Ruminant lungworms
Jacob Avula, Tim Pasma
Animal Health Laboratory, University of Guelph, Guelph, ON
AHL Newsletter 2024;28(2):9.
Sheep and goats are parasitized by 3 species of lungworms; namely, Dictyocaulus filaria, Muellerius capillaris and Protostrongylus rufescence. Of these, only Muellerius capillaris has been isolated from cases here in AHL. To date, there have been 60 positive cases, and a highly significant number of them were from goats.
Muellerius capillaris are very thin worms found in alveoli and coiled in pulmonary parenchyma, producing greyish nodules. Eggs laid by adult female worms hatch and the first stage larva (L1) crawl up the bronchi, reach the throat where they are swallowed and then passed out in the feces. These larvae need a snail or slug (intermediate host) for further development. Once they enter the snail, the larvae develop into the infective third stage. When the sheep/goat ingest these snails, the infective larvae are released in the gastrointestinal tract, and then start migrating to their site of predilection - the lung – where they grow to the adult stage.
The main clinical signs of lungworm infection in sheep or goats are dyspnea and persistent cough. They may also have reduced weight gains. Diagnosis is based on clinical signs and isolation of first stage larvae in feces using the Baermann test. The larvae measure 300-320 um and are easily identified by the presence of a kinked tail with accessory spine towards the end of the tail (Fig. 1). A time-series observation was made on Muellerius capillaris larval recovery using the Baermann apparatus at different time points after storing a positive sample in the refrigerator. The sample was set up in the Baermann on days 6, 13, 22 and 29 after collection, and larvae were successfully recovered at all time points.
Cattle are parasitized by only one species of lungworm; namely, Dictyocaulus viviparous. To date, 6 positive cases have been recorded at AHL. These worms are larger (4-8 cm) than Muellerius and live in smaller bronchi. The ovoviviparous eggs laid by the female worms are coughed up, swallowed and hatch as they move through the gastrointestinal tract. The L1 are passed out in feces where they develop to the infective third stage. Cattle eat the larvae while grazing, which then move through the intestinal wall and finally reach lungs, settling in bronchi.
The main clinical signs of infection are dyspnea, coughing with extended neck, nasal discharge and weight loss. The coughing sounds like a dry non-productive exhalation (‘husk’).
Diagnosis is based on clinical signs and harvesting of L1 in feces using the Baermann apparatus. The larvae measure 300-360 um and have characteristic dark food granules in the intestinal cells (Fig. 2). A time-series observation was made on Dictyocaulus viviparus larval recovery using the Baermann apparatus at different time points after storing the positive sample in the refrigerator. The sample was set up in the Baermann on days 3, 11 and 13 after collection, and larvae were successfully recovered at all time points.
A negative fecal result is not proof of absence of the disease, especially in adult cattle with mild symptoms in which larvae are rarely found. For Baermann testing (AHL test code “ Baer”), at least 15-20 g of fresh feces for sheep, and 40-50 g for cattle are required. AHL
Figure 1: L1 of Muellerius capillaris with kinked tail and accessory spine.
Figure 2. L1 of Dictyocaulus viviparus shows dark food granules in the intestinal cells.
References
1. Helminths, arthropods and protozoa of domesticated animals. 7th ed. Soulsby EJL, ed. Bailliere Tindal, 1982: 262-274.
2. Veterinary clinical parasitology. 8th ed. Conboy GA, Zajac AM, eds. Wiley-Blackwell, 2012: 104-107.
3. Lungworm in cattle: https://wormboss.com.au/roundworms/lungworm