It is apparent that these are not the same, e.g. here
What does “exposure” mean, and how does one test positive for it if one is not infected?
IANAD… but as I understand it they are doing nasal swabs and checking for Anthrax spores to test for exposure. Of course if you contracted the Anthrax disease they could culture live bacteria out of your body and verify the infection that way. Apparently it takes something like 20,000 spores of Anthrax to gurantee you will get the disease… so someone could have been exposed to the spores and easily not catch the disease… or so I understand.
Exposure means that at least one spore made its way into/onto your body. I think that they’re doing swabs of people’s nasal passages and culturing what they find there.
Infection means spores get in and begin reproducing faster than the body’s immune system can take care of them immediately. The number of spores required for pulmonary anthrax (the most severe type, gotten from breathing in spores) is about 8-10,000, in very very fine particles that can penetrate into the deepest part of the lungs. Since the spores will naturally grow in a sort of clumpy way, this making very fine particles is apparently the tough part if you’re out to grow your own anthrax stocks.
Exposure means that you have had some contact between your body, either internal, or external, and a viable spore or living cell of Bacillus anthracis. You are exposed to many such disease pathogens every day, although generally not that particular one.
Most of the time, exposure does not become an infection, and in many cases infection does not manifest as clinically identifiable disease. Your immune response, the virulence of the particular strain, the number of, and viability of the spores, and the route that the spores take all affect the likelihood of disease.
Swabbing your nose, and then culturing the swab can prove that you did get exposed to anthrax, but cannot prove that you did not. The same is true for swabbing your entire mailroom. There is no common test that will identify non-viable spores, which are far more abundant in most samples than viable ones. Antibody tests can prove that you have been infected by anthrax before, but not how recently, unless you are still sick, and multiple tests are done. The symptoms of anthrax are evidence that you have been infected, but by themselves are possibly indicative of many diseases.
If you have any disease symptoms, you should probably report them to your physician, although by the doctrine of the zebra his diagnosis might not be that you have anthrax, since even this week there are far fewer cases of anthrax than there are of other diseases with similar symptomology.
The CDC has [everything you want to know about Anthrax.](http://www.cdc.gov/ncidod/dbmd/diseaseinfo/anthrax_g.htm#What is anthrax)
Thanks for the responses, but I’m still a bit unclear. If exposure means that you have spores in your body then how is infection determined? GilaB says that
But how is this determined?
If you are INFECTED with anthrax, you will be sick. If you are EXPOSED BUT NOT INFECTED you will not be sick (from anthrax).
so the difference between being exposed and being infected is whether you’ve shown symptoms of the sickness?
Not necessarily showing symptoms. Infection means that there is anthrax living and reproducing in your body, even if they have not yet made you sick (but they would eventually).
An example of exposure without an infection would be if it got on your skin and you washed it off. Or if it got in your lungs but your immune system managed to kill it all.
So again, what is the difference between test results that show exposure but no infection, and test results that show infection?
Izzy,
There are a number of tests being done in various places around the country today. The most common is to culture a sample taken from a person or place. Culturing encourages viable spores, or living bacilli to grow and reproduce, when they have done so, you have proof that spores or bacilli were present. That constitutes exposure if the source was a person’s body. It represents possible exposure if it was taken from a place where people are.
Exposure means it was there, and so were you. If you live in an apartment building, and I dump anthrax spores into the lobby, you are not exposed, until you come into the lobby. Exposure is necessary, but not sufficient to produce infection. Exposure is certainly not just a yes no value, either. Anthrax requires a rather high level of exposure, as such things go. Tuleremia is occasionally induced in humans by a single organism. It takes thousands of Anthrax bacilli to do that.
Infection means that the bacilli have entered your body, after you have been exposed. Nasal swabs won’t determine that. They can only prove that you have been exposed, and cannot prove that you have not been exposed. Another variable that complicates this process is that a large percentage of most samples of anthrax spores are not viable. They are dead. They can’t grow, and are no threat. They don’t provide positive culture results, and they don’t make you sick. The only way to definitively prove infection with anthrax is to do blood cultures, or serum cultures, or wound cultures of lesions suspected of being related to anthrax, and then testing them for the presence of living bacilli.
Infection is not a simple yes no result either, nor is it a no chance death sentence if you are infected. One thing not mentioned much is that the immune system can, and does fight anthrax fairly well, without antibiotics. That is the reason that you hear that you have to inhale thousands of spores to be infected. The fact is that even one spore technically infects you, but you are not going to develop symptoms, and your antibody response will be very mild. You will not succumb to the disease. If you inhale ten thousand bacilli (which sounds like a lot, but would be a very small pile of powder if you saw it) which are all viable, and take them into your lungs then you will probably become infected.
That means that each of those ten thousand bacilli will set up shop making little bacilli, and your immune response is just not going to keep up. So, the numbers of anthrax bacilli increase rapidly. You begin to show symptoms. At that point, if you don’t start taking antibiotics you might well die. You might not, though, people have survived anthrax without medicine. But, you will be seriously ill, and if you are weakened by any other significant pulmonary dysfunction, your chances of surviving even with antibiotics get pretty small.
So, exposure is an opportunity to be infected. Infection is an opportunity for the bacillus to survive in your body. Serious illness is the success of that effort by a large number of those bacilli.
So, are we clear yet?
Tris
“Here Kitty, Kitty, Kitty.” ~ Erwin Schrodinger ~
Excellent explanation, Triskadecamus. How about explaining the interpretation of serological tests next (e.g., single high titer versus rising titers).
When you test for antibodies specific to a certain pathogen you are looking for the surface bonding sites that help the immune system identify the pathogen. The presence of a specific antigen means that the organism in question has been present in the host (person) at some time in the past. (The person has had some level of exposure to the pathogen, or to an immunization using the same surface bonding sites.)
The trouble is from a single test it is not possible to definitively determine whether this occurred recently, currently, or in the more distant past. The immune system continues producing antigens for long periods of time, often years. This is the reason that vaccines work. Since you want to begin treatment before the onset of serious symptoms, but you don’t want to needlessly risk the use of invasive treatments, often a second test is done after the presence of antibodies is discovered. If the new test indicates that the subsequent concentration of antigens is significantly greater than the first, the host (person) is probably actively infected, rather than immune from prior exposure.
A comparatively high number of people in the animal husbandry industry have tested positive for anthrax antibodies, although they have never had symptoms of, or been immunized for anthrax. The existence of such antibodies is often considered evidence of a prior “sub clinical” infection. They had anthrax, and never knew it.
Tris
“I believe in general in a dualism between facts and the ideas of those facts in human heads.” ~ George Santayana ~