#17,220
In addition to its aggressive, global spread in migratory birds, the ability of HPAI H5N1 to spill over into mammals is viewed as a worrisome sign that clade 2.3.4.4b H5Nx viruses may be moving closer to becoming a public health threat.
Ten days ago, we looked at a report in WOAH: France Reports Cat Infected With Avian H5N1, involving a cat on a poultry farm in Western France. In the United States, the USDA maintains a growing list of mammalian species affected.
Most are carnivores, or scavengers, who likely fed on an infected bird carcass. Foxes have been the most commonly reported terrestrial mammal infected.
Not quite two weeks ago, in WHO Rapid Risk Assessment on A(H5N1) clade 2.3.4.4b viruses (Includes 2 Severe/Fatal Human Infections), we learned of 2 severe (1 being fatal) human infections with this virus. The report also stated:
For now, their assessment is `. . . the risk of infection for humans remains low and no sustained human-to-human transmission has been reported', but the virus continues to evolve.Additionally, continuous infection in wild and migratory birds has led to multiple separate incursions in domestic species. These circumstances have led to increased opportunities to generate multiple genotypes with varied clinical signs. Some of the recent viruses have caused severe infections with neurological signs in mammals.[5]
Three weeks ago, in the ECDC/EFSA Avian influenza overview September – December 2022 we learned that 8 new genotypes have appeared in Europe over the past 3 months, while in November we saw several new genotypes described in North America.
While we've seen reports of mammalian infection with HPAI H5N1 from a number of countries, today Denmark's SSI reports their first detection in multiple dead foxes collected in the first half of 2022 (translated excerpts below).
Highly pathogenic avian influenza has been detected in Danish foxes for the first time
Highly pathogenic avian influenza H5N1 has been detected in samples from 4 wild Danish foxes. The foxes have presumably died as a result of infection with highly pathogenic bird flu. The foxes have been autopsied by the Pathology Service at the University of Copenhagen and influenza has been detected by analyzes carried out at the Statens Serum Institut. The tests for influenza have been carried out in connection with the Danish Food and Drug Administration's monitoring of highly pathogenic avian influenza in wild birds and mammals.
Last edited on January 9, 2023
The foxes have been found dead just outside the fox pits
Three fox puppies that have tested positive for highly pathogenic bird flu have been found dead outside a fox pit at Odder. The fox cubs have been seen alive, and one of them was photographed on 25 April 2022. The cubs were subsequently found dead on 28 April 2022, together with the carcass of a duck, which was presumably a black duck. Based on fur and weight, the 3 fox puppies are estimated to be around 4-5 weeks old. This means that they are puppies that have just started to come out of the grave. Samples could not be taken from the bird because the organs and trachea were eaten away. The necropsy findings were similar in all puppies. The carcasses were found to be of normal size and the lungs were found to have dark areas with thickening and blood accumulation. The puppies also had signs of fatty liver, in that the livers were enlarged, light in color and with reduced texture. Stomach and intestine were found with sparse contents.
The last fox - an adult male fox - was found dead on 17 January 2022. This fox was just outside a fox pit on Djursland. The fox was very emaciated. As with the puppies, the male fox had signs of pneumonia and fluid in the chest cavity. The stomach was empty. The intestinal tract was found with very sparse contents of inconspicuous appearance and consistency.
Surveillance of influenza in wild mammals
In connection with the influenza surveillance, a total of 19 foxes have been investigated that died in the period January-November 2022. Of these foxes, 8 were found to be ill and euthanized or died (fallen wild), while the remaining 11 were killed in connection with hunting or regulation. In addition, a smaller number of other predators (two ferrets, a raccoon, a badger and an otter) were examined with negative results. The monitoring of influenza in mammals is initiated at the end of autumn 2022, therefore some time has passed since the foxes were found until they have been examined and tested positive.
The background to the initiation of monitoring of bird flu in mammals
Since autumn 2020, there have been widespread outbreaks of highly pathogenic avian influenza in wild birds, poultry and other captive birds in Europe, including in Denmark. From several countries, findings of the same highly pathogenic avian influenza viruses in a number of wild mammals have been reported at the same time. So far, most findings have been in foxes that exhibited neurological symptoms that led to their death or were found dead. Other species that have been found positive include mink, raccoon, raccoon, otters and seals.
In an infection trial from the Netherlands, 2008, it is shown that that foxes can become infected with highly pathogenic avian influenza if they eat infected bird carcasses. The infection can, like rabies and distemper, attack the animal's brain, and can cause altered behavior and death. When mammals are infected with influenza virus from birds, an adaptation of the virus to mammals can occur, which can be important for further infection. Viruses from the Danish foxes will in the coming time be investigated in more detail and compared with other viruses, among other things from Danish wild birds.
