11.   Both viruses are transmitted by mosquitos, who carry them in their salivary glands.

12.   A basic safety concern is that we still do not have enough information on whether viruses can be transmitted from pigs to humans.

13.   A rapid growth in the night-feeding Culex nigrapalpus mosquitoes that transmit the virus.

14.   A small number of women with low HIV levels transmitted the virus to their newborns.

15.   A vast majority do not know they are infected or that they can transmit the virus to others through sex or needle sharing.

16.   AIDS specialists say the practice can result in vaginal tears that help transmit the virus.

17.   But because such close contact is involved, scientists have difficulty in separating the role of touch and airborne particles in transmitting Ebola virus in such circumstances.

18.   But scientists are puzzled about exactly how the virus is transmitted.

19.   But such tests cannot tell who infected whom, nor how Acer might have transmitted the virus.

20.   But Weber and other experts said early diagnosis of HIV had important public health benefits because it helped infected individuals prevent transmitting the virus to their sex partners.