| Summary: | "The protozoan Neospora caninum is a common cause of bovine abortion, and can also cause disease in dogs. Several aspects regarding its transmission were investigated. Dogs fed experimentally infected calf tissues shed significantly greater numbers of N. caninum oocysts than dogs fed experimentally infected mouse carcasses. As few as 300 oocysts were used to infect calves, and N. caninum was cyclically transmitted between dogs and cattle. These data indicate that a single dog can potentially infect hundreds or thousands of cattle. Pregnant cows were orally administered N. caninum oocysts, to investigate the occurrence of transplacental infection and abortion, and 17 of 19 cows became infected, while 8 negative control cows remained uninfected (p < 0.001). Transplacental infection occurred in 6 fetuses, and 1 of these aborted. All 6 cows with infected offspring had continuously rising antibody titers, whereas 10 of 11 infected cows with uninfected offspring had falling titers after an early apex. The risk of transplacental infection was increased by later exposure times and increasing numbers of oocysts (p < 0.01 for the 2 combined variables). The internal transcribed 1 (ITS1) region of rDNA was investigated in 6 strains of N. caninum, and intra- and inter-strain variations were observed. Coyotes (Canis latrans) were shown to be another definitive host of the parasite, which shed oocysts after ingesting infected calves. Tissues from naturally infected white-tailed deer were fed to dogs, and oocysts produced were identified as N. caninum using PCR. These oocysts induced infection in a calf after oral administration. The ITS1 sequence of the new strain (""NC-deer1"") is identical to N. caninum from domestic animals, indicating that transmission between wild and domestic animals is not rare. In addition, N. caninum antibodies were detected in 39% of gray wolves (Canis lupus ), 11% of coyotes, 26% of white-tailed deer, and 13% of moose ( Alces alces). These results are consistent with a sylvatic cycle of N. ...
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