Impaired pulmonary gas exchange in ewes naturally infected by small lungworms.

Respiratory rate and blood gases were studied in 2 groups of ewes: the ewes in group 1 (9 ewes) acted as uninfected controls and those in group 2 (6 ewes) were infected with small lungworms (Muellerius, Cystocaulus, Protostrongylus and < 1% Neostrongylus). The respiratory rate was higher in infected (49 +/- 19 breath min-1) than in uninfected ewes. (20 +/- 3 breath min-1); it was strongly reduced after treatment (49 vs 22) in infected ewes. The partial carbon dioxide arterial tension (PCO2), total CO2 and HCO3- were higher (respectively 77 vs 39 mmHg, 38 vs 23 mmol-1 and 35 vs 23 mmol-1) in infected compared with uninfected ewes, whereas arterial pH (7.2 vs 7.4) and partial oxygen tension PO2 were lower (41 vs 81 mmHg) in infected ewes. Group 2 was treated with fenbendazole (at 15 mg kg-1 bodyweight) to eliminate small lungworms, and the respiratory rate and blood gases were measured 3 weeks after treatment. The values after treatment were similar to those in uninfected ewes. It is concluded that heavy infections by small lungworms in ewes impairs gas exchange, but that gas exchange improves rapidly after treatment.