Dictyocaulosis in Dairy Cattle

            With the advent of management changes in the dairy industry from confinement to intense grazing, previously discarded diseases might recur.  One such disease to consider is dictyocaulosis, caused by the parasite Dictyocaulus viviparous.  This disease is predominantly a problem in areas which have a mild climate, a high rainfall and abundant permanent grass, and has been reported in several states including Indiana.  Dictyocaulosis is prevalent among calves and heifers during their first grazing season, while older animals in general are immune.  To attain and maintain this immunity the incidence of infection with this parasite has to be high.  Therefore, naïve cows or cows who did not maintain their immunity could become (re)infected with D. viviparous after being turned out on pasture. 

            D. viviparous has a direct life cycle.  The adult worms live in the trachea and bronchi and produce eggs containing fully developed larvae (ovo-viviparous).  These eggs are coughed up, swallowed, and hatch during their transport through their transport through the gastrointestinal tract.  These first stage larvae develop to infective third-stage larvae on the pasture.  Ingested L3 larvae penetrate the intestinal mucosa and mould to L4 larvae in the mesenteric lymph nodes.  These larvae subsequently travel via the lymph and blood to the lungs where they end up in the alveoli by breaking the capillaries.  The final molt occurs in the bronchioles and the emerging young adults move up the bronchi.  The pre-patent period is 3-4 weeks.

            Within an affected group of cattle, the clinical signs may vary.  A few animals are affected mildly; an intermittent cough, especially when exercised.  The majority of the animals are affected moderately; a frequent cough, tachypnea and increased lung sounds.  A few animals are affected severely; a deep harsh cough, tachypnea, dyspnea, open-mouth breathing, increased lung sounds, salivation, anorexia and sometimes mild pyrexia.

            Dictyocaulosis can be diagnosed by several techniques.  The Baermann sedimentation technique is a sensitive method to detect first stage larvae of D. viviparous in the feces.  Theselarvae are large, slow-moving and contain dark food granules.  Unfortunately, this technique is of no diagnostic value during the pre-patent infection.  A better diagnostic procedure during the pre-patent period is a transtracheal wash, in which eggs of D. viviparous, (immature) adults, eosinophils, neutrophils and macrophages may be observed.

            During post-mortem examination various gross changes can be noticed, depending on the stage of infection.  Atelectasis may be discerned due to the blockage of small bronchi and bronchioles, in response to the inflammatory response provoked by the presence of L4 larvae in the alveoli.  The adult worms produce an inflammation in the larger airways, which may result in consolidation of the dorsocaudal aspects of lung lobes.  In severe cases, an extensive pulmonary edema and interstitial emphysema may be noticed.  The adult worms can be observed either directly in the trachea and bronchi or after flushing the respiratory tract with water.  The adults are slender, thread-like worms up to 8 cm long.

            In conclusion, with the advent of intense grazing management in the dairy industry, dictyocaulosis needs to be included in the differential diagnosis for pneumonia in dairy cattle.  An accurate diagnosis of D. viviparous can be made based on the history of pasture grazing, clinical signs and the various diagnostic procedures.

-by Josef Steenbergen, Class of 1999

-edited by VictoriaOwiredu-Laast, DVM