Schistosomiasis: Diving into hot water

By Dr Eddy Bajrovic*

On a scorching hot day, there’s nothing more refreshing than to dive into cool water.
But, would you think twice about taking a refreshing dip if you knew that the river or lake contained crocodiles or sharks? Of course you would!
What about thousands of tiny parasites that could cause the widespread and potentially fatal tropical disease, schistosomiasis?
You might be surprised to learn that you probably would still dive in, if the findings of a new European study are a guide.
The study involved a survey of a group of travellers who visited Lily Waterfalls, a popular tourist destination on the east African island of Madagascar. 
Of the 37 who ventured into the water, 28 (78%) became infected. Of the 18 (45%) of these who were warned about the risk of infection by their doctor or others, 16 (89%) still took a plunge.

The irresistible lure of cool water

This study involved only a few dozen people whose ages ranged from 15 to 67. But, along with other larger studies conducted over the years, it once again shows that for travellers of any age the lure of a swim in cool water is stronger than their fear of what might lurk beneath the surface (with the possible exception, I suspect, of sharks or crocodiles!)
In Australia, schistosomiasis occurs mainly among returned travellers, as well as migrants and refugees from endemic areas. Its incidence is increasing with the ever-rising popularity of eco-tourism and adventure holidays involving activities like white-water rafting and canoeing in the many regions where the tiny parasites are found.
Tour operators often fail to mention risks like schistosomiasis and warning signs on the shore are rare. 
So, when you’re hot and everyone else is swimming in a lake or a river it’s hard to resist the temptation not to dive in, too.

About schistosomiasis…

While they might not be as lethal as sharks or crocodiles, there are plenty of good reasons to stay out of water that might contain schistosomiasis parasites.
IT’S A BIG PROBLEM: Also known as bilharzia, schistosomiasis is the second most prevalent tropical disease after malaria, with 200–209 million people infected each year, according to the WHO. It’s a leading cause of death in many parts of the world because, when left untreated, infection can cause long-term – even lethal – medical complications. 
IT’S COMMON: Several species of schistosomes are found in freshwater rivers and lakes in Africa, the Middle East, South America, the Caribbean, and South-East Asia. (Owing to the absence of suitable snail hosts, transmission cannot occur in Australia.) In a study of travellers to Africa’s Lake Malawi, attack rates were higher for longer stays – around 90% for those who stayed for more than 10 days – while infection rates among rafters on various African rivers ranged from 50-100%.
IT’S A SERIOUS RISK: The risk of infection is often significant for travellers, especially in Africa. And, if one swimmer in a group is infected, it’s highly likely others in their group will be, too. 
HOW INFECTION OCCURS: After developing within the ‘host’ snail, the parasites are released into the water. They enter the skin when people swim or wade close to shore – or even walk barefoot on the banks. Infection is more likely to occur in still rather than flowing water, and in the early morning and late afternoon.
WHAT HAPPENS NEXT: One reason why schistosomiasis is so serious is that most people have no symptoms when they are first infected. However, within days they may develop a rash or itchy skin (swimmer’s itch). Within 1-2 months of infection, more obvious symptoms may develop, including fever, chills, cough, and muscle aches (Katayama Fever). Without treatment, schistosomiasis can persist for years and damage the liver, intestine, spleen, lungs, and bladder. The parasite can also invade the spinal cord and brain causing paraplegia and coma. Severe disease is more likely to occur in patients with heavy and prolonged infection. 
HOW TO AVOID IT: There is no vaccine or preventive medication, but prevention is simple: Avoid swimming or wading in fresh water (salt water and chlorinated pools are safe). If you remember AFTER taking the plunge, rub dry all wet skin briskly with a towel soon after getting out – the larvae can’t survive drying and die quickly out of water. (However, this is no guarantee one or more parasites won’t have already have penetrated the skin.)
HOW IT’S DIAGNOSED: If you get fresh water on your skin in an area where schistosomiasis occurs during overseas travel, talk to your doctor about getting tested and treated. Depending on the type of snail the parasite emerged from, incubation takes between 6-12 weeks, with eggs visible in stool or urine samples under a microscope. Screening returned travellers without symptoms who may have been infected can be done with a simple blood test. The test should be done at least 3 months after exposure, at which time antibodies should be present if infection has occurred. 
HOW IT’S TREATED: Fortunately, schistosomiasis is easy to treat. The usual medication recommended is Praziquantel (Biltricide), an effective and safe treatment, with three doses of 20mg/kg taken 4 hours apart. The course may have to be repeated over subsequent months to ensure all the eggs have been eliminated. Self-medication immediately after exposure is not likely to be effective: Praziquantel acts against mature schistosome parasites and is most effective if taken after the parasite has developed to the adult stage, which is at least 4–6 weeks after infection.

Pre-travel warning quickly forgotten

As well as wanting to learn if the Lily Falls travellers were aware of schistosomiasis before they left home and what impact, if any, the warning had, the researchers wanted to determine if doctors should modify their pre-travel warning about schistosomiasis to make it more memorable, and how they should approach diagnosis and treatment of a potentially infected traveller.
In short, the findings indicated that pre-travel counselling from doctors and others is quickly forgotten when the temperature rises and cool water beckons, so the pre-travel warning about a risk of schistosomiasis needs to be more compelling.
The problem is that while doctors and nurses experienced in travel medicine are familiar with the presence and dangers of schistosomiasis, GPs see few, if any, cases of the disease – or other tropical diseases for that matter. So, it’s rarely on a GP’s radar – before or after travel.

A lesson for doctors, too

A diagnosis may be missed because of the delay in symptoms appearing or because symptoms are often not specific. They can even disappear by themselves – or appear to – with without any treatment.
However, if the infection is left untreated, returned travellers are at risk of developing ectopic lesions especially in the central nervous system or the genital tract, which may have potentially serious long-term consequences.
The research team’s most important piece advice to doctors who see a returned traveller with a fever is to always include a differential white blood cell count in their initial diagnostic testing. If the test detects a possible eosinophilia, the search should begin for a parasite as the cause of the infection.
 Definitely worth remembering if you swam in fresh water during an overseas holiday and develop a post-travel fever.
Learn more about schistosomiasis.

Travelling overseas? Find out if schistosomiasis is a risk by calling Travelvax Australia’s free travel health advisory service on 1300 360 164. You can also make an appointment at a Travelvax clinic to receive any vaccines or medication required or recommended for your trip.

* Dr Bajrovic is the Medical Director of Travelvax Australia.