Tropical diseases

Tropical bowel infestations and infections

 

A wide variety of parasites cause gastrointestinal disease. Many are clinically unrecognized until their later stages, and in some societies their effects are regarded by the patient as a normal fact of life. Other infections present acutely, without any preceding chronic symptomatology. Almost all the clinically important intestinal parasites occur worldwide and the number of patients infected is almost incomprehensible. Parasitic infection should be considered as one of the causes of chronic ill health in any patient living in or coming from the tropics, or indeed, from any area where there is malnutrition or substandard living conditions. The clinical presentation may vary from an irritating chronic cough to acute intestinal obstruction: no age is exempt, but children are particularly afflicted.

Ascariasis

The Nematode round worm, Ascaris lumbricoides, (alone or occasionally together with A. suum) probably infects 25 % of the world's population, but in the tropics the infection rate may be as high as 90 % in some populations. This is not surprising, because during a busy period of 6-12 months, one (very) fertile female worm can produce up to 200 000 ova every day! This bounty is acquired by humanity from contaminated food, water and soil, and re-infection is common. The worm is most frequently found in patients aged from 1-15 years and no intermediate host is needed. Clinically there may be no symptoms, or there may be ill health, vague abdominal pain, colic or acute obstruction. In children, ascaris are one of the commonest causes of jaundice.

a	Figure 25. Ascariasis a) Multiple worms in the right lower abdomen of a child, outlined by gas and faecal content in the bowel. (Nigeria) b) Ultrasound scan of ascaris in the cystic duet and the gallbladder, which is dilated. (Brazil; courtesy of Professor J Cerri) c, d) Worms shown during gastrointestinal barium studies. Most of the worms have ingested barium. (c = Pakistan; d = China)
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c
d

In the acute stage there may be fever, cough, even haemoptysis or chronic recurrent "bronchitis", symptoms for which the possibility of a worm infection is not even considered unless a high peripheral eosinophilia provides a clue to the correct diagnosis. Curing a cough with an antihelmintic always surprises clinicians! A chest radiograph may be very non-specific, but in a few patients there may be transient, ill-defined, soft and asymmetrical densities around the larvae as they pass through the lungs. Some may progress to bronchopneumonia, and if an adult worm has been regurgitated and inhaled, there may be atelectasis or lobar pneumonia.
The worms may be visible on a plain radiograph of the abdomen, seen as a coiled, hazy indistinct "ball of wool" when the worms are outlined by bowel gas (Fig. 25 a). But ultrasound is more accurate. The body of the worm shows as two hyperechoechoic lines on either side of a hyperechoechoic space when seen on a longitudinal scan relative to the worm. If scanned transversally, there will be a round, hyperechoechoic centre (the worm's alimentary canal) surrounded by a hyperechoechoic ring (the worm's body). This is the characteristic "target sign", and may also be seen in the biliary tract (Fig. 25 b). Ascaris is the only intestinal worm which ingests barium and it does this most reliably after the patient (and the worm) has fasted overnight (Fig. 25 c, d). There will be then be one or more white lines (the worm's alimentary canal) within the stomach or small bowel, perhaps surrounded by a clear space on either side (the negative shadow of the worm's body) within the barium column. There may be excess intestinal secretions: worms are irritating.

Most of the Ascaris inhabit the small bowel and their movements can be monitored by ultrasound or barium studies. A few will be in the stomach or duodenum, but the majority will be in the lower ileum, with some in the caecum and colon (Fig. 26). Ascaris is a common cause of intestinal obstruction in children in any region where infestation is more than usually prevalent. The level of the obstruction is usually ileocaecal, especially if the child has be en given an anthelmintic which has caused a mass of dead worms. Ultrasound is a rapid way to demonstrate the tangled, obstructing bodies. In many parts of the world an erect plain radiograph of the abdomen of a child which shows multiple small bowel fluid levels is recognised as yet another complication of ascaris infections. The worms may have to be removed surgically, which is yet another good reason to be a radiologist!

