Influence of virus dose on experimental anaemia due to chicken anaemia agent

Intramuscular inoculation of susceptible 1-day-old chicks with graded doses of chicken anaemia agent (CAA) showed that the ability of CAA to produce anaemia was related to the dose of virus inoculated. Doses of CAA in excess of 10(5.75) TCID50 invariably produced anaemia but doses below 10(3.3) TCID50 produced anaemia in only a small proportion of inoculated chicks, even though most of these birds seroconverted to CAA and excreted enough virus to infect in-contact chicks. Virus spread from inoculated chicks to in-contact chicks was also less efficient using low doses of CAA. The implications of these findings for testing avian vaccines for contamination with CAA are discussed.