Capillaria philippinensis / Capillaria hepatica

Capillaria philippinensis & hepatica are nematodes that cause infections via the ingestion of eithCer eggs ( as in the case of C. hepatica) or raw / undercooked fish ingestion in the case of C. philippinensis where infective larvae are found in the mesenteries.

Disease / Pathology

Capillaria philippinensis & Capillaria hepatica, though of the same genus, produce distinctly different diseases in their hosts. C. philippinensis causes intestinal capillariasis due to the parasite localizing in the host intestines while C. hepatica produces hepatic capillariasis due to the parasite localizing in the liver of the host. Both parasitic infections can be deadly.

Capillaria philippinensis can be a serious and fatal infection. Infections are acquired by ingesting contaminated uncooked or undercooked fish. The worms have the capability of auto infection in the host and thereby result in large numbers of worms and larvae being present. Malabsorption in the small intestine occurs. The worms are small at 3-4mm in length, depending on the sex ( females are larger at an average of 4mm long). Eggs can be detected in the stool by ova and parasite examination and are 45u by 21u, Two morphologic types can be seen, with and without shells.

Capillaria hepatica are closely related to Trichuris trichiura (whipworm). Infections are acquired by the ingestion of eggs found in contaminated soil. Reservoirs of the parasite are domestic and wild animals (especially rodents such as rats). The parasite is found in hepatic tissue. Adult worms are similar to Trichuris worms but more delicate in appearance. The eggs are also similar as well and measure 51-67u by 30-35u with an outer shell that has numerous pores that give the surface a velvety appearance. The disease produced is a visceral larvae migrans where the production of coalescing solitary abscess cavities can be seen in radiological findings that can be mistaken for other hepatic diseases such as carcinomas and granulomatous diseases. Patients will present with hepatomegaly and other signs of liver involvement such as elevated liver enzymes. Abdominal pain and loss of appetite is common along with malaise and eosinophilia of the peripheral blood. Dissemination can occur and infections can be fatal.

Location in the Host

Capillaria philippinensis is located in the intestines while Capillaria hepatica is located in the liver.

Geographic Distribution

Capillaria philippinensis is found in the Philippines and Thailand while Capillaria hepatica is cosmopolitan in distribution.

Capillaria philippinensis lifecycle

Image courtesy of CDC

Capillaria hepatica lifecycle

Image courtesy of CDC

Morphology & Diagnosis

Capillaria philippinensis & Capillaria hepatica eggs differ in how they are detected because of the nematode’s location in the host. The eggs of C. hepatica will not be seen in the stool examination as the nematode is located in the liver and is a form of visceral larva migrans. Eggs are visualized in biopsy material from the liver. The eggs of C. philippinensis however can be detected in the stool examination.

The eggs of C. philippinensis are 45 by 21u and two different forms of the eggs can sometimes be seen, those with shells and those without shells. Internal autoinfection occurs and eventually results in a large population of worms and larvae in the intestinal mucosa.

The eggs of C. hepatica are not detectable in the feces as they are located in the liver but rather best detected by liver biopsies. Radiologic findings and abnormal liver chemistries can also point to this infection but can also lead to misdiagnoses as these diagnostic tests results can be similar to those seen in other diseases of the liver ( carcinoma, granulomatous disease, etc…).

Images

Capillaria phillipenensis egg (45um – 21um) in formalin concentrate stained with Lugol’s iodine – illustration by W. Vientos