Causative agent: Dictyocaulis hadweni, Dictyocaulus filaria, Dictyocaulus vivparus.
Dictyocaulis spp have been isolate from bison in Kansas (49), Montana (42), Oklahoma (43), and Alberta(19). Mature lungworm live in the bronchi of the lungs of infected animals. They produce eggs that hatch into larva, which are swallowed and passed out in the feces. The larva can survive overwinter on pasture. Dry, warm and sunny weather will destroy larva. Lungworm larvae that are consumed by bison on pasture pass through the wall of the bison’s intestinal tract and then enter the venous drainage of the intestine. Once in the circulatory system the larvae pass through the heart and lodge in the lung.

Clinical signs:
The clinical signs associated with lungworm in bison include increased respiratory rate, cough, slight nasal discharge, increased heart rate, mild fever (19).These clinical signs are difficult to recognize in bison on pasture. Often the first indication of clinical lungworm infection is dead bison (19). The disease is most commonly seen in late summer (19).

Postmortem findings:
Postmortem findings include pulmonary edema, emphysema and large quantities of bloody froth in the trachea and bronchi containing adult lungworm (19).

Fecal samples can be examined for the presence of lungworm larva. Routine flotation techniques will not detect lungworm larva. A Baerman sedimentation procedure must be performed on fecal samples. The ideal time for testing is the spring (April, May, June), to determine if any lungworm have been maintained in the herd over winter. In areas where lungworm has been a problem in previous years, bison should be tested in late July and August to determine if they are becoming infected while on pasture.

Ivermectin, oxfendazole, fenbendazole, albendazole, febantel, and levamisole have been used to treat lungworm infection in cattle (9).None of these products have been approved for use in bison.
Treatment should be instituted in late spring, just before the herd goes out to pasture. Reducing the worm load in bison at this time will result in a reduction in the number of eggs that are deposited on the pasture over the course of the summer. Pregnant cows, and cows with calves at foot will be difficult to handle during the spring of the year. If lungworm is suspected, oral fenbendazole can be provided in the feed, or in the salt.
If outbreaks occur in the summer, yearlings and two-year-olds can be rounded up and treated with ivermectin. Cows with calves at foot can be treated, on pasture, with fenbendazole in the salt. Routine treatment of bison in the late fall or early winter with ivermectin may not prevent the occurrence of clinical cases of lungworm. During the winter lungworm in the bronchi of cattle may enter a hyperbiotic state. When lungworm larva are in this state they stop growing, and may be resistant to agents that would otherwise kill them.

Programs to control lungworm in bison should include well timed administrations of anthelmintics as well as pasture management programs that are aimed at reducing the number of larva consumed by bison while on they are on pasture.
Since lungworm larva cannot withstand dry, sunny and warm conditions, contaminated pastures should not be grazed early in the spring. In areas where lungworm is endemic, pastures that have been grazed during the late summer should not be grazed until mid summer of the following year. Often even a few weeks of warm, dry weather will be enough to destroy most of the existing lungworm larva on the pasture. A simple two-pasture rotation system can be setup, in which one pasture is used for spring to early summer grazing and another is used for summer and fall grazing.
In endemic areas, bison should be treated with anthelmintics just prior to being turned out to pasture. If anthelmintics were to be used during the summer, it would be advantageous to administer them just before bison are moved from one pasture to another.
Fecal sampling should be part of any lungworm control program. Surveys of the herd should be done in early spring (March, April, May) to determine if bison in the herd are shedding lungworm larva. If they are, the herd can be treated at that time to reduce the number of larva shed onto the pasture. Fecal sampling should also be done during mid to late summer to predict whether clinical cases are impending. If so, treatment can be instituted.


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