According to the CDC study, a swine-derived influenza A virus has been detected in humans in Denmark

According to the CDC study, a swine-derived influenza A virus has been detected in humans in Denmark

In a recently published study in the Emerging infectious diseases Journal, researchers discovered a patient infected with swine influenza A virus (IAV) during routine surveillance at the National Influenza Center in Denmark. The influenza variant detected appeared to be different from all variants previously found in Denmark.

Lernen: Schwerer Fall einer zoonotischen Infektion beim Menschen mit dem vom Schwein stammenden Influenza-A-Virus, Dänemark, 2021. Bildnachweis: Liya Graphics/Shutterstock

background

According to official records, during the 2021-22 flu season in Denmark, 16,160 cases were due to the influenza A virus, predominantly the H3N2 subtype. There were no human cases of swine influenza virus during this period. Since the 2009 influenza A (H1N1) pandemic, there have been no reports of sustained human-to-human transmission of IAV. Additionally, there have been only sporadic reports of human infections with porcine IAVs. However, the zoonotic potential of IAVs is of great concern.

Case report

A young man in his 50s who works in a pig slaughterhouse in Denmark was admitted to hospital on November 24, 2021 after an acute onset of illness. He had dizziness at night, followed by chest pain, pain radiating to the left arm, diarrhea, and malaise, but no fever. The patient suffered repeated convulsions and required admission to the intensive care unit (ICU) and ventilation to stop the seizures and cope with falling oxygen levels.

He had no cardiovascular, renal, neurological or other impairments, including pneumonia, that could explain his sudden bout of severe illness. However, a throat swab sample from the patient tested positive for IAV. Remarkably, no other colleague at the patient's workplace reported the occurrence of influenza.

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With antiviral drugs (oseltamivir) and supportive care, the patient's clinical condition improved over the next two days, allowing him to be discharged from the hospital. The researchers sent the remaining sample material to the Danish National Influenza Center, which confirmed it was positive for the pandemic H1N1 strain.

Further analysis by whole genome sequencing revealed that its consensus sequence is of the H1N1 subtype. Notably, the virus was more similar to swine IAVs than to human influenza strains. The team uploaded this sequence to the Global Initiative to Share All Influenza Data (GISAID) database.

The sequence had no match to IAV sequences in GISAID, as revealed by searching with the Basic Local Alignment Search Tool (BLAST); However, a comparison with internal sequences of swine influenza viruses from Denmark showed high similarity to 2021 swine IAVs. This virus strain had several genetic and antigenic differences from other influenza A viruses detected in Denmark. Additionally, it exhibited poor reactogenicity to currently used human seasonal influenza vaccines. In addition, its phylogenetic analyzes revealed that most gene segments were similar to the H1N1 subtype. On the contrary, its neuraminidase and non-structural segments belonged to clade 1C of avian swine influenza A(H1N1), which occurs in Eurasia.

Conclusion

Previously, in Denmark, an elderly patient with comorbidities suffered a classic influenza-like illness (ILI). However, the case reported in this study was unique in that a previously healthy adult suffered a severe and sudden illness. Another striking observation was that this patient suffered from convulsions, which are rare in adults and typically accompanied by fever or encephalitis. Therefore, the infecting virus strains in these two cases are likely genetically different.

Detection of an IAV variant through routine surveillance highlighted the importance of continuous monitoring of human and porcine IAVs with zoonotic potential. In addition, the need to take immediate countermeasures for those who come into contact with pigs due to their profession and ILI experience was underlined.

Reference:

• Andersen KM, Vestergaard LS, Nissen JN, George SJ, Ryt-Hansen P, Hjulsager CK, et al. (2022). Schwerer Fall einer zoonotischen Infektion beim Menschen mit dem vom Schwein stammenden Influenza-A-Virus, Dänemark, 2021. Neu auftretende Infektionskrankheiten. doi: https://doi.org/10.3201/eid2812.220935 https://wwwnc.cdc.gov/eid/article/28/12/22-0935_article

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