Final answer:
The parasitic helminth Strongyloides stercoralis may be the cause of the boy's malnourishment and weakness. A stool examination called the stool ova and parasite (O&P) exam is used to diagnose the infection, which can then be treated with medications.
Step-by-step explanation:
The parasite responsible for the boy's malnourishment and weakness is likely Strongyloides stercoralis, a soil-transmitted helminth. This parasite has both free-living and parasitic forms, with the parasitic form infecting the body through the skin, especially through bare feet. Once in the body, the larvae travel to the lungs, are coughed up and swallowed, and eventually reach the intestine where they reproduce and lay eggs.
To diagnose this condition, a stool examination called a stool ova and parasite (O&P) exam is typically performed. This exam involves direct examination of a stool sample for the presence of parasites and their eggs or larvae. Treatment for strongyloidiasis usually involves medications such as metronidazole or tinidazole, followed by other medications to eliminate any remaining cysts.