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PARASITOS Y ENFERMEDADES PARASITARIAS
DE LOS ANIMALES DOMESTICOS


Dictyocaulus viviparus

Clinical signs

In herd outbreaks of parasitic bronchitis, a spectrum of clinical signs may be seen as illustrated in the following table.

Clinical sign

Mild infections

Moderate infections

Severe infections

Coughing Intermittent. More pronounced on exercise Frequent even at rest. A deep, harsh cough
Respiratory rate Often normal Tachypnea 40- 60/minute Severe tachypnea >80/minute
Lung auscultation Often normal, sometimes occasional squeaks Diaphragmatic lobes - pronounced squeaks and crackles. Diaphragmatic lobes - pronounced squeaks and crackles.
Other signs None Usually none Respiratory distress (dyspnea), gasping for air with head and neck outstretched. Salivation, loss of appetite, fever.

Clinical signs in parasitic bronchitis are associated with a progressively developing bronchitis and pneumonia - coughing, tachypnea, fever, anorexia, loss of weight and dyspnea. In adult cattle milk production will be affected. Respiratory distress   is characterized by animals assuming the "air hunger" position - head and neck held straight out horizontally with tongue protruded.

Diagnosis

The clinical signs of coughing in cattle either on pasture or with a recent history of grazing is usually strongly indicative of parasitic bronchitis due to Dictyocaulus viviparus.

dictyol1sm.gif (7115 bytes)Confirmation of the diagnosis comes from finding characteristic first stage larvae(L1s) in the feces of animals with patent infections by using a Baerman apparatus. The image on the right shows such a larva. They are 310-360 microns long and 16-19 microns wide and the latter two thirds of the body contains prominent dark brown food granules present in the intestinal cells.  Since D. viviparus is the only lungworm of cattle, finding these L1s in cattle feces is diagnostic. In a herd outbreak of suspected parasitic bronchitis repeat fecal samples should be taken and examined for L1s since clinical signs in heavy infections are usually first seen during the prepatent period. This is particularly true in cooler, temperate areas where heavily contaminated pastures with Dictyocaulus L3s may produce severe outbreaks in calves soon after turnout to pasture in the spring. At necropsy, adult worms may be easily seen in the bronchi of infected lungs.

The absence of L1s in the feces of animals with severe clinical signs of parasitic bronchitis usually means that these cattle are strongly immune but are undergoing a severe challenge infection, with large numbers of developing larvae being destroyed by the immune response.

    

 

Parásitos y enfermedades parasitarias de los animales domésticos
Dr. Colin Johnstone (autor principal)
Derechos de copia © Universidad de Pennsylvania