Mexico reported the first human case of H5N2 avian influenza, confirmed yesterday, after viewing the laboratory tests, also by the World Health Organization (WHO). This is a 59 year old man deceased in April, suffering from other illnesses.
The H5N2 avian flu in the Central American country was responsible for at least three recent outbreaks on the farms of poultry. It is not yet known how the victim contracted the flu, given that in her case there was no evidence of exposure to animals. Family members and contacts have tested negative for the various flu strains, but serological tests are underway to determine whether there has been contagion in the past.
The WHO specifies in a note that the case does not change the risk level for avian flu in the population, which is judged «Bass». Mexico specifies that the cause of the man’s death was not avian flu.
Human cases monitored
«Even in the future sporadic human cases of infection by avian viruses will be possible, given the high presence of this disease in the world – comments al Courier Calogero Terregino, Director of the European Reference Laboratory for Avian Influenza of the Experimental Zooprophylactic Institute of Venice (IZSVe) -. Human infections with H5N1, H5N6, and H5N8 have been reported previously. The fact that it’s now H5N2 It doesn’t change the situation that much».
According to the latest report from the European Food Safety Authority (EFSA) dated December 2023-March 2024 «human infections with avian influenza remain rare and no human-to-human infection was observed.” In addition to the three workers who fell ill in the United States (see later, ed), the report mentions five human infections from H5N1 on Cambodia (including one death) e seven in China (with two victims) from avian flu H5N6, H9N2 and H10N5 (first time of human contagion also for this strain).
The virus in dairy products
The H5N2 virus from the Mexican case is not present in Europe (and Italy) and is not the same strain of the virus called «highly pathogenic» H5N1 (called B3.13 by Department of Agriculture USA) which worries scientists and has affected (for the first time in history) cattle in the United States. This epidemic has reached 83 herds infected in 9 states. It is monitored with great attention due to the proximity of the animals to humans and because the virus was found (from analyzes carried out by Food and Drug Administration USA) in a large percentage of commercial dairy products, Texas wastewater, raw milk, and muscle tissue of a sick cow, which would suggest an underestimation of real cases due to the presence of probable ones asymptomatic subjects in livestock and perhaps even in humans.
Cats and 60 types of mammals
These data, together with the consideration that avian flu has infected numerous cats and mammals of 60 species (the last species are i micewith 11 specimens in New Mexico), have raised concerns that H5N1 could make the leap and become more widespread by finding (efficient) ways to be transmitted from human to humanthe prelude to the next one pandemic which many predict will be flu-type.
The peculiarity of the epidemic in the USA
H5N1 has already infected humans: three employees in the USA of dairy farms who came into direct contact with sick animals (two of them with conjunctivitis and one with conjunctivitis and cough). «In 20 years within its natural reservoir, represented by migratory birds, the H5N1 virus (subtype 2.3.4.4b) has traveled around the world – clarifies on the Courier Giovanni RezzaEpidemiologist, Professor of Hygiene at Vita-Salute San Raffaele University, Milan -. It has infected around 900 people (half of whom died), but fortunately for us it has not yet learned to transmit efficiently from person to person. The current concern derives from the extension of the outbreaks in the USA and from the fact that humans are frequently exposed to cows.”
In cattle, H5N1 has never been detected in Europe
The involvement of cattle, in fact, is new and a peculiarity of the US epidemic: «The genotype circulating in the United States is not present in Europe – he confirms Calogero Terregino -, because it derives from a mixing of genetic material that occurred with the viruses circulating in American avian fauna.”
What is the situation in Europe and Italy? H5N1 is widespread in the avian fauna of all continents (an ABC report on May 20 reported an avian flu epidemic in Antarctica), but, despite very high circulation in the years 2021-2022, currently in Europe «the overall number of “highly pathogenic” virus detections in birds was significantly higher inferior to previous years”, we read in the EFSA report. «In Italy we have only had six cases», declares Terregino and «in the spring-summer periods the migratory birds that carry the viruses return to the breeding sites, interrupting the transmission chain».
Furthermore, H5N1 has never been detected in cattle in Europeit seems not even in the past: «We have begun to carry out a verification activity with serological tests among cattle where the virus has circulated more in the past and they are also doing it in Germany and France with negative results for now», specifies Terregino.
The open questions
Regardless of what strain may be involved, «avian influenza represents one of the threats epidemiological conditions that require constant monitoring due to its pandemic potential – declares al Courier Alessandro VespignaniPhysics teacher at the Northeastern Universityfounding director of Northeastern Network Science Institute of Boston and President of the ISI Foundation, Institute for Scientific Exchange -. A element even more worrying it would be the notification of a increasing number of human infections. Even if there were not yet human-to-human transmission, a greater number of infections would indicate greater adaptation of the virus to the human organism.”
It is difficult to predict if it will happen, when and wherebut «the presence of the virus in the food chain due to the contagion of dairy cattle has required an increase in the level of epidemiological monitoring and control», specifies Vespignani.
Another uncertainty is what could be the degree of pathogenicity of avian flu once it has passed to humans, given that in birds it is a flu with serious and lethal outcomes. We don’t know: «It is difficult to predict the severity of the disease. For example, the virus that is now being transmitted among cattle it has less serious effects compared to those in birds”, says Vespignani.
It’s not like Covid: we are better prepared
«In the absence of certainties, we need to prepare for the worst case scenario but avoid it useless alarmism not based on evidence, improving surveillance systems and response capacity”, underlines Rezza.
The good news is that we would not be faced with the same situation experienced with Covid: «There are already ready vaccines which can be adapted quickly and current antiviral drugs appear to be effective”, assures Vespignani.
In Italy it is also active all year round national plan to combat avian flu: «Cases of mass mortality in wild birds or in poultry farms are reported», explains Terregino. Is there already any monitoring of cattle? «The trade associations have been invited to report any suspected cases and, in view of the winter, we are trying to include cattle among the species to be sampled when there are epidemiological links with the outbreaks”.
