Biology - Angiostrongyliasis, Abdominal
Causal Agent
The nematode (roundworm) Angiostrongylus (=Parastrongylus) costaricensis is the causal agent of abdominal angiostrongyliasis (intestinal angiostrongyliasis). The related species A. cantonensis (rat lungworm), which causes neural angiostrongyliasis, is discussed here.
Life Cycle
and are ingested by a suitable gastropod intermediate host 
. After two molts, third-stage (L3) larvae are produced, which are infective to mammalian hosts 
. When the gastropod is ingested by the definitive host, the L3 larvae migrate to the lymphatic vessels of the abdominal cavity and develop into adults 
. Some L3 larvae may also be shed into the environment by snails via slime trails, though it is not known if ingestion of these larvae represents a major transmission route. These young adults then migrate from the lymphatics to the mesenteric arteries, where they become sexually mature, approximately 24 days after larvae are ingested. Humans become infected by eating raw or undercooked gastropods that contain third-stage larvae or by eating food items contaminated with gastropod tissue or perhaps larvae shed in slime 
. In humans, larvae undergo their usual migration and may reach sexual maturity and produce eggs (and L1 larvae) (unlike A. cantonensis) 
. The presence of larvae, adult worms, and eggs causes a local inflammatory reaction in the intestinal wall. Parasites and eggs are usually degenerated by this host reaction, and eggs do not appear to be shed in human stool.
Hosts
The main definitive host for A. costaricensis is the hispid cotton rat (Sigmodon hispidus); but adult worms have been found in other rodent species, such as black rats (Rattus rattus), short-tailed zygodonts (Zygodontomys brevicauda), spiny pocket mice (Heteromys adspersus), and pygmy rice rats (Oligoryzomys fulvescens). Slugs in the families Veronicellidae and Limacidae are the typical intermediate hosts.
Aberrant abdominal infections have been documented in humans, non-human primates, and other mammals, including raccoons and one opossum.
Geographic Distribution
Abdominal angiostrongyliasis has mainly been reported from parts of Latin America and the Caribbean. Although A. costaricensis has been found in various animals in the southern United States, the sporadic human cases identified in the United States are thought to have been travel associated.
Clinical Presentation
The clinical manifestations of abdominal angiostrongyliasis (A. costaricensis infection) arise from the parasite’s invasion of the gastrointestinal wall, and may mimic those of other conditions, such as appendicitis, Crohn’s disease, or Meckel’s diverticulum. Eosinophilia is commonly noted. Intestinal obstruction, perforation, and other complications may occur, as may ectopic infection (e.g., in the liver).