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Metastrongylus elongatus are a species of parasitic nematode, often called lungworms, within the genus Metastrongylus. These are known to infect swine hosts and cause the disease metastrongylosis.

Hosts
The intermediate hosts are earthworms and the definitive hosts of the disease are swine. All ages of swine are susceptible but the majority of infections occur mostly in young pigs over six weeks of age

Life cycle
The life cycle of Metastrongylus elongatus is indirect, requiring two separate hosts for development, and is acquired through a fecal-oral route of transmission.

Eggs passed in feces of infected pig hatch into first stage larvae and can survive in the feces or moist soil surrounding it for long periods of time. The larvae are then ingested by earthworms, where they develop into the third stage within 10 days. However, they can remain dormant inside the earthworm, without harm, for up to 18 months before moving on to the definitive host. Pigs that root in pastures containing moist soil are then susceptible to consuming earthworms carrying the larvae. After being eaten, the larvae travel through the digestive system and are able to penetrate the intestinal lining. The larvae subsequently migrate through the veins and lymph to reach the lungs (occasionally ending up in the liver). There they mature, and after about 25 days are able to produce larvated ova. These ova are coughed up into the pharynx, swallowed, and then passed out through the feces.

The cycle is completed when the larvae hatch and are consumed by another earthworm.

Epidemiology and Clinical Signs
The parasitic disease caused by any Metastrongylus species is termed Metastrongylosis. Although Metastrongylus elongatus is the most common offender of infection out of the five main species, infections with more than one species of Metastrongylus at once can commonly occur.

Once the larvae reach the terminal ends of the pulmonary bronchioles, they break into the alveolar sacs and mature. Exudate forms around the lungworms and their ova which can partially or completely obstruct airways causing coughing, or in severe cases, alveolar emphysema and collapse of lungs (atelectasis). Bronchopneumonia can commonly result as a secondary infection.

It is even possible for some larvae to accidently migrate to the liver, where they can cause scarring.

Signs of the disease become apparent about 4 weeks after ingestion.

Some clinical warning signs include chronic coughing, general unthriftiness, rough hair coat, undernourishment, pulmonary lesions, and symptoms similar to ascaris infections. If secondary pneumonia takes place, there may be shortness of breath and an abdominal type respiration (“thumping”).

In a Finnish wild boar farm, the farmer also noticed poor growth and gait abnormalities.

Diagnosis is done by laboratory fecal exams to check for the shed ova or, more commonly, by postmortem examination.

Disease Control
Infection is common in areas where pigs are raised outdoors with access to soil. Lungworms theoretically occur in any countries where swine and earthworms are present and in close proximity. The ability of the larvae to survive in feces and earthworms for such long periods of time is largely responsible for high rates of infection and difficulty ending an outbreak once it has begun.

Development of confinement housing and, as a result, lack of access to soil has been found effective in decreasing prevalence of the lungworm. Anthelmintics, such as avermectin, levamisole, and fenbendazole are known to be effective in controlling the parasite.

Recent experiments suggest that a concurrent PCVAD (Porcine circovirus type 2-associated disease) condition may trigger metastrongylosis, which may subsequently resuly in severe, sometimes fatal, pulmonary disease.

It has also been found that ‘’Metastrongylus’’ species are capable of harboring Swine Influenza Virus (SIV) and transmitting it from animal to animal.