Current information on the domestic yak (Poephagus grunniens or Bos grunniens) in the Himalayan agroecological zone in Nepal is limited. Despite their isolation, yak may contact other domestic livestock particularly during the winter when they are at lower altitudes and as such they may be exposed to infectious disease. Faeces from 50 adult yak from a herd of 123 adults and 27 calves in the Kaski region of the Nepali Himalaya were analysed for the presence of gastrointestinal parasites using standard flotation and sedimentation methods. In this herd, 18 per cent (95% CI 9% to 31%) of the samples showed evidence of nematode infection, with trichostrongyle and Nematodirus/Marshallagia species eggs being detected. No trematode eggs were detected in any samples, and no Galba species or other snails were found in the environment. The herd appeared healthy with low intestinal parasitic burdens. Our findings may indicate Nematodirus/Marshallagia species infection to be exclusive to yak in this region.
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Current information on the domestic yak (Poephagus grunniens or Bos grunniens) in the Himalayan agroecological zone in Nepal is limited due to their isolation, inaccessibility and migratory nature, hampering study and connection with livestock services. Indeed, the number of domestic yak, yak hybrids (chauri) and wild yak in Nepal is unknown, with current estimates between 9000 and 95,000.1–3 Furthermore, information on disease is even less well documented.
Despite their isolation, yak may contact other domestic livestock including cattle, buffalo, goats, and so on, indirectly, particularly during the winter when they are kept at lower altitudes and as such they may be exposed to similar infectious diseases, although current disease information is unavailable.1 There are a few reports attempting to document the point prevalence of parasitic nematodes and trematodes in yak in different regions of Nepal, although most lack adequate description of the sampling strategies employed.4 5 Acharya et al 6 report data from 96 yak from six herds in Mustang district, of which gastrointestinal nematodes were detected in 78.13 per cent and trematodes in 35.42 per cent of the animals sampled.
In February 2017, as part of a clinical investigation we carried out a survey to estimate the prevalence of parasitic nematodes and trematodes from a single mixed herd of yak and chauri in the Kaski district.
The herd comprised 123 adult yak/nak (female yak) and 27 calves grazing subalpine pasture at an altitude of between 2800 and 3100 m. The herds were all watered in a single location daily and it was at this site that we carried out faecal sampling. To reduce the likelihood of resampling the same individual twice only fresh faeces were collected in the period immediately after watering. This approach also ensured all animals were present at the time of sampling, meaning it could be reasonably assumed any samples collected would be representative of the adult herd overall. Sample size calculations based on an expected prevalence of 5 per cent7 suggested that 50 samples should be sufficient to detect this prevalence with a precision of 5 per cent.
Freshly voided faeces from 50 adults were collected and then sealed individually in plastic bags before being transported back to laboratories at the Himalayan College of Agricultural Sciences and Technology in Kathmandu. The samples were analysed individually for the presence of parasites. Salt flotation and enumeration using the McMaster method was carried out for nematodes with a sensitivity of 50 epg8 and sedimentation for Fasciola species eggs was performed using a Flukefinder (Richard Dixon, USA; www.flukefinder.com). Results are displayed in table 1.
In addition to faecal sampling we also interviewed the yak herder and owner about their management, and carried out a survey of the environment in close proximity to the watering area as we considered it potentially suitable for the maintenance of Galba truncatula, an intermediate host of Fasciola hepatica previously identified in Nepal.9
Outcome and follow-up
In this herd, 18 per cent (95% CI 9% to 31%) of the samples showed evidence of nematode infection by faecal egg count, with trichostrongyle (6 per cent of samples (95% CI 1% to 17%)) and Nematodirus species or Marshallagia species (14 per cent of samples (95% CI 6% to 27%)) eggs being detected. No Fasciola species or other trematode eggs were detected in any samples, and following a systematic time limited search no Galba species or other snails were found. These results indicate lower levels of infection and fewer helminth species compared with the yak sampled by Acharya et al.6 However, to our knowledge, herd level prevalence has not been reported previously for any study.
The main outputs from the herd were breeding males, chhurpi (cheese), hair/fibre products and blood used at traditional blood drinking ceremonies. According to the owner and yak herder, they had no interaction with veterinary services and carried out no preventive healthcare measures. They had in the past used a traditional amchi healer when mortality incidence rates were very high (eg, ~50 per cent), although such visits required a journey of two days’ walk.
One particular observation we wish to highlight is the detection of Nematodirus species and/or Marshallagia species eggs. Due to the morphological similarities of their eggs, it was not possible to further distinguish between these two genera on this occasion. To this end, further investigation to determine genus/species level is indicated.
A recent study of the gastrointestinal parasites of yak in the nearby Mustang region reported Nematodirus species infection by faecal egg count.6 Similarly, yak on the Indo-Nepali border have previously been identified with Nematodirus species infection, although species level identification was not given,10 while N filicollis infection in yak has been documented previously in Tajikistan.11 12 Marshallagia species infection has also previously been documented in yak in the Qinghai province of China.13
Interestingly, studies documenting parasitic species of sheep and goats from the Kaski region did not detect Nematodirus species or Marshallagia species infection in either sedentary or migratory flocks.14 Although further investigation is required, our finding may indicate Nematodirus/Marshallagia species infection to be exclusive to yak in this region. This may be the result of the increased spatiotemporal isolation of yak from other ruminant species, particularly when grazing higher altitude pasture and/or some degree of host specificity.
Despite the absence of Fasciola species or other trematode eggs we cannot rule out infection entirely, since sedimentation methods have a relatively low diagnostic sensitivity.15 Further sampling and testing using other methodology, for example, postmortem or serology, to further validate this finding would therefore be useful. Furthermore, the failure to identify a viable molluscan intermediate host species may be explained to some extent by the fact that we visited during the dry season. Consequently, presence of such species cannot be ruled out.
This short report highlights the severe lack of public knowledge on the Nepali yak and a lack of communication between yak herders, government officials and the scientific and veterinary communities. The herd appeared healthy at the time of our visit, and had very low intestinal parasitic burdens. Reports of severe mortality rates from unknown causes are alarming. Yak and chauri are considered an essential and integral part of life in the Himalayan agroecological regions, while the lack of interaction with veterinary or extension services hampers the delivery of any meaningful assistance. We would strongly recommend a programme of activity to engage with all animal keepers in order to promote animal welfare and to safeguard the livelihoods of those dependent on their animals. The enormous physical and practical difficulties of working in the Himalaya are not to be underestimated but should not be considered prohibitive.
Contributors JWA and JGB conceived the project idea and carried out the fieldwork and laboratory analysis. UMS provided laboratory space and support and BRJ provided invaluable supervision, liaison, translation and guidance within the country. All authors contributed to the writing of the manuscript.
Funding Funding for this project was provided by a grant from the ODA Research Seed Fund from the Higher Education Funding Council for England.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
Data statement There are no additional data available for this article.
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