Most fish fans have probably heard of flatfish species like halibut and turbot. But who is familiar with flatworm species like the liver fluke? That is a worm shaped like a flatfish. The liver fluke grows to a mere three centimetres long and it lives in the bile ducts of the liver. Which explains the name.

Watercress
Liver fluke infections pose a serious health problem for sheep and cattle. The animals infect themselves by eating grass that is contaminated with small larvae of this parasite. Liver fluke infections also occur in humans. Although exceptional, they have been found in the Netherlands during abdominal operations. Dozens of cases are known of in Belgium and several hundred in France. The most important source of contamination with liver fluke in humans is the consumption of wild watercress. That grows near pools and along ditches. It is a popular vegetable in France.

Water snail
An intermittent host plays an important role in the contamination with liver fluke: the small water snail. It can be found in pools and ditches. The small water snails become contaminated with liver fluke through the manure of sheep or cattle. The young liver flukes develop further in the snails and these later release small infectious larvae that attach themselves to the grass along the water and to the wild watercress if it grows there. The larvae are not visible to the eye, as they are only a quarter of a millimetre in size. And they are not removed by rinsing off the watercress. There are no specific symptoms associated with liver fluke infection in humans, but the liver does not function properly.

watercress

water snail

Damages
Cows and sheep infected with liver fluke can become severely ill. During the notorious liver fluke year of 1968, up to 80% of the sheep on some farms in the Netherlands died as a result of the infection. Large-scale contaminations occur following wet summers, like in 2007. The Study Group Liver Fluke Prognosis provides a prognosis every autumn regarding the severity of the problems to be expected. It is then possible to timely treat any cattle or sheep that have been grazing on wet pastures. To prevent infections in animals and humans, one would need to suppress the water snail. But an effective means to that end is lacking. It would involve letting the pools and ditches run dry.

Symptoms in ruminants
A farm in the vicinity of Utrecht sees the milk production of the cows declining while the yearlings and the sheep in particular are losing weight. The veterinary surgeon is called in. The animals have yellow mucosae and are anaemic. When a few sheep and a yearling die, an autopsy is performed at the Faculty of Veterinary Science. The cause of death is a severe contamination with liver fluke. The sheep, yearlings and the dry cows on the farm are subsequently medicated. The lactating cows are medicated later during their non-lactating period, as the agent is secreted in the milk.

Field work
Professor Swierstra is willing to have a look on the farm for himself and to draw up an action plan. He is a parasitologist and the chairman of the Study Group Liver Fluke Prognosis. When, sometime later, the regular veterinary surgeon inquires how things went with the field work, the farmer replies that the professor has not been yet. That is strange. Well, there was someone at the farm two weeks ago who collected small snails along the ditches, but that wasn’t the professor. What actually happened?

Fierljeppen
The man who had collected the snails had used a pole to jump the ditches as he made his way through the polder. But upon coming across a wider canal, the pole proved too short or his run-up too slow and he fell into the water. Soaking wet and covered in duckweed, he showed up in the kitchen of the farm. There, he undressed down to his underwear and the farmer’s wife dried his clothes next to the stove. In the meantime, they enjoyed a cup of coffee around the kitchen table. A very friendly man, to be sure. But he could not possibly have been the professor. Just imagine: a professor in his underwear at the kitchen table!

fierljeppen (Friesian for pole jumping)

Status
Professor Swierstra (because it was him, it turns out) was not concerned at all with academic status and class distinction. He was always himself and far ahead of his time in that respect.