Tropical diseases

Tropical pulmonary disease

 

Patients in or from the tropics can also get "ordinary" infections. They suffer from pneumonia, lung abscesses, bronchiectasis and particularly tuberculosis as do patients from many other parts of the world. However, if malnourished, immunosuppressed or suffering from malaria or other parasitic infections, their pulmonary diseases may be more severe than is usual in the western world. Measles (rubeIla), chicken-pox (varicella) and whooping cough (pertussis) can be severe illnesses with accompanying pneumonia. The pulmonary changes of amoebiasis, ascariasis, filariasis and other parasitic infections have already been noted, but there are other specific pulmonary infections which need to be considered (see below, page 1301 for tropical eosinophilic lung).

Paragonimiasis

This is the result of an infection with one or other lung flukes of the genus paragonimus, usually P. westermani. (There are 15 other species of paragonimus, which can infect man.) The infection is found throughout the tropics but particularly in Asia, and is usually mistaken for tuberculosis. Paragonimiasis is acquired by eating raw or inadequately cooked crabs, crayfish, and occasionally from eating animals which also enjoy fresh water crabs. The life cycle is similar to that of schistosomiasis, and includes warm water snails, but there is no direct infection of man. Clinically, the majority of patients, even with heavy infections, are not ill. The minority will complain about chest pain, chronic cough and chocolate-coloured sputum, while remaining remarkably well in general health. At this stage the sputum often contains multiple recognizable eggs of P. westermani.

Apart from the lungs, cerebral involvement is not uncommon and causes convulsions, fever, headache or other neurological symptoms. Some species prefer the central nervous system and the lungs may remain clear, but this is in less than 20% of the patients.

a	b
Figure 32. Paragonomiasis. a) Bilateral interstitial and basal consolidation in a patient with paragonomiasis. (China) b) Tomography of the right upper chest showing the nodular and fibrotic pattern of paragonomiasis. This is indistinguishable from tuberculosis. (China)

Chest radiographs in the acute stage show a predominantly exudative basal pneumonia, sometimes with pleural effusion. The lungs clear after a few weeks, leaving either small nodules or cysts, which are the most characteristic findings (at this stage there will be mature worms in the pulmonary parenchyma) (Fig. 32). This pulmonary pattern may persist for years without causing clinical ill health. Most of the cysts are in the periphery of the mid lung or at the lung bases, but they can occur in the upper part of the lungs. A pneumothorax is not uncommon. The cysts are from 0.5 - 4 cm in diameter and change constantly, with varying patterns of surrounding re action. Hilar adenopathy is very uncommon. These ring-shadows may be seen in 80% or more of patients and can be recognized on plain radiographs or CT. In some cases, the tortuous burrows through which the worm moves may be recognized, close to the cysts. When the parasite dies, there is a fibrotic reaction and the cyst disappears, leaving a residual density with surrounding fibrosis. Even these fibrotic lesions may disappear. It should be noted that in some patients, treatment of the infection causes a hypersensitive reaction, with transient fluffy densities throughout the lungs. This may incorrectly suggest that the patient's condition is worsening.

Cerebral paragonimiasis results in elevated intracranial pressure: the multiple cerebral cysts may calcify and may occasionally be seen on plain skull radiographs, but are more easily recognized on CT or MR. With scanning, the cysts may be se en before they have calcified, and are almost always multiple and bilateral. For some unknown reason, involvement of the frontal lobes and cerebellum is uncommon. Some patients develop one larger cyst or even a cerebral abscess. About 80% of the patients with a cerebral infection will have lung infection also. The cysts of paragonimiasis may be mistaken for those of cysticercosis, in which the cysts are smaller, discrete and fewer in number.

P. Westermani may be found in the abdomen or elsewhere in the body and be recognized with ultrasound or CT scanning. A plastic peritoneal reaction may occur, causing intestinal obstruction. The cysts may calcify in the soft tissues and in the liver.

Melioidosis

Infection with the gram negative bacillus, Pseudomonas pseudomallei, is known as melioidosis. While occurring most commonly in South East Asia, cases have be en reported from many other parts of the world, usually in visitors returning from Asia. The exact method of infection is unknown, but may be due to contaminated dust or soil, perhaps from insect bites.

Clinically, the disease may be asymptomatic or subclinical. It is easily mistaken for tuberculosis or other fungal infection, both clinically and radiologically. Those with clinical symptoms may present with an acute illness with a high temperature. Others, who have a less acute infection, present with haemoptysis and a low fever or, less commonly, as a chronic extrapulmonary infection.

The radiological appearance of the chest suggests tuberculosis. In the acute variety, there will be multiple irregular nodular densities which may coalesce or cavitate. There may be lobar pneumonia, or both appearances may be seen simultaneously in different parts of the lungs. When the infection is less acute, there can be lobar consolidation and cavity formation (Fig. 33). In both forms, acute and subacute, pleural involvement and hilar adenopathy are uncommon. In those without clinical

a	Figure 33.Melioidosis. a) Bilateral fluffy nodules throughout both lungs. (Vietnam) b) Two thin-walled cavities (tomogram). (Vietnam)
b

symptoms, tuberculosis is the usual diagnosis because of upper lobe infection and cavity formation.

The extrapulmonary infections produce subcutaneous or muscle abscesses with sinuses, osteomyelitis, septic arthritis, and even abscesses in the spleen, brain, kidneys and liver. Bone infection cannot be easily distinguished from any other type of osteomyelitis, and the soft tissue abscesses are very non-specific.

 

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