Why do viruses cross over from animals to humans?

I find this a fascinating question. We have many examples of this: Ebola, HIV, some “types” of tuberculosis, and multiple flu viruses.

ah1n1-bigWhen humans have close contact with animals the viruses that specifically attack one of them can cross over to the other and back again. As an HIV specialist, I remember a genetic timeline drawing showing that HIV went from apes to humans and back to apes! Apes bite and draw blood. Maybe the butchering process of the apes caused blood to enter broken human skin.

Aside from the hunting and butchering of animals causing mixing of fluids, many in poor countries have their animals in the same shelter as where the humans live all day long. Viruses mutate or change many, many times so that increases the chance that a virus may be able to enter the other host when it causes the first host to cough.

The sheer numbers are staggering. If you have a monoculture (a group of 1 specie such as a cornfield or a pig or turkey farm) then the ability for viral mutation is greatly increased. If you spray the cornfield with a poison, then it may kill 99.9% of the insects but 0.1% may survive—sounds small. But of a million insects, a thousand would survive due to mutations and pass this mutation down to their offspring.

Many of the viruses are quite lethal when they first emerge in humans from animals. Killing your host is a bad idea. Biology and evolution depends on an organism having offspring. So it is far more advantageous for the virus to not kill the host but keep it well enough to pass its offspring to other victims. Those viruses successful in this strategy win the evolutionary battle and have more offspring and infect more so they become more dominant and famous. A great book about this is Guns, Germs, and Steel, by Jared Diamond, which isn’t an easy read for non-scientists.
Cover your mouth when you cough, please.

My husband is now HIV+
Hi…I’m 30 years old. Last July my husband had a ganglion on his neck, I wanted him to go to the doctor, but he didn’t want to. One time, I discovered him looking at his anus using a mirror, we did argue until I agreed to look at his anus. I though it was hemorrhoids, we went to the doctor and it was warts or what the doctor called “HPV, human papilloma virus”, he also had syphilis and was HIV positive. It’s a nightmare. I was also examined, but I was ok, I was HIV negative. I have been doing the test again after 6 months and it’s still negative. We still live together, but we don’t have sex, we have an 8 years old daughter. What can I do?

Dear Lady,
I am grieved by your problem. I have run into many women who find out late that their husband has HIV and they do also. I have run into a few surprised husbands also. Sex outside of a relationship is something people do not want to talk about. Sometimes these bad decisions are a result of drinking alcohol.

After the emotions settle down, many couples can live together happily with forgiveness and a resolve to make the relationship work. Some have resumed sexual relations with condoms.

HIV doesn’t get transmitted every time there is contact. It is easier to catch HIV through the anus than the vagina, and much harder through the mouth. Sores on either or both parts involved will increase the risk.

HPV comments: HPV around the anus almost always means the person had sex there. HPV can be treated successfully over months. It is harder to resolve if the HIV is not controlled and the immune system has not recovered some. Sex can pull on a wart and cause a little bleeding causing easier transmission of HIV and, of course, the wart virus (HPV, human papilloma virus). If it is around the anus, there could be tiny ones around the penis outside of the area a condom covers. If no warts appear there for 6 months, then it is probably safe to assume there is no wart infection there. A female condom protects from warts (syphilis and herpes too) much better than a male condom. Syphilis is usually easy to cure.

A child can only be infected by being born to an HIV positive mother or having sex with an HIV positive person.

I encourage you to be strong. You will get through this. If you attend an HIV support group for heterosexuals, you will discover that many others have experienced the same thing.