Credit CDC
#18,280
While they haven't gotten the attention they deserve, rodents - which are often abundant around poultry and dairy farms - likely contribute to the spread of HPAI viruses (see 2016's The role of rodents in avian influenza outbreaks in poultry farms: a review).
Previously, in 2015's Taking HPAI To The Bank (Vole), we looked at that species' susceptibility to both H5N1 and H7N1, while more recently - in Nature: Decoding the RNA Viromes in Shrew Lungs Along the Eastern Coast of China - we looked at a study that found a wide range of zoonotic viruses - including HPAI H5N6 - in shrews.
A lot seems to depend upon both the host species, and the subtype/clade of the infecting influenza virus. Some rodents may develop mild, even asymptomatic, infection while others may quickly succumb to the virus.
Up until two months ago, rodents had never been included in the USDA's list of mammalian wildlife infected with H5N1 (see USDA Adds House Mouse To Mammals Affected by H5N1).
Since early June we've seen nearly 100 rodents (house mouse, deer mice) added to the list, and they now comprise nearly 25% of all of the confirmed mammals on the list. We've also seen the recent addition of domestic cats (n=53), prairie voles (n=1), and desert cottontails (n=1) to that list.
And just last week, in Emer. Microbe & Inf.: HPAI Virus H5N1 clade 2.3.4.4b in Wild Rats in Egypt during 2023, we a surprisingly high percentage of wild rats testing positive for H5 antibodies in Egypt.
All of which brings us to a new study, published today in Pathogens, where researchers challenged several rodent species (house mice, brown rat, black rat) with two (older 2010, 2007) HPAI H5N1 viruses, and found they are both susceptible to the virus and could potentially play a role it its evolution and spread.
Due to its length and technical nature, I've only posted the link, abstract, and some excerpts. Follow the link to read it in its entirety. I'll have a brief postscript after the break.
Susceptibility of Synanthropic Rodents (Mus musculus, Rattus norvegicus and Rattus rattus) to H5N1 Subtype High Pathogenicity Avian Influenza Viruses
Tatsufumi Usui 1, Yukiko Uno 1, Kazuyuki Tanaka 2, Tsutomu Tanikawa 2 and Tsuyoshi Yamaguchi 1,*
Abstract
Synanthropic wild rodents associated with agricultural operations may represent a risk path for transmission of high pathogenicity avian influenza viruses (HPAIVs) from wild birds to poultry birds. However, their susceptibility to HPAIVs remains unclear.In the present study, house mice (Mus musculus), brown rats (Rattus norvegicus), and black rats (Rattus rattus) were experimentally exposed to H5N1 subtype HPAIVs to evaluate their vulnerability to infection. After intranasal inoculation with HA clade 2.2 and 2.3.2.1 H5N1 subtype HPAIVs, wild rodents did not show any clinical signs and survived for 10- and 12-day observation periods.Viruses were isolated from oral swabs for several days after inoculation, while little or no virus was detected in their feces or rectal swabs. In euthanized animals at 3 days post-inoculation, HPAIVs were primarily detected in respiratory tract tissues such as the nasal turbinates, trachea, and lungs. Serum HI antibodies were detected in HA clade 2.2 HPAIV-inoculated rodents.These results strongly suggest that synanthropic wild rodents are susceptible to infection of avian-origin H5N1 subtype HPAIVs and contribute to the virus ecosystem as replication-competent hosts. Detection of infectious viruses in oral swabs indicates that wild rodents exposed to HPAIVs could contaminate food, water, and the environment in poultry houses and play roles in the introduction and spread of HPAIVs in farms.
(SNIP)
Wild rodents, such as house mice (Mus musculus), brown rats (Rattus norvegicus), and black rats (Rattus rattus), may be the most prevalent mammals in the world’s poultry farms. Animals that are frequently observed on farms are more likely to be at risk than those that are rarely observed on farms [4]. Bacterial infections such as Salmonella, Campylobacter, and Escherichia coli are known as rodent-borne diseases on poultry farms.
