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.
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.
