Kinetics of maternal immunity against rabies in fox cubs (Vulpes vulpes).
BACKGROUND
In previous experiments, it was demonstrated that maternal antibodies (maAb) against rabies in foxes (Vulpes vulpes) were transferred from the vixen to her offspring. However, data was lacking from cubs during the first three weeks post partum. Therefore, this complementary study was initiated.


METHODS
Blood samples (n = 281) were collected from 64 cubs (3 to 43 days old) whelped by 19 rabies-immune captive-bred vixens. Sera was collected up to six times from each cub. The samples were analysed by a fluorescence focus inhibition technique (RFFIT), and antibody titres (nAb) were expressed in IU/ml. The obtained data was pooled with previous data sets. Subsequently, a total of 499 serum samples from 249 cubs whelped by 54 rabies-immune vixens were fitted to a non-linear regression model.


RESULTS
The disappearance rate of maAb was independent of the vixens' nAb-titre. The maAb-titre of the cubs decreased exponentially with age and the half-life of the maAb was estimated to be 9.34 days. However, maAb of offspring whelped by vixens with high nAb-titres can be detected for longer in RFFIT than that of offspring whelped by vixens with relatively low nAb-titres. At a mean critical age of about 23 days post partum, maAb could no longer be distinguished from unspecific reactions in RFFIT depending on the amount of maAb transferred by the mother.


CONCLUSIONS
The amount of maAb cubs receive is directly proportional to the titre of the vixen and decreases exponentially with age below detectable levels in seroneutralisation tests at a relatively early age.
Müller
Thomas
T
Institute for epidemiological Diagnostics, Federal Research Centre for Virus Diseases of Animals, WHO Collaborating Centre for Rabies Surveillance and Research, D-16868 Wusterhausen, Germany. Thomas.Mueller@wus.bfav.de
Selhorst
Thomas
T
Schuster
Peter
P
Vos
Ad
A
Wenzel
Ulf
U
Neubert
Andreas
A
D000367:Age Factors; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D005589:Foxes / Q000276:immunology*; D006207:Half-Life; D007109:Immunity; D007700:Kinetics; D011818:Rabies / Q000276:immunology*
D000914:Antibodies, Viral