Lung worm, Hoose, Dictyocaulus viviparous – The Facts

Lungworm infection is one of the most important respiratory diseases of cattle in Ireland. Outbreaks can be widespread and unpredictable resulting in reduced animal performance and in severe cases animal losses. Martina Harrington, Teagasc Cattle Specialist has detailed advice on Lungworm in cattle

As a very wise man said to me lately, once you see mushrooms, you know its lungworm weather and you should be extra vigilant. We have had a long dry spell, followed by heavy rains – an ideal set of conditions for both.

What is it?

A roundworm parasite similar to gut worms that completes its life cycle in the lungs

It can cause..

Bronchitis and Pneumonia which can result in an increase in coughing and faster breathing rate.

Susceptible Animals and Risk

With exposure animals will develop immunity to lungworm. Therefore the animals at greatest risk are calves. The aim is to give them enough exposure in their first grazing season to build immunity but not restrict their performance.

Autumn born sucklers and dairy bred calves are most at risk in spring as they are eating a lot of grass but have very little immunity. The risk for spring born claves increased as their grass intake increases.

Note: A dangerous level of infection can happen after only one day of grazing if pasture is heavily infected.

Lungworm Life Cycle       

• Infective larvae on grass are eaten by the animal
• Larvae pierce the intestinal wall and move into the blood and lymphatic system to get to the lungs.
• In the lungs they the leave blood and puncture the lung tissue & grow into worms
• Adults then lay eggs
• The eggs are coughed up and swallowed
• The eggs hatch in the intestine and produce larvae – stage 1
• The larvae is passed in the dung
• In the dung the larvae grow into stage 3
• Stage 3 larvae spreads onto grass and is eaten by animals

It takes 24 – 28 days from the day larvae been eaten to the passing of eggs.

In the dung pat L1 develops to L3, the rate is dependent on the weather. In warm humid conditions it could be in less than 7 days. In hot dry days the larvae stay within the dung pats and down at the base of grass for moisture.

Pathways for larvae

Larvae need to move out of the dung pats and onto grass. The two main pathways are:

1. Rain – the droplets splash the larvae out of the dung and it attaches itself to the grass
2. The fungus Pilobolus has a mechanism where it “explodes”. This pushes the larvae up into the air and can spread the larvae up to 3m.

Clinical signs

Clinical signs of disease include

• Intermittent coughing particularly after moving stock.
• Moderately affected animals will have coughing bouts even when they are resting and may show signs of increased difficulty in breathing.
• Heavily affected animals suffering from respiratory disease have an increased breathing rate accompanied with opened mouth breathing with head and neck outstretched. The tongue will also appear as they try to cough. The cough will be the harsh deep ‘husk’ cough. Cattle can lose condition rapidly. 

The nature and severity of lungworm infection depends on the number of larvae that are present.

Once you hear coughing in a group of animals, the whole group should be treated as soon as possible after the appearance of clinical signs in order to limit the impact of the infection. Adult animals de develop immunity to both stomach and lungworm, however if there is an underlying health issue, do not rule lungworm out completely. 

Always be on the look out for signs of animals coughing, this is key!

Lungworm Control

The unpredictability of disease due to lungworm makes it difficult to prevent or control.

The three major groups of anthelmintics are all effective against lungworm. If coughing is detected in a group of cattle at grass and hoose is suspected, all cattle in the group should be dosed.

Calves that were heavily infected need to be closely observed in the 1-2 days post treatment.

Dung sampling is not relevant in the case of lungworm as by the time eggs reach the dung, the damage is already done. 

Building natural immunity

As a word of caution care needs to be taken when using long acting anthelminthic in the 1st grazing season because you may limit the animals exposure to lungworm larvae and cattle will remain susceptible to reinfection the following season due to not developing natural resistance.

We also want to avoid resistance building due to bad practice

Best Practice when dosing

• Ensure the correct dosing technique is used and that the animals are treated according to the manufacturer’s instructions and dose rates. I.e. intra muscular vs sub cutaneous
• Dosing equipment should be checked before treatment to ensure it is delivering the correct amount.
• Animals should be weighed or a few of the biggest animals in the group selected and weighed to determine the dose rate and all dosed to the weight of the heaviest animal
• Continual use of anthelmintics from the same class should be avoided and combination anthelminthic products (flukicide + wormer) only used when it is necessary to target both fluke and worms.
• Keep the cleanest grazing such as reseeds, after grass, for the most naïve animals such as calves.
• Calves can also be grazed ahead of older animals or mixed with sheep to reduce the worm challenge.
• If using avermectin in calves with say a 5 week persistency, calves should be dosed every 6-7 weeks to allow them to build natural immunity to worms, however faecal egg sampling will show if worms are present
• Cows are immune to gut & stomach worms as are older cattle (usually).
• A good biosecurity protocol for all bought-in animals should be implemented to prevent bringing resistant worms onto the farm. Bought in stock should be treated with an anthelmintic and housed for 48 hours. They should then be turned out to a contaminated pasture recently grazed by cattle.

Further information on lungworm is available in the AHI leaflet on Lungworms (PDF) and always talk to your vet

The Teagasc Beef Specialists issue an article on a topic of interest to Suckler and Beef farmers every Wednesday here on Teagasc Daily. Teagasc provides a Local Advisory and Education service to farmers. Find your local Teagasc office here