Dictyocaulus spp

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Adults Dictyocaulus spp in the lung of a 3 year old cow

Dictyocaulus spp are a parasitic lungworm of cattle that cause bronchitis and pneumonia ('parasitic pneumonia', 'hoose pneumonia') in cattle worldwide. It is one of the most important parasites in grazing cattle, and outbreaks result not only in clinical disease but also economic losses.

A number of Dictyocaulus species are known to infect cattle, including:

  • Dictyocaulus viviparus

Life cycle

Adult females in the bronchi lay larvated eggs that hatch either in the bronchi. The eggs are laid in the lungs and may hatch there or in the intestine (after being coughed up and swallowed). First stage larva emerge from the cow in the feces. The larvae reach the ensheathed infectious third-stage (L3) by about 4 days. L3 are either washed out of the fecal pads or expelled from the fecal pad when they happen to be on a sporangium of the fungus Pilobolus which explodes to release its spores. On pasture the L3 will migrate up grass blades and be eaten by the cow. The L3 exsheath in the small intestine, penetrate the bowel wall and molt to L4 in the mesenteric lymph nodes. They then migrate to the lungs via the thoracic duct. They reach the lungs about 2 weeks after they were ingested. They molt to the adult stage at about 15 days of infection and begin laying eggs around 22 days post-infection (PI). The adult worms begin to be expelled at about 50 days PI, and most are gone by 70 days PI. A few adults or late stage larvae may over winter in the lungs of an infected animal and L3 may over winter on pasture by migrating down into the root mat and soil.

Clinical signs

Weight loss, intermittent afrebrile cough and failure to thrive are common signs in early stages of the disease. In the prepatent phase, D. viviparus causes blockage of bronchioles, resulting in obstruction of the airways and collapse of alveoli distal to the block. Sudden deaths have been reported due to severe interstitial emphysema. In dairy herds, milk yield noticeably drops in affected cattle.

In chronic cases, a nonsuppurative, eosinophilic, granulomatous pneumonia is observed, complicated by interstitial emphysema, pulmonary edema, and secondary bacterial infection.

Diagnosis

Diagnosis is based on isolation of nematode eggs in feces or ELISA detection of antigens in bovine milk[1] or serum samples[2].

Treatment

In acute cases, broad-spectrum antibiotics are recommended to minimise secondary bacterial infections.

Treatment is effective using various anthelmintic preparations. These include the benzimidazoles (fenbendazole, oxfendazole, and albendazole) and macrocyclic lactones (ivermectin, doramectin, eprinomectin, and moxidectin). Levamisole is used in cattle but treatment may need to be repeated 2 weeks later because it is less effective against larvae during the early stages.

Vaccination strategies are also indicated for lungworm-naïve animals when introduced into an adult herd[3].

Single mass-treatment before the grazing season may be useful to break a series of annual lungworm outbreaks. However, it is not a secure method to prevent parasitic bronchitis for more than one year[4].

References

  1. Ploeger HW et al (2012) The value of a bulk-tank milk ELISA and individual serological and faecal examination for diagnosing (sub)clinical Dictyocaulus viviparus infection in dairy cows. Vet Parasitol 184(2-4):168-179
  2. Goździk K et al (2012) Optimization of in-house ELISA based on recombinant major sperm protein (rMSP) of Dictyocaulus viviparus for the detection of lungworm infection in cattle. Res Vet Sci 93(2):813-818
  3. Holzhauer M et al (2011) Lungworm outbreaks in adult dairy cows: estimating economic losses and lessons to be learned. Vet Rec 169(19):494
  4. Ploeger HW & Holzhauer (2012) Failure to eradicate the lungworm Dictyocaulus viviparus on dairy farms by a single mass-treatment before turnout. Vet Parasitol 185(2-4):335-338