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It is estimated that 2-3% of the British population may be infected with Toxocara (dog and cat roundworm) of which 100 cases of eye disease largely in children arise.

Many studies have looked into these issues and the interested web-reader can find more detail about these aspects by clicking on the links as below.

1.See Pet House Council - the facts about Toxocara which states that:

...there are approximately two cases of illness due to infection per million of the population a year. [equates to around 130 cases]

2.See Soil contamination with Toxocara spp. eggs in public parks in the Midlands which concludes that:

Research has been conducted into seroprevalence in UK adults, with values ranging between 2.1% and 2.6% having been recorded (de Savigny et al, 1979). Far higher rates are found in children; studies in the US and UK recorded a prevalence of 13.4% (Walsh and Haseeb, 2012) and 14.3% (Josephs et al, 1981) respectively.

3.Rates in the USA, Europe and the Caribbean are also high. See Veterinary and public health aspects of Toxocara spp which states that:

The seroprevalence of Toxocara spp. antibodies varies between countries. Anti-Toxocara spp.-antibodies were found in 4.6–7.3% of children in the USA (Herrmann et al., 1985), in 2.5% in Germany, and in up to 83% in the Caribbean (Thomson et al., 1986). In the Netherlands, the prevalence was found to be 4–15% in individuals under 30 years of age and 30% in adults older than 45 years, with an average figure of 19% (De Melker et al., 1995). Continuous re-infection is probably the cause of the higher prevalence in adults.

4.And also Fighting feline worms: Toxocara in cats and its role in human toxocarosis which notes that:

...surveys across Europe showing that between 2% and 31% of people have antibodies to Toxocara spp. (Overgaauw & Van Knapen 2013).

5.Puppies and the pregnant bitch are the main source because the eggs appear in their faeces (however, they take two weeks to become infectious, so fresh faeces are not too bad!).

See Veterinary and public health aspects of Toxocara spp which states that:

Nearly 100% of puppies are infected in utero by re-activated somatic larvae from day 42 of the gestation period (Lloyd et al., 1983). This transplacental migration and intra-uterine infection is the most important mode of transmission in pups. It results in egg excretion after a minimum period of 16 days after birth (Lloyd, 1993). After birth, puppies and kittens also acquire infection through ingestion of larvae in the milk (Parsons, 1987), which can be passed for at least 38 days after parturition (Zimmerman et al., 1985),

These faeces can be picked up by children playing on contaminated ground.

All cats and dogs (especially puppies and kittens) must be regularly wormed.

Symptoms of roundworm infection in humans are:

  • Nothing at all, just worms in the stool.
  • Sight loss due to inflammation in the optic nerve, retinal fibrosis and possibly detachment, squint, eye pain, red eye. 97% just have symptoms in one eye.
  • Visceral larva migrans: as the worms migrate through the gut they cause fever, malaise, cough, pain, wheeze and possibly failure to thrive. The child, usually under 5, usually gets better without being diagnosed.
  • Overt toxicara: childhood fever, cough, disturbed sleep, abdominal pain, head ache, behavioural disturbance, swollen liver, swollen glands and wheezing.

Diagnosis is made by seeing worms in the stool (they are a pale round bodied worm up to 6 inches in length) or doing blood tests for antibodies to toxocara at the Diagnostic And Reference Parasitology Service (formerly known as the "Scottish Parasite Diagnostic Laboratory"), Email: ggc.glasgowsmrl@nhs.scot Tel: 0141 242 9631 or see Diagnostic And Reference Parasitology Service (formerly known as the "Scottish Parasite Diagnostic Laboratory"

Ideally a stool sample should be sent to the London School of Hygiene and Tropical Medicine - see London School of Hygiene and Tropical Medicine - we can send you a kit for this test. See Ordering Tests

Treating roundworm

Treatment is with mebendazole (Vermox) 100mgs twice daily for three days. It can be bought over the counter from chemists. The whole family should be dosed.

See Boots the Chemist - OTC Mebendazole 100mg

Please note, Vermox should not be used during pregnancy


Thread worms are very common and cause no serious illness. They tend to crawl out of the anus in the evenings and at night (how do they know when it's night-time? I've often wondered! Maybe it's simply when we cease to be active, and they would come out in the day if we slept then.) to lay their eggs before they die. This usually causes itching, which is wonderful for the worm because the child scratches, gets the eggs stuck on the fingers and under the finger nails and promptly re-infects itself next time the fingers goes into his mouth, or even better for the worm, somebody else's mouth! The adult worm lives about 6 weeks.

Ideally the diagnosis should be made by seeing the worms, usually on the child's bottom, just round the anus. They are called thread worms because they look like pieces of white cotton thread about a centimetre long, often wriggling. Some people don't bother to treat because these worms are harmless. If the child never scratched their bum and kept their hands scrupulously clean, eventually the worms would die out. And pigs might fly.

There is a theory, growing in popularity, that worms are protective against the development of allergy. Type I allergy is mediated by white blood cell called eosinophils and mast cells. The normal function of these two cells is to fight and get rid of worms. It may well be that if there are not any worms about, these cells turn their attention to things which they should really ignore such as house dust mite, animal dander or foods. In Africa, people with type I allergy are relatively protected against worms and this has positive survival value. In Western societies, where worms have largely been eliminated through good hygiene, type I allergy is a nuisance.

See Worms and allergy which concludes that:

As a result, patients infected with worms have a decrease in both type 1 and type 2 responses. The main mechanism involved in this down-modulation is increased production of IL-10, but expansion of regulatory T cells and NKT cells may also participate

and also see - Worms: Pernicious parasites or allies against allergies?

Treating threadworm

Treatment is mebendazole (Vermox) 100mg one dose, repeated one week later. It can be bought over the counter from chemists. The whole family should be dosed.

See Boots the Chemist - OTC Mebendazole 100mg

Please note, Vermox should not be used during pregnancy


These are acquired in the same way as round worms and are seen in the stool. These worms have bodies which are flatter and clearly segmented. They break off in the gut in bits and often several sections can be seen moving in the stool (sorry, I suddenly feel a bit sick!).

Treating Tapeworm

Once diagnosed, treatment is with Niclosamide (Yomesan), which is only available on a named patient basis.

Rarely hydatid cysts develop in the liver or brain (possible cause of epilepsy) and treatment is surgical.

Again blood and stool specimens should be taken and I can send you a kit for these tests. See Ordering Tests

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