VERTICAL TRANSMISSION OF TOXOPLASMA-GONDII FROM CHRONICALLY INFECTED HOUSE (MUS MUSCULUS) AND FIELD (APODEMUS-SYLVATICUS) MICE DETERMINED BY POLYMERASE-CHAIN-REACTION

Captive-bred Mus musculus (house mice) and Apodemus sylvaticus (field mice) were each infected with 50 oocysts of Toxoplasma gondii M1 strai n per os and infection in them and their offspring was assessed by pol ymerase chain reaction (PCR) amplification of the T. gondii B1 gene in brain tissue and by serology, using the modified agglutination test ( MAT). The chronically infected female A. sylvaticus (n = 10) and M. mu sculus (n = 23) were mated at least 6 weeks after infection land subse quently to produce up to 6 litters) and their pups examined 3 weeks af ter weaning at 6 weeks of age. By PCR, in offspring of A. sylvaticus a nd M. musculus respectively, vertical transmission was demonstrated in 82.7% (n = 83) and 85.0% (n = 207) of all pups (N.S., P > 0.05), 95% (n = 21) and 100% (n = 30) of all litters (N.S., P > 0.05), with a mea n (+/- S.E.) proportion of each litter infected of 0.87 (0.06) and 0.8 6 (0.04) (N.S., P > 0.05). There was no change in any of these variabl es between first and subsequent litters. By serology, whilst MAT sugge sted 100% vertical transmission in A. sylvaticus, it under-estimated r ates of infection in offspring of M. musculus. A limited series of bio assays from M. musculus tissues confirmed the good correlation of PCR and the poor correlation of MAT with mouse inoculation. These results indicate that vertical transmission in A. sylvaticus and M. musculus i s extremely efficient and probably endures for the life of the breedin g female. This mechanism favours parasite transmission and dispersion by providing a potential reservoir of infection in hosts predated by t he cat.