Liver fluke (Fasciola hepatica) co‐infection with bovine tuberculosis in cattle: A prospective herd‐level assessment of herd bTB risk in dairy enterprises

Abstract

Co-infection of tuberculosis (TB) and helminths is recognized as a significant problem in regions where such pathogens are endemic and chronic cases exist. Co-infection can modulate the immune system leading to interference with diagnostic tests, increased pathological impacts and pathogen persistence. However, research has found that such interactions between pathogens can be context and species specific. Recent studies have suggested that liver fluke, Fasciola hepatica, infection may impact on immunological responses and diagnostics for bovine tuberculosis (bTB; caused by Mycobacterium bovis) in cattle. Where evidence of such interaction exists, there would be an onus on policy makers to adjust eradication programs to minimize impacts. We assessed the association between herd-level bTB breakdown risk and seasonal variation in liver fluke exposure based on 5,753 bulk tank milk (BTM) samples from 1,494 dairy herds across Northern Ireland. BTM was tested by an IDEXX antibody specific enzyme-linked immunosorbent assay (ELISA) using the 'f2' antigen as a detection agent. The ELISA determined the result based on a sample to (known) positive ratio (S/P%) from which binary status and categories of exposure were derived. Associations were tested using multivariable random effects models. Models predicting bTB risk were not improved with the inclusion of liver fluke exposure levels. Variations in modelling liver fluke exposure (S/P%, binary, categories of exposure) and bTB risk (skin test breakdowns, post-mortem confirmed breakdowns, breakdown size and lag effects) also failed to support associations (neither positive nor negative) between the pathogens at herd-level. These results, along with previously published animal-level data from Northern Ireland, suggest that the nexus between bTB and F. hepatica may have small size effects at the population-level. However, our results also highlight the high prevalence of F. hepatica in cattle in our study population, and therefore we cannot fully discount the potential hypothesis of population-level depression of immune response to M. bovis due to co-infection. K E Y W O R D Sbulk milk sampling, concurrent infection, endemic disease, Fasciola, Mycobacterium

Co-infection of cattle with Fasciola hepatica or F. gigantica and Mycobacterium bovis: A systematic review

“…Studies 10, 12 and 13 [44,45,47,48] were undertaken in an effort to follow up the previous findings and used large sample sizes and numerous modelling approaches to try to identify any possible association between the two pathogens. This collection of studies was the most thorough in controlling for confounders and the most rigorous in reporting all aspects of the study.…”

Fascioliasis may promote tuberculous infectivity in small ruminants

“…The co-infection relationship between Fasciola spp. and Mycobacterium bovis has been extensively studied in cattle ( Byrne et al, 2019 , Claridge et al, 2012 ), as globally, both pathogens are common in animals. However, the interaction of these pathogens in small ruminants has not yet been fully elucidated in Bangladesh and remains to be investigated.…”

“…Although fascioliasis and TB are widespread diseases in animals, they have always been considered separately despite showing a concurrent infection in nature only apparent through abattoir findings. However, co-infection of TB and helminths, particularly F. gigantica, is a serious issue in these disease-prone areas ( Byrne et al, 2019 ). Fasciola infected animals have significant elevation of immunoglobulin E levels, eosinophilia and Th2 immune responses ( Ezenwa et al, 2010 ), which reduces M. bovis- specific Th1 responses ( Flynn et al, 2010 ), resulting in a delay in bacterial clearance from Fasciola infected animals ( Ezenwa et al, 2010 ).…”

Paroxysmal dyskinesia in sphynx cats

“…It is abundant in the UK in both sheep and cattle, with a prevalence of around 80 to 90 per cent in dairy cattle herds. 1,2 Furthermore, it costs between three and five pounds to treat each sheep infected with liver fluke. 3 I am conducting my master's research on the prevalence and management of liver fluke in the UK, with the aim of providing an up-to-date view of the distribution of liver fluke and the attitudes that farmers have towards it.…”