PCR for chlamydia - analysis technique

2023 Author: Alfred Shackley | [email protected]. Last modified: 2023-05-21 13:14

Modern medicine continues to develop towards the development of not only new methods of treatment, but also the diagnosis of diseases. Flawlessly accurate methods of "identifying" many of them were discovered a long time ago.

But most of them need revision and improvement due to the large number of diagnostic errors, restrictions on the stages at which they become recognizable for the doctor and equipment, and so on. Moreover, this applies to pathologies that have recently been discovered or isolated as an independent disease.

The shortcomings of modern diagnostic systems affect them especially clearly, making it difficult not only to study and collect statistics where it is necessary to collect new data in the first place, but also to create drugs against them.

Features of the disease

Chlamydia is just one of the infectious pathologies discovered relatively recently - less than 30 years ago. We are talking about the infection of the human body with protozoa - chlamydia.

In theory, it should have proceeded according to the type of trichomoniasis, since its causative agent, Trichomonas, is in many ways similar to chlamydia, but that was not the case.

It turned out that chlamydia is a much more secretive parasite than Trichomonas, but no less dangerous, especially for the reproductive function of the body.

And just their ability to masterly hide (in the literal sense of the word, since they reproduce exclusively inside cells, behind their membrane) from all classical diagnostic methods once strongly shifted the timing of the discovery of this pathology. In this sense, new diagnostic methods like PCR have become a real salvation for science, since without them the diagnosis of a number of diseases is either completely impossible or gives erroneous results much more often than we would like.

Informativeness of PCR

PCR or, more precisely, polymerase chain reaction is a laboratory diagnostic method that allows you to identify in biological samples taken from a patient, fragments of foreign DNA belonging to any pathogen. Usually there are not so many of them in the sample taken, which is the reason for the problem of standard diagnostics.

Insufficient sensitivity of devices allows you to see only whole, healthy microorganisms or antibodies to them, and even then if the equipment or the laboratory assistant does not lose sight of them. Well, and if not a single specimen of the pathogen has entered the sample, or antibodies to it are not produced by the immune system at all, the results of the analysis are false-negative.

But PCR is an analysis using a very accurate technique, since it allows you to isolate from the samples the smallest traces of foreign organisms in the form of fragments of their DNA, which, of course, is not similar to the DNA of the body's own cells. But since it is impossible to determine the type of pathogen only by these "pieces", the next stage of PCR is the accelerated multiplication of the found material. And only when its volume increases several thousand times, the doctor can already tell which disease-causing organism it belongs to.

As for chlamydia, this disease, which, by the way, is not only sexually transmitted (it can also be caught in a reservoir contaminated by them), without accurate diagnostic methods could not be detected at all. If this infection was more obvious in terms of symptoms or at least the immune response to it, it could have become known by the middle of the twentieth century.

But almost the only sure sign of it is persistent infertility, inexplicable by other factors. That is, the sign is very doubtful, because infertility can occur for hundreds of different reasons. As for antibodies, the immune defense does not produce them simply because it does not notice chlamydia.

These protozoa rarely reveal themselves, getting into the intercellular space, because they reproduce exclusively inside the cells. Chlamydia and Trichomonas are not able to independently extract energy from food, and for this they need "energy stations" of cells - mitochondria. And inside the cells, leukocytes have no access - only lymphocytes (lymph immune bodies) can penetrate there. Therefore, infection with them practically does not have the typical symptoms of infection - it does not give any pronounced itching, or inflammation, or a rise in temperature, etc.

But chlamydia sooner or later infect the ovaries in women and the testes in men, leading to the complete, so to speak, worthlessness of sperm, eggs and placenta. And even if a woman accidentally (in this case, it is really an accident) is lucky to become pregnant, it is unlikely that she will be able to bear the fetus for the entire prescribed period. In more than 80% of cases, this infection leads to miscarriages long before the term, even at 7 months, from which the doctors can still try to "grow" the baby in artificial conditions.

For all these reasons, chlamydia, as soon as it entered the official list of diseases, hastened to call it a "commercial" diagnosis. That is, a pathology so difficult to define that medicine often uses it to prescribe treatment (of course, not free) even to healthy, uninfected people. And in fact, although the option with a false prescription should not be completely ruled out, until recently this often happened not at all through the fault of a dishonest doctor, but because of diagnostic errors.

How to pass correctly

l PCR analysis?

So, PCR as a diagnostic method is valuable in that it allows you to accurately establish:

• the presence of pathogens in the body even before the first symptoms of the disease appear;
• the presence or absence of latent infections - that do not cause an immune response (the production of special antibodies) or do not give symptoms characteristic only of them;
• the type of pathogen, even if, when taking a sample for analysis, it was not possible to obtain a single complete copy of its DNA.

But the increased accuracy of PCR diagnostics is both its advantage and disadvantage. For example, it is clear that if something extraneous simply from the environment gets into the sample taken for PCR (and there are always enough bacteria in it), the result will also turn out to be false positive.

Likewise, PCR does not distinguish past infections from current ones. That is, if we have recently been ill with something, and in the sample taken from us, traces of the pathogen bodies already destroyed by immunity or antibiotics are found, we, again, will receive a false "response".

Therefore, PCR is not an analysis of feces, which is more convenient and logical to take at home, since the requirements for it are nominal. We can take a sample with a contaminated instrument or place it in a container that is far from sterile. Plus, you need to take into account that you can simply take it in the wrong place, and get the answer that we are completely healthy, although in fact this is far from the case.

So only a doctor has the right to take samples for PCR, in conditions of ideal sterility.

He does not require special preparation, and it makes sense to pass the analysis in the following cases:

• In the process of planning pregnancy in women - so that later there would be no complications and even a miscarriage;
• Already after the onset of pregnancy in a woman - so that the doctor can promptly put the expectant mother and her child under special control in connection with the discovery of chlamydia in her and the fact that with it, pregnancy is almost never problem-free;
• If a smear from the skin of the genitals contains impurities characteristic of sepsis, but does not contain its specific pathogens;
• If the smear contains many pathogens of various types, including opportunistic microflora. For this pathology, a weakening of the local immunity of the genital tract is typical, therefore, an overly "dirty" smear will certainly interest a gynecologist.

Usually, PCR analysis in women is carried out precisely by taking a smear from the vagina.

But no one seriously expects to find there directly the protozoa themselves, since they can live only in the cells of the body.

And the secretions contain a maximum of residual traces of their presence - "fragments" of DNA from chlamydia that died for some reason. Since chlamydia can be contracted not only through sexual contact, PCR is indicated for carrying out, including in children. For example, PCR analysis in children is taken if their parents were diagnosed with such a diagnosis, the child was born to an infected mother, or there is a suspicion that he simply picked it up in a public pool, shower, etc.

At the same time, the methodology for conducting it in children of any age is no different from that in adults. So, additional troubles here will be associated only with the treatment of chlamydia if the result is positive.