Toxocariasis
Toxocariasis is an infection with the larvae of roundworms that live, as adults, in the intestines of dogs, cats and foxes.
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Medicines commonly prescribed for Toxocariasis
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: TABLET, 400 mgActive substance: albendazoleManufacturer: Glaxosmithkline S.A.Prescription required
Toxocariasis is an infection with the larvae of roundworms that live, as adults, in the intestines of dogs, cats and foxes. For a human being the parasite is a dead end: it never matures into an adult worm and never produces offspring. The larva travels through the tissues for a while and then dies. Most of the time this leaves no trace at all, but occasionally it reaches the eye or sets off a long-running inflammation in the internal organs, and then it becomes an illness worth recognising and treating.
How the larvae reach people
An infected animal passes the parasite's eggs in its faeces. At that moment the eggs are harmless: they have to ripen in soil for several weeks or longer, depending on warmth and moisture, before they can infect anyone. That is why nobody catches toxocariasis from fresh droppings, while the earth in a yard, the sand in a play area, a vegetable patch and ordinary street dust build up eggs over years, since they survive both frost and drought.
From there it is simple and unappealing: an egg reaches the mouth. From hands not washed after play, from a carrot pulled straight out of the ground, from salad leaves given a hurried rinse. Less often it comes from undercooked liver or meat of animals in whose tissues larvae had lodged.
Toxocariasis does not pass from person to person under any circumstances. That is the commonest worry people bring: if one child is ill, they are no danger to the rest of the family, not at home, not through shared cutlery, not at nursery. Everyone becomes infected separately, and always from soil or sand. Nor can you catch it from the dog you have just stroked, because the eggs on its coat have not yet ripened.
Why children are affected most
Pre-school and early-school children have a far closer relationship with soil and sand than adults: they dig, they build, they put their fingers in their mouths and sometimes taste the sand outright. A separate risk group is children who habitually eat things that are not food, such as earth or chalk. Adults are infected less often, usually through the garden or through the habit of eating unwashed produce.
Two ideas are worth keeping apart here: "there is a dog in the house" is not the same as "the child will catch it". A well-kept animal that is wormed regularly and cleared up after adds almost no risk. A neglected sandpit that stray cats have been visiting for years is a far bigger problem.
Most of the time the body deals with it alone
The overwhelming majority of encounters with this parasite go unnoticed. The larva crosses the intestinal wall, travels in the bloodstream, becomes stuck in the liver, lungs or muscle, is walled off by inflammation and dies there. The person never finds out, or puts a couple of off-colour days down to a cold.
Sometimes the only trace is a laboratory finding: a raised eosinophil count spotted by chance in a blood test taken for something else. On its own that finding is neither a diagnosis nor a reason to worry, but it explains why a doctor suddenly starts asking about the dog, the sandpit and the vegetable patch.
Two forms of the illness genuinely matter, and they look nothing like each other.
The eye form: when a child starts to see less well
This form is uncommon but the most galling, because lost sight recovers poorly. A larva reaches the eye, and the inflammation that builds up around it damages the retina.
Almost always one eye is affected, and that is where the difficulty lies. An adult notices that, with the good eye covered, the other one sees through a haze, or that a dark patch has appeared in the field of vision. A child notices nothing: the other eye works, the picture holds together, there are no complaints. Parents pick it up later and for a completely different reason.
Reasons to take a child to an eye specialist without delay:
- an eye has started to turn, when it never did before, especially late in the day or when tired;
- the child screws up their eyes, moves close to the screen or tilts their head to one side;
- in certain lighting the pupil gives back a whitish reflection instead of a red one;
- complaints of pain, redness, floaters or flashes;
- reduced vision in one eye picked up at a routine check.
A squint that appears suddenly in a child who used to look straight ahead always warrants an examination of the back of the eye, rather than waiting to see whether they grow out of it. There are many possible causes and toxocariasis is only one of them, but this particular cause is a race against time: the sooner the inflammation is settled, the more retina is saved.
