Journalism Archive

Hunting for parasites in Cambodia

THE MERE thought of a parasite is enough to make most people cringe, but new research on parasitic worms in Cambodia has a few scientists wriggling with excitement.

Philipp Bless, from the Swiss Tropicaland Public Health Institute in Basel, Switzerland, looks less like a scientist and more like a tourist at first glance.

Sporting a basic t-shirt, cargo pants and a black baseball cap with sunglasses, the 25-year-old is conducting field research on a specific type of parasite, in collaboration with the National Centre for Parasitology, Entomology and Malaria Control in Phnom Penh.

The project is part of a larger study supported by the United Bank of Switzerland Optimus Foundation, which primarily funds initiatives that seek to improve the health of children.

In a laboratory at the centre, Bless – who will use his research as part of his Masters degree –  and his colleagues are trying to determine whether a type of parasite that commonly infects cattle and buffalo, known as Fasciola hepatica, is also infecting children in Cambodia.

“Scientifically, I would be the first one to identify human infections of this parasite [in Cambodia], at least amongst all known English literature,” says Bless.

According to a 2006 report by the World Health Organisation (WHO), about 2.4 million people worldwide have this type of parasite, commonly known as liver flukes, or helminths, a name derived from the Greek word for worm.

A separate WHO report, published two years later, recognized Cambodia’s success in a number of programs to reduce their numbers in the Kingdom over the past decade, while also indicating that more studies are needed to determine their distribution and numbers.

As part of the quest to find more data, Bless and his fellow researchers are on the hunt, actively searching for parasitic worms.

Yesterday, they travelled to a slaughterhouse in Kandal province to collect a sample of nearly 100 worms, found inside the livers of cattle. Bless says that the parasite he is searching for has a close relative that looks almost identical, which is why he has to send the samples back to Switzerland for DNA analysis.

“After getting permission from the commune authorities and owner [of the slaughterhouse], I explained to the workers what we are looking for and showed them some pictures.

One worker said ‘Oh yeah, everyday I see some. How many worms do you need?”, Bless recalls with enthusiasm in his voice.

Bless says that these parasites are interesting because they can infect both humans and animals. He explains that the life cycle has four main stages and is similar in both instances.

Once contaminated vegetables or water is consumed, the parasite migrates from the intestines and eventually settles in the liver over a period of a few days.

“The worm locates in the bile ducts of the liver, sucking up mostly blood and that can lead to a bunch of complications,” says Bless. The worms can also eat their way through liver tissue, causing inflammation and scar tissue.


As the parasites feed on the liver, he explains in detail, they eventually become sexually mature over a period of months. Once the eggs are let loose, they eventually make their way out of the body through the digestive system.

At this point, Bless explains that the life cycle for these small creatures has a bit of a catch: the eggs need fresh water and a snail to help them further develop. As future generations develop inside the infected snail, a process proceeds akin to a snail’s pace, gradually producing a form of the parasite that invades larger mammals to become the adult worm.

Standing under a shelter at the slaughterhouse during a brief downpour, Bless takes a look at the samples, explaining that the adult worms are easy to see because they are 2-3 centimetres long, fairly flat and wide in shape, with a distinct light colour compared to liver tissue.

That the cattle have worms is no surprise to Bless and his support staff at the centre.

In 2002, a limited study found that nearly 60 per cent of the buffalo and cattle in Kandal province were infected with the parasites.

Despite their findings, Bless says that people shouldn’t be too alarmed. The owner of the slaughterhouse assured him that infected livers are discarded, although at the moment, he was unsure how.

Bless also explains that the immature yet infectious form of the parasite, found on water plants such as watercress, is killed when the vegetables are cooked properly or washed thoroughly with clean water.

Referring to his notes on previous studies, Bless says that death caused by the parasite is “practically unheard of”, although they are known to cause a number of health complications.

According to research on fascoliasis, a human disease caused by these parasites, severe cases can stunt a child’s physical and intellectual development. It’s also known to cause fatigue, indigestion, fatty food intolerance, gall stones, jaundice, enlarged organs and pain.


In animals such as cattle and buffalo, Bless says the parasites can take their toll on agriculture by causing infected animals to produce less milk, meat and offspring. They can also become weak, leaving them vulnerable to other diseases or predators.

Galina Nicolaevna (Nicola) Krushina, a physician at Naga Clinic in Phnom Penh, says that few people ever get to actually see the parasites that infect them.

“It’s only eggs we see in the stool, and from that you judge the presence of the parasite,”she explains.

Nicola doesn’t bat an eye as she explains the number of parasites that she diagnoses on a constant basis at the clinic.

“It’s typical, normal, it’s every day because they [parasites] are very common all over the tropics, not just in Cambodia.”

Originally from Bulgaria, Nicola has 32 years of experience as a doctor in Africa and has been working at the clinic in Cambodia for the past two years.

“Everybody who has lived in the tropics longer than six months has one. If he doesn’t, he has one hell of good luck,” she says frankly.

For her, diagnosing a patient is straight-forward.

“The complaints are very typical. Fullness, tiredness, indigestion, constipation, diarrhea.”

She says the parasites are easily treated with medication that eliminates the uninvited guests within three to six days.

Patients who are eager to eliminate their parasites present a paradox for research, according to Bless, because the medication is inexpensive compared to the regiment of tests that would be required to identify exactly what type of parasite is causing the problem.

“The drugs are so cheap and often with just a few tablets the worms are gone.”

While a large number of these parasites are likely being flushed down the toilet, Bless is hopeful that his field research will be successful. If he’s able to confirm that the parasite he is seeking is inside these cattle, Bless says the next step will be to collect blood samples from 150 to 250 primary school students, to detect if they have been infected by the parasite as well.

Researchers expect to finish collecting their data in Cambodia by the end of the month and anticipate publishing their work at the end of the year.


Published in the Phnom Penh Post, 05 May 2011, page 6.

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