SDL: Lungworm in ruminants Flashcards
What causes parasitic bronchitis in ruminants?
Parasitic bronchitis is caused by infection with the nematode Dictyocaulus viviparous
(otherwise known as lungworm, husk, hoose)
What is the lifecycle of Dictyocaulus viviparous (lungworm)?
- The adults live in the bronchi and trachea of cattle
- Females lay eggs containing L1, which are coughed up and swallowed and hatch when passing through the intestinal tract, and are therefore released in the faeces
- In the optimum conditions, L1 develops to L3 within a week
- When ingested, L3 penetrate the intestinal wall, migrate via the blood and lymph and reach the lungs as L4
- Once L5, the larvae migrate up the bronchi to the URT
- PPP 3-4 weeks
- The larvae can overwinter, but only survive on pasture for a limited period
- The presence of arrested L5 stages in the respiratory tract enables the parasite to overwinter in the host and resume development in the spring.
What are the clinical signs of lungworm (parasitic bronchitis) in cattle?
- Coughing
- Classic stance: head extended and tongue protruding
- Increased rate and depth of respiration
- +/- Dyspnoea in more severe cases
- +/- mild pyrexia
- +/- limited nasal discharge
- Variable weight loss
- May be differentiated from IBR as it gets progressively worse
- +/- reduced milk yield
- Ocular discharge is NOT associated with lungworm, but is with IBR
What sample is required to carry out the Baermann test and what does it demonstrate?
- Sample required: 50g faeces
- Feature demonstrated: L1 larvae
What are the diagnostic considerations with the Baermann test?
Clinical signs may precede patency. Adult animals with reinfection syndrome do not show patent infections
What sample is required to carry out an ELISA (adult antigen) to test for lungworm, and what does it demonstrate?
- Sample required: Red top vacutainer (serum)
- Feature demonstrated: Antibodies to D.viviparus expressed as positive, inconclusive or negative
What are the diagnostic considerations with an ELISA test for lungworm?
Animals seroconvert four to six weeks post-infection. Antibody levels remain elevated for 3-4 months and most animals will be seronegative after winter housing. Indicates exposure to the parasite in that grazing season. Does not in itself confirm the presence of disease.
What sample is required for haematology when using it to diagnose lungworm, and what does it demonstrate?
- Sample required: Purple top vacutainer (EDTA)
- Feature demonstrated: Eosinophilia
How many animals should you sample in an outbreak of lungworm?
Ideally in case of outbreaks in adult cattle sample at least 6 affected animals.
Give example treatments that may be used for lungworm.
- Albendazole
- Febantel
- Oxfendazole
- Fenbendazole
- Eprinomectin
- Netobimin
Do cattle become immune to lungworm?
- Immunity develops very quickly in comparison to other parasitic diseases
- Immunity is not totally protective and can be overcome by overwhelming infection
- Immunity also falls over 12 months if not reinforced, leaving the animal with only partial or no protection
- With partial immunity, clinical signs are present but the parasite doesn’t go through the whole life cycle to patency
How can lungworm be controlled within herds?
- If a herd is completely free of infection, attempts to maintain this could be made 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
- Vaccination should be the foundation of any control strategy
ELISA blood sampling can be used to assess exposure to parasitic bronchitis for calves under any system. When is the best time to sample?
- It takes 4-6 weeks for antibody levels to rise following infection and these antibody levels only remain positive for 3-4 months
- Therefore the best time for sampling would be no later than 6 weeks post-housing
