“The H5n1 virus epidemic is already more widespread than previously thought”: what we know

Attention remains high over the avian influenza epidemic that has hit cattle farms in nine American states. In recent weeks the H5n1 virus has already caused a confirmed case in humans, and has been identified …

“The H5n1 virus epidemic is already more widespread than previously thought”: what we know

Attention remains high over the avian influenza epidemic that has hit cattle farms in nine American states. In recent weeks the H5n1 virus has already caused a confirmed case in humans, and has been identified in the milk of infected cows, prompting the American Centers for Disease Control and Prevention (CDC) to advise against the consumption of raw milk (i.e. not subjected to pasteurization, a process that should eliminate any viable virus) to minimize the risk of further infections among citizens. Now, research from the Baylor College of Medicine in Houston has also found the presence of viral particles in the wastewater of nine Texas towns, a discovery which, although it does not necessarily indicate that the virus is spreading in the population, confirms the suspicion that the epidemic within the American state's farms is more widespread than the official numbers say. With the risk – always present – that the high circulation favors the adaptation of the virus to our species, and could trigger a new pandemic.

The situation

The H5N1 virus, responsible for avian influenza, was identified for the first time in China in 1996, and worries experts because, although at the moment it is poorly capable of infecting our species, in the sporadic cases of human infections recorded in recent decades it has always shown a high mortality (above 50%, although the figure is probably inflated by the fact that to date only patients with severe forms of the disease have been tested).

The natural reservoir of the virus are migratory birds, which since at least 2003 have been supporting the circulation of an epidemic that has circled the planet several times, devastating poultry farms and wild bird populations all over the world. H5N1, in its variants defined as highly pathogenic, is a virus that causes very serious infections in birds, but is not particularly good at infecting mammals, and when it does (it has already been confirmed in at least 40 species), in many cases it results in mild symptoms or asymptomatic infections. The more a virus circulates, however, the more it has the opportunity to adapt to the organism of new hosts. Each new epidemic in mammals therefore risks producing new variants, which could sooner or later prove dangerous for our species too.

For this reason, the situation has been carefully followed by health authorities around the world for several weeks: since March the avian virus has already caused two infections in humans (one in Vietnam and one in the United States, in both cases linked to contagion from an infected animal, and not, fortunately, from human to human), and has led to an epidemic of infections among dairy cows on American farms. Animals of high zootechnical importance, which therefore have many opportunities to come into contact with humans, and thus transmit the virus to our species.


American health authorities are working to limit the true extent of the ongoing epidemic. In fact, avian flu in cattle causes banal symptoms, and in many cases asymptomatic infections, which make it difficult to identify with certainty all the herds involved. Furthermore, American farmers have not always been collaborative, and this has complicated the work of epidemiologists. However, sample analyzes carried out on milk present in supermarkets revealed widespread contamination by H5N1 viral particles, which although not considered dangerous for consumers (in pasteurized milk these are probably virus fragments inactivated by heat), demonstrates circulation in farms higher than that certified by animal tests.

Another form of indirect monitoring that can be implemented is the study of city wastewater, in which the viruses expelled in the feces of humans and (if the purification plants also collect waste from livestock farms) by animals are concentrated. The CDC is working on it, and has announced that in the next few days they will begin to disseminate the results of the analyzes online. Meanwhile, researchers from Baylor College have published the results of their monitoring, carried out in 10 Texas cities between March 4 and April 25 of this year: in 9 of the cities studied, the wastewater contained traces of the H5N1 virus, often at levels comparable to that of seasonal influenza.

The type of analysis carried out does not allow us to discern the origin of the virus (i.e. whether it comes from infected humans or animals), and the absence of confirmed cases in the human population of the cities suggests that the samples found are of animal origin. But it is still a confirmation of the high circulation that the avian virus is having at least in some areas of the States.

Are we ready for a new pandemic?

For this reason, many experts these days are asking us to pay attention to the initiatives necessary to be ready in case the avian flu turns into a new pandemic. An editorial in the Lancet cites in this regard the indications of the European Center for Disease Prevention and Control and the European Food Safety Authority: improving monitoring and sharing of data, checks and accurate management of fur animals and poultry, vaccination of livestock breeding and the human population at risk (reduces the chances of a double infection, which could facilitate the reassortment of the genetic material of the two viruses, and therefore the birth of a pathogenic variant for our species).

In this sense, these are measures that require strengthened collaboration between health authorities around the world (more desirable than ever after what we saw with Covid 19). On a national level, however, what could we do in Italy? The updated pandemic plan was announced in January by the government, but – although considered adequate by specialists – it is not yet operational. To be ready, and avoid the emergency management that characterized the latest pandemic, it is therefore time to hurry. “We should have an updated pandemic plan – declared Gianni Rezza, extraordinary professor of Hygiene at the Vita-Salute San Raffaele University in Milan and former Director General of Health Prevention at the Ministry of Health, to Adnkronos Salute. I believe it is ready, even if not yet approved, it seems to me. I hope it happens soon, clearly with adequate funding.”