#17,937
Nine months ago, South Africa - which has been dealing with sporadic outbreaks of HPAI H5Nx since H5N8 arrived in 2017 - announced the emergence of a new, HPAI H7N6 virus (see WOAH report) which has spread rapidly through that nation's poultry industry.
The virus appears to have started out as a low path (LPAI) H7N6, carried relatively harmlessly by wild birds, that made its way into domesticated poultry, and then mutated into a HPAI virus. This is a process we've discussed often, most recently in this PLoS Pathogens study.
According to a report published last October in The Conversation:
The strain is well-adapted to chickens – it infects them easily and replicates effectively in them, in preference to other avian species – and spreads very easily between birds and farms. An estimated 10 million have become infected while 6 million died from the H7N6. A further 1.7 million died from H5N1 earlier in the year.
While HPAI H5Nx has spread globally over the past couple of years, this emerging HPAI H7N6 strain has so far remained largely confined to South Africa, although neighboring Mozambique reported an outbreak of H7Nx in October of last year.
We've looked at several outbreaks of H7N6 over the years, including:
Australia: Victoria Reports Outbreak From 3rd Avian Flu Subtype (H7N6) In A Month
Frontiers in Microbiology: A Novel Reasortant H7N6 Is Transmissible in Guinea Pigs via Respiratory Droplets
Japan: Aichi Prefecture Strain Identified As H7N6
Today's article further identifies Mozambique's H7 virus as HPAI H7N6, links it to the South African outbreak, and discusses its zoonotic potential and its impact on local poultry production. Due to its length, I've only posted some excerpts.
Follow the link to read the report in its entirety. I'll have a postscript after the break.
H7N6 highly pathogenic avian influenza in Mozambique, 2023
Iolanda Vieira Anahory Monjane, Hernâni Djedje, Esmeralda Tamele, Virgínia Nhabomba,
Almiro Rogério Tivane, Zacarias Elias Massicame, show all
Article: 2321993 | Received 12 Dec 2023, Accepted 16 Feb 2024, Published online: 29 Feb 2024
https://doi.org/10.1080/22221751.2024.2321993
ABSTRACT
On 13 October 2023, the National Directorate for Livestock Development in Mozambique was notified of a suspected outbreak of avian influenza in commercial layers. Samples were screened by real-time and conventional RT–PCR and were positive for both H7 and N6. Full genome sequences were obtained for three representative samples. Sequence analysis of the H7 cleavage site confirmed that the viruses were highly pathogenic (i.e. 333- PEPPKGPRFRR/GLF-346).
In addition, the H7 and N6 sequences were highly similar (from 99.4-99.5% and 99.6-99.7% for the HA gene and the NA gene, respectively) to the sequences of a H7N6 virus identified in the Republic of South Africa in May 2023 indicating a similar origin of the viruses. The identification of H7N6 HPAIV in Mozambique has important implications for disease management and food security in the region.
Highly pathogenic avian influenza (HPAI) is caused by H5 and H7 subtypes of type A influenza virus. In the last number of years, global attention has been focused on the spread and impact of H5Nx viruses that have caused devastating outbreaks in both domestic and wild bird populations worldwide [Citation1]. However, H7 subtype viruses have also caused numerous outbreaks in domestic poultry. Examples include H7N1 outbreaks in Italy; H7N2 outbreaks in Australia, USA, UK; H7N3 in Canada, Chile, Italy, Mexico, Pakistan; H7N4 in Australia; H7N7 in Australia, Germany, Italy, Spain, the Netherlands, United Kingdom; H7N8 and H7N9 in the USA [Citation2, Citation3].
The most recent outbreaks caused by an H7 subtype virus were reported in the Republic of South Africa (RSA) in May 2023 [Citation4]. This H7N6 virus has resulted in the death or culling of tens of thousands of poultry (layers). Following the occurrence of the H7N6 (and previous H5N8, H5N1, H5N2 outbreaks) in the RSA, the Ministry of Agriculture and Rural Development (MADER) in Mozambique suspended the importation of live domestic and wild birds and poultry products from the RSA on 6 October 2023. Additionally, prevention and surveillance measures were reinforced throughout the national territory.
