Infectious Disease and Microbiology – Capillaria Species

Overview

Capillaria species are nematode helminths that can infect different human organ systems depending on the species involved. The three clinically important species are Capillaria philippinensis, Capillaria hepatica, and Capillaria aerophila.

They are associated respectively with intestinal, hepatic, and pulmonary capillariasis.

Microbiologic Characteristics

Capillaria species are parasitic roundworms (nematodes).

Human disease varies according to the tissue tropism of the species:

• C. philippinensis → intestine

• C. hepatica → liver

• C. aerophila → respiratory tract

Epidemiology

Capillaria philippinensis

This species is most strongly associated with:

• The Philippines

• Thailand

Cases outside these endemic regions are uncommon.

Capillaria hepatica

Human infection is rare but has been reported sporadically in multiple countries around the world.

Capillaria aerophila

Human pulmonary infection is very uncommon, with historical cases reported from regions including the former Soviet Union.

Transmission

The route of acquisition depends on the species.

For C. philippinensis, infection is particularly associated with consumption of raw or inadequately cooked fish containing infective larvae.

This dietary exposure is one of the most important clues to intestinal capillariasis.

Intestinal Capillariasis

Capillaria philippinensis causes intestinal capillariasis.

Patients may develop:

• Chronic diarrhea

• Abdominal pain

• Weight loss

• Malabsorption

• Weakness

• Protein loss

Heavy infection can become severe because repeated autoinfection may increase the intestinal parasite burden.

Advanced disease can cause marked nutritional depletion and electrolyte abnormalities.

Hepatic Capillariasis

Capillaria hepatica causes infection of the liver.

Possible manifestations include:

• Fever

• Hepatomegaly

• Abdominal discomfort

• Eosinophilia

• Inflammatory liver disease

The parasite lays eggs within hepatic tissue rather than releasing them normally into the intestinal lumen, so stool testing is generally not useful for this form.

Pulmonary Capillariasis

Capillaria aerophila can infect the respiratory tract.

Possible manifestations include:

• Cough

• Fever

• Dyspnea

• Bronchitic symptoms

• Pulmonary inflammation

Because pulmonary infection is rare and nonspecific, diagnosis may be difficult without parasitologic evidence.

Diagnosis

Intestinal Capillariasis

Diagnosis is made by identifying:

• Eggs

• Larvae

• Occasionally adult parasitic forms

in stool specimens.

Repeated stool examinations may improve diagnostic sensitivity.

Hepatic Capillariasis

Diagnosis generally requires histopathologic examination of liver tissue.

Liver biopsy may demonstrate:

• Characteristic eggs

• Larval or adult worm structures

• Associated inflammatory reaction

Pulmonary Capillariasis

Diagnosis may rely on demonstrating parasitic material in respiratory specimens or tissue, together with an appropriate clinical and epidemiologic setting.

Treatment

Intestinal Capillariasis

The source regimen lists:

Mebendazole 200 mg orally every 12 hours for 20 days

An alternative is:

Albendazole 200 mg orally every 12 hours for 10 days

Treatment should be combined with correction of dehydration, electrolyte disturbance, and nutritional deficiencies when present.

Hepatic Capillariasis

Historically, thiabendazole has been used.

Albendazole is another treatment option.

Because hepatic disease is uncommon, therapy is often individualized according to disease severity and specialist guidance.

Pulmonary Capillariasis

Potential treatment options include:

• Mebendazole

• Albendazole

Clinical response should be monitored carefully because cases are rare and treatment data are limited.

Prevention

Prevention is particularly important for C. philippinensis.

The main measure is:

Avoid eating raw or inadequately cooked fish in endemic areas.

Additional precautions include:

• Thoroughly cooking freshwater fish

• Safe food preparation

• Good sanitation

• Avoiding fecal contamination of food and water

High-Yield Clinical Pattern

Person from the Philippines or Thailand

• ●

Raw fish consumption

• ●

Chronic diarrhea

• ●

Weight loss and malabsorption

→ Think intestinal capillariasis due to Capillaria philippinensis

High-Yield Species Distinction

C. philippinensis

→ Intestinal disease

C. hepatica

→ Hepatic disease

C. aerophila

→ Pulmonary disease

Exam Essentials

Genus: Capillaria

Organism type: Nematode helminth

Important species: C. philippinensis, C. hepatica, C. aerophila

Major geographic clue for C. philippinensis: Philippines and Thailand

Major exposure: Raw or undercooked fish

Intestinal disease: Chronic diarrhea and malabsorption

Hepatic disease: Hepatomegaly and eosinophilic liver inflammation

Pulmonary disease: Respiratory symptoms

Diagnosis of intestinal disease: Eggs or larvae in stool

Diagnosis of hepatic disease: Liver biopsy

Treatment of intestinal disease: Mebendazole or albendazole

Prevention: Avoid raw fish in endemic areas

Key clinical pearl: Capillaria philippinensis should be considered in patients from endemic Asian regions who develop persistent diarrhea and severe malabsorption after eating raw fish.