Ascaris is the commonest cause of jaundice in children in Africa, Asia and South America. Ultrasound will demonstrate the worm within the biliary tract, either as a target sign or a linear shadow. If in the cystic duct, it will probably cause obstruction. The worm can, of course, also be seen by CT or intravenous cholangiography. Cholecystitis and hepatic abscesses can be caused by worms and ascaris have been found in subphrenic

a

Figure 26. Ascariasis a) Worms in the lower ileum and a few in the duodenum and jejunum. The bowel is mildly dilated and oedematous. The worms have not ingested much barium. (Nigeria) b) The alimentary tract of a long worm containing barium. There are excess secretions in the upper small intestine. (China) abscesses, or, occasionally, in the peritoneal cavity. Even if the worm is in the biliary tract, oral therapy will probably be successful.

b

Strongyloidiasis

Infection with S. stercoralis is particularly significant in any patient who is immunosuppressed. In others, the infection is usually asymptomatic or, at the worst, causes mild peptic ulcer symptoms or occasional colic. Strongyloides are more common in adults than in children, and infection occurs through the skin, usually the fool. As with many other worms, there are early chest symptoms (cough) and a peripheral eosinophilia. Although imaging is not the way to recognise strongyloidiasis, radiologists should be aware of the parasite's effects and complications.

In the early stages of S. stercoralis infections, contrast studies of the alimentary tract, using microfine, non-flocculating barium, will show mucosal oedema from the pylorus to the upper jejunum, sometimes also in the stomach. Barium passes rapidly and the bowel is apparently inflamed and irritable. The appearance may be indistinguishable from sprue.

In the later stages, the bowel becomes fibrosed and more rigid, peristalsis is absent: the mucosa is atrophied: ulceration occurs and the

Figure 27.Strongyloidiasis. Distended, gas-filled loops of small bowel due to strongyloides. (Nigeria)

appearance may incorrectly suggest obstruction (Fig. 27). The colon may be involved and in patients with severe immunosuppression (e.g. as in AIDS) very severe colitis may occur, leading eventually to sepsis and death. Barium contrast studies of the large bowel at this stage show severe ulcerating colitis with sinus formation.

Giardiasis

This is yet another alimentary parasite which should be known to radiologists, although it is not their responsibility to make the diagnosis. Giardia lamblia are ingested through contaminated food and especially water, and have been found throughout the world, wherever there are water reservoirs. Most patients are unaware of their infection, others have vague abdominal symptoms with intermittent diarrhoea and malabsorption. It must be remembered that having Giardia lamblia in the alimentary trace does not mean that this is the cause of the patients symptoms; other diseases must be excluded.

When barium is used for contrast studies of the gastrointestinal tract, it should always be microfine and non-flocculating. Using this for patients with giardiasis, barium studies of the duodenum and jejunum will show mucosal thickening, marked spasm and distortion: there may be rapid transit of barium, with segmentation and increased intraluminal fluid. Sprue may be suspected. It is seldom that giardia infection spreads below the jejunum, except when the patient is immunosuppressed or suffers from dysgammaglobulinaemia, when there will be a nodular pattern in the small intestine due to hypertrophy of the Peyer's patches.

It is only because Giardia is much more localized to the upper small bowel that this infection may be distinguished from strongyloidiasis by barium studies.

Hookworm (ancylostomiasis).

"Hookworm" is an infection with a nematode worm, usually Ancylostoma duodenale or Necator americanus, or both. (A. ceylanicum can also be pathogenic for man.) The worms enter the body through the feet and spread through the lymphatics and blood to the lungs and eventually down the oesophagus to the jejunum. Although the origin has been known for nearly a century, millions of people are still infected and it is a common cause of chronic anaemia in many tropical countries. Some patients will be symptom-free, others will have severe infections and a marked peripheral eosinophilia. It is essential to differentiate between hookworm infection and hookworm disease, between the mild and the severe. At the onset of infection, and while the worm is migrating and developing, the clinical complaints are pruritis and erythema: the "ground itch" of barefoot people. Within 3-14 days there may be a cough and low fever, but the chest radiograph will be normal. There can then be a long latent period, particularly if the host is otherwise healthy. But in the malnourished or otherwise unhealthy, there may be mild gastric symptoms, and if the parasite load is heavy, anaemia and further malnutrition result.

