Changes

*1st spiral is greater than half the total length

*1st spiral is greater than half the total length

*The shell opens on the right (when held with the opening upwards)

*The shell opens on the right (when held with the opening upwards)

*feeds on green slime

*Feeds on green slime

*can multiply rapidly if food is abundant

*Multiplies rapidly when food is abundant

*most die during the British winter (unless very mild)

*Most die during the British winter (unless very mild)

*survivors lay eggs in spring, which hatch in June.

*Survivors lay eggs in spring, which hatch in June

==== Habitats ====

==== Habitats ====

*''Lymnaea'' is found in muddy areas (but not on highly acidic soils)

*''Lymnaea'' are found in muddy areas (but not on highly acidic soils)

*habitats may be permanent (dry summer) or temporary (wet summer).

*Habitats may be permanent (dry summer) or temporary (wet summer)

=== Epidemiology ===

=== Epidemiology ===

In temperate areas, there are two superimposed epidemiological cycles, known as the summer and winter infections of the snail. On mainland Britain, the summer cycle predominates as a high proportion of snails perish during the winter, but very occasionally, weather sequences allow the winter cycle to affect the pattern of disease. On the west coast of Ireland, the winter cycle of events determines the timing of clinical outbreaks.

In temperate areas, there are two superimposed epidemiological cycles, known as the summer and winter infections of the snail. On mainland Britain, the summer cycle predominates as a high proportion of snails perish during the winter, but very occasionally, weather sequences allow the winter cycle to affect the pattern of disease. On the west coast of Ireland, the winter cycle of events determines the timing of clinical outbreaks.

→ hatch in '''June''' (i.e. coincident with snail hatch)

 

→ hatch in June (i.e. coincident with snail hatch)

→ miracidia infect newly hatched snails

→ miracidia infect newly hatched snails

→ develop and multiply in snail hepatopancreas during summer

→ develop and multiply in snail hepatopancreas during '''summer'''

→ cercariae shed from late August onwards

→ cercariae shed from '''late August''' onwards

→ metacercariae ingested by sheep

→ metacercariae ingested by sheep

→ immature flukes migrate through liver

→ immature flukes migrate through liver

→ '''acute''' disease '''September-November'''; or '''chronic''' diesease '''January''' onwards.

→ '''acute''' disease '''September-November'''; or '''chronic''' diesease '''January''' onwards

 

=== Winter Infection of the Snail ===

=== Winter infection of the snail ===

Eggs dropped in late summer:

Fluke eggs passed in '''late summer''':

→ infect snails

→ infect snails

→ development resumes when temperature >10°C

→ development resumes when temperature >10°C

→ cercariae shed from July

→ cercariae shed from '''July'''

 

=== Geographical Distribution of Disease ===

=== Geographical distribution of disease ===

Transmission is dependent on the snail, and therefore associated with snail habitats. These are more plentiful in high rainfall areas such as found on the western side of the British Isles, or alongside drainage canals in low-lying areas such as the Romney Marsh (or the Netherlands). It is important to remember that sheep and cattle are often bred in Ireland or western Britain and transported to the east of th country for fattening. Infected animals may therefore be found in areas where no transmission occurs.

Transmission is dependent on the snail, and therefore associated with snail habitats. These are more plentiful in high rainfall areas such as found on the western side of the British Isles, or alongside drainage canals in low-lying areas such as the Romney Marsh (or the Netherlands). It is important to remember that sheep and cattle are often bred in Ireland or western Britain and transported to the east of the country for fattening. Infected animals may therefore be found in areas where no transmission occurs.

 

=== Weather patterns and disease risk ===

=== Weather Patterns and Disease Risk ===

'''Wet summer'''

'''Wet summer''':

Many fluke and snail eggs hatching and snail habitats expanded, therefore:

Many fluke and snail eggs hatching and snail habitats expanded, therefore:

→ high density of metacercariae on herbage

→ high density of metacercariae on herbage

→ '''increased''' risk of disease.

→ '''increased''' risk of disease

 

'''Dry summer'''

'''Dry summer''':

Few fluke and snail eggs hatching and snails restricted to permanent habitats, therefore:

Few fluke and snail eggs hatching and snails restricted to permanent habitats, therefore:

→ few metacercariae confined to restricted areas

→ few metacercariae confined to restricted areas

→ '''reduced''' risk of disease.

→ '''reduced''' risk of disease

 

=== Forecasting Fasciolosis ===

=== 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.

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 drought in late summer can reverse a potentially dangerous trend, and so unqualified forecasts should not be issued prematurely.

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.

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 ===

=== Diagnosis ===

'''Acute fasciolosis''':

'''Acute fasciolosis'''

*clincal history (season, grazing)

*Clincal history  

**Season

 

**Grazing

*Post-mortem examination

**lethargy, weight loss

**anaemia (pallor)

**hypoalbuminaemia (bottle-jaw)

=== Control ===

=== 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.

'''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

 

 

iii) the persistent effect of the drug (i.e. the period after dosing, during which the animal is protected from reinfection).

#The likely intensity of challenge (local knowledge/fluke forecast)

#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).

'''Vaccination'''  

*A recombinant vaccine providing 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.

'''Molluscicides'''  

*These 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.

'''Alternative strategies'''  

*An ability to recognise and define the extent of snail habitats allows alternative cost-effective control options such as fencing and drainage