Doctors' Notes: All about travel parasites and their problems

Republished from Toronto Star's Doctors' Notes

In my work as a travel and tropical medicine specialist, this is one of my busier times of year as large numbers of people return from March Break vacations to warm, sunny places.

In the winter, I see a lot of people coming home from holidays in the Caribbean. In the summer, my colleagues and I see more people who have visited places like India, Africa, South America or Southeast Asia. It’s not uncommon for people to pick up a parasite while travelling in these parts of the world.

When it comes to travel-related illness, the most common is travellers’ diarrhea. It is acquired mostly via contaminated food or water. Between 30 to 50 per cent of vacationers come back home from the tropics with gastrointestinal problems — mostly caused by bacteria.

But the same symptoms can also be caused by intestinal parasites, such as a common bug called giardia. Single cell organisms like this one are one major category of parasite.

It might be surprising, but not all parasites cause problems. Many of us carry these kinds of microscopic bugs in our bodies our whole lives — and never have any issues. For example, in Toronto, about 10 per cent of kids in daycare have giardia in their guts. And most of them are well.

But, if you were to travel and become infected with a different strain of giardia, you could become quite sick and experience diarrhea, bloating, gas, fatigue and weight loss. This has to do with gut immunity, and whether you’ve already been exposed to the particular parasite or not.

In parts of Ontario and British Columbia, an illness called giardiasis can cause similar stomach symptoms. The strain that causes it is better known as “beaver fever” because beavers are one of the parasite’s carriers. The strain can pass from beaver to human via contaminated water in rivers, lakes and ponds. One of the ways you can get it is from swallowing lake water when you’re swimming. You can prevent this illness by avoiding drinking untreated water and washing your hands well.

When it comes to travel parasites, some are bothersome, but fortunately most are not fatal or dangerous. One exception of course is malaria, a very dangerous parasite transmitted by mosquitoes.

Another category of parasite is those that can affect our skin, such as cutaneous larva migrans. Two or three times a week in my office I’ll see people who are experiencing intense itching, usually in one or both of their feet on which they visualize a linear, irregular slow moving track. The feeling is so strong some people tell me they’d consider sticking their bare feet in the snow for relief. Infected cats and dogs can carry this parasite and leave larva in their droppings.

Common in the Caribbean, and particularly in Jamaica, barefoot vacationers enjoying a day at the beach may pick the parasite up as they stroll along the sand. Since humans are the wrong host for this kind of hookworm, it reacts by crawling just under the surface of the skin. So, it’s a good idea to wear closed-toe shoes if you’re out for a walk during a beach holiday.

The third major group of parasites are intestinal worms, such as roundworm. These can live in your system without causing symptoms and some people only become aware of them when they pass a roundworm during a trip to the bathroom.

But, to put things into context, a huge proportion of the world’s population lives with worms. Most don’t know they have them because the worms aren’t numerous enough to cause symptoms. And, once they’re in a human body, most worms can’t multiply.

I’ve been working in this area for more than 40 years, and in that time I’ve led and seen a large amount of research into helping people around the world whose parasites cause serious illness.

Malaria still kills nearly half a million people every year. Intestinal parasites affect more than 1.5 billion people annually and can lead to severe malnutrition and negative effects on growth and cognitive development. Other parasites such as schistosomiasis lead to chronic disease and death.

One of my colleagues at the University of Toronto’s Faculty of Medicine, Dr. Isaac Bogoch, has found a way to adapt cellphones with special camera lenses and lights so that they can be used as microscopes to diagnose intestinal parasites. This is especially helpful in rural and under-serviced areas such as parts of Africa, where resources are scarce. Some of the devices he’s developed are already available for use in the field and more are being developed.

The idea of having a parasite is disturbing to a lot of people, but the issue is more complex than it sounds at first. It’s true that some can make you very sick, but ultimately, not all parasites need to be treated and they don’t all cause damage to our bodies. Most illness from parasites depends on parasite load, heavy in developing countries but light in most travellers.

But, if you’ve been travelling and have symptoms that concern you, it’s worth a visit to your doctor.

Dr. Jay Keystone is a professor in the Division of Infectious Diseases at the University of Toronto’s Faculty of Medicine. He is also a senior staff physician in the Tropical Disease Unit at Toronto General Hospital and the Director of Toronto Medisys Travel Health Clinic. Doctors’ Notes is a weekly column by members of the U of T Faculty of Medicine. Email doctorsnotes@thestar.ca.