The intestine of ferret--a possible site of influenza virus replication.

Anal virus shedding and stimulation of the immune response were observed in ferrets after oral and rectal administration of influenza A/Hongkong/1/68 (H3N2) virus. Despite of the low pH in the stomach, the virus had reached the intestines after oral administration and was found in high concentration in faeces and in mucosal cells lining the colon. Using immunofluorescent staining, the virus antigen was detected in cytoplasm of columnar epithelial cells. Virus replication also occurred in the respiratory tract, probably as result of inhalation of anally shedded virus. However, the virus replication in the lungs did not seem essential for virus isolation from the intestines. Taking into account the very short food passage time in ferrets the results could indicate the replication of influenza A/Hongkong/1/68 virus in the digestive tract of ferrets.

[Effect of low pH values on the infectivity and neuraminidase activity of human and animal strains of influenza virus type A]. / Uber den Einfluss niedriger pH-Werte auf die Infektiosität und Neuraminidaseaktivität menschlicher und tierischer Stämme des Influenzavirus Typ A.

The influence of acidic pH on the infectivity and neuraminidase activity of human, equine and avian type A influenza virus strains has been studied. Following exposure to pH 3 human and equine strains lost their infectivity completely, whereas all investigated strains of the subtypes Hav6N2 and Hav7Neq2 retained a certain amount of infectivity. In contrast to human and equine strains the avian strains retained also 38% of their original neuraminidase activity after acidic treatment. Partial retention of infectivity and the relative stability of the neuraminidase following exposure to acidic pH are supposed to be linked together in avian influenza virus strains implicating neuraminidases for their ability to prevent the aggregation of virions.