Another type of oral sex is oro-anal sex, which is the stimulation of your partner's anus with your tongue or lips. Since the anus isn't the cleanest area of the body, this act might lead to the transfer of germs to the mouth. Some diseases that can occur are salmonella, Hepatitis A, B, and C, and worms.
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Bacterial infections transferred by oro-anal sex
As we’ve indicated above, contact between the mouth and the anus will probably result in the transfer of ‘bottom germs’ – though these will not necessarily cause disease.
Bowel organisms
There is evidence that the bowel organisms Salmonella, Shigella and Campylobacter can all be transmitted by oro-anal contact. These can all cause abdominal pain and diarrhoea. Infections with Salmonella and Shigella can occasionally be very serious.
Hepatitis A
Hepatitis A is a common viral infection that can cause jaundice and abdominal pain. It is not usually life-threatening, although sufferers can feel very ill.
The virus is often found in faeces in high concentrations and will almost inevitably be present on the apparently clean anal skin of infected individuals. It can be transmitted by oro-anal contact.
Several epidemic outbreaks have been reported among gay men, but heterosexual couples practising oro-anal contact are just as likely to be at risk.
Hepatitis B
Hepatitis B is a viral infection. It is common in hot countries and around the Mediterranean. It used to be rare in the UK, but rates are rising. It is particularly common among people who have had a previous sexually transmitted disease, and among drug users. It can cause a very serious, potentially fatal, liver disease and chronic liver damage. It is most commonly transmitted by inoculation of infected blood, by sharing needles for injection, needlestick injuries and the medical use of infected blood products. Virus particles are found in semen, stool and saliva, as well as blood. There is clear evidence that it can be transmitted through vaginal and anal intercourse, but it is unproven whether it can be transmitted through oral sex. Certainly, there is a theoretical risk of transmission.
Hepatitis C
Hepatitis C is a viral infection transmitted in a similar way to hepatitis B and often affects drug users. Some people with hepatitis C infection were infected with blood products, such as transfusions, prior to adequate screening procedures in the 1980s. There is limited evidence that hepatitis C may be transmissible through receptive oro-genital contact.
Worms
Threadworms, and probably other worms, can be transmitted by oro-anal contact or by fellatio after anal intercourse.
http://www.netdoctor.co.uk/menshealth/facts/infectionoralsex.htm
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