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Differential Diagnosis

In an endemic area such as the Philippines, capillariasis must be considered in the differential diagnosis of the malabsorption pattern. Tropical and non-tropical sprue cause more marked intestinal dilatation and hypersecretion and fewer mucosal fold changes than are seen in capillariasis. Diseases such as lymphangiectasia, amyloidosis, Whipple's disease, and eosinophilic gastroenteritis show more pronounced changes in the mucosal folds but less extensive fragmentation than seen in capillariasis.

The most practical differential diagnosis (considering the endemic locations) would include other parasitic diseases, such as giardiasis, strongyloidiasis, and hookworm disease. In giardiasis, there is greater irritability and distortion of the mucosal fold pattern and increased secretions; the changes are most pronounced in the duodenum and proximal jejunum with the ileum being spared in most patients. Hookworm disease only occasionally produces small bowel radiographic changes of mucosal edema and malabsorption and usually spares the ileum. Strongyloidiasis will often show greater distortion of the folds due to edema, inflammation, and even ulceration of the mucosal surface, as well as the malabsorption changes noted in capillariasis. In some cases there is a striking similarity of the small bowel pattern in capillariasis and strongyloidiasis. Examination of the stool for characteristic ova and larvae may be the only way to differentiate between these parasitic diseases.

PULMONARY CAPILLARIASIS

Capillaria aerophila is a rare cause of acute bronchitis and bronchiolitis in humans. The parasites are tiny worms possessing a characteristic anterior stichosome and bacillary band and are ubiquitous nematodes in dogs, cats, and foxes. Ova are shed in the sputa or feces of dogs, cats, and rarely humans, and mature in moist soil until ingested by a suitable host. The parasite can be found in North and South America, Asia, Europe, and Australia. As of 1977, ten human infections had been reported from the previous Soviet Union, Iran, Morocco, and Taiwan as a result of swallowing eggs of C. aerophila in contaminated soil on hands, fruits, or vegetables.

The parasite attaches to and develops in the epithelial lining of the respiratory tract, invading the mucosa of bronchioles and laying eggs which can cause acute bronchitis and bronchiolitis with episodes of asthma and a mild (9-12%) eosinophilia. The eggs are subsequently coughed up and swallowed and can be identified in a search of the patient's sputum or stool.

On chest radiographs, the lungs may show hyperventilation from an acute obstructive airway process (bronchiolitis) as well as diffuse perihilar infiltrates and a reticulonodular pattern. Bilateral hilar lymph node enlargement may be present and at times is striking (Fig. 14.5). These radiological features can resemble those found in patients with tropical pulmonary eosinophilia.

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Fig. 14.5A,B. Capillaria aerophila infection showing changes over a 12-day period. There is bilateral hilar and paratracheal lymphadenopathy with extensive perihilar infiltrates and diffuse reticulonodular densities within the lungs. (Courtesy of Dr. R. Aftandelians, Tehran).

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