Thoracic (Lungworm)

Thoracic (Lungworm)

Lungworm (Dictyocaulus eckerti) is the most important and serious parasitic disease of young farmed deer. The cattle lungworm (D. viviparus) has also been shown to affect deer, although it is less well adapted to red deer.

How does the problem spread?
What are the symptoms?
Effect on deer production
Control and treatment
Which stock to treat
When to treat
Which anthelmintic?
Preventing and addressing drench resistance
Strategies to prevent worm resistance

How does the problem spread?

Adult worms live in the air passages in the lungs. They look like 40-50mm threads. Outlined below is the life cycle.

Diagram A: Life Cycle of lungworm in Red Deer

  1. First-stage larvae passed in faeces.
  2. Infective third-stage larvae on pasture are eaten. They pass down through the stomach, penetrate intestinal mucosa and migrate via lymphatic and blood circulation to the lungs.
  3. Development to fifth-stage larvae and maturation to adulthood in air passages of the lungs.
  4. Adult worms inhabit airways and lay eggs.
  5. Eggs coughed up and swallowed, hatch to first stage larvae and are passed out in faeces.
  6. Infective larvae consumed with herbage.

Cold weather or hot dry weather slows larval development on pasture. However lungworm are hardy and can over-winter in cold climates, surviving at 4°C for a year.

What are the symptoms?
Parasitism can be confused with other deer health issues, particularly gastro-intestinal parasites. Coats look rough and growth rates drop. A more particular sign to lungworm infection is a soft bronchial cough (usually indicating a heavy parasite burden).

Effect on deer production
Young deer aged three to five months in their first autumn are the most susceptible to infection. This is because they have not yet developed full immunity and lungworms are often in high numbers in autumn. All age groups may carry infestations at any time but generally young stock or heavily stressed animals that are untreated will develop severe infestations. Moderate infestations may cause production losses and heavy infestations may be fatal (because of blocked airways). Pneumonia can result from damaged lungs.

Wapiti deer appear to be more susceptible than red deer and take longer to develop immunity.

The faecal larvae count (FLC) is currently the only laboratory test for lungworm. It requires 5 to 10 grams of faeces collected from the rectum and submitted to a diagnostic laboratory in a small pottle. Usually samples are collected from 5 to 10 deer to get a good estimate of parasite burdens in the group.

FLCs can be used to monitor lungworm burdens in young (2 to 6 month) old deer in late summer/autumn. Regular counts (every week from late January) are needed to  detect when lungworm burdens first occur and to monitor changes over time. Start drenching as soon as there is a sudden rise in FLC. FLC are really only useful in young deer in their first autumn and can be misleading in the following spring.

On farm poor growth rates and coughing(especially when moving a mob) indicates lungworm.

Control and treatment
Control and treatment should go hand-in-hand. Control should focus on:

  • reducing the reinfection challenge to young deer; and
  • eliminating the existing lungworm burden with anthelmintics.
  • Control options to reduce reinfection challenge include-
  • grazing at-risk blocks with older deer, adult sheep or cattle;
  • replacing older pastures with new pasture species less likely to harbour parasites, such as brassicas;
  • treating deer with anthelmintics before there is an outbreak to avoid building up large parasite populations on pasture; and
  • providing optimum nutrition to increase young deer's ability to resist the effects of parasitism.
  • Treatment of parasitic infestations by anthelmintics is important for the maintenance of deer production.

Which stock to treat
The class of stock requiring treatment are typically young deer (three to six months old) in their first autumn. Immunity builds after this time. The whole mob should be treated, not just those showing signs of parasitism.

Adult red deer are relatively resistant to lungworm, as long as they are well-fed and not suffering environmental stress. This means they will have minimal lungworm burdens, which will not have any effect on production. However, some red deer that have been stressed, such as red stags after the rut and hinds lactating during drought conditions, may be susceptible and require treatment.

Yearling and adult wapiti deer are also more susceptible than red deer and may require treatment.

When to treat
Late summer/autumn (Febuary to June) is the key risk period for young deer so treat at intervals during this time, according to the anthelmintic used. Seek veterinarian advice on this. The aim is to break the lungworm life cycle.

The timing for treatment depends on both the faecal sample results and the season. Infection rate usually increases during late summer and early winter. However, if the summer is particularly warm and wet then worming may be required as early as January. The interval between treatments depends on the persistence of the anthelmintic in the animal (see below)and the level of challenge by infective larva .

Note it is very unwise to leave young deer undrenched in autumn because they can develop large burdens very quickly if untreated. They have not had time to develop immunity.

