The human immune system has a particularly valuable property: It can form after surviving infection with a pathogen antibodies, prior to re-infection with the same disease. In some cases – in the case of measles, for example – to have survived of infection life-long immunity against the pathogen. In other cases, the protection lasts only for a shorter period of time, usually years.
Also, in the case of the novel Coronavirus Sars-CoV-2 experts believe that patients form after infection with the Virus the antibodies and thus the immunity. “We don’t know yet how long this lasts,” says Isabella Eckerle, head of the research group “Emerging Viruses” at the University hospital in Geneva. “If we assume an analogy to other coronaviruses, one might assume a period of a few years: In the case of Sars, for example, antibodies are three-to-five-years undetectable. It is not so that you can become infected after a few days or weeks with exactly the same Virus again.”
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For the confusion last week, had taken care of a case in Japan in which a former convalescent Covid-19-patient’s again positive to the Virus was tested. The woman had recovered first, apparently, of the infection, but severe symptoms developed. Doctors of the hospital in Wuhan, were published last Thursday in the journal “Jama” a short Report that points in a similar direction to report on a further four, apparently convalescent patients who had been initially classified as healthy and, in the case where the pathogen is in the connection again could be detected. Than healthy patients whose symptoms have disappeared, and in which the Virus in two consecutive Tests with at least one day a distance of not more could be detected, therefore, apply.
For experts, these cases are no big Surprise and no reason for concern. “We are aware of such findings from other respiratory disease-causing viruses, such as influenza virus,” said researcher Isabella Eckerle. “Are towards the end of the disease, if the Patient is already healthy again, to find the remains of the Virus in the respiratory tract.”
Test method fails already in the genome
You have to be very careful with that, such test results as reinfection – interpret so as to re – infection with the pathogen, not least because the testing methods used were “extremely sensitive”, says the expert. “We will test the genetic material on the existing Virus. So long as remnants of the Virus are present, the Test remains positive, although the Virus may be infectious.”
Mundane reasons can ensure that a Test is sometimes positive, sometimes negative. The Material for the Test is obtained by a swab in the nasopharynx, so Eckerle. The procedure is uncomfortable for the patient. “Should approach the appropriate personnel, for example, to timid, can be tested a sample once in a negative. The smear test is carried out correctly, according to it, the next Time, again the Virus.”
The Coronavirus is detected by means of PCR method. This is a molecular biological Test, which looks for viral genetic material. “Viral RNA can often be long detected when the infectious Virus is gone yet,” stresses Florian Krammer, a Professor of Vaccinology in New York. “It happens in the case of measles, but also in the case of Zika and Ebola.” In the case of the positively tested patients that would be: The Coronavirus would be still detectable, the recovering patients with a high probability but not infectious.
But as the second Disease flare-up in the Japanese patient can then be explained? The woman had recovered first, but then again, severe symptoms developed. In the four patients in the Jama report, this was after the appearance of recovery has not been observed. Three of them were only suffering mild, the fourth Patient had shown no symptoms.
Virus is added to Virus
According to Eckerle, Co-infections, may provide for the peculiarities of the Japanese case. “Data available now, that Covid-19 can be associated with other virus infections, and patients are then tested, for example, two virus positive. The Test to Sars-CoV-2 would be due to the remaining genetic information continue to be positive, the symptoms come from a new, different disease.”
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Christian Drosten, Director of the Institute for Virology at the Charité hospital in Berlin, is sceptical about the case reports. Especially the findings of the Jama report was not, in his opinion, is not convincing at all. The detection with the PCR method could vary after the first symptom week, significantly, stresses the Drosten. “Sometimes positive, sometimes negative, regardless of the symptoms.” The scientific basis of the publication is porous,” says Drosten was”. “To say the least”.
The detection with the PCR-method also has an impact on when Covid-19-patients must be from the hospitals dismissed. It was “pragmatic and sensible”, to go with the assessment of the patient according to the clinical symptoms, says antivirus researcher Isabella Eckerle. “You should have a lot of patients in the clinics, it is counterproductive to keep the healthier patients while in the hospitals, until the Tests prove negative.”
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