Farm specific transmission patterns of Fasciola hepatica in Danish dairy cattle based on different diagnostic methods and monitoring of grazing management

A recent survey based on meat inspection data showed that approximately 30% of Danish cattle farms were infected with liver flukes, leading to significant economic losses. Despite the widespread problem, up-to-date knowledge on transmission patterns, diagnostic methods and practical measures for control is still lacking. We therefore initiated a longitudinal, observational study in a few infected dairy farms to elucidate farm specific transmission patterns based on different diagnostic methods and grazing management. Two organic and two conventional dairy farms with high F. hepatica antibody levels in bulk tank milk were selected. From each farm a cohort of 40 animals from different age groups (calves, heifers, primiparous and multiparous cows) were sampled 7 times between April 2015 and January 2017. Diagnostic methods included faecal egg count by sedimentation, serum ELISA and coproantigen ELISA. Additionally, monthly bulk tank milk samples were analyzed by ELISA. The analyses are ongoing, but preliminary results indicate that F. hepatica is mainly transmitted via summer infection of snails as most animals seroconvert in late autumn without shedding of eggs. However, infection early in the grazing season due to overwintered snails has also been observed. One farm where cows are stabled have had some older cows continuing to shed F. hepatica eggs, suggesting long life span of F. hepatica, although other routes of infection cannot be ruled out. The final results will provide novel and practical information about different diagnostic tests and transmission patterns related to grazing management on farm-level

Farm-level risk factors for Fasciola hepatica infection in Danish dairy cattle

Recent studies suggest that liver fluke (Fasciola hepatica) infections in cattle have increased in Denmark in recent years. This study aimed to identify potential farm level risk factors for liver fluke infection in Danish dairy farms using two different diagnostic methods. Based on liver condemnation data of all individual cattle slaughtered in Denmark, 145 and 77 farms were selected as cases and matched controls. The selection criteria were; 1) minimum 50 animals were slaughtered in 2013, 2) minimum three cases of liver condemnation due to liver flukes in 2013 (case) / no history of liver condemnation due to liver flukes for the last three years (control), and 3) control farms were located within 10 km from the case farms. Bulk tank milk (BTM) samples from the farms were analysed using enzyme-linked immunosorbent assay (ELISA), and telephone interviews were used to obtain information on the type of production, the farmers’ knowledge about liver fluke infection, grazing pattern, anthelmintic treatments and management routines. Preliminary results based on 132 case and 64 control farms indicate that grazing was significantly associated with liver fluke infection (p=0.006). However, in 12 case herds, grazing was not applied (all-in systems), suggesting indoor rearing does not completely prevent liver fluke infections, although misdiagnosis or incorrect registration at slaughter is possible. The percentage of farms allowing heifers to graze on wet areas was significantly higher in case than control farms (p<0.001). Using grazing for heifers and drinking from natural waterways were associated with liver fluke infections (p=0.07 and p=0.01). Approximately 30% of case farms tried actively to avoid infection by anthelmintic treatment or preventive management measures. The prevalences of liver flukes estimated by BTM ELISA were 75% and 12.5% for case and control groups, respectively. The negative ELISA results in some of the case herds may be due to their low in-herd prevalence, but it is still under investigation. Based on the risk analysis, we expect grazing management can be improved on many infected farms as part of the control of liver fluke. The substantial discrepancy between different diagnostic methods should be taken into account for future studies

Detection and molecular characterization of the mosquito-borne filarial nematode Setaria tundra in Danish roe deer (Capreolus capreolus)

Setaria tundra is a mosquito-borne filarial nematode of cervids in Europe. It has recently been associated with an emerging epidemic disease causing severe morbidity and mortality in reindeer and moose in Finland. Here, we present the first report of S. tundra in six roe deer (Capreolus capreolus) collected between October 2010 and March 2014 in Denmark. The deer originated from various localities across the country: the eastern part of the Jutland peninsular and four locations on the island Zealand. With the exception of one deer, with parasites residing in a transparent cyst just under the liver capsule, worms (ranging from 2 to >20/deer) were found free in the peritoneal cavity. The worms were identified as S. tundra by morphological examination and/or molecular typing of the mitochondrial 12S rRNA and cox1 genes, which showed 99.1–99.8% identity to previously published S. tundra isolates from Europe. Roe deer are generally considered as asymptomatic carriers and their numbers in Denmark have increased significantly in recent decades. In light of climatic changes which result in warmer, more humid weather in Scandinavia greater numbers of mosquitoes and, especially, improved conditions for development of parasite larvae in the mosquito vectors are expected, which may lead to increasing prevalence of S. tundra. Monitoring of this vector-borne parasite may thus be needed in order to enhance the knowledge of factors promoting its expansion and prevalence as well as predicting disease outbreaks

Farm-level risk factors for Fasciola hepatica infection in Danish dairy cattle as evaluated by two diagnostic methods

The prevalence of bovine fasciolosis in Denmark is increasing but appropriate guidelines for control are currently lacking. In order to help develop a control strategy for liver fluke, a risk factor study of farm management factors was conducted and the utility of bulk tank milk (BTM ELISA) as a tool for diagnosis in Danish dairy cattle farms was assessed. This case-control study aimed to identify farm-level risk factors for fasciolosis in Danish dairy farms (&gt; 50 animals slaughtered in 2013) using two diagnostic methods: recordings of liver condemnation at slaughter, and farm-level Fasciola hepatica antibody levels in BTM. A case farm was defined as having a minimum of 3 incidents of liver condemnation due to liver fluke at slaughter (in any age group) during 2013, and control farms were located within 10 km of at least one case farm and had no history of liver condemnation due to liver fluke during 2011-2013. The selected farmers were interviewed over telephone about grazing and control practices, and BTM from these farms was collected and analysed by ELISA in 2014. The final complete dataset consisting of 131 case and 63 control farms was analysed using logistic regression. Heifers grazing on wet pastures, dry cows grazing on wet pastures, herd size, breed and concurrent beef cattle production were identified as risk factors associated with being classified as a case farm. With the categorised BTM ELISA result as the response variable, heifers grazing on wet pastures, dry cows grazing on wet pastures, and purchase of cows were identified as risk factors. Within the case and control groups, 74.8 and 12.7% of farms were positive for fasciolosis on BTM ELISA, respectively. The differences are likely to be related to the detection limit of the farm-level prevalence by the BTM ELISA test, time span between slaughter data and BTM, and the relatively low sensitivity of liver inspection at slaughter. Control of bovine fasciolosis in Denmark should target heifers and dry cows through grazing management and appropriate anthelmintic treatment, and BTM ELISA can be a useful diagnostic tool for fasciolosis in Danish dairy farms