CREDIT CDC
#18,394
Given the news last week that a pig in Oregon tested positive for the H5N1 virus, the following review article - recently published in the Journal Viruses on the ecology and distribution of influenza A viruses in swine - is especially timely.
Swine (and Equines) are the only hosts known to be susceptible to all 4 types of influenza (A, B, C & D), and reassortment in swine has been linked to the generation of previous pandemic viruses.
Of the CDC's IRAT (Influenza Risk Assessment Tool) list of 25 zoonotic influenza A viruses with pandemic potential, 4 are swine variant viruses and the virus with the highest emergence & impact score is a Swine Variant H1N1 from China.
Although the following review covers a lot of ground, it mentions the H5N1 virus 11 times, and `avian' flu viruses more than 50 times. Anyone looking for a comprehensive review of influenza A viruses in swine will find it very much worth reading.
Due to its length, I've only posted some excerpts. Follow the link to read it in its entirety.
Influenza A Viruses in the Swine Population: Ecology and Geographical Distribution
by
Nailya Klivleyeva 1, Nurbol Saktaganov 1, Tatyana Glebova 1,*, Galina Lukmanova 1, Nuray Ongarbayeva 1 and Richard Webby 2
Viruses 2024, 16(11), 1728; https://doi.org/10.3390/v16111728
Submission received: 27 September 2024 / Published: 1 November 2024AbstractDespite the efforts of practical medicine and virology, influenza viruses remain the most important pathogens affecting human and animal health. Swine are exposed to infection with all types of influenza A, B, C, and D viruses. Influenza viruses have low pathogenicity for swine, but in the case of co-infection with other pathogens, the outcome can be much more serious, even fatal. Having a high zoonotic potential, swine play an important role in the ecology and spread of influenza to humans.
In this study, we review the state of the scientific literature on the zoonotic spread of swine influenza A viruses among humans, their circulation in swine populations worldwide, reverse zoonosis from humans to swine, and their role in interspecies transmission. The analysis covers a long period to trace the ecology and evolutionary history of influenza A viruses in swine.
The following databases were used to search the literature: Scopus, Web of Science, Google Scholar, and PubMed. In this review, 314 papers are considered: n = 107 from Asia, n = 93 from the U.S., n = 86 from Europe, n = 20 from Africa, and n = 8 from Australia. According to the date of publication, they are conditionally divided into three groups: contemporary, released from 2011 to the present (n = 121); 2000–2010 (n = 108); and 1919–1999 (n = 85).1. IntroductionInfluenza viruses (IVs) belong to the Orthomyxoviridae family and have a segmented genome with single-stranded, negative-sense RNA. Based on genetic and antigenic differences, IVs are divided into four genera, A, B, C, and D, which infect different species of mammals and birds with the four types of IV that occur in swine [1,2,3,4]. Among the four types of IVs, influenza A viruses (IAVs) are highly significant pathogens responsible for serious epidemics in humans and domestic animals. Figure 1 presents different species of animals infected with the four types of IVs.
Figure 1. Influenza A, B, C, and D in different species of mammals.
The IAV genome consists of eight RNA segments: PB2, PB1, PA, hemagglutinin (HA), NP, neuraminidase (NA), M, and NS [1]. Two surface antigens, HA and NA, are mainly subject to antigenic variability, while internal proteins (NP and M) are relatively conservative. HA and NA play an essential role in the initial stages of cell infection [5]. HA binds to host cell receptors that contain terminal sialic acid residues (-2,6-SA or -2,3-SA). The HA gene is in charge of attaching viral pieces to the host cell receptor. NA removes the cell surface receptor (sialic acid); this is crucial for releasing viral particles from the cell surface and virus spillover [5].Based on major antigenic differences in surface proteins (HA and NA), 18 HA subtypes (H1–H18) and 11 NA subtypes (N1–N11) have been identified. The H1–H16 and N1–N9 virus subtypes have been identified in waterfowl, which are believed to constitute the natural IAV reservoir [6,7,8], while the H17–H18 and N10–N11 subtype sequences have been found in bats [9,10,11]. Only a limited number of subtypes have been found in mammals, such as H1 and H3 viral subtypes, which we identified and circulate in both humans and swine [12,13,14,15,16,17,18,19]. Figure 2 presents subtypes of H1–H18 hemagglutinins and N1–N11 neuraminidases of influenza viruses in different species of mammals.
Figure 2. Influenza subtypes of viruses H1–H18 and N1–N11 in different species of mammals.IAVs’ epidemiology and ecology are complicated by their multi-host and segmented genome. IAVs are among the main pathogens in swine that give rise to acute respiratory infections and cause significant economic losses for swine farms.In addition to swine IAVs, human and avian IAVs can also infect swine. Swine are believed to serve as an intermediate “mixing vessel” for generating a variety of novel IVs [20]. The co-infection of swine with two or more IAV strains can induce reassortment [21,22], which in turn can promote the emergence of new IV strains [23,24,25]. There are numerous reports of zoonotic infections in humans with swine IAVs and reverse zoonotic infections in swine with human IAVs [26,27,28,29,30].
(SNIP)
5. Conclusions
Swine play an important role in the formation of present-day influenza ecology. Swine have specific receptors for avian, porcine, and human IAV in the tracheal epithelium, which may contribute to the emergence of new reassortant variants that could potentially pose a public health threat [8,249,303]. The complex interaction of IAVs of human, avian, and porcine evolutionary origin in swine is supported by the detection of multiple IAV subtypes in swine populations, including H1, H2, H3, H4, H5, H7, and H9 [304]. Swine play an important role in the epidemiology of IV, which is dangerous to humans [305]. For example, influenza A(H1N1)pdm09 is thought to have been present in swine herds for several months before it became a pandemic strain in humans [35].Human-to-swine transmission of IV occurs much more frequently than swine-to-human transmission [30]. Despite the genetic diversity of SIVs found in the swine population, only H1 and H3 IAVs formed stable lineages similar to human IVs. The nature of H1 and H3 viruses nevertheless differs between the two host populations. In addition, the distribution of subtypes and genotypes of endemic IAVs varies greatly by geographic region due to the repeated introduction of avian and human influenza viruses. An exception is H1N1pdm09, which is mainly widespread due to multiple human-to-swine reintroductions [57,102,167,176,306,307,308,309,310,311,312]. New cases of infection with avian influenza H5N1 virus have been confirmed in dairy cattle and pigs [313,314]. However, no information has been found on the presence of swine-origin IVs in dairy cows.The continuous monitoring and genome-wide genetic characterization of SIVs make it possible to obtain a complete picture of the infectious disease process, predict the epidemiological and epizootic situation, and choose the right strategy and tactics for preventive and anti-epidemic measures. Understanding the transmission modes is of decisive importance for developing effective control strategies and making reasonable surveillance recommendations.This study may provide the information needed to develop a more effective method for monitoring SIVs and selecting countermeasures to prevent interspecies transmission, which could become a potential pre-pandemic situation.