The visceral form: temperature, cough, abdominal upset
Here the larvae are numerous and spread through the internal organs. The picture builds slowly, over weeks, and for that reason rarely looks like an acute illness.
- a temperature, often not a high one, that goes on for a long time and has no other explanation;
- a dry cough, wheeze and episodes resembling asthma;
- abdominal pain or heaviness, an enlarged liver and, less often, spleen;
- an itchy rash and bouts of hives;
- listlessness, loss of appetite, a child who stops gaining weight;
- enlarged lymph nodes, aching muscles and joints.
None of these signs points to the parasite on its own; a dozen other conditions begin the same way. The value is in the combination: a lingering temperature and cough in a child who plays in sand, alongside a high eosinophil count, make up a picture worth testing this specific idea against.
How the diagnosis is made
Looking for the parasite's eggs in a stool sample is pointless: there are no adult worms in the human gut, so there is nothing to shed. A stool test contributes nothing here, even though it is the test most often ordered out of habit.
The diagnosis is built differently. The basis is a blood test for antibodies to Toxocara, together with a full blood count that shows the eosinophils, and biochemistry. The surroundings count too: a dog at home, a garden, a child's habit of putting their hands in their mouth. If organ involvement is suspected, an abdominal ultrasound is done, and for chest symptoms an X-ray or a CT scan. The eye form is confirmed by an ophthalmologist examining the back of the eye, and there the blood test may come back negative: a single larva in the eye provokes only a weak immune response.
One more thing is worth knowing. Positive antibodies in someone with no symptoms are a very common finding, particularly where there are many dogs and the climate is warm. They record an encounter with the parasite at some point in the past, not an illness now, and on their own they need no treatment.
How it is treated
If there are no signs of illness there is nothing to treat, positive antibodies notwithstanding. Larvae that have reached a dead end will die by themselves.
The visceral form is treated with a course of antiparasitic medicine; the choice of drug and the length of the course depend on which organs are involved. Corticosteroids are sometimes added, because the simultaneous death of many larvae stirs up inflammation in itself and that has to be held in check.
The eye form is managed by an ophthalmologist, and there the first priority is not killing the parasite but saving the retina, with anti-inflammatory treatment applied locally or taken by mouth. In some cases surgery is needed, to remove strands in the vitreous or to deal with a detached retina. Taking "something for worms" on your own in that situation is not merely useless: it costs weeks.
What genuinely lowers the risk
None of the following looks like serious medicine, yet together these measures work better than any drug.
- Worm the dog and the cat regularly, following the schedule your vet sets. Puppies and kittens need it more often than grown animals, because they shed by far the most eggs.
- Wash hands after coming in from outside, from the sandpit or the garden, and after handling the animal, and always before eating.
- Cover the sandpit when it is not in use. A lid or a sheet of tarpaulin removes the cats and most of the problem at a stroke.
- Pick up after the dog straight away, and keep animals from fouling the places where children play.
- Wash vegetables, herbs and berries, home-grown ones above all. "It came out of my own garden, why wash it" is the commonest route of infection in adults.
- Explain to small children that soil and sand are not food, and keep an eye on those too young to be told.
- Wear gloves for gardening and do not eat with unwashed hands outdoors.
- Cook meat and offal through.
Online consultation
An online appointment suits exactly the questions people usually arrive with: what positive Toxocara antibodies mean in a test taken "just in case", whether a raised eosinophil count needs anything done about it, whether the whole family should be tested when one child is unwell. The doctor will gather the context, from pets and garden to sandpit and a child's habits, will say which tests are worth doing and which have been ordered for no reason, and will explain what to do with results you already hold. If the picture suggests organ involvement, you will be told which specialist to see and how quickly. Sudden loss of vision, or a squint that has just appeared in a child, is not something to settle online: that needs an ophthalmologist in person within days.
This material is for information only and does not replace medical advice.
Consult with a doctor about Toxocariasis
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Online doctors for Toxocariasis
Discuss your symptoms and possible next steps for Toxocariasis with a doctor online.
