Metastrongyles - Lung Worms!

Two versions of these lovely worms. The first is Angiostrongylus cantonensis, adults of which live in, you guessed it, the lungs! Typically rat lungs though, not human lungs. They lay their eggs in the lungs, and when the larva hatch, they break into the respiratory tract and migrate up the trachea, where they are then swallowed and pass out of the rat body. They are then ingested by snails or slugs. In these hosts, the larva progress from L1 stage to L3 stage, at which point they are infective again. New rats then either eat the snails, or eat food that the snails have passed over, which deposits it on the new food source. Once they are eaten, the larva migrate to the central nervous system, where they can develop in the brain. They then migrate back to the lung.

Humans are infected either when they eat the infected snail or slug, or when they eat something such as lettuce that the slug has passed over. When the larva tries to migrate to the brain, it causes eosiniphilic meningitis and meningoencephilitics. Most larva die in the brain, which can cause an even worse inflammatory reaction. The only real treatment for this one is corticosteriods, as apart from surgery there is no real way to get the larva out of the brain.

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The other kind is Angiostrongylus costaricensis. These are also typically found in rats, though they live in the mesenteric arteries. The female Angiostrongylus costaricensis deposits eggs in the rat intesten, which are passed with the feces. Again, slugs/snails are the intermediate hosts, and once they are ingested again by rats, they migrate via the lymph system and blood to the mesenteries. This one presents pretty differently, typically as acute abdominal pain, low-grade fever for 2-4 weeks, a tumor like painful mass, and high eosiniphilia. Surgery is possible, as are anti-helminthic treatments.

Both adult worms look pretty similar. They are slender with a reduced or rudimentary buccal capsule. 3-5 cm in length. The females have a spiral shape down their length, caused by uterine branches.

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