Prevalence and risk factors associated with gastrointestinal parasitic infections in pigs from four districts of Tripura, India

Introduction

Pig farming has been recommended as a favourable livelihood option for rural households in the North Eastern Region (NER) of India because of its minimal capital investment, wide adaptability, high fertility and fecundity, comparatively low feed and management input, favourable feed conversion ratio, ready market access and low associated risk. Pig rearing contributes substantially to income generation, capital accumulation, employment and household nutritional and social status in this region. The NER contributes about 40% of India's pig population, and the traditional system of pig farming and pork consumption is deeply embedded in local culture, with over half of the country's pork production being consumed within the region. According to the 20 th Livestock Census, India's pig population stands at 9.06 million, constituting around 1.7% of the nation's total livestock population (BAHS, 2019) [3] and about 0.98% of the global pig population of 977.02 million (FAOSTAT, 2016) [11] . Among Indian states, Assam holds the largest share of the national pig population (21.87%), followed by Jharkhand (13.3%), Meghalaya (7.4%) and West Bengal (5.6%) (BAHS, 2019) [3] . Parasites are prevalent in domestic pigs in almost all production systems worldwide. Unlike in ruminants, where parasitic diseases are managed proactively because of their well-documented impact on host performance and associated economic losses, GI parasites in pigs rarely cause peracute clinical disease and are consequently often neglected by farmers, veterinary parasitologists and clinicians alike. Recent reports on pig production systems indicate that, after African swine fever and classical swine fever, parasitic infections are probably among the most significant constraints affecting domesticated pigs in tropical and sub-tropical regions (Ajayi et al., 1988; Salifu et al., 1990; Elsrony et al., 1997) [2,22,10] . GI parasitic infections in pigs cause significant financial losses through mortality, reduced weight gain, impaired feed conversion, carcass condemnation and reduced reproductive performance. These parasites damage the intestinal mucosa, predisposing animals to secondary enteric infections and thereby increasing morbidity and mortality. In India, most pigs are reared under a free-range or semi-scavenging system in which animals feed on raw garbage, kitchen waste and faecal matter, considerably increasing their exposure to GI parasites. The major GI parasites reported in pigs worldwide include Ascaris suum, Oesophagostomum spp., Strongyloides ransomi, Hyostrongylus rubidus, Trichostrongylus axei and Trichuris suis (Manuel et al., 1989; Dutta et al., 2005) [17,9] . Several of these parasites are also zoonotic, adding a publichealth dimension to their control. Despite this burden, systematic data on the prevalence and risk factors of GI parasitism in pigs remain limited for many parts of India, including Tripura. The present study was therefore undertaken to determine the prevalence, parasite spectrum and sex-, ageand breed-related risk factors of GI parasitic infections in pigs of four districts of Tripura.

Materials and Methods

Study area and sample collection

The study was conducted in four districts of Tripura, India, viz. Sepahijala, Gomati, Khowai and West Tripura. A total of 489 faecal samples were collected directly from the rectum or immediately after defecation from pigs of different age, sex and breed groups over a three-month period from June to August 2024. The pigs sampled comprised local/non-descript pigs (n=185), crossbred pigs (n=162) and Large White Yorkshire pigs (n=142, including animals recorded as purebred White Yorkshire and Large White Yorkshire crosses, which were pooled for analysis), belonging to 327 female and 162 male pigs reared mostly by small and marginal farmers under free-range or semi-intensive husbandry. Samples were transported to the Department of Veterinary Parasitology, R.K. Veterinary College, Agartala, for processing.

Examination of faecal samples

Each faecal sample was examined for the presence of nematode eggs, cestode eggs and Eimeria oocysts using the standard salt flotation and sedimentation techniques described by Soulsby (1982) [25] . Eggs, larvae and oocysts were identified on the basis of their morphological characteristics, following Soulsby (1982) [25] .

