Gastrointestinal parasite infections in Nepalese Gurkha recruits arriving in the United Kingdom from 2012-2020

Abstract

Background: Gastrointestinal parasite (GIP) infections are a major cause of global morbidity, infecting hundreds of millions of people each year and potentially leading to lifelong infection and serious complications. Few data exist on screening for GIP infections in migrants entering the UK or on the current performance of different traditional diagnostic approaches. This study aimed to describe the prevalence of GIP infections in Nepalese Gurkha recruits screened on arrival in the UK.

Methodology/principal findings: We present a retrospective analysis of data from screening male adults (18-21 years) who arrived in the UK from Nepal between 2012 and 2020. Three separate faecal samples were obtained from participants at weekly intervals and processed for formalin-ethyl acetate (FEA) concentration/light microscopy and charcoal culture. Serum samples were analysed for IgG antibodies to Strongyloides stercoralis by ELISA. Results were available from 2,263 participants, of whom 463 (20.5%, 95% CI 18.8%-22.2%) had a positive diagnostic test for at least one GIP infection. A total of 525 potential infections were identified. Giardia duodenalis was most common (231/2263, 10.2%), followed by S. stercoralis (102/2263, 4.5%), and hookworm species (86/2263, 3.8%). Analysis (microscopy and culture) of the initial stool sample diagnosed only 244/427 (57.1%) faecally identified pathogens, including 41/86 (47.7%) hookworm infections. The proportion of participants infected with any GIP showed a downward trend over the study period. Log-binomial regression showed risk of infection decreasing by 6.1% year-on-year (95% CI 3.2% - 9.0%). This was driven predominantly by a fall in hookworm, S. stercoralis and Trichuris trichiura prevalence.

Conclusions/significance: The level of potentially pathogenic GIP infection in young Nepalese men migrating to the UK is high (20.5%) and requires a combined diagnostic approach including serology and analysis of multiple stool samples incorporating specialised parasitological methods. Advances in molecular approaches may optimise and simplify the intensive screening strategy required.

Fig 1. Number of Nepalese Gurkha recruits arriving in the UK and undergoing screening for GIP, each year from 2012–2020.

Fig 2. Bar chart and logistic regression curve of combined gastrointestinal parasite (GIP) infection prevalence in Nepalese Gurkha recruits who migrated to the UK by year, 2012–2020.

Details of GIP infections identified are shown in Table 1. Logistic regression was statistically significant (p<0.001, OR 0.923, 95% CI 0.886–0.960) for a negative association with total GIP prevalence and time in years. If data for outlier year 2013 are excluded, this association is stronger (p<0.001, OR 0.903, 95% CI 0.865–0.942). Figures are %, bars show 95% CI. Logistic regression curve shown with 95% CI.

Fig 3. Bar chart and logistic regression curve of yearly prevalence of G. duodenalis infection prevalence in Nepalese Gurkha recruits who migrated to the UK 2012–2020. Logistic regression was not statistically significant (p = 0.625, OR 0.987, 95% CI 0.935–1.041) for an association between change in Giardia prevalence and time in years.

Figures are %, bars show 95% CI. Logistic regression curve shown with 95% CI.

Fig 4. Bar chart and logistic regression curve of yearly prevalence of hookworm infection in Nepalese Gurkha recruits who migrated to the UK 2012–2020.

Logistic regression was statistically significant (p<0.001, OR 0.791, 95% CI 0.729–0.860) for a negative association with hookworm prevalence and time in years. Figures are %, bars show 95% CI. Logistic regression curve shown with 95% CI.

Fig 5. Bar chart and logistic regression curve of yearly positive S. stercoralis results (both charcoal culture and IgG ELISA), in Nepalese Gurkha recruits who migrated to the UK 2012–2020.

Logistic regression was statistically significant (p = 0.013, OR 0.908, 95% CI 0.842–0.980) for a negative association with a positive S. stercoralis test and time in years. Figures are %, bars show 95% CI. Logistic regression curve shown with 95% CI.

Fig 6. Bar chart and logistic regression curve of yearly prevalence of T. trichiura ova detection in Nepalese Gurkha recruits who have migrated to the UK 2012–2021.

Logistic regression was statistically significant (p<0.001, OR 0.677, 95% CI 0.577–0.795) for a negative association with T. trichiura prevalence and time. Figures are %, bars show 95% CI. Logistic regression curve shown with 95% CI.