As a result of the intensification of these measures, on 13 October 2023, MADER was notified of the suspected occurrence of avian influenza in a commercial poultry farm in the district of Morrumbene, Inhambane province, 500 km northeast of the capital Maputo. The birds showed enteric and respiratory symptoms with increased morbidity and mortality (the mortality was an average of 400 birds per day). The farm consisted of three sheds housing 45,000 birds (approximately 15,000 thousands birds perished). Abnormal mortality was recorded by the farm on September 25th with a total of 64 dead birds. On September 29th, the company reported the death of 102 birds in shed #1. On October 5th, the two remaining sheds recorded unusual mortality with cases increasing in shed #2 from 14 to 28 and in shed #3 from 12 to 57. Two days later the number of dead birds increased dramatically to 128 in shed #2 and 214 in shed #3. Virus spread was believed to have been due to poor biosecurity and the movement of individuals between the sheds. It was also determined that 45,000 live birds (17 weeks of age) were introduced into the farm between 30 August and 7 September 2023 in three different batches of 15,000 birds per batch, from an establishment certified as free of avian influenza in the North West province of the RSA.
(SNIP)
The zoonotic potential of this new virus should be considered. H7N2, H7N3, H7N7 viruses have all been previously associated with conjunctivitis and/or respiratory symptoms in humans while in 2003 in the Netherlands a fatal case occurred following an infection with H7N7 [Citation8, Citation9]. In March 2013, cases of human avian influenza A(H7N9) were reported in China and to date there have been 616 recorded deaths due to this virus [Citation10]. More recently, in 2018, a human infection by an H7N4 virus was reported in China [Citation11].
To date, there have been several identifications of H7N6 subtype viruses in wild birds but they have all been of low pathogenicity. There have been some recent reports of low pathogenic H7N6 viruses in poultry in Chile and Cambodia but none of these viruses have caused significant disease [Citation12, Citation13].
Currently, there is not enough data publicly available on the circulation of H7N6 in the southern African region to make meaningful comparisons and to identify a definitive source of the outbreak in Mozambique but there is no doubt that there is a molecular epidemiological link between the H7N6 viruses identified in Mozambique and those in the RSA. Analysis of viruses from similar outbreaks in the region will add greatly to understanding the movement and potential impact of this new subtype. In the meantime, a risk based active surveillance should be initiated with national veterinary authorities remaining vigilant and prepared to control and manage possible future outbreaks of H7N6.
While the following FAO map makes it appear as if avian flu is quite limited in Sub-Saharan Africa, the reality is that surveillance, testing, and reporting across most of this region is nearly non-existent (see 2017's The Challenge Of Avian Flu Surveillance In Sub-Saharan Africa).
Until LPAI H7N9 appeared in China during the winter/spring of 2013, Low Path H7 viruses were generally regarded as less of a threat than H5 avian viruses, and primarily a risk to poultry.
Human infection with any H7 virus (LPAI or HPAI) until then had been rare, and generally mild (see
All of that changed when LPAI H7N9 - which is carried asymptomatically in birds - began infecting humans and driving a yearly epidemic with an estimated 30% Case Fatality rate in humans. Over 1,500 cases and > 600 deaths were officially reported by China over 5 years.
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| H7N9 Waves - Credit EID Journal |
Researchers tested 30 LPAI H7 viruses collected from North America on DBA/2J mice, and found 90% of them produced varying degrees of mortality. Remarkably 75% (24 of 30) were as pathogenic as the 2013 Anhui strain of H7N9. Duck borne viruses tended to be more pathogenic than shorebird viruses.
These viruses replicated beyond the respiratory system of these mice (including in their hearts and brains), and while they bound preferentially to avian α2,3 receptor cells, they demonstrated some ability to bind to mammalian α2,6 receptors.
WHO Update & Risk Assessment On Avian H7N4
J Infect Dis: Serological Evidence Of H7N2 Infection Among Animal Shelter Workers, NYC 2016
