Acute swine influenza outbreak in a large farm

In Poland, during January 1999 in a large farm producing 12 000 fatteners a nd 14 000 weaners a sudden massive infection of the respiratory tract, typi cal for swine influenza broke out successively in all groups of pigs. The o utbreak was detected first in 6-month-old fatteners. In a group of about 50 00 fatteners coughing, sneezing, lack of appetite and fever above 41 degree sC were observed. The next day similar symptoms appeared in weaners. Within a few day coughing and sneezing were observed in about 2400 three to four- week-old piglets and in the group of 300 one to three-day-old piglets. Some sows were also infected. Three days after the outbreak occurred, 60-80% of the animals exhibited symptoms of infection. A week later the clinical pic ture returned to normal. During pathological examination of dead animals, changes in the lungs typic al for swine influenza were observed. Gross lung lesions of swine influenza were found mainly in the apical and cardiac lobes. The altered lung areas were depressed and consolidated, dark red and sharply demarcated. Bronchial and mediastinal lymph nodes were also hyperemic and enlarged. In some case s interlobular oedema was evident. By serological examination, performed in pairs of sera taken during the outbreak and 4 weeks later, seroconversion to H1N1 reference strain was discovered. The titer of sera during the first examination was 1:32, while 4 weeks later the mean titer was higher (1:64) and in some samples (35%) it reached >1:128. Samples of lungs were used for the isolation of the virus in ten-day-old em brionated SPF chicken eggs. The isolates were characterised as H1N1, and th eir titer was estimated as 1:128 and 1:256.