In chronic infection, causing anaemia, a chest radiograph may show cardiomegaly. A barium contrast study will show a normal gastro-intestinal tract in many patients, but in others there will be a deficiency or malabsorption pattern. There is a marked geographical variation in the reported imaging abnormalities, possibly due to association with a variety of other parasites. Hookworms have been known to occur in tissues

Figure 28.Helminthoma. A large mass arising from the medial wall of the caecum (barium enema). (Zimbabwe)

outside the bowel, but for all practical purposes ancylostomiasis is a small bowel infection.

Helminthoma

Almost any parasite can migrate into the bowel wall, yet this happens surprisingly seldom. When it does occur, there is an inflammatory, granulomatous reaction forming a tumour, the helminthoma. The intestinal parasites which most commonly infiltrate are nematodes, and one in particular, oesophagostomum. Ascaris and ancylostoma rarely aIso cause the same re action. There is a different result when a parasite perforates completely through the bowel wall, causing a localized peritoneal abscess, compared with the granulomatous reaction which occurs first within the wall itself and then subsequently perforates. Clinically, when this occurs, most patients will be suspected of having appendicitis or perhaps intussusception or perforated diverticulum. The correct diagnosis of helminthoma is very seldom made before surgery (and not always even at surgery). With a barium enema or ultrasound scan, a mass can be demonstrated in the wall of the bowel, often eccentric, and sometimes leaving the lumen open (Fig. 28). Very seldom is the whole internal diameter of the bowel affected, although it may be narrowed due to pressure.

The mucosa appears intact and the mass is often surprisingly well defined. Helminthomata occur most commonly in the caecal area, less often in the sigmoid and only occasionally elsewhere in the bowel. Clinically or radiologically the mass might appear to be an inflammatory abscess or a bowel tumour. A radiologist will only make the correct diagnosis if he or she has a very high index of suspicion and a great deal of good luck! Usually the diagnosis is made by the histopathologist, who may be as surprised as everyone else.

Other intestinal parasites

Two other parasites should be mentioned. The nematode Capillaria philippinensis was first described in humans in 1963 and occurs almost exclusively in the Philippines. It causes a severe protein loosing enteropathy. The radiological appearances are those of malabsorption; patients with severe infections can be acutely ill and die quite rapidly: those who survive are liable to have several relapses.

Trichuriasis is often clinically silent and is not a "radiological" disease, but the worms may be found if a contrast enema is carried out for some other reason. A double contrast barium enema can demonstrate the tiny whipworm, Trichuris trichiura (30-50 mm) throughout the whole length of the colon, accompanied by a granulomatous mucosal pattern, with excess mucus. The actual radiolucent lines of the "whips" may be seen and it is possible to differentiate the male from the female, although this is not really helpful information. Judging by their numbers, the worms manage to do this very well on their own.

Liver flukes: clonorchiasis

In East Asia, from Indochina to Japan, infection with the liver fluke Clonorchis sinensis occurs quite commonly: it is one of the risks of eating raw fish. The end-result may be severe cholangiohepatitis with the bile ducts becoming dilated and thickened, most severely in the left lobe of the liver. The process begins in a few segmental ducts and then spreads until almost the whole intrahepatic biliary tract is elongated, tortuous, and dilated, often partially filled with debris (Fig. 29). Eventually, the extrahepatic ducts become involved. If the patient is jaundiced, this suggests that there is added infection, calculus formation, or even pancreatitis.

