A missionary from the United States is sent to work in a geographic region of a Central American country where Onchocerca volvulus is endemic. Infections resulting from this tissue nematode (onchocerciasis) are a cause of “river blindness,” because microfilariae migrate through subcutaneous tissues and concentrate in the eyes. Which drug should be used prophylactically to prevent onchocerciasis?
Ivermectin prevents onchocerciasis and is the drug of choice in the individual and mass treatment of the disease. The only other drug listed with any activity against Onchocerca volvulus is diethylcarbamazine. Suramin (not listed) also has activity against onchocerciasis, but like diethylcarbamazine, it is less effective and more toxic than ivermectin. The answer is C.
A nonindigenous person who develops onchocerciasis in an endemic region and receives drug treatment is likely to experience a severe reaction. Symptoms include headache, weakness, rash, muscle aches, hypotension, and peripheral edema. Which statement concerning this reaction is accurate?
(A) Extensive fluid replacement is essential
(B) Symptoms are more intense in indigenous adults than nonindigenous adults
(C) The reaction is due to treatment with suramin
(D) The reaction is due to killing of microfilariae
(E) The symptoms are characteristic of treatment with diethylcarbamazine
The symptoms described are those of the so-called Mazzotti reaction. They are due to the killing by ivermectin of microfilariae, and their intensity correlates with skin microfilaria load and is not a drug toxicity. The reaction occurs more frequently and with greater severity in nonindigenous persons than in the indigenous inhabitants of endemic areas. The answer is D.
Which statement about pyrantel pamoate is accurate?
(A) Acts as an antagonist at GABA receptors
(B) Equivalent in efficacy to niclosamide in the treatment of tapeworm infections
(C) Eradicates adult worms in the colon but not the eggs
(D) Hepatotoxicity is dose-limiting
(E) Synergistic with praziquantel in cestode infections
Pyrantel pamoate, an agonist at nicotinic receptors, is equivalent to albendazole and mebendazole in the treatment of common nematode infections. It acts on adult worms in the colon, but not on eggs. The drug causes only mild gastrointestinal side effects and is not hepatotoxic. It is not effective in the treatment of infections caused by cestodes or flukes. The answer is C.
A student studying medicine at a Caribbean university develops intestinal bilharziasis and oxamniquine is prescribed. Which statement about the proposed drug therapy is accurate?
(A) Hospitalization is recommended if the patient has a history of seizure disorders
(B) Oxamniquine is not effective in the late stages of the disease
(C) Oxamniquine is safe to use in pregnancy
(D) The drug is an antagonist at GABA receptors in trematodes
(E) The drug is very effective in tapeworm infections
Oxamniquine may cause seizures, especially in persons with a history of convulsive disorders. Such persons should be hospitalized or treated with praziquantel. Oxamniquine is effective in all stages of disease caused by S mansoni, including advanced hepatosplenomegaly, and it has been used extensively for mass treatment. The drug is not effective in other schistosomal diseases, and it is contraindicated in pregnancy. The answer is A.
A 22-year-old man from South Korea has recently moved to Minnesota. He has symptoms of clonorchiasis (anorexia, upper abdominal pain, eosinophilia), presumably contracted in his homeland where the Oriental liver fluke is endemic. He also has symptoms of diphyllobothriasis (abdominal discomfort, diarrhea, megaloblastic anemia), probably caused by consumption of raw fish from lakes near the Canadian border. Which drug is most likely to be effective in the treatment of both clonorchiasis and diphyllobothriasis in this patient?
Praziquantel is a primary drug for treatment of infections caused by the Oriental liver fluke and by the fish tapeworm. Both types of infection are transmitted mainly via the consumption of raw fish. Niclosamide is also a primary drug for fish tapeworm infections, but it is not active against Clonorchis sinensis. Albendazole is not effective in fish tapeworm infections, but it is useful in the pork tapeworm larval stage (cysticercosis). Pyrantel pamoate is not active against cestodes or trematodes. The answer is D.
Which helminthic infection does not respond to treatment with praziquantel?
(D) Pork tapeworm infection
In hydatid disease, praziquantel has marginal efficacy because it does not affect the inner germinal membrane of Echinococcus granulosus present in hydatid cysts. The answer is A.
Which drug enhances the actions of GABA in nematodes causing muscle paralysis?
Ivermectin causes muscle paralysis in nematodes by actions on GABA receptors. Pyrantel pamoate blocks nicotinic receptors relaxing nematode muscles. Diethylcarbamazine also cause muscle relaxation but the mechanism is unknown. Dizziness (no driving for 24 h) is a common adverse effect of oxamniquine. The answer is C.
Which parasite is susceptible to niclosamide?
(A) Ascaris lumbricoides (roundworm)
(B) Echinococcus granulosus (hydatid disease)
(C) Fasciola hepatica (sheep liver fluke)
(D) Necator americanus (hookworm)
(E) Taenia solium (pork tapeworm)
Niclosamide is not active against nematodes or flukes with the exception of the large intestinal fluke. It is a co-drug of choice (with praziquantel) to treat common tapeworm infections and is usually effective in a single dose. The drug is minimally absorbed from the gastrointestinal tract and causes few side effects. The answer is E.
Which adverse effect occurs with the use of albendazole during intestinal nematode therapy?
(D) Peripheral neuropathy
Doses of albendazole required for intestinal nematode therapy are almost free of adverse effects even in the malnourished or debilitated patient. Gastrointestinal distress may occur in children with ascariasis who are heavily parasitized, together with a slight headache or dizziness. Avoid the drug in children younger than 2 years because of rare reports of seizures. The answer is E.
A malnourished 12-year-old child who lives in a rural area of the southern United States presents with weakness, fever, cough, abdominal pain, and eosinophilia. His mother tells you that she has seen long, thin worms in the child’s stools, sometimes with blood. A presumptive diagnosis of ascariasis is confirmed by the presence of the ova of A lumbricoides in the stools. However, microscopy reveals that the stools also contain the eggs of Necator americanus. The drug most likely to be effective in the treatment of this child is
Mebendazole is effective against both nematodes causing infection in this child. Albendazole and pyrantel pamoate (not listed in this question) are also primary drugs for the treatment of combined infections due to hookworm and roundworm. The answer is C.