971
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Changes
→Weather Patterns and Disease Risk
→ '''reduced''' risk of disease.
→ '''reduced''' risk of disease.
=== Forecasting Fasciolosis ===
Several prediction models have been developed. They evaluate the wetness of the soil from May to October by taking account of rainfall patterns and evapo-transpiration. Seasonal weighting factors are applied. June is a particularly influential month.
A drought in late summer can reverse a potentially dangerous trend, and so unqualified forecasts should not be issued prematurely.
A high snail density will only lead to disease if infection is present (i.e. if fluke eggs have been deposited onto the habitat by farm or wild animals). Local biological interpretation of computer generated predictions is therefore required.
These forecasting models can provide valuable information for the farming community. MAFF (before DEFRA) used to provide an annual forecast, but this is now discontinued.
=== Diagnosis ===
'''Acute fasciolosis''':
*clincal history (season, grazing)
*post-mortem examination.
'''Chronic fasciolosis''':
*clinical history (season, grazing):
**lethargy, weight loss
**anaemia (pallor)
**hypoalbuminaemia (bottle-jaw)
**gamma-glutamyl transpeptidase increase (i.e. increase in hepatic enzymes)
**fluke eggs in faeces.
=== Control ===
'''Anthelmintics''' - few flukicides kill all parasitic developmental stages. Not all products, therefore, are suitable for controlling acute outbreaks. The anthelmintic with the broadest spectrum of activity against immature and adult ''F. hepatica'' is triclabendazole. Triclabendazole-resistant ''F. hepatica'' populations are beginning to emerge. The more potent products tend to be the most expensive. Many flukicides bind to plasma protein and have long plasma half-lives.
'''Chemoprophylaxis''' - there are several control objectives:
a) to prevent fluke eggs dropping onto snail habitats - this can be done by treating sheep/cattle with an adulticidal drug in the late winter/early spring.
b) to protect animals grazing pasture known to be contaminated with metacercariae - the choice of drug, time of treatment and dosing interval will depend on:
i) whether preventing acute or chronic disease
ii) the likely intensity of challenge (local knowledge/fluke forecast)
iii) the persistent effect of the drug (i.e. the period after dosing, during which the animal is protected from reinfection).
'''Vaccination''' - a recombinant vaccine which provides approximately 70% protection for cattle is being developed. It exerts its effect by stimulating a range of immune responses not normally seen in chronically infected animals (including TH1-type responses).
'''Molluscicides''' - have been employed with success in the past, but are no longer used. This is because they have to be applied before any fluke forecast can be issued. (Farmers are unwilling to invest in control measures before they are known to be necessary). Also, they have to be applied very carefully as snails can rapidly recolonise sprayed land if any habitat has been missed.
'''Alternative strategies''' - an ability to recognise and define the extent of snail habitats allows alternative cost-effective control options such as fencing and drainage.