Figure 29.Clonoarehiasis. A T-tube retrograde cholangiogram showing the dilated, saccular biliary tract, filled with debris. (Korea)

Most patients with clonorchiasis will eventually develop calculi around debris in the bile ducts and gallbladder, together with an E. coli or Typhi cholangitis. There may be liver abscesses and eventually severe hepatobiliary dam age and cirrhosis. Cholangiocarcinoma occurs quite frequently in chronic cases.
Ultrasound and CT of the liver demonstrate the grossly dilated and thickened biliary tract, with ducts which may be as much as 2 cm in diameter. Transhepatic cholangiography confirms the diagnosis and will often show the small calculi and biliary sand. Occasionally, the actual flukes may be visible as small curved translucencies, but they may be difficult to distinguish amongst the debris. The ducts become very irregular, due not only to infection but to adenomatous hyperplasia of the mucosa. Stricture formation can occur and the resulting hepatic abscesses must be distinguished from the malignant disease which may occur concurrently.

Typhoid, parathyphoid and salmonella infections

These enteric fevers are still a major health problem in many parts of the world, particularly where a hot climate contributes to rapid dehydration. They are spread by ingesting contaminated water and food, occasionally

a	b
Figure 30. AP (a) and lateral (b) views of the dense chronic bone reaction due to typhoid osteomyelitis. There is a central sequestrum. (Pakistan)

by direct cross infection. Clinically these "dysenterys" can be misleading, starting with fever, headache, gene al malaise and abdominal pain. Typhoid produces a high fever and bradycardia, followed by delirium and stupor.

For the radiologist, the principle finding in typhoid is grossly distended small bowel due to paralytic ileus. Fluid levels on an erect abdominal radiograph are uncommon. Perforation occurs in many typhoid patients, usually at the end of the third week of infection, but in some countries perforation occurs earlier, even during the first week. After perforation there is often a large amount of free intraperitoneal gas, and the distended bowel wall is outline d between the intestinal gas and the intraperitoneal gas. There is almost always peritonitis also. There is little indication for any contrast examination during the acute infection. When chronic, both typhoid and salmonella infections can cause segmentation

Figure 31.Lymphogranuloma. Barium enema. Note the smooth tapering rectum of lymphogranuloma venereum (small arrows). There is a perirectal abscess (arrowheads). (China)

and hypomotility of the small bowel.

Typhoid and salmonella also infect bone, and salmonella osteitis is especially common in infants and young children with sickle cell anaemia. This osteomyelitis progresses more slowly and with less acute symptoms when compared with pyogenic infections (Fig. 30). Biopsy may be necessary to make the correct diagnosis, especially in the spine. There is seldom a paravertebral abscess.

Lymphogranuloma venereum

Appropriately, the last gastrointestinal disease to be considered is lymphogranuloma venereum, affecting the rectum and lower colon. It is caused by Chlamydia trachomatis and, except in rare cases involves only the rectosigmoid, the lower colon, the genital tract, the surrounding tissues and regional lymph nodes. Clinical proctocolitis and suppurating lymphadenopathy are common. The infection is acquired by sexual contact: transmission by any other route is very uncommon.
Ultrasound will show the thickening of the rectal wall and the surrounding oedema and inflammatory reactions. A barium enema will show spasm, narrowing of the rectum and lower colon, and then loss of the normal colonic pattern (Fig. 31). Eventually, there will be loss of haustration, multiple fistulae, perirectal abscesses and sinuses. The disease progresses to fibrosis and stricture formation and may involve the last 25 cm of the large bowel. In women, rectovaginal fistulae may develop. The differential diagnosis will include mycotic infection, amoebiasis and tuberculosis (because of the fistulae formation), but in practice there is usually little doubt about the correct diagnosis.

 

Philip E.S. Palmer, with Stanley P. Bohrer, Carlos Bruguera, Xing-Rong Chen, Mahmoud R. EImeligi, Hassen A. Gharbi, S.B. Lagundoye, M. W. Wachira