Diagnosis
Diagnosis of Angiostrongyliasis is complicated due to the difficulty of presenting the angiostrongylus larvae themselves, and will usually be made based on the presence of eosinophilic meningitis and history of exposure to snail hosts. Eosinophilic meningitis is generally characterized as a meningitis with >10 eosinophils/μL in the CSF or at least 10% eosinophils in the total CSF leukocyte count. Occasionally worms found in the cerebrospinal fluid or surgically removed from the eye can be identified in order to diagnose Angiostrongyliasis. Lumbar puncture
Lumbar puncture should always be done in cases of suspected meningitis. In cases of eosinophilc meningitis it will rarely produce worms even when they are present in the CSF, because they tend to cling to the end of nerves. Larvae are present in the CSF in only 1.9-10% of cases. However, as a case of eosinophilic meningitis progresses, intracranial pressure and eosinophil counts should rise. Increased levels of eosinophils in the CSF is a hallmark of the eosinophilic meningitis. Brain imaging
Brain lesions, with invasion of both gray and white matter, can be seen on a CT or MRI. However MRI findings tend to be inconclusive, and usually include nonspecific lesions and ventricular enlargement. Sometimes a hemorrhage, probably produced by migrating worms, is present and of diagnostic value. Serology
In patients with elevated eosinophils, serology can be used to confirm a diagnosis of angiostrongyliasis rather than infection with another parasite.
Worms usually appear in the anterior chamber and vitreous and can sometimes be removed surgically. Incubation period
The incubation period in humans is usually from 1 week to 1 month after infection, and can be as long as 47 days. This interval varies, since humans are accidental hosts and the life cycle does not continue predictably as it would in a rat. Cause
Transmission
Transmission of the parasite is usually from eating raw or undercooked snails or other vectors. Infection is also frequent from ingestion of contaminated water or unwashed salad that may contain small snails and slugs, or have been contaminated by them. Reservoirs
Rats are the definitive host and the main reservoir for A. cantonensis, though other small mammals may also become infected. While Angiostrongylus can infect humans, humans do not act as reservoirs since the worm cannot reproduce in humans and therefore humans cannot contribute to their life cycle. Vectors
Angiostrongylus cantonensis has many vectors among invertebrates, with the most common being several species of snails, including the giant African land snail (Achatina) in the Pacific islands and apple snails of the genus Pila in Thailand and Malaysia. The golden apple snail, Pomacea canaliculata, is the most important vector in areas of China. Freshwater prawns, crabs, or other paratenic, or transport, hosts can also act as vectors. Organism
Morphology
A. cantonensis is a nematode roundworm with 3 outer protective collagen layers, and a simple stomal opening or mouth with no lips or buccal cavity leading to a fully developed gastrointestinal tract. Males have a small copulatory bursa at the posterior.