Stomach fluke, Calicophoron calicophorum is the most commonly found stomach fluke in cattle. Other related species in the Paramphistome family that are known to infect cattle include Orthocoelium (Ceylonocotyle) streptocoelium and Paramphistomum ishikawai. Sheep can also be infected with P. ishikawai.
Stomach flukes cause sporadic disease in young cattle 6-18 months of age. Typically, cattle become infected by grazing fluke-contaminated ‘green pick’ in dry winters following an unseasonably wet summer that enabled enormous explosions of snail numbers.
During dry spells, snails can survive by burrowing into the mud where they can remain dormant until the rains return. Infective metacercariae encysted on herbage are also tolerant of dry conditions and survive long after the season has dried out.
Most cattle carry small numbers of stomach fluke without any signs of infection or loss of productivity. By contrast, disease may occur in previously non-immune adult cattle moved from farms outside the endemic stomach fluke region, to farms where stomach fluke is endemic. Cattle rapidly develop a strong resistance to reinfection with this parasite.
Adult stomach fluke have a fleshy, pear-shaped body, 5–12 mm long by 2–4 mm in diameter in the lower body, and are pink or light red. Juvenile fluke are 1–2 mm long.
Adult stomach fluke inhabit the rumen (first stomach or paunch), and sometimes the reticulum (second stomach or honeycomb) of cattle. Juvenile fluke are found in the upper small intestine.
Figure 1. Stomach fluke, Calicophoron sp., adult surrounded by immature worms. Image courtesy of Constantin Constantinoiu
This is a two-host indirect life cycle similar to that of the liver fluke, except that adult flukes live in the rumen of cattle not in the bile ducts, and the immature life stages develop in freshwater planorbid snails not lymnaeid snails. Planorbid snails are 2-5 mm in diameter and are commonly called the red ram’s head snail.
Adult flukes in the rumen and reticulum pass eggs in the dung. Eggs hatch in water when temperatures reach 24°C to 32°C. Released free-swimming miracidia invade a freshwater snail and undergo further development and multiplication. Cercariae released from the snail form cysts, the metacercariae, on grasses and weeds growing in wet areas.
Cattle become infested during grazing by ingesting the infective cysts. Once in the small intestine, cysts break open and release the pre-adult flukes that attach to the walls of the anterior small intestine. After feeding they move to the rumen or reticulum to commence egg-laying. Unlike liver fluke, stomach fluke do not migrate through the tissues of cattle, instead they are wholly retained within the gastrointestinal tract.
In extremely heavy infections, young flukes can be held in the small intestine for several months where they cause severe disease associated with destruction of the lining of the small intestine during feeding.
The pre-patent period for C. calicophorum is about 80 days.
Figure 2. Stomach flukes attached to the stomach of a cow. Image courtesy of Grant Parker, Queensland Department of Agriculture and Fisheries
Most cattle are unaffected by stomach fluke infections. Moderate infections may produce reduced weight gains or milk production, intermittent diarrhoea or ill-thrift.
Acute infections may develop rapidly in young susceptible yearling calves due to massive numbers of pre-adult fluke developing in the small intestine. Signs include a loss of appetite, lethargy and weight loss. A profuse fetid diarrhoea containing immature fluke and dehydration may start 2 to 4 weeks after calves have been exposed to contaminated pastures, and can be followed by death.
Figure 3. Paramphistomum cervi adults shown attached to the rumen wall of a cow. Image courtesy of the National Centre for Veterinary Parasitology, ncvetp.org
Eggs of the stomach fluke are detected during laboratory analysis of dung samples for liver fluke. Like liver fluke, eggs only appear in the faeces of the host 10-12 weeks after infection.
Fencing to restrict access to wet snail habitats will aid in control. Talk to your vet about ‘off label’ products that have reported activity against adult and immature flukes.