Lungworm strikes again - 'Reinfection Syndrome' explained

Unlike stomach worms, for which selective targeted treatment can be used in some instances, lungworm is better treated as a whole group due to its complicated immunity story, advises farm vet Hazell Mullins.

Coughing is a tell-tale sign of Lungworm.

I am happy to report that the unwanted soundtrack of cows coughing in the parlour is no longer invading the usual serenity of milking. Now, it certainly wasn’t an instant overnight fix, as when it comes to Lungworm, it can take up to two weeks for signs to completely clear.

Whilst out TB testing this week, I heard one group of cows in particular start to cough. The farmer wondered why, despite their age, they were still being infected with lungworm. This is where my attempt at explaining “reinfection syndrome” began by the van and the reason behind a part two article on lungworm. A novel, “The Chronicles of the Lungworm,” would be a heavy read.

It all centres around immunity; Lungworm is a cool operator compared with most stomach worms. One thing that can be said about lungworm is that it is far from ageist, as age is no barrier to infection. Larval immunity only lasts for approximately six months, which, when you compare it with other parasites, is a very short timeframe. 

Adult lungworm immunity lasts for two years which is a huge improvement on a poor six months. This adult lungworm immunity is great for reducing the level of eggs produced, but unfortunately, it is the larval migration that caused the majority of the damage in the lungs.

Over the winter period, the animals will exceed this six-month period where they do not face a larval challenge, and hence, their immunity wanes. This means that all animals are not naïve again for the next grazing season. 

Due to the seasonality of our farming systems, high burdens of infected larvae can be consumed at different points over the summer. I mentioned last week that June was an ideal month weather-wise for the dispersal of larvae on pasture, with hot, dry weather followed by rain. Despite the sun's brief appearance, it was enough to create the ideal lungworm multiplication environment in the fields.

Cleverly, Lungworm has developed a very clever strategy for causing havoc with grazing herds in Ireland. It is truly the mastermind of parasites. The burden of lungworms also comes into play alongside waning immunity when it comes to “Reinfection syndrome”; high levels of the larvae can overwhelm an already diminishing immunity in the adult cow. It can then cause an over-exaggerated immune response in the lungs, causing excess inflammation and coughing.

This was evident on our farm for sure this year; the cows grazed a field where the calves were recently, and like clockwork, ten days later, this cough appeared.

At first I tried to convince myself it may be dust off the ration in the parlour but it escalated quickly. They had consumed a large amount of larvae in one grazing session, and this, coupled with a weakening immunity, resulted in this “Reinfection syndrome” . 

Due to the nature of this infection being a pre-patent infection, meaning that no eggs are produced due to the lack of adults present, a faecal sample would not be of much benefit in diagnosing. 

A bronchoalveolar lavage is a diagnostic test your vet can perform, especially if there is little to no clinical improvement post-treatment. It involves injecting and flushing the lung via a tube in the trachea and collecting a sample. This is then tested for the presence of lungworm larvae, parasitic specific white blood cells , bacteria and viruses.

Thankfully, we do have a non-milk withdrawal product available for treatment. Eprinomectin is available in both a pour–on and injectable form. The commandments of dosing also apply for cows: dose to the heaviest in the group, store correctly, calibrate equipment correctly, watch for rain with pour-on use, and use subcutaneously only for the injectable form.

We only have one drug available to use with no milk withdrawal, so we need to ensure we use it responsibly to limit resistance. Always talk to your vet about treating lungworm. Albendazole is also licensed for dairy cows, but its use would be limited to dry cows. It is an option for dried autumn calving cows showing signs of lungworm.

Unlike stomach worms, for which selective targeted treatment can be used in some instances, lungworm is better treated as a whole group due to its complicated immunity story. Lungworm can predispose to secondary pneumonia, so always keep a close eye on the herd post-dosing and call your vet if you have any concerns.

Hopefully, now you can now see why the Lungworm Chronicles needed two articles this month; it really is a very complex and interesting parasite. For this reason, advice from your vet is crucial when it comes to Lungworm in your herd whether that is in calves or the troublesome “Reinfection Syndrome”.

This week, I am in Mitchelstown TB testing and then heading to Ballygarry Estate Hotel in Tralee for David Kingston and Caitriona O Neill’s wedding - which will be a West Cork invasion of the Kingdom. It’s my first wedding since my own last May, and I am looking forward to just being a guest again without any of the planning. Wishing the happy couple a lifetime of joy and adventures together.