Expats accustomed to not having to think much about parasites in Costa Rica, in contrast to other places where amoebas lurk in every ice cube, shouldn’t forget about Angiostrongylus costaricensis.
This is a nematode and actually has rats as its main host, with snails and slugs as an intermediate vector where early-stage larvae develop. Humans can contract an infection through eating inadequately cooked snails in cultures where those are consumed, but here accidental ingestion of a small slug or slug slime in poorly washed greens is the likeliest cause. Hydroponic lettuce is reputedly safer as the salt used and lack of soil makes for an environment hostile for the mollusks. Anything that has been on the ground where there are snails or slugs is potentially a risk.
The nance is one such food item since it is normally picked up off the ground after ripening. This is a yellow fruit a little smaller than an olive which is prevalent in Costa Rican cooking as preserves and wine. To eat raw it should be washed carefully with soap.
This nematode species wasn’t even described to science until 1971 by two biologists from the University of Costa Rica, Pedro Morera and Rodolfo Céspedes. The unfortunate scientific moniker A. costaricensis, refers to the fact that the original specimens were recovered from the intestinal linings of several children in this country. Since then, it has been established to be present in most of tropical America.
Similarly, the Asian Angiostrongylus cantonensis is better known as it is a cause of eosinophilic meningitis, a rather serious nervous system disorder. The local version here is much more benign with immune response eventually dealing with the invasion. The most serious manifestation is usually the establishment of an adult nematode in the intestinal lining when it then can require surgery to remove.
Initial symptoms are normally abdominal pain which can lead to misdiagnosis as appendicitis or some other problem of the liver and digestive system. There is a blood test for Angiostrongylus which
allows for firm confirmation of the invasion. Given high tolerance and eventual autoimmune response, unless there are problems with the intestines due to the 15-millimeter (about six tenths of an inch) adults which can require surgery, no action is normally taken.