Comparison of common antibiotic therapies for haemophilus pleuropneumonia in pigs.

Three experiments were done to evaluate some antibiotic therapies that are used commonly to treat pigs infected with Haemophilus pleuropneumoniae. Haemophilus-free piglets, 12 weeks of age, were challenged in a chamber with an aerosol of H. pleuropneumoniae serotype 1 and were medicated with antibiotics at various times before or after challenge. Antibiotic formulations which are commonly used to treat pneumonia in swine were used. They were chloramphenicol, penicillin, and a long-acting formulation of oxytetracycline given intramuscularly; and oxytetracycline, chloramphenicol and spiromycin (investigated as a potentially useful antibiotic) given in solution as the sole source of drinking water. Infection, disease (death, fever, gross lung lesions) and growth rate were measured in pigs following experimental challenge.The therapeutic effect of these antibiotic formulations was evaluated for prevention of the disease (52 pigs), treatment of acute disease (36 pigs), and treatment of chronic pneumonia (45 pigs). Injectable, long-acting oxytetracycline prevented all manifestations of disease (P<0.05) when given 24 hours before challenge. When treatment commenced immediately after the first signs of disease, each of the injected antibiotics reduced death rate (P<0.05), but they neither improved average daily gain nor reduced the incidence of infection and lung lesions. Chronically infected carrier pigs were produced by first immunizing them with a Haemophilus vaccine and then challenging them three weeks later. None of the treatments reduced the proportion of carriers of H. pleuropneumoniae.