In this latest video from MedCram, Dr. Seheult evaluates a new study that was just published that discusses the airborne nature of H5N1. Influenza in general is divided into types. There is an influenza type A, B, C, D. The bird flu that we are talking about H5N1 is a subtype of influenza A. There are other subtypes and these are in general characterized by avian, swine, or human. The H1N1 is a swine flu that has caused issues in the past.
How does analysis of wastewater help us?
One thing that can be determined from analysis of wastewater is to see if there is a type of influenza that is predominant during the season. It is important to note that the wastewater does not only contain human waste but also can contain waste from other animals. Findings from the wastewater do not necessarily indicate that this is actually causing any symptoms. There are graphs and charts that can be used to review emergency room visits, and review of positive tests for Influenza A can also be monitored for symptomatic infections.
Wastewater can provide some insight as to trends that are going on with current infections. Something that is really easy to determine from wastewater is whether something is from the influenza A virus subtype. In the recent release from the CDC’s national wastewater surveillance system which has over 600 sites with a variety of partners reporting Influenza A virus data to the CDC. It found that for the week ending in May 4, 2024, that there was one state that had high Influenza A virus levels and the week prior, ending April 27, 2024 it showed that there were three states that had high Influenza A levels. So what does that actually mean? It can mean a variety of things including that H5N1 is going up in animals.
So how do we evaluate whether this surge that is seen in wastewater is actually her, possibly reflecting that there is an increase in H5N1 and possibly having it become airborne. So from the human aspect we would be able to determine that something like this is happening. If we started to see an increase in hospitalizations with the H5N1 virus. Wastewater analysis is very sensitive, but it is not very specific.
Is H5N1 able to be airborne?
Dr. Seheult also goes on to discuss an article that was recently published in Nature. The study involves looking at minks. Minks are interesting because they have a very similar airway compared to humans that is easily subjected to the same infections that humans get. In this study they are looking at how likely it is and how pathogenic a H5N1 virus could be in humans using minks as a model.
This article looks at a particular strain (H5N1 clade 2.3.4.4b) that back in 2022 was causing infection amongst farmed minks and seals. The study used a ferret model which again is similar to human airways and they showed that an H5N1 isolate derived from mink transmits by direct contact to 75% of exposed ferrets and in airborne transmission studies, the virus transmits to 37.5% of contacts. For the direct contact transmission this is not new information because it is known that influenza virus spreads via droplets. What is new is that the study found that the virus can be aerosolized and spread airborne. The study reports that the sequence analysis showed no mutations with the transmission and that H5N1 has a low infectious dose and remains virulent at low doses. The isolate carries the adaptive mutation PB2T271A , and if this mutation is reversed, then there is a reduction in mortality in airborne transmission according to the study. The study goes on to report that this is the first report of aH5N1 clade 2.3.4.4b virus exhibiting direct contact in airborne transmissibility and ferrets and that these data can indicate a heightened pandemic potential of the panzootic H5N1 viruses and it is emphasized the study for the need for continued efforts to control any outbreaks of H5N1 . Some things to consider when interpreting the results of the study as per the authors is that the ferrets used in these studies had no pre-existing immunity to influenza, whereas the majority of humans have been exposed to H1N1 and H3N2 seasonal influenza viruses.
However, in the big scheme of things, it is important to monitor this as this does have the potential to have a large impact if a mutation occurs that allows for airborne transmission. For now, as of May 2024, the percentage of hospitalizations and emergency room visits from Influenza A is on the decline.
LINKS / REFERENCES:
Highly Pathogenic Avian Influenza (Ohio State University) | https://ohioline.osu.edu/factsheet/vm…
Risk assessment of a highly pathogenic H5N1 influenza virus from mink (Nature) | https://www.nature.com/articles/s4146…
How CDC is monitoring influenza data to better understand the current avian influenza A (H5N1) situation in people (CDC) | https://www.cdc.gov/flu/avianflu/h5-m…