Schizo or Schisto – get your head around these little parasites

Schizo or Schisto ?

Schistosoma flukes could have your brain confused, wondering why, where and what has caused your symptoms of diarrhoea, fever and a rash.  And it could be anything up to 3 months after you have been wading in a dam fishing, or have taken a dip in a river before symptoms appear – so the correlation may not be instantly clear.

So what is a Schistosoma fluke?  It’s a tiny flat worm that has a complex life cycle involving specific freshwater snail species as intermediate hosts.

The worm starts life as an egg in a freshwater source such as a pond, dam, lake, or stream. It hatches into a larva and if the right type of aquatic snails live in that water, the larva will find and enter a snail. There it passes through several stages of development. During the last phase in the snail, the parasite turns into a larva that can swim. It then leaves the snail and returns to the water, where it may come into contact with a person; the larva can survive in the water for up to 2 days without a human host. When people bathe, wade, swim, or wash clothes in the water, the parasite (It is only 400 microns in length) can burrow into bare skin and enter the bloodstream. Once it is in the blood, it matures into an adult worm – and that grows to 10-20mm long.

Depending on the species, the female adult worms lay their eggs within blood vessels near the person’s bladder or liver. The eggs gradually move to the urinary tract, liver, and intestines and over time, some eggs are excreted when the person urinates or has a bowel movement. If faeces (excreted waste) from an infested person contaminate a freshwater source such as a pond, the eggs can enter the water and begin the parasite life cycle all over again (could be from sewage from a disfunctional treatment plant or even an infected cow).

Even brief exposure to contaminated fresh water, through activities such as wading, swimming, or bathing, can result in an infection known as schistosomiasis – or as we commonly know it, Bilharzia. So named after German physician Bilharz way back in Egypt in 1851 when he discovered this. The first record in Southern Africa was in 1863 when Dr J Harley, a general practitioner in Port Elizabeth, diagnosed young boys from Uitenhage in the Eastern Cape with schistosomiasis.

Human schistosomiasis cannot be acquired by contact with salt water (oceans or seas) and is found mainly in the eastern half of Southern Africa and especially on the lowveld (coastal plain). It is also common in South America, the Caribbean, Asia and other parts of Africa and some 700 million people live in 70 countries where it is prevalent.  It cannot be passed from one human to another.

Is this a modern day disease?  No!  Based on the phylogenetics (evolutionary biology) of the host snails it seems likely that this little flatworm evolved in Gondwana between 70 million and 120 million years ago.

So what to look out for? The first symptom of this disease is a slight rash around a concentrated area where the parasitic larva entered through the skin. Two to twelve weeks later fever, diarrhea, cough or rash may develop. You might also see blood in the stool or urine and sometimes there is abdominal pain. Long term problems with the bladder, kidneys, bowel, lungs or liver can occur if not treated properly. Those who have been infected a long time (it can hang around for a long time) may experience liver damage, kidney failure, infertility, or bladder cancer (squamous cell carcinoma). In children, it may cause poor growth and learning difficulty.

So is it easily treated? Diagnosis of infection is usually confirmed by serological studies or by finding eggs during microscopic examination of stool or urine samples. The eggs can be found as soon as 6-8 weeks after exposure but are not always detectable. There is treatment for Bilharzia and safe and effective drugs are available for the treatment of this disease. You will be given pills to take for only 1 to 2 days.

Can I prevent it?  Travelers should be advised to avoid wading, swimming or other fresh water contact in endemic countries. Untreated piped water coming directly from canals, lakes, rivers, streams or springs may contain cercariae (the larva), so heating bathing water to 50°C for 5 minutes or filtering water with fine mesh filters can eliminate the risk of infection.

If such measures are not feasible, allow bathing water to stand for 2 days because cercariae rarely remain infective longer than 24 hours.

Swimming in adequately chlorinated swimming pools is virtually always safe, even in endemic countries.

Application of an astringent (drying agent), such as rubbing alcohol to the skin immediately after swimming may also help to reduce fluke penetration.  (This may be a handy item for fishermen and boating enthusiasts to carry with them.)

For poor people living in rural areas where they wash clothes and the children bath in rivers and streams, there is an annual need to take a course of the medicine praziquantel.


 Can it be eradicated?

Introducing fresh water lobsters is one suggestion but that has proved a disaster in Kenya, South Africa and elsewhere, where the “Cajun Lobsters” (they are red and not indigenous) have eaten their way through snails AND fish eggs and hatchlings and have depleted natural fish stocks. And they are able to survive out of water for a long time and walk for miles (especially when it is raining) to get to other water sources. I could not find a source whereby anybody has found a chemical treatment that kills only the host snail.  Keeping the ecology of water systems balanced and not allowing over-fishing, where the species that eat the snails are taken out is key. Tilapia, where they are naturally occurring, can keep snail numbers down to a degree (and on Lake Malawi, in shallow waters where the snails occur and the fish that eat them live, fishing is banned for 100m from shore). Protecting the balance of the fish species, their breeding places and not allowing poaching and over fishing is paramount.

What about Swaziland and Lake Jozini?

It is best to regard ALL waterways and dams as harbouring the Bilharzia host snails throughout inland waters in Southern Africa – and so take great precaution when fishing and boating. However, one big advantage that we have on Lake Jozini is that there is an annual outlet of water each October, to feed water to the Makatini Flats below the dam wall. This is for the fisheries and small scale farmers, which action quickly reduces the water levels in the dam.  Thus, the snails get stranded on the mud banks and they die.  But take all precautions, just in case. We wouldn’t recommend swimming anyway – the crocs and hippos are likely to be far more of a concern than the snails!

By the way, Royal Jozini’s water that is fed to the lodge homes is all purified and is good and safe to drink.

So why not book a bush break to enjoy Royal Jozini Big 6’s magnificent views, pristine bushveld and flora and fauna?  You don’t even have to get your feet wet unless you take a dip in a swimming pool.  Good launch sites for boats with a floating jetty to keep you dry, too!

email me, Lynda, with your preferred dates.  Don’t let a little parasite stop you but if you are worried, bring a little alcohol along!

With thanks WHO, Wikipedia, Ecosystems, Centre for Disease Control and many other resource sites on the web.