Lungworm and Respiratory Disease in Ruminants Flashcards
Describe the characteristic clinical signs demonstrated by cattle suffering from lungworm?
- Spring-born suckled beef calves grazed with their dams until housed or sold do not usually develop clinical signs, although coughing due to a mild infection is common
- Sudden heavy pasture larval challenge, due to prevailing weather conditions, may lead to clinical signs of re-infection husk
- Lungworm infection is characterised by bronchitis and pneumonia and typically affects young cattle during their first grazing season on permanent or semi-permanent pastures
- Most of the major clinical signs occur during the prepatent and patent phases and are caused by primary parasitic pneumonia. The gradual development of bronchitis and pneumonia results in coughing and increased breathing rate, accompanied by varying degrees of anorexia, weight loss and laboured breathing. Fever may occur when there is secondary bacterial infection. The severity and duration of signs relate to the number of larvae ingested and the rate of ingestion
- Infection is associated with two main lesions. A parasitic bronchitis characterised by the presence of large numbers of adult worms in frothy white mucus in the bronchi; and secondly, the presence of collapsed areas around infected bronchi. This is a parasitic pneumonia caused by the aspiration of eggs and L1 into the alveoli. During the post-patent phase, although the clinical signs are abating, the tissues are still inflamed and residual lesions may persist for weeks to months. In about a quarter of severely affected animals, there can be a flare-up of clinical signs, which is frequently fatal
- The appearance of coughing and an increased rate and depth of respiration in any age group of cattle at grass should trigger a suspicion of parasitic bronchitis.
- Overall, clinical signs include:
- Widespread coughing in grazing cattle
- Loss of condition
- Increase in respiratory rate (Tachypnoea)
- Difficulty breathing (Dyspnoea)
- Reduced milk yield in adult cows
Why has there been an increase in the number of reported cases of lungworm over the last couple of decades? (NB there is probably more than one reason)
- One of the reasons for the increase in disease observed since 1993 may be the increased movement of cattle within both the UK and Europe. Lungworm can also be introduced to a herd from a contiguous premises, either by airborne spread (the Pilobulus fungus can propel infective larvae over 1 m) or by mechanical transmission via infective faeces. Unless a dairy herd has an effective closed herd policy and good perimeter security it is vulnerable to the introduction of parasitic bronchitis.
- The present epidemic in adult cattle is likely to be related to an ‘immunity gap’ created by a break in the continuity of exposure to the parasite within herds. It is likely that this immunity gap has occurred in previous years, due to changing weather conditions (dry summers being disadvantageous to the parasite). However, the principal differences between previous instances and the current situation are that:
- There is now no background widespread vaccination to buffer variations in the development and maintenance of immunity within herds.
- Increased movement of livestock has increased the risk of introduction of the disease into susceptible herds.
- Increased use of powerful chemoprophylactic regimens, particularly over consecutive grazing seasons, many be erecting pharmacological barriers to the maintenance to immunity within infected herds. The equilibrium between parasite and host has been disturbed, as has the balance of maintained immunity within endemically infected herds. It is likely that this unstable situation will continue unless effort is put into reconsidering the control of parasitic bronchitis.
List the possible methods of prevention / control of lungworm in cattle
- The first objective might be to assess the relative risk to disease in the herd. Is the disease endemic or not’? If there is a past history of parasitic bronchitis on the farm, this may be easy to determine; otherwise, other evidence may be necessary. It might be very difficult to demonstrate complete freedom from the disease
- If the herd is considered truly free of infection, an attempt could be made to maintain that herd status by:
- Adopting a true closed herd policy.
- Treatment and quarantine of any added animals.
- Sound perimeter security, preferably with the absence of cattle on contagious premises.
- Long-acting anthelmintic treatments in the form of boluses or strategic treatments such as the 3, 8. 1 3 system can provide protection from disease as long as the anthelmintic is active; however, there is still an opportunity for disease to develop if animals are grazed after this active period has expired.
- Vaccination should be the foundation of any disease control strategy since, although long-acting/continuous release treatments protect calves in their first grazing season, they do not address the problem of lifetime immunity.
- Small degrees of exposure to field infection may not result in a solid immunity in unvaccinated animals but will do so in vaccinates. Vaccination in the first year at grass will also provide an initial immune stimulus to those animals receiving long-acting anthelmintic preparations which may not allow exposure to field infections
Why might treating badly affected animals with anthelmintics lead to exacerbation of clinical signs or even death in some cases?
Severely affected animals may require antibiotic treatment to control secondary bacterial pneumonia and, if anorexia is present, rehydration with electrolytes. Non-steroid anti-inflammatory agent should also be used as a support therapy. The worst affected animals should be housed, especially in poor weather conditions. Treatment may initially exacerbate the signs due to mortality of worms in the airways. Additionally, despite treatment, some cases may relapse a few weeks after treatment due to the severity of the lung pathology.
