The science

Here you will find more in depth information on the science behind our research.

Why is our research important?

The prevalence (level of disease) of fasciolosis in the UK is increasing. A recent study conducted by our group found that three quarters of dairy herds in England and Wales are infected with liver fluke. This is likely to be due to a combination of factors: an increase in resistance to the drugs used for control; a change in climate – wetter summers and mild winters – meaning development of the parasite within the snail is enhanced; and an increase in the movement of cattle and sheep around the country, which has the potential to spread the parasite to new areas. Farming methods and practices are also changing and collectively this means that the prevalence and economic and welfare significance of liver fluke is increasing.

One of the biggest problems the human race faces is an increasing population that is becoming more affluent, this means the world needs more and higher quality food. The effect of liver fluke on livestock productivity means better control of fasciolosis is intrinsically linked to food security, which is so important for the future.

Drug Resistance

Farmers often repeatedly treat their animals with flukicides even if they do not have a confirmed diagnosis. This has contributed to the level of drug resistance that we see in liver fluke. The liver fluke group has developed a faecal egg count reduction test that can be used on composite faecal samples to measure the presence of drug resistance in fluke populations. This test is being using to estimate the prevalence of drug resistance on farms in the UK.

Previous attempts, using a candidate gene approach, to elucidate the genetic basis of drug resistance to triclabendazole in liver fluke have not, to date, been successful. The liver fluke group has sequenced the genome of Fasciola hepatica, and have developed a panel of genetic markers to probe the genome. We are using these genetic markers as part of a unique, approach to identify the genes, or genes, associated with resistance.

Working towards a vaccine

There is currently no effective vaccine against liver fluke. However, in light of the level of resistance to triclabendazole, a vaccine would be the most effective method of control. We are working with University College Dublin towards a vaccine for liver fluke. The objectives of this project are:

1) To define the effect of liver fluke on the immune system of calves naturally exposed to infection. Flow cytometry is being used to measure changes in circulating mononuclear cell populations specifically CD4, CD8 and γδ T lymphocyte cells as well as monocytes. We are also measuring proliferation and cytokine responses of the PBMCs to detect evidence of immunoregulatory responses. This links to our previous work where we showed that in the presence of fluke, dairy herds are less likely to be diagnosed with bovine TB, an observation we suggest is due to the ability of the parasite to suppress pro-inflammatory immune responses (Claridge et al., 2012).

2) Developing a model to assess the effectiveness of a vaccine. The model created builds on an existing model for liver fluke in sheep (Smith, 1984) by adding natural variability between hosts in terms of susceptibility to infection. This variability, in combination with stochastic variation, in processes such as death of immature flukes leads to a range of fluke burdens, similar to that typically seen in the field. The model's main purpose is to assess the effect that a prototype vaccine might have on fluke burden and egg output. The vaccine is expected to act in three ways: by increasing the juvenile (immature) death rate; by increasing the maturation time; and by decreasing the fecundity of adult flukes. These effects have been incorporated into the model along with parameters that allow us to vary the proportion of the animal population protected and duration of protection. The aim is to determine a vaccination strategy that will result in fewer cases of disease (i.e. fewer animals with high fluke burden) and reduced contamination of pasture (i.e. reduced egg output).

Improving control

The first step to improving control is to improve our ability to diagnose live fluke infection in herds. We currently use a bulk milk tank ELISA to identify infected dairy herds but this test is not appropriate for use in beef herds. We also want to develop a diagnostic test for rumen fluke, since there is a question over whether this parasite, closely related to liver fluke, actually causes disease or not.

Next we will look at snail habitats using satellite maps, rather than having to visit individual farms, and investigate how cow behaviour, e.g. grazing patterns, affects transmission of liver fluke from cow to snail and vice versa.

Finally we will investigate other on-farm risk factors, which will usually relate to husbandry practices, for liver fluke infection. Taken together and using advanced modelling techniques we can then identify farm management practises that can be manipulated, such as grazing area or water supply, to reduce the fluke challenge on a farm. We can also use our models to assess the cost-benefit of any changes we make. Ultimately we aim to develop control programmes that rely less on drugs, and more on improved farm management, which may slow the development of drug resistance.