalence observed in our study is relatively low (12.4%). In Thailand, Srikitjakarn et al. [10] found a T. vitulorum prevalence of 58% in calves during their first 3 months of life. More recently, Holland et al. [11] observed a prevalence of 8% in Vietnamese calves aged 1-2 months, and Rast et al. [1] found a prevalence of 22.6% in buffalo and cattle calves aged <3 months in northern Lao PDR.
In our study, the main risk factors for T. vitulorum infection appeared to be host species and, not surprisingly, age. The apparent association with strongyle prevalence might be explained as an artefact due to the collinearity between strongyle infection and age (results not shown). Indeed, strongyle infections tend to be more common in older animals.
Roberts [12] reported clinical signs in toxocariasis, especially in buffalo calves. They included, poor hair coat, eczema, stools resembling white scour and having a foul smell, inappetency with intermittent colic and bloat [12]. More recent literature reports that calves with toxocariasis could have either pale colored or black diarrhea, or could be asymptomatic [13,14]. In our study, there was no association between T. vitulorum infection and fecal consistency. Further studies are needed to determine the contribution of T. vitulorum towards the overall clinical impact of disorders in calves of less than 3 months.
In conclusion, T. vitulorum is important in Cambodia, especially in buffalo cattle and animals between 4-8 weeks of age. Farmers should be aware of the potential impact of this parasite, and treat their animals appropriately. Anthelmintic treatment with either pyrantel or benzimidazoles at the age of 2-3 weeks has proved to be very effective in eliminating T. vitulorum both in cattle and buffalo calves in Cambodia (data not shown) and should be recommended to livestock owners in order to prevent potential pathologies caused by this parasite.
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