Which parasites can cause lung worm in sheep in the UK?
- Dictyocaulus filaria
- Protostrongylus rufescens
- Muellerius capillaris
What age group of sheep are most commonly affected by lungworm? Why is the disease not seen in other animals?
- When seen, clinical signs are usually due to D filaria infections and occur most commonly in young sheep during the autumn and winter, although cases can be seen between June and November – a warm, wet summer enhances the survival of the larvae.
- The spring hatching of first-stage larvae from ewe and yearling faeces or overwintering third-stage larvae on the pasture provide a source of infective Dictyocaulus species larvae. During the grazing season, at least three generations of parasites can be present, with adult worms developing four weeks after infection. Most lambs are infected in their first year, resulting in a light, prolonged infection. Strong immunity develops following exposure so there are usually few worms in older sheep, unless they are suffering from a concurrent immuno suppressing condition
How could an organic sheep farmer prevent or control lungworm?
- In most flocks, anthelmintics used for the routine treatment of parasitic gastroenteritis also effectively control lungworm. Avoiding pasture that was used for sheep grazing the previous year will help to prevent exposure to high levels of lungworm larvae carried over from the previous season
Clean Grazing
- If enough land is available, clean grazing is a very effective way to reduce worm challenge and improve lamb growth. Rotational use of land for cattle, sheep and silage/hay (in this order) will allow lamb production on safe pasture. If cattle are not available, grazing lambs on aftermath alone will provide a benefit.
Nutrient Supplementation
- Our own pen and grazing studies have shown that protein supplementation to ewes results in reduced worm egg output and increased milk production. Both contribute to a higher weaning weight of lambs, and recent research has shown that lambs from protein supplemented ewes require less drenching. Studies have also shown that protein supplementation to wormy lambs improves their resilience and resistance. Protein supplementation is therefore an option to be considered for both ewes and lambs. This could be done through hard feed or with red clover in the pasture.
Bioactive Forage
- These are forages with anti-parasitic properties. Several forages have been tested in the UK, including bird foot’s trefoil and chicory. Chicory research has shown benefits on lamb production and worm control. Our own grazing studies have shown direct anthelmintic effects of pure-stand chicory (Puna-II) as well as consistently reduced worm egg output. Lambs grazing chicory grow faster than their grass/clover counterparts, and also require less drench. Chicory has an excellent nutritional value and its leaf structure may reduce worm larvae migration. Lambs benefit through reduced challenge and improved nutrition which increases their resilience.
Drench on Worm Egg Counts
- Regular worm egg counting can help identify which parts of the farm are more “dirty” than others, and also assist drenching decisions. You may find that you can delay or skip drenches based on this information. We will provide kits and regular testing.
Drench Poor Growers Only
- Information from regular weighing of sheep can be used to inform drench decisions. This is helped by novel weighing equipment that allows drafting off animals that have not grown as much as expected. Drenching poorer performers only may cut down on the total amount of drench used. If you have this equipment you could use it for drenching decisions, or alternatively draft off lambs to finish on chicory or red clover paddocks.
What is the toxin through to cause fog fever? What is the classic presenting history for the disease and how is it treated?
Also known as Acute Bovine Pulmonary Edema and Emphysema (ABPEE).
Fog fever is an acute pneumonia of adult cattle which occurs within four to 10 days of moving from an over grazed pasture or dry feed, to a fresh, lush green pasture. The condition develops rapidly.
It typically occurs in Autumn, five to 10 days after the change to lush grass.
Cause
The affected cattle have been on dry feed for an extended period of time and the rumen fermentation pattern has adapted to this situation. With the change to lush green pasture the dietary protein concentration increases dramatically. One of the amino acids in this plant protein, tryptophan, is the culprit. The tryptophan in the feed is converted by rumen bacteria to a substance called 3-methylindole (3-MI) at a very high rate.
This 3-MI is absorbed through the rumen wall and circulated around the body. The 3-MI is toxic to the primary cells that line the interior surface of the lungs. Thus, as the high levels of 3-MI move from the rumen to the lungs more and more lung tissue is destroyed.
Differentials for:
- A group of adult suckler cows at grass which have developed respiratory signs over the last 48 hours. (2)
- Atopic rhinitis
- IBR (rare)
Differentials for:
- A single adult dairy cow which has developed respiratory signs over the last month (2)
- Diffuse fibrosing alveolitis
- Chronic suppurative pneumonia
Differentials for:
- A straw yard full of 3-10 month old barley beef bulls which have developed respiratory signs over the last 48 hours (1)
- Pneumonia
