autoinfection

Autoinfection is a mode of infection in which a pathogen or parasite completes part or all of its life cycle within the same host, allowing ongoing infection without exposure to an external source. The term is used primarily in parasitology and infectious diseases. It is distinct from autoinoculation, where a patient transmits an organism to a new body site, and from reinfection acquired from another host or environment.

Mechanisms include parasitic worms that generate infectious stages within the host. Strongyloides stercoralis exhibits autoinfection when rhabditiform larvae in the intestine molt into filariform larvae that penetrate the intestinal mucosa or perianal skin, reentering the host’s circulation. This can sustain infection for years and, in immunocompromised individuals, lead to hyperinfection with widespread dissemination. Hymenolepis nana, the dwarf tapeworm, can also autoinfect: eggs ingested by the same host hatch into larval forms that develop directly into new cysticercoids within the intestine, enabling persistent heavy infection even without external exposure.

Clinical significance: Autoinfection allows prolonged or escalating parasite burdens, sometimes culminating in life-threatening illness in vulnerable individuals. Symptoms depend on the organism but may include abdominal pain, diarrhea, weight loss, and systemic symptoms. In strongyloidiasis, autoinfection is a key feature and poses a risk for hyperinfection syndrome in corticosteroid-treated or immunosuppressed patients.

Diagnosis and treatment: Diagnosis relies on stool microscopy, serology, or molecular testing, depending on the organism. Treatment typically involves antiparasitic agents such as ivermectin or albendazole for Strongyloides and praziquantel for Hymenolepis nana, with management of immunosuppression where applicable. Preventive measures emphasize hygiene, sanitation, and reducing exposure to infectious stages to limit new infections and reinfection, even as autoinfection can sustain the disease within a host.