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INTRODUCTION
Vertical (transplacental or transmammary) transmission of Toxoplasma gondii and its influence on the maintenance of T. gondii in natural populations has been a matter of debate (Johnson, 1997). Although it has long been known that congenital infection with T. gondii in mice and guinea pigs can occur while the dam is chronically infected (Remington et al. 1961), more recent studies have ignited debate as to whether vertical transmission occurs in other chronically infected animals. Recent studies have verified the high frequency of congenital transmission of T. gondii in chronically infected mice and it was proposed that congenital transmission in chronically infected mice can maintain T. gondii infection in wild mouse populations (Owen and Trees, 1998; Marshall et al. 2004). Recent data also suggest that T. gondii can be transmitted via successive vertical transmission within families of sheep (Morley et al. 2005).
Evidence for vertical transmission in marsupials to date is anecdotal (Boorman et al. 1977; Dubey et al. 1988), and the dynamics of vertical transmission in marsupials is poorly understood. However, considering the potential impact of toxoplasmosis in marsupials and the current efforts associated with wildlife conservation, it is important to examine the causes of infection of Australian marsupials with T. gondii. Australian marsupials are highly susceptible hosts for T. gondii and the parasite causes both chronic and acutely fatal infection (Beveridge, 1993). Information on the occurrence of vertical transmission in chronically infected marsupials may benefit captive breeding programmes of Australian marsupials by ensuring only T. gondii-free animals are bred, thereby improving animal health and assisting animal conservation and management.
In order to better understand T. gondii transmission in marsupials, we tested the dam and pouch young of western grey kangaroos (Macropus fuliginosus) and a woylie (Bettongia penicillata) for evidence of T. gondii infection. The MAT (modified agglutination test) and DAT (direct agglutination test) were used to test for anti-T. gondii IgM in sera of western grey kangaroo dams. Experimental studies in eastern grey kangaroos demonstrate that differences in titre between MAT and DAT are indicative of an IgM response and acute T. gondii infection (Johnson et al. 1989). Subsequent studies in a range of marsupial species have successfully used...