Case 4

1.What is the differential diagnosis in this case ? 

The differential diagnosis in this case is limited because the worm is visible to the naked eye.

• Ascaris lumbricoides is the largest and most common of the intestinal helminths, and measure 1.5-3 cm in length. 

• The adult female of Enterobius vermicularis (pinworm) is 10 mm long and may occasionally be visible. 

• The adult whipworm (Trichuris trichuria) is 30-50 mm long, and is seen only on a prolapsed rectum. 

• Ancylostoma duodenale and necator americanus measure 10 mm in length; the ad worm is not seen in stool.

• Strongyloides stercoralis is only 2 mm long, and the worm is not seen in stool. 

2. How would you establish the diagnosis? 

• The diagnosis is established by finding characteristic eggs in the feces.

  • Eggs are elliptical in shape, measure 30 by 50 pm, and have a rough, wavy, albuminous coat over their shell. 

  • They are highly resistant and may remain viable up to 6 years. 

• The pulmonary phase may be diagnosed by finding larvae and eosinophils in sputum. 

3. What is the life cycle of this parasite? 

• Adult ascarids live in the small intestines.

• Eggs are deposited in the lumen, passed in feces, and must embryonate for 3 weeks in the soil before becoming infectious. 

• After ingestion, the hatched larvae penetrate intestinal mucosa and invade portal venules. 

• They are carried to the liver, and travel via the hepatic vein to the right heart and into the lungs. 

• Larvae enlarge and rupture into alveoli, are coughed up and subsequently swallowed. 

• Upon reaching the small bowel, they mature, mate and deposit eggs. 

• Pulmonary involvement results in fever, cough and wheezing (hypersensitivity). 

• Heavy worm loads can lead to obstruction of appendix or bile duct.

4. List the medically important nematodes. 

• Nematodes (or round worms) can be divided into intestinal and tissue dwellers. intestinal nematodes that are human parasites include Enterobius, Trichuris, Ascaris, Ancylostoma, Necator and Strongy1oides. 

• Animal parasites that can cause human disease are Capillaria, Anisakis, Toxocara, and Ancylostoma brazilienses. 

• Tissue nematodes include members of the family Filarioidea (Wuchereria bancrofti, Brugia malayi, Loa loa, Onchocerca volvulus). Animal parasites (Toxocara canis, Trichinella spiralis, Ancylostoma braziliense) are capable of infecting - humans, but cannot complete their life cycle in the human host.

5. How would you treat this patient? 

• Mebendazole and Pyrantel pamoate are highly effective. Mebendazole is preferred if Trichuris trichiura is also present. 

The mother mentions that she was treated for a parasitic infection, but cannot remember the name. She has cirrhosis of the liver with ascites and signs of portal hypertension. 

6.  What parasitic infection is she likely to have? 

This patient has schistosomiasis. Schistosomes are flukes that inhabit the portal vascular system. 

Three species are important -

•  S. mansoni

•  S. hematobium

•  S. japonicum

7. Describe the pathogenesis of this infection. 

There are 3 clinicopathologic stages of schistosomiasis. 

A. Early stage - penetration of skin by cercariae results in hypersensitivity and a  pruritic., papular skin rash (swimmer's itch)

B. Intermediate stage - prolonged febrile period with circulating immune complexes. Fever, chills, abdominal pain, intestinal inflammation and encephalitis occur (Katayama fever)

C. Chronic schistosomiasis - retained eggs induce the formation of eosinophilic granulomas, fibrosis and scarring. Obstruction to blood flow is common. S. hematobium produces bladder lesions with hemorrhage and obstruction. Chronic urinary carriage and bacteremia with salmonella can occur. S. mansoni and japonicum produce congestion and ulceration of the bowel wall. Eggs deposited in the intestinal veins are carried by portal blood flow to the liver inflammatory reaction results in periportal fibrosis and hepatic enlargement. Recurrent Salmonella bacteremia is related to parasitization of the schistosome gut by Salmonella.

8.What treatment would have been prescribed for her' 

There is no specific therapy for dermatitis or Katayama syndrome. 

Praziquantel is active against all 3 species.

Metrifonate may be used for S. hematobium and oxamniquine for S. mansoni.