Queens with no signs of disease may still be carrying Bordetella bronchiseptica (Bb). The stress of giving birth may cause these cats to pass Bb to their offspring.
In adult cats the signs of Bb infection are often relatively mild but the immune system of the new born kitten is poorly developed and may not be able to fight this infection. Kittens with Bb infection are more likely than adults to develop severe disease. Unlike most cases of 'cat flu' a most alarming aspect of Bb infection is that it can cause sudden death in young kittens. Such kittens are overwhelmed by infection and rapidly develop a fatal pneumonia.
Cats kept in catteries are most likely to carry Bb infection and so kittens obtained from breeding catteries and rescue shelters are particularly at risk. These kittens may also be more 'stressed' and, therefore, more likely to suffer from disease caused by Bb infection. Prevention of infection in young kittens requires that their mothers are adequately protected by intranasal vaccination. As soon as the kittens are 4 weeks of age they too can be protected by the same safe vaccination.
Kittens with Bb infection are more likely than adults to develop severe disease.