Wild rodents are also believed to play a role in the transmission of viruses such as AIVs, avian paramyxovirus 1, avian gammacoronavirus, and infectious bursal disease virus. Therefore, rodent control programs have been empirically and aggressively recommended as biosecurity measures for poultry operations to prevent the introduction and spread of rodent-mediated pathogens in farms. In the case of avian influenza, wild rodents are suspected to be HPAI vectors in poultry farms [4,5].During the initial outbreak of H5N1 subtype HPAIV in Hong Kong in 1997, HI antibodies were detected in the sera of some brown rats captured in live poultry markets, although a virus was not isolated [6]. In 2015, an epidemiological study of house mice on farms experiencing HPAI outbreaks in Ohio, USA, did not find any virus-positive or antibody-positive cases [3]. However, in May 2024, H5N1 subtype HPAIV infections were reported in 66 house mice in New Mexico, USA, where H5N1 subtype HPAIV infections had occurred in dairy cattle (https://wahis.woah.org/#/in-review/4451 (accessed on 10 July 2024)). Although few in number, these cases of natural infection in brown rats and house mice imply that at least some synanthropic rodents are susceptible to HPAIV.
(SNIP)
Conclusions
The present study examined the susceptibilities of common rodents that inhabit poultry farms, including house mice (Mus musculus), brown rats (Rattus norvegicus), and black rats (Rattus rattus) to H5N1 subtype HPAIVs by experimental infection.
Our results revealed that synanthropic wild rodents can be infected with HPAIVs in a subclinical manner and were able to actively shed the virus from the oral cavity for 3–5 days after HPAIV exposure. The primary site of HPAIV multiplication was the respiratory tract, with little or no discharge from the gastrointestinal tract. Because the course of HPAIV infection typically varies among virus strains, laboratory investigations using a variety of virus strains, especially those prevalent in recent years, are required.
Replication-competent hosts in poultry farms definitely present a high risk in terms of avian flu control and public health concerns. Further rodent control measures are required for biosecurity. While aiming to eliminate wild rodents from poultry farms, hygiene management must be taken to prevent the spread of the disease to other animals and to protect humans from HPAIV infection.
Obviously, these tests need to be repeated with newer subtypes/clades of the virus as soon as possible since the H5N1 clade 2.3.4.4b virus (which includes scores of genotypes) has vastly increased its host range - in both birds and mammals - since 2020.
While it remains incomplete, our understanding of the ecology of the H5N1 virus continues to expand.
- Six months ago cattle, goats, and alpacas weren't considered susceptible hosts, now they are.
- Last week, we saw evidence that sheep may be susceptible as well (see Preprint: Highly Pathogenic Avian Influenza H5 Virus Exposure in Goats and Sheep (in Pakistan)).
- Although long suspected, blowflies are now considered plausible `mechanical' vectors of HPAI viruses
- In 2020 the USGS found long-term (up to 7 months) survival of influenza A viruses in wetlands in both Alaska and Minnesota (see Proc. Royal Society B: Influenza A Viruses Remain Viable For Months In Northern Wetlands - USGS)
- Last May, in Viruses: Assessment of Survival Kinetics for Emergent Highly Pathogenic Clade 2.3.4.4 H5Nx Avian Influenza Viruses we looked at the survivability of 5 different HPAI H5 clade 2.3.4.4b viruses collected between 2014 and 2021, in a laboratory environment at 3 different temperatures (measured in days).
- And while still controversial, we've seen a number of studies suggesting long-distance airborne spread of avian flu viruses, including 2019's Nature: Airborne Transmission May Have Played A Role In Spread Of U.S. 2015 HPAI Epizootic and 2022's HPAI (H5N8) Clade 2.3.4.4b Virus in Dust Samples from Poultry Farms, France, 2021.
Admittedly, adding rodents as vectors to this list isn't much of a stretch.
While none of this speaks to whether HPAI H5 will ever spark a pandemic, it does remind us how well-adapted the virus has become over the past two decades, and how much more challenging it may be to contain it going forward.