Age categorisation

For analysis of age-related prevalence, pigs were grouped into three categories based on age at the time of sampling: piglets (≤ 3 months, n=85), growers (>3-6 months, n=214) and adults (>6 months, n=190).

Statistical analysis

Data were compiled in Microsoft Excel and analysed using GraphPad Prism software. Pearson's chi-square test was used to test for a significant association between sex, age group and breed with the prevalence of GI parasitic infection; a pvalue <0.05 was considered statistically significant.

Results and Discussion

Of the 489 faecal samples examined from pigs of the four districts of Tripura, 305 were positive for one or more GI parasites, giving an overall prevalence of 62.37%. District [16] reported 60.62% prevalence in pigs at and around Ranchi, Jharkhand, and Das et al. (2024) [7] reported a very similar 61.65% prevalence in pigs from three districts of Tripura. Kumar et al. (2024) [15] recorded a somewhat higher prevalence of 64.4% in pigs of Meerut district, Western Uttar Pradesh, while Kaur et al. (2017) [13] reported an overall prevalence pattern in pigs of Punjab that was significantly higher in pigs above one year of age (56.5%) than in younger pigs (39.6%). Considerably higher prevalence rates have been reported by Adhikari et al. (2021) [1] (91% in indigenous pigs of south-central Nepal) and Charitha et al. (2022) [4] (80.98% in free-range pigs), which may reflect differences in husbandry system, sampling season, agro-climatic conditions and diagnostic sensitivity between studies. Unlike several earlier Indian reports in which Ascaris spp. was recorded as the single most prevalent GI parasite of pigs (e.g., Das et al. 2024 [7] , who reported 32.47% prevalence of Ascaris spp. in Tripura), strongyle-type eggs were clearly predominant in the present study. This most likely reflects the largely free-range and scavenging husbandry practised in the study area, in which pigs graze on open, often waterlogged or marshy ground that favours the survival and development of strongylid larvae to the infective (L3) stage, combined with continuous faecal contamination of the environment and minimal deworming intervention (Roepstorff and Nansen, 1994) [21] . The comparatively lower and near-negligible prevalence of Balantidium coli (0.41%) suggests that, despite its zoonotic potential, this ciliate protozoan is currently a minor component of the parasite fauna of pigs in the study area.

Sex-wise prevalence of gastrointestinal parasite infection in pigs

The present investigation comprised 162 male and 327 female pigs of different ages. The prevalence of GI parasites was 61.73% in males and 62.69% in females, and this difference was not statistically significant (χ²=0.04, df=1, p=0.836). This finding is in agreement with Nsoso et al. (2000) [19] , who similarly reported no significant sex-wise difference in GI parasite prevalence in pigs of Botswana, and suggests that, in the largely free-ranging husbandry system prevailing in the study area, both sexes are exposed to comparable levels of environmental parasite challenge. This contrasts with some other reports in which prevalence differed significantly by sex higher in females in Das et al. (2024) [7] , Tamboura et al. (2006) [27] , Obonyo et al. (2012) [20] and Dey et al. (2014) [8] , and higher in males in Sowemimo et al. (2012) [26] underlining that the direction and significance of any sexrelated difference in GI parasitism is likely to be strongly influenced by local management practices (e.g., differential exposure of breeding sows versus fattening males) rather than by a consistent, biologically fixed sex effect.

Age-wise prevalence of gastrointestinal parasite infection in pigs

Age-wise, the prevalence of GI parasites was 63.53% in piglets (≤3 months), 67.76% in growers (>3-6 months) and 55.79% in adults (>6 months), a difference that was statistically significant (χ²=6.20, df=2, p=0.045). The highest prevalence in grower pigs is consistent with the findings of Das et al. (2024) [7] , Sharma et al. (2020) [23] , Chou et al.

