Baylisascaris is a genus of roundworms that infect more than fifty animal species. Life cycle Baylisascaris eggs are passed in feces and become active within a month. They can remain viable in the environment for years, withstanding heat and cold. Animals become infested either by swallowing the eggs or eating another animal infested with Baylisascaris. Disease progression After an animal swallows the eggs, the microscopic larvae hatch in the intestine and invade the intestinal wall. If they are in their definitive host they develop for several weeks, then enter the intestinal lumen, mature, mate, and produce eggs, which are carried out in the fecal stream. If the larvae are in a paratenic host, they break into the bloodstream and enter various organs, particularly the central nervous system. A great deal of damage occurs wherever the larva try to make a home. In response to the attack, the body attempts to destroy it by walling it off or killing it. The larva moves rapidly to escape, seeking out the liver, eyes, spinal cord or brain. Occasionally they can be found in the heart, lungs, and other organs. Eventually the larva dies and is reabsorbed by the body. In very small species such as mice, it might take only one or two larvae in the brain to be fatal. If the larva does not cause significant damage in vital organs, then the victim will show no signs of disease. On the other hand, if it causes behavioral changes by destroying parts of the brain, the host becomes easier prey, bringing the larva into the intestine of a new host. Clinical signs in humans Skin irritations from larvae migrating within the skin. Respiratory discomfort, liver enlargement, and fever due to reaction to larvae migration. Eye and brain tissue damage due to the random migration of the larvae. Nausea, a lethargic feeling, incoordination and loss of eyesight. Severe neurological signs including imbalance, circling and abnormal behavior, caused by extensive tissue damage due to larval migration through the brain, eventually seizures and coma. Treatment While deworming can rid the intestine of adult Baylisascaris, no treatment has been shown to alleviate illness caused by migrating larvae. Despite lack of larvicidal effects, albendazole (20–40 mg/kg/d for 1–4 weeks) has been used to treat many cases. Baylisascaris species Each Baylisascaris species has a host species that it uses to reproduce. The eggs appear in the host species' feces.