Page 179 - The Veterinary Laboratory and Field Manual 3rd Edition

148 Susan C. Cork and Mani Lejeune

Figure 3.25 The life cycle of Dictyocaulus viviparous (bovine lungworm). The adult bovine lungworm is
found in the trachea and bronchi resulting in bronchitis and pneumonia with coughing and respiratory
distress. The disease associated with the parasite is known by many names, for example, husk, parasitic
pneumonia and dictyocauliasis, and typically affects young cattle in their first grazing season. The disease
process can be divided into four phases (1) penetration phase (days 2–7, ingested larvae make their way
to the lungs), (2) prepatent phase (days 8–25, larvae arrive in the lungs, signs of bronchitis develop and
heavily infected animals may die), (3) patent phase (days 26–60), adult worms produce eggs, lung tissue
fills with eosinophils, the extent of the lung damage depends on the number of worms present and the
immune response of the animal and (4) the post patent phase (days 61–90, recovery period as the immune
system clears the infection and debris is coughed up and swallowed). Complications may occur if second-
ary bacterial infection results in severe pneumonia. (A) The infective L3 stage is ingested and passes into
the intestinal tract. (B) The L4 stage develops and passes in the blood and lymph to reach the lungs. (C)
Adult worms mature in the lungs and eggs hatch, the L1 migrates to the trachea. The L1 is then coughed
up and swallowed to pass out in the faeces. Larvae and not worm eggs are passed in the faeces (see
Figure 3.7). (D) The prepatent period is 3–4 weeks (this is the time between ingestion of the infective
stage and the presence of larvae in the faeces), note that clinical signs may develop before the infection is
patent. (E) The L1 develops into the L2 and L3 in the environment, this takes about 5 days under optimal
conditions. The larvae are motile which allows them to move away from the faecal pat. In some cases,
a fungus (Pilobolus sp.) assists the transfer of larvae from the faecal pat to pasture or bedding material.
Illustration: Louis Wood.

• Oslerus osleri, Crenosoma vulpis (dogs) and Nematodes that live in other organs
Aelurostrongylus abstrusus (cats) can occur in
the respiratory tract of carnivores. A modified There are several other nematodes of veteri-
Baermann is preferred for detecting L1. nary importance that live in the kidneys (for
example, Stephanurus dentatus in pigs) and the
heart and blood vessels (for example, Dirofilaria

Vet Lab.indb 148 26/03/2019 10:25