Protostrongylus rufescens is a species of parasitic roundworms that infects sheep and goats as well as other wild ruminants. It is sometimes called the red lungworm.
It is found almost worldwide, often found together with other pulmonary roundworms (e.g. Dictyocaulus filaria, Muellerius capillaris, etc). Surveys in slaughterhouses in Germany showed up to ~30% of sheep to be infected with this worm species.
Other less frequent related species are Protostrongylus brevispiculum, Protostrongylus hobmaieri, and Protostrongylus stilesi).
These worms do not affect cattle, pigs, dogs, horses or cats.
The disease caused by Protostrongylus rufescens is called protostrongylosis or protostrongyliasis.
Is livestock infected with Protostrongylus rufescens contagious for humans?
- NO: The reason is that these worms are not human parasites.
Final location of Protostrongylus rufescens
Predilection sites of adult Protostrongylus rufescens are bronchi and bronchioles in the lungs.
Anatomy of Protostrongylus rufescens
Adult Protostrongylus rufescens are slender worms up to 70 mm long, whereby males are shorter than females. They are of a reddish to brownish color. As in other roundworms, the body of these worms is covered with a cuticle, which is flexible but rather tough. Typical for males of this species is that the posterior end is coiled like a corkscrew. The worms have a tubular digestive system with two openings, the mouth and the anus. They also have a nervous system but no excretory organs and no circulatory system, i.e. neither a heart nor blood vessels. The female ovaries are large and the uteri end in an opening called the vulva. Males have a copulatory bursa with two thick striated spicules for attaching to the female during copulation.
L1-larvae, not eggs are shed in the feces of the infected host.
Protostrongylus rufescens has an indirect life cycle. Goats, sheep, and other wild ruminants (e.g. moufflons, chamois) are final hosts. Intermediate hosts are several snails (Helix, Helicella, Theba, Abida, Zebrina, etc.) and slugs (Limax, Agriolimax, etc).
Adult worms in the lungs lay eggs where L1-larvae developed that hatch still in the bronchi and trachea. These larvae are coughed to the mouth together with the respiratory secretions and subsequently swallowed and passed in the feces. Once in the environment these larvae penetrate into the snails very quickly and develop to infective L3-larvae in a few weeks to several months, strongly depending on weather conditions and snail species. Such infective larvae can survive up to 2 years inside their intermediate host.
Livestock becomes infected after eating contaminated snails or slugs while grazing. L3-larvae are released after digestion. They cross the gut's wall and migrate to the lungs through the lymphatic system and the blood stream. Once in the lungs the larvae cross the alveolar mucosa to the lumen of the alveoli and remain in the bronchi and bronchioles where they complete development to adults and start producing eggs. The host's lungs react building nodules that contain necrotic material, eggs masses, worms, etc. surrounded by connective tissue.
The prepatent period (time between infection and first larvae shed in the feces) is 2 to 3 months.
Harm caused by Protostrongylus rufescens, symptoms and diagnosis
Protostrongylus rufescens is one of the causative agents of verminous bronchitis in sheep and goats, but not as harmful as Dictyocaulus filaria. Infected animals often show no or only slight clinical signs such as general weakness or mild respiratory disturbances. Heavy infections may cause bronchopneumonia and pleurisy (inflammation of the lining surrounding the lungs), particularly in weak animals (old, sick, undernourished, etc.). Infections with secondary bacteria can also happen.
Acquired natural resistance of sheep and goats to these worms after repeated exposure seems to be quite low, not enough to prevent worm development in such animals.
Diagnosis is based on clinical symptoms and is confirmed by larvae found in the feces (300 to 400 micrometers long) with a characteristic tapering tail and a wavy outline but without dorsal spine. At necropsy typical nodules are found in the lungs.
Prevention and control of Protostrongylus rufescens infections
Prevention is difficult because snails and slugs that act as intermediate hosts cannot be easily reduced in the pastures. Since the need humidity for development and survival, effective drainage or anything else that keeps the pastures dry will reduce the snail population. Some preventative measures used against gastrointestinal roundworms can be also appropriate against Protostrongylus rufescens and are explained in a specific article in this site (click here).
Chemical control of the snails with molluscicides (i.e. snail killers) such as copper sulphate, sodium pentachlorophenate, niclosamide, etc. can make sense for very specific purposes, e.g. for treating places where livestock congregates (water holes, feeding areas, salt licks, shade trees, etc) to keep them free of snails. However, trying to eradicate snails from a property is hopeless and useless. It is virtually impossible to treat every place where they can survive and they reproduce extremely quickly. Cleaned pastures would become re-infested very fast. In addition it would be also very harmful for the environment. In fact, such molluscicides (mainly niclosamide) are approved only in a few countries as an aid in the prevention of human schistosomiasis (also called bilharziosis or snail fever).
Chemical control is difficult. Most usual anthelmintics such as broad spectrum benzimidazoles (albendazole, febantel, fenbendazole, oxfendazole, etc.) or levamisole are not or only partially effective against these worms. Most macrocyclic lactones (e.g. abamectin, doramectin, eprinomectin, ivermectin, moxidectin) are effective against adult worms at the usual therapeutic dose, but may not control the larvae.
So far no vaccine is available against Protostrongylus rufescens. To learn more about vaccines against parasites of livestock and pets click here.
Biological control of Protostrongylus rufescens (i.e. using its natural enemies) is so far not feasible. Learn more about biological control of worms.
You may be interested in an article in this site on medicinal plants against external and internal parasites.
Resistance of Protostrongylus rufescens to anthelmintics
There are a no reports on confirmed resistance of Protostrongylus rufescens to anthelmintics.
This means that if an anthelmintic fails to achieve the expected efficacy against Protostrongylus rufescens chance is very high that it was not due to resistance but to incorrect use, or the product was unsuited for the control of these parasites. Incorrect use is the most frequent cause of failure of antiparasitic drugs.
Ask your veterinary doctor! If available, follow more specific national or regional recommendations for Protostrongylus rufescens control.