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CONTRIBUTOR(S): Mike Taylor, Andrew Forbes,

Lungworm

Lungworm

Lungworm is an economically important parasitic nematode infection of the respiratory tract of cattle. The causative parasite (Dictyocaulus viviparus) is widespread throughout the British Isles, Western Europe and other parts of the world being commonest in temperate climates with a high rainfall.


Lungworm
©Peter Jackson

How is lungworm infection spread?

Disease due to lungworm may also be referred to as parasitic bronchitis, colloquially known as “husk” or “hoose”. It typically in young calves at grass for the first time when members of a group may be coughing and showing other respiratory symptoms. Adult cattle usually acquire immunity to lungworm infection but if immunity becomes reduced or impaired, may cough and in dairy cows show a drop in milk yield.

As with many other parasitic nematodes, infection is acquired by the ingestion of infective larvae from pasture. The epidemiology is complex and outbreaks are often unpredictable because initial infections are often not detectable.

Infective larvae are susceptible to desiccation and survive on pasture for only a limited period, but some can survive over-winter and be a source of infection the following year.

High summer temperatures limit the development and survival of the larvae on pasture, whereas in areas with a high average summer rainfall, the larvae may survive longer. Wet weather conditions promote the release of infective larvae from the faecal pat, which may also spread by wind on the spores of a fungus.

The larvae may also be dispersed by mechanical means such as boots, animals’ feet and birds.

Disease outbreaks, which are usually due to a second generation of worms ingested from pasture, occur most commonly in late summer.

In previously exposed herds, asymptomatic carrier animals may excrete low numbers of larvae in the feces. Yearlings are the most important carriers but adults may also act as carriers and excrete small numbers of larvae.

What are the effects of lungworm?

Mild or moderate lungworm infections usually produce varying degree of coughing. Severely affected cattle cough frequently and show respiratory distress characterized by heavy breathing and a classic ‘air-hunger’ position of mouth breathing with the head and neck outstretched, and the tongue stuck out each time they try to cough.

Non-immune adult milking cows can show a sudden and dramatic decrease in milk yield and frequent coughing. Losses in severe lungworm outbreaks in growing cattle can average £50-£100/$63-$125 per animal and in adults lost milk production may reach £3/$3.5 per cow per day (2017).

What risk factors influence disease occurring?

Lungworm infection is widespread and is capable of existing unsuspected for many years. It is only when a combination of circumstances favorable to the parasite arises that outbreaks of disease may occur.

In areas where the disease is endemic then disease outbreaks may occur each year unless controlled.
On farms where clinical disease has not been seen previously, it shouldn’t always be assumed that infection has come from outside the farm.

Infection is almost invariably associated with young cattle at grass, but it can on occasions be transmitted indoors by eating hay or straw that has been contaminated by carrier animals. Lungworm infection in older cattle, which have acquired immunity, is not usually associated with clinical signs. Occasionally, however, coughing may occur in previously immune animals exposed due to a massive challenge with larvae, as might occur on pasture recently vacated by calves suffering from clinical husk.

It can be difficult to differentiate this syndrome from the early stages of a severe primary infection in non-immune cattle.

Lungworm disease is now seen more commonly in adult cattle that have failed to develop immunity in earlier years.

What steps should I take to prevent lungworm infection?

The unpredictability of disease due to lungworm infections precludes the use of clean grazing strategies used for controlling gut parasites.

The best method of preventing lungworm disease in first-year calves is immunization with lungworm vaccine, but this is only practical in autumn/winter-born calves in which the course of vaccination can be completed before turnout. Vaccination is not justified in regions with a low incidence of lungworm disease or on farms with no previous history of lungworm.

In such herds, a policy of preventing the introduction of infection should be rigorously enforced by good quarantine measures.

What treatments are available?

Wormers for controlling gut parasites are also effective against lungworms. The most commonly used are products containing avermectins (ivermectin, doramectin or eprinomectin ) or milbermycins (moxidectin), which also provide variable periods of protection from re-infection. White drench wormers (containing fenbendazole, albendazole etc) and worming products containing levamisole are also effective against lungworm.

Affected cattle should be treated as soon as possible because severely affected animals may either not respond, or symptoms may worsen as dead or dying worms block the lower airways.

Treated cattle should be removed from infected pasture and transferred to cleaner pasture if available, or housed in well-ventilated facilities.

For severely affected animals showing severe respiratory distress, wormers on their own may not be enough and may require veterinary attention for secondary bacterial infections and pneumonia and other conditions that can result in death if left untreated.

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