Volume CXXXII, Number 4 October 4, 2002 f

Carrying more than your bag
JEFF BENSON, M.D.

Dear Dr Jeff: "I keep hearing about strep carriers, herpes carriers, hepatitis carriers, even meningitis carriers. What is this carrier business all about anyway? If carriers are really infected, why don't they get sick? And can they get other people sick?" D.F.

Dear D.G.: A great many "carrier" states have been identified, and they all involve our bodies' tolerating an otherwise infectious agent. The micro-organisms involved are able to find safe harbor in an immunologically protected site. Strep carriers, for instance, have tonsils that are chronically infected with streptococci. Carriers' immune systems are unable to clear the bacteria, but fortunately they don't get sick from them often. They can, of course, infect others, who might prove more susceptible. Antibiotics are only temporarily helpful, if at all, in suppressing the strep carrier state. Studies have shown carrier rates of up to 20 percent in most populations.
Some carrier states are actually fostered by antibiotic treatment. Salmonella, for example, which causes dysentery, are almost always cleared by your body's own defenses. If treated with antibiotics, however, the bacteria may end up in your gall bladder, beyond the reach of the medications and your immune system. You wouldn't be ill yourself, but you would be shedding the bacteria in your stool and putting others at risk.

All of the Herpes viruses remain in your body after the initial infection. You may have developed antibodies to the virus that will protect you from new exposures, but you are stuck with the original virus for life. It will remain dormant in nerve roots around your spinal cord, and reactivate periodically, travelling back down the nerve to your skin. Varicella, the Herpes virus which causes chicken pox, may lay dormant for decades, protected from your immune system in the "sanctuary" of your nerve roots. If you're unlucky, it will reactivate, and emerge as the painful "shingles" of Herpes Zoster. During a Zoster outbreak, you are highly contagious, but it would be chicken pox that you'd be transmitting to the non-immune.

In this country there are an estimated 1.5 million Hepatitis B carriers (and over 4 million Hepatitis C carriers.) Most hepatitis cases are acute and resolve with protective immunity. Up to 10 percent of Hepatitis B infections in the U.S. become chronic. For some reason, the virus is not cleared from your liver, and may remain present in varying amounts in your body fluids, especially blood. Most carriers are not particularly infectious. Commonly available blood tests can determine their degree of viral activity and infectivity.

Worldwide, a chronic carrier state for Hepatitis B is very common, and most infections are passed on in utero. Infant carrier rates in Asia, for instance, have been found as high as 90 percent. Chronic hepatitis usually remains dormant, but it can also activate, causing liver damage. Congenitally acquired chronic hepatitis, like some other congenital viral infections (e.g. Epstein Barr Virus), can cause cancers later in life.

Some STDs have very high asymptomatic carrier rates. You might be infected with something, have no signs or symptoms whatsoever, and yet be quite capable of unwittingly infecting someone else. Chlamydia, for instance, can be asymptomatic in 80 percent of infected women, and 40 percent of infected men. Human Papilloma Virus is thought to be harbored by 3 out of every 4 college students, and yet causes visible lesions in fewer than 1 percent.

At any given time, Meningococcus (the bacterial cause of the rare but fulminant kind of meningitis) resides harmlessly in the nasopharynxes of some 15 to 20 percent of the population. During an outbreak, however, carriage rates may rise as high as 75 percent in closed communities such as barracks and dormitories. None of the carriers themselves become ill with the infection. The problem is simply that having more of the bacteria around, increases the chances that someone susceptible will be exposed and fall ill. The meningitis vaccine will not protect you from becoming a carrier, but it will certainly help protect you from getting infected and sick from someone else's bacteria. Remember, though, that even with carrier rates of over 40 percent, the attack rate is still less than 0.00033 percent.

In fact, carrier states are really far more the rule than the exception. We are all carriers of vast populations of symbiotic micro-organisms, which generally are helpful, sometimes even essential. The total numbers of microbes in our bodies greatly exceed the total numbers of our own cells.
Obviously, carriage of pathogens is a different matter. What to do?
First, it makes a great deal of sense to get vaccinated against vaccine-preventable infections. Hepatitis B vaccination, for example, has been universally recommended for newborns since 1991, and adolescents since 1996, and remains readily available for all. If you never got yours, come in to see us at the Health Center. In fact, we offer a considerable array of vaccinations, and would be happy to discuss them all with you.

Second, protect yourself against possible infections. Familiarize yourself with safer sex guidelines and universal precautions around blood and body fluids. Be thoughtful, be prepared, and be careful.

Third, protect others against possible infections. Think about your own past exposures and possible carrier states. Get regular check-ups, and get tested if appropriate. We'll be glad to talk it through with you.

Last, but by no means least, take care of yourselves. Take good care of yourselves!

Jeff Benson, M.D.
Dudley Coe Health Center