Q: Does herpes show up right away or does it take a while before you know you have it? I had a blood test for herpes two years ago with my last pregnancy and it was negative. Now I'm pregnant again and I have a positive reading. Would that mean that I was infected with herpes sometime between the two babies? How often are the blood test results wrong?

A: There are two herpes simplex viruses, HSV type 1 and HSV type 2. Both are common. HSV-1 usually causes cold sores, and HSV-2 is the main cause of genital herpes. However, type 1 can cause genital sores and type 2 can sometimes cause cold sores.

HSV-2 is transmitted by sexual contact. Many people have the virus without knowing it, and people without symptoms can shed the virus and infect their sexual partners.

Typical symptoms of HSV-2 include small blisters and painful ulcers on the genitals, swollen lymph glands, and fever. Headache and urinary symptoms can occur. Symptoms usually develop two to seven days after infection, but some people have few or no symptoms.

The symptoms of genital herpes usually resolve in a week or two, but the virus lurks in the body and recurrent symptoms are very common. Antiviral medicines (acyclovir, valacyclovir, famciclovir) can shorten symptoms and prevent recurrences while the drug is being taken. However, these medicines cannot cure the infection, and recurrences may occur after treatment stops.

It’s hard to say what your blood tests mean. The older herpes blood tests were quite inaccurate, but the best of the new type-specific tests are about 95% reliable. Ask your doctor about the tests you’ve had – and since the result of your recent test seems surprising to you, ask to have it repeated in a top-notch lab.

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