Although AIDS is classified as an infectious disease,its transmission would seem to require sexual contact or direct entry of virus-infected blood or blood products into the circulation.There is a little evidence that AIDS is transmitted by any non-sexual form or person-to-person contact.
The first recognize case of AIDS occured in male homosexuals and this individuals constitute the main risk group(about three-quarters of reported cases occur in homosexual or bisexual males).
AIDS has been diagnosed in female sexual partners of affected males and in Africa the condition would seem to be spread predominantly by heterosexual intercorse,or by exposure to blood through insect bites or scarification.
A retrovirus known as human T-cells lympotropic virus type III(HTLV III) was identified as the probable cause of AIDS.This virus has been repeatedly isolated from the blood ,semen or saliva of affected individuals.
Although the HTLV-III virus has been identified as the probable agent causing AIDS and AIDS related illness,some individuals who have been exposed to ,or are infected by,the virus do not show an evidence of such disease.
This suggests either a long incubation period or the operation of the other factors during the incubation period,which together with the HTLV-III virus,precipitate the loss of cell-mediate immunity.
One possible factor is seminal fluid,which is thought to have a physiological role as an immunological agent after normal heterosexual intercourse.Repeated exposure to this immunosuppresive agent after intercourse,in conjunction with a virus-infected ejaculate,would certainly explain the high-risk category of homosexual or bisexual males.
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