In a rare case of female-to-female transmission, a 46-year-old woman in Texas has likely acquired HIV from her female partner, officials said on Thursday.

For six months, the two women had been in a monogamous sexual relationship, LiveScience reported.

According to a new case report by the Centers for Disease Control and Prevention, one of the women was HIV-positive and had not taken medication for the human immunodeficiency virus in two years.

According to LiveScience, HIV is the virus that causes the acquired immunodeficiency syndrome (AIDS).

Although the second woman had previously tested negative for HIV, she became infected with the virus during the relationship.

Other risks such as using injection drugs or having a heterosexual sexual relationship in 10 years could not be counted as factors that could have caused the virus since the woman refrained from participating in either of the two.

In previous cases, researchers have often been unable to determine if another factor, such as injection drug use, had caused the infection, prompting reports of HIV transmission between two women to be rare, LiveScience reported.

However, transmission of the virus between two women is theoretically possible since HIV can be present in vaginal fluid and menstrual blood, the researchers said.

"In the current case, the two women reported sexual practices that could have transmitted the virus: They had unprotected sex that involved oral contact with vaginal fluids, shared sex toys, had unprotected sex during menstruation and sometimes engaged in rough sex that induced bleeding," LiveScience reported. (The authors defined "unprotected sex" as any sexual activity without using barrier precautions.)

"Although rare, HIV transmission between [women who have sex with women] can occur," the report said.

"Discordant couples of any sex should know their HIV status and receive education and counseling services, especially instruction in safer sex practices," the CDC said. Discordant couples are those in which just one person is infected with HIV.

As control of the virus with HIV medications can reduce the risk of transmission to an uninfected partner, people with HIV should continue to receive medical care for their infections, the report said.

The report will be published tomorrow (March 14) in the CDC's Morbidity and Mortality Weekly Report, LiveScience reported.