A work published in ‘Eurosurveillance’ explains that it would be environmental pollution. This is genetic material from the virus present in dust that enters the airways of workers
Last October, the Castilla-La Mancha health ministry reported that a worker at a poultry farm in Guadalajara had tested positive for H5N1 bird flu, a case to which a second case was added days later, reported by the WHO.
Both workers were the first cases in Spain of a jump of this avian infection in humans, which strengthened surveillance and epidemiological controls on the transmission of zoonotic diseases, also taking into account the increase in outbreaks that have occurred in other countries and in different species occurred. animals.
A new analysis of the two asymptomatic cases of bird flu H5N1 discovered in Spain in autumn 2022 has confirmed the theory that there were no real infections, but that both were in contact with genetic material from the virus spreading in the environment. found. Spain will change the protocols, according to the analysis published in Eurosurveillance.
The work, which has had the collaboration of animal health and public health authorities, sheds light on the known cases of detection of highly pathogenic H5N1 bird flu viruses in humans in Spain.
The authors report that both workers tested positive for the detection of genetic material of this virus in nasopharyngeal swabs during the initial assessment of all workers on the farm or who had been involved in slaughtering the birds and subsequent cleaning. It also indicates that they showed no symptoms, all subsequent tests came back negative, and they did not develop antibodies to the virus.
Absence of antibodies
According to the authors, “the absence of symptoms in both workers, together with the laboratory results, which showed a very low viral load and the absence of specific H5 antibodies against the A/H5 virus, suggested that the positive PCR results were the most probably due to environmental contamination”, conclusions which coincide with previous health reports indicating that the positive results were the result of “a context of high presence of the virus on the affected farm” and that he therefore could not rule out that more cases could be to arise.
Ursula Höfle, a researcher at the Institute for Research in Hunting Resources IREC (CSIC-UCLM-JCCLM) of the University of Castilla-La Mancha points out to SMC Spain that the data from the study concludes that it was not an infection as such, which would mean “the entry of the virus into the cells of the airways and replication and amplification, and this in turn would have caused a reaction in people’s antibodies”
They assume, says this professional, “that what has been detected is rather a possible environmental contaminant – genetic material from the virus present in dust deposited in workers’ respiratory tracts -, and that in order not to cause a false alarm, it is necessary to use surveillance protocols that only detect real infections as such.
This would mean that screening exposed workers on affected farms is a measure that would improve the early detection of zoonotic infections. But the experts warn that the right conditions for conducting the tests to avoid contamination and the criteria for interpreting the results must be taken into account.
According to Elisa Pérez, of the National Institute for Agricultural and Food Research and Technology (INIA-CSIC), “it had already been noted on many occasions that these two positive cases in the workers of the Guadalajara farm may have been false positives,” said she. SMC told this researcher who had previously suggested the possibility that it was an infection of the nasal mucosa rather than an active infection.
Low capacity in humans
Gustavo del Real, also of INIA, spoke along the same lines, telling SMC that “the outcome of this viral outbreak demonstrates that for now this H5N1 virus has little capacity to efficiently transmit to humans and that it is continuously and systematically occurring in wild and domestic birds. “, an idea refuted by Höfle, who points out that Eurosurveillance’s work is consistent with the data confirming that “to date there is no adaptation of the virus to infect humans or to transmit between humans”, and emphasizes also the importance of distinguishing between the detection of genetic material of a pathogen and the confirmation of a true infection.
“It is very important not to confuse the detection of genetic material with an infection. We have become accustomed to the polymerase chain reaction (PCR) as a diagnostic tool, especially with covid-19.”
However, and in her opinion, a positive PCR by itself does not really confirm that the specific fragment of the genetic material we are looking for is present”, this expert also insists that once exposure is confirmed, “the acceptance of the need to follow biosecurity and personal protection measures for all farm workers,” concludes Höfle.
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