Angiostrongyliasis is a parasitic infection caused by a rat lungworm, Angiostrongylus cantonensis. Infections are mainly seen in endemic areas and in travelers, and meningitis, encephalitis, as well as ocular and gastrointestinal infection are recognized forms of angiostrongyliasis.
Human infection by Angiostrongylus cantonensis occurs through consumption of raw or undercooked food and vegetables that contain larvae or eggs of this parasite [1]. Rats or monitor lizards are primary hosts that shed the parasite through feces, while snails, prawns, freshwater shrimps, fish and crabs (depending on the geographic area) serve as paratenic (intermediate) hosts [1] [2] [3]. The Pacific and the Carribean islands, Latin America and Southeast Asia are considered to be the endemic regions of this parasite, but sporadic cases in travelers and the local population have been reported worldwide [3] [4]. The incubation period of infection may be quite long, ranging from several days to several months [4], and three clinical syndromes have been described - central nervous system (CNS), ocular and gastrointestinal infection [1] [3] [4] [5] [6]. Eosinophilic meningitis is a term used to describe the main subtype of infection, and presents with acute severe headaches, whereas seizures and acute loss of consciousness and even coma are typical for eosinophilic encephalitis, a more dangerous, and even fatal form of the disease [5]. On the other hand, blurred vision may be the only symptom of ocular angiostrongyliasis [7]. Gastrointestinal infection manifests as relapsing abdominal pain, tenderness, vomiting, fever (although rare), and a mass in the right lower abdominal quadrant, which may often mimic appendicitis or intestinal perforation [4] [6].
The diagnosis of angiostrongyliasis may be difficult to attain, given the fact that the incubation period may be quite long, but the majority of studies have confirmed that symptoms develop in a matter of weeks after ingestion of the parasite [3] [4]. Having in mind these findings, an adequately obtained patient history may be the most valuable procedure in the diagnostic workup, during which information about recent travel and possible consumption of foods that could have been contaminated by parasitic eggs or larvae are obtained. Severely ill patients (especially those suffering from CNS infection) may not be able to provide such data, requiring additional tests to confirm angiostrongyliasis as the underlying cause. The terms "eosinophilic meningitis" and "eosinophilic encephalitis" are used because lumbar punctures reveal a high eosinophil count in the vast majority of patients since eosinophils are produced in the defense against parasitic infection [3]. Although serological testing for this parasite exists, being both highly specific and sensitive [3], its availability is scarce [5], implying that the diagnosis rests on patient data and results from lumbar punctures. Some patients may be diagnosed post-operatively when histopathological examination of the removed tissue reveal the presence of parasites, and so far, the gastrointestinal system, but also the liver and the testes, were organs from which the parasite was isolated [4].