Key times to consider treating adults is when some stress affects their condition eg  hinds before calving and/or weaning where their Body Condition Score (BCS) is less then 3, and stags  after the rut. Stocking rate also dictates the timing and number of treatments, with more intensive grazing systems needing more monitoring and perhaps more treatments than extensive systems. Adult deer with poor trace element status and tight feed conditions might develop clinically significant lungworm burdens. Similar deer with good nutrition may not. For this reason an integrated approach to managing animal health is best.

Which anthelmintic?

  • All anthelmintic programmes should be developed in consultation with a veterinarian.
  • Triple Combination Drench for parasite control is the recommended approach. Pour-ons are not recommended due to   their poor effectiveness which has encouraged development of anthelmintic resistance by  gastrointestinal parasites. 

Treatment considerations:

  • Benzimidazoles (white drenches): they have no persistent activity and must be used three-week intervals during the risk period in autumn. On their own their efficacy against lungworm is limited
  • Avermectins and moxidectin: they are highly effective and can be used at longer intervals.
  • Note that Levamisole is not effective against lungworm in deer.
  • Always dose to the heaviest deer in the mob. Caution must be used where there is a big variation in weight within the mob and the dose adjusted according to liveweight.
  • ML drenches are very effective against lungworm but using only an ML drench is not a good option. At best you lose the opportunity to delay the onset of drench resistance by GI worms and at worse you are actively encouraging GI worm resistance. 
  • Best practice recommendation is to use a Triple Combination drench. ML Injection (Cydetin or Exodus) at 1ml per 50kg and an oral combination of Oxfen C Plus and Oxfen C mixed in equal parts and given at 1ml per 5kg.

Preventing and addressing drench resistance

There are no records of lungworm drench resistance to date. Indications on farm are that in years of high lunworm challenge the persistant activity of ML drenches no longer applies. Hence drench intervals in presence of high challenge need to be reduced to3 weeks.

Massey University tested the efficacy of pour-on Moxidectin, pour-on Ivermectin and oral Ivermectin in weaners on the Massey deer research unit. All drenches achieved 99.98% or better kill of lungworm and large intestinal worms, but efficacy against abomasal parasites was variable and as low as 12% for oral ivermectin. This research was based on worm counts. Faecal egg and larval count reduction tests seem less reliable in deer than other species. This is the first research report of drenches failing in deer.

Since then every deer farm investigated  has shown some level of resistance of gut worms to ML drenches. Due to the cost of slaughter trials and total worm counts this has been less than twenty farms but due to past drench practices the issue of drench resistance is likely to be widespread. Drench resistance is a huge risk for the deer industry as there are fewer drench options for deer.

Strategies to prevent worm resistance

1. Avoid high risk drench and stock management practises

  • Do not under-dose 
  • Do not use Pour-on
  • Do not drench adult deer routinely
  • Quarantine drench all incoming deer
  • Avoid finisher only deer blocks
  • Do not use long acting drenches e.g. capsules or long acting injection

2. Create a refugia of drench susceptible worms

Preventing the dominance of drench-resistant parasites on pastures is important. One option is to keep a number of healthy deer in a mob undrenched. They are then likely to shed non-drench resistant parasites onto pasture, diluting the proportion of resistant parasites. This is known as refugia. Avoid drenching deer immediately prior to putting them on ‘clean’ pastures as the deer will shed only resistant worms creating a population of resistant worms on these ‘clean’ pastures.

3. Use a triple combination drench

  • A triple combination has been shown to be the only effective way to control worms when drench resistance is present
  • When resistance is present injectable moxidectin is more effective than oral moxidectin
  • Combination drenches delay the onset of resistance.
  • Best practice recommended Triple Combination drench is:- ML Injection (Cydetin or Exodus) at 1ml per 50kg and an oral combination of Oxfen C Plus and Oxfen C mixed in equal parts and given at 1ml per 5kg. But we recommend talking this through with your vet.

Take care when using this recommended combination:-

Mix and Use Basis. The mixture of equal parts Oxfen C Plus and Oxfen C should be on a mix and use basis. The two oral drenches are compatible and unused mixture will be fine in the short term but aim to minimise the amount not used at any one drenching episode. As with any anthelmintic the mixture should be shaken well before use.

Default Withholding Time. The mixture of equal parts Oxfen C Plus and Oxfen C when given at 1ml per 5kg is off label use of these anthelmintics. (The dose rate of oxfendazole exceeds label dose and no levamisole containing products are registered for use in deer).  A default withholding time of 91 days applies.

Toxicity. High doses of levamisole are toxic to livestock including deer. Care must be taken to ensure the mixture of Oxfen C Plus and Oxfen C is in equal parts i.e. one for one. Dose to the heaviest in the mob butcare must be taken when there is a large variation of liveweight within the mob. Adjust the dose rate to suit.