(2004) [5] and Dey et al. (2014) [8] , and is generally attributed to increased exposure of growers to infective parasite stages while foraging independently soon after weaning, at a stage when protective immunity is not yet fully established (Roepstorff and Nansen, 1994; Damriyasa and Bauer, 2006) [21, 6] . The comparatively lower prevalence recorded in adult pigs is consistent with the development of acquired resistance to re-infection following repeated parasite exposure (Sharma et al., 2020) [23] . Within the piglet category, it was notable that all 16 of the youngest pigs sampled (1.2-2 months of age) were negative for GI parasites, which may reflect limited environmental exposure and residual maternally derived protection at this very early age; this observation, however, is based on a small subset of animals and warrants confirmation in a larger, age-stratified sample.

Breed-wise prevalence of gastrointestinal parasite infection in pigs

In the present study, 185 local/non-descript, 162 crossbred and 142 Large White Yorkshire pigs of different age groups were examined. The prevalence of GI parasites was significantly associated with breed (χ²=22.50, df=2, p<0.001), being highest in crossbred pigs (71.60%), followed by local/non-descript pigs (66.49%), and lowest in Large White Yorkshire pigs (46.48%). This pattern differs from several earlier Indian reports, including Das et al. (2024) [7] , Muraleedharan et al. (1994) [18] and Krishna Murthy et al.

(2016) [14] , in which local or non-descript pigs recorded the highest prevalence, generally attributed to unhygienic, unorganised farming practices with minimal anthelmintic use (Singh and Rath, 2013) [24] and close proximity to water bodies, forest and bushland that favours parasite transmission (Kabir et al., 2011) [12] . In the present study, however, crossbred pigs recorded the highest prevalence, which may reflect closer co-mingling of crossbred animals with freeranging local pigs and shared contaminated grazing or scavenging grounds in the sampled farms, higher stocking density under semi-intensive rearing, or comparatively lower innate parasite resistance relative to indigenous genotypes that have undergone longer local adaptation. The markedly lower prevalence in Large White Yorkshire pigs is consistent with this breed typically being reared under more confined, organised conditions with reduced access to contaminated pasture and more regular veterinary care. As breed and management system are closely confounded in extensive field surveys of this kind, further studies that separate the effects of genotype and husbandry system are warranted to confirm the breed-specific risk indicated here.

Parasite-wise prevalence

The relative frequency of the individual parasite genera recorded across all four districts is presented in Fig. 4. Strongyle-type eggs were, by a wide margin, the most frequently recorded finding, underscoring the importance of pasture-and soil-borne nematode transmission under the prevailing free-range husbandry, and indicating that strongyle control (e.g., through rotational grazing, drainage of waterlogged areas and strategic anthelmintic use) should be prioritised in any parasite-control programme designed for pigs of this region.

Conclusion

The present study recorded an overall GI parasite prevalence of 62.37% in pigs of four districts of Tripura, with both nematode and protozoan infections present and mixed infections accounting for over a quarter of positive cases. Strongyle-type infections were the single most important parasitic problem in the study population, followed by Ascaris spp. and Eimeria spp. Prevalence did not differ significantly by sex but was significantly higher in grower pigs and in crossbred and local/non-descript pigs than in adult pigs and Large White Yorkshire pigs, respectively. These findings highlight the need for regular deworming timed around the post-weaning grower stage, improved sanitation and pasture management, and closer veterinary attention to crossbred and local pigs reared under free-range systems, in order to reduce the substantial economic and zoonotic burden posed by GI parasitism in pig production in Tripura. Further studies incorporating quantitative faecal egg counts and molecular species identification of strongyle-type eggs are recommended to refine control strategies.

Acknowledgement

AcknowledgementThe authors thank the authorities of SVVU, NRC-Pig, Pig farmers of Sepahijala, Gomati, Khowai and West Tripura districts, Pig farmers of Krishna district, Andhra Pradesh for their cooperation during sample collection, and the Department of Veterinary Parasitology, College of Veterinary Science &A.H R.K. Nagar, Agartala, for laboratory facilities. Financial assistanceNo specific grant was received for this research.

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