Vertical Transmission of a Murine Retrovirus, ts1

Mechanism of maternal retroviral transmission remains an unsolved problem. The current investigation is a part of our ongoing research on vertical transmission of MoMuLV-TB ts1 in BALB/c mice. A total of 270 adult mice and 165 fetuses were used. Forty-four experimental mice were injected with 0.1 mL of 4.0 × 10 6 ffu/mL of ts1 virus at 72 h after birth; 24 controls were injected with DMEM. Almost half of the females went through two rounds of pregnancies. In the first round, 135 experimental and 57 control pups were produced. Forty-three experimental and 20 control pups were followed until they developed clinical symptoms. The second round of pregnancy produced a total of 46 mid-gestational and 119 full-term fetuses. PCR, and light and electron microscopy were performed to evaluate viral transmission. Overall, 99% vertical transmission occurred in pups of infected mothers. Twelve percent of mid-gestational and 39% full-term fetuses were PCR positive. We have established that, if mothers are infected with ts1 virus at 72 h after birth, then nearly 100% vertical transmission occurs, via in utero , intrapartum, or breast milk. Thirty-nine percent transmission occurred in utero alone. This is an excellent model to study the transplacental and post-gestational transmission of retroviruses, such as ts1.