The full blood count showed that the child had a very high peripheral eosinophil count in addition to the iron deficiency anaemia. The paediatrician was asked to check if the child had had any respiratory symptoms including a dry cough or wheeze in the last few months. The child’s mother confirmed that the child had a cough and wheeze for a couple of weeks two months ago which had settled of its own accord.
“This sounds like ascariasis” commented the Microbiologist. “Surely it can’t be; that only occurs in tropical countries and they haven’t been anywhere” replied the Paediatrician.
Ascariasis is the infection caused by the intestinal worm Ascaris lumbricoides. This roundworm is found throughout the World, even in the UK, although it is true that more than 90% of the World’s infections occur in Asia, Africa and South America. A. lumbricoides is the largest roundworm known to infect humans, growing to whopping 30-35cm in length and approximately 1cm in diameter. It has one of the most revolting life-cycles I know, and whenever I present the life-cycle to students and junior doctors there is always someone who looks like they might vomit…but maybe that’s because this session always seems to be just before lunch!
The truly revolting life-cycle of Ascaris lumbricoides (warning – this will put you off your lunch!)
Soil is contaminated by stool containing microscopic eggs from A. lumbricoides. After a few weeks these embryonate and become infectious. Once these infectious eggs have been accidently eaten they take about 4 days to hatch into tiny larvae in the intestine. These larvae penetrate through the gut epithelium and migrate through the blood and lymphatics to the lungs where they mature within the patients alveoli over a couple of weeks into larger worms about the size of large earth worms. These are then coughed up and swallowed to mature into the large adult worms in the small intestine where the females start to produce thousands of eggs a day in order to continue the life-cycle. Patients with ascariasis often report that they have coughed out worms or had the unpleasant sensation of chewing spaghetti! I told you it was revolting!!! (But you will never forget this)
Despite its dramatic life-cycle most infections with A. lumbricoides are asymptomatic.
Some patients have respiratory symptoms during the early stages of infection due to the presence of larvae in the alveoli. This is known as Loeffler syndrome and is due to the eosinophillic pneumonitis that occurs (these patients have a high eosinophil cell count in their peripheral blood). Symptoms occur within the first 2 weeks of infection and consist of a dry cough, shortness of breath, wheeze, fever and occasionally mild chest pain. Loeffler syndrome usually only lasts 5-10 days. It is often mistaken for a viral chest infection because people don’t associate respiratory symptoms with gastrointestinal disease.
The presence of worms in the intestine leads to more obvious symptoms especially abdominal pain, vomiting and diarrhoea; however there are a number of rare but potentially serious complications as well.
- Intestinal obstruction – heavy infections (>60 worms) can obstruct the lumen of the bowel, especially at the ileocaecal valve, and also block the appendix leading to appendicitis (1 in 500 children with ascariasis get intestinal obstruction)
- Malnutrition – high burdens of worms can impair absorption of vitamins, minerals, proteins and fats leading to malnourishment and if this continues growth retardation can occur in children
- Hepatobiliary involvement – very occasionally adult worms “get lost” and migrate up into the biliary tree leading to cholangitis, pancreatitis, obstructive jaundice and even liver abscesses
Occasionally the burden of worms is so large that they can be seen on abdominal X-rays but this is very unusual. The most common way is to use a microscope to look for eggs (ova) in a stool specimen; the clinician should request a study for “ova, cysts and parasites” or “OCP”. The stool sample is usually centrifuged in a special container in order to concentrate the eggs in to a smaller volume and make them easier to see. The eggs have a distinctive appearance and once seen are easily recognised. Don’t be surprised if the patient has more than one type of parasite as patients can “collect” different parasites as they are all faecal oral spread and exposure to a potential source of one type usually means exposure to more than one type!
PCR is becoming more widely available and will probably replace microscopy in the future as it is less time-consuming and can be done by non-specialist staff… oh dear, that’s progress for you!?
Get this thing out of me!
Patients are often pretty upset about knowing they have a 30 cm worm inside them and need reassurance that they can be treated quickly. A single dose of Albendazole cures nearly 100% of people whereas Mebendazole cures around 95%. Alternative treatments include Ivermectin, Levamisole and Nitazoxanide. Almost all of the antiparasitic drugs are unlicensed in the UK; this doesn’t mean they don’t work or shouldn’t be used; just that no one has gone through the expensive process for getting a license for drugs used so infrequently.
As the treatments are so effective there is not really any need to test for cure but if symptoms continue or recur then not only the patient but also the other household members should be tested as sometimes there is another family member affected who provides a reservoir of eggs to infect everyone else and they all need treating. Parents and patients should be warned that the drugs work by paralysing the worms which cannot then feed, die and detach from the gut wall to be passed in the stool… sometimes they stay inside and are broken down by the body… either way passing a worm will freak out a lot of people and they should be warned to expect it.