Influenza A virus subtype H3N8

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Influenza A virus subtype H3N8
Virus classification OOjs UI icon edit-ltr.svg
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum: Negarnaviricota
Class: Insthoviricetes
Order: Articulavirales
Family: Orthomyxoviridae
Genus: Alphainfluenzavirus
Species:
Influenza A virus
Serotype:
Influenza A virus subtype H3N8

H3N8 is a subtype of the species Influenza A virus that is endemic in birds, horses and dogs. It is the main cause of equine influenza and is also known as equine influenza virus. In 2011, it was reported to have been found in seals. [1] Cats have been experimentally infected with the virus, leading to clinical signs, shedding of the virus and infection of other cats. [2] In 2022 and 2023, three people in China were infected with H3N8, [3] with one fatality, marking the first time a human has died from this strain of flu. [4]

Contents

Introduction

Phylogenetic tree of 57 equine influenza viruses Fmicb-09-01941-g002.jpg
Phylogenetic tree of 57 equine influenza viruses

Equine influenza (EI) is a highly contagious respiratory disease of horses and related animals such as donkeys, mules and zebras (collectively known as equines). Equine influenza is caused by a type A influenza virus in the family Orthomyxoviridae (genus Influenzavirus). Transmission of the equine influenza virus (EIV) to humans has not occurred during outbreaks of the disease in horses. A lineage of H3N8 has been found to infect humans, with the first two cases in China in April and May 2022, [5] and a third case in March 2023, which was the first death. [3]

History

In 1963, the H3N8 (A/equine/2/Miami/63) subtype created an epidemic of equine influenza in Miami and subsequently spread throughout North and South America and Europe, creating massive outbreaks during 1964 and 1965. Since 1963, the H3N8 virus has drifted along a single lineage at a rate of 0.8 amino acid substitutions per year. Between 1978 and 1981, there were widespread epidemics of the A/equine/2 strain throughout the US and Europe despite the development of vaccines. Since the late 1980s, evolution of the H3N8 virus has diverged into two families: an "American-like" lineage and a "European-like" lineage. [6] A 1997 study found H3N8 was responsible for over one quarter of the influenza infections in wild ducks. [7]

H3N8 has been suggested as a possible cause of the 1889–1890 pandemic in humans, and also another epidemic in 1898–1900. [8] [9] Before the identification of H3N8 as a possible cause of the 1889 pandemic, the H2N2 subtype was suggested. [10] [11] [12] At this point, it is not possible to identify the virus for either the 1889 or 1900 outbreak with certainty. [13]

Route of transmission

Transmission routes of EIV Fmicb-09-01941-g003.jpg
Transmission routes of EIV

Equine influenza virus (H3N8) can be spread by a few different routes. The ultimate source of the virus is respiratory tract secretions. Coughing horses can release the virus into the air, where it can spread up to 30–50 metres. It can also be spread by direct contact between horses, or indirectly via a person's hands or clothing, or on inanimate objects (e.g. buckets, tack, twitches). However, the virus doesn't survive outside of a horse for long [14] The virus is delicate within the environment and easily killed by heat, cold, desiccation, and disinfectants. [15] The virus multiplies in epithelial cells of upper respiratory tract. Dispersed by aerosol droplets when horse coughs or exhales. The virus can survive in the environment, on different surfaces, for up to 48 hours. Spread of the disease has been associated with the movement of people, pets, horse equipment and tack where proper biosecurity procedures have not been followed [16]

Subclinical infection with virus shedding can occur in vaccinated horses, particularly where there is a mismatch between the vaccine strains and the virus strains circulating in the field. Such infections contribute to the spread of the disease. [17]

Incubation period

The time from when a horse gets exposed to the time when it gets sick. It is quite short for equine influenza: typically 1–3 days and up to 7 days. This makes disease control easier, as infected horses can be identified sooner, meaning that appropriate control measures can be enacted more quickly. Diseases that have very long incubation periods can be more difficult to control. [14]

Pathophysiology

Life cycle and pathogenesis of EIV Fmicb-09-01941-g004.jpg
Life cycle and pathogenesis of EIV

Aerosolized influenza virus is inhaled and embeds in the respiratory mucosa, of the upper and lower respiratory tract. The virus is attracted to the glycoproteins and mucopolysaccharides of the mucus coating the respiratory mucosa. If the infecting dose of virus is high, abundant viral neuraminidase breaks down the mucosal layer, allowing access of the virus to the underlying epithelial cells. The virus then attaches to epithelial cells through binding of the hemagglutinin spike to the N-acetylneuraminic acid receptor on the cell. The virus then enters the cell by endocytosis into the cell cytoplasm where it replicates to produce new virions that are released back into the respiratory tract by budding from the infected cell. The virus disperses throughout the trachea and bronchial tree within 3 days, causing hyperemia, edema, necrosis, desquamation, and focal erosion. Viremia is rare, but is possible if the virus crosses the basement membrane and enters the circulation, potentially causing inflammation of skeletal and cardiac muscle (myositis and myocarditis), encephalitic signs, and limb edema [6]

Diagnosis

Fever of 102.5–105.0 °F (39.2–40.6 °C), frequent dry cough for several weeks, ‘drippy’ nose with discharge and secondary bacterial infection are some of the clinical signs of Equine influenza virus infection. isolation of influenza virus from nasopharyngeal and or large rise in antibody titer in equine-1 or 2 serum can be used as diagnosis in horses. Other clinical findings may include a serous or light mucoid nasal discharge, epiphora, tender but rarely swollen submandibular lymph nodes, hyperemia of nasal and conjunctival mucosa, tachypnea, tachycardia, limb edema, muscle soreness and stiffness. [15]

Period of infectivity

The length of time a horse can spread the virus after being infected. It is a very important concept, because horses can still infect other horses after they have gotten over their own illness. Viruses that are shed for long periods of time after a horse gets better are much harder to control. Horses tend to be most infectious (i.e. shedding the most virus) in the first 24–48 hours after they develop a fever, but they can shed the virus for up to 7–10 days after their signs of illness disappear. [14]

See also

Related Research Articles

<i>Influenza A virus</i> Species of virus

Influenza A virus (IAV) is a pathogen that causes the flu in birds and some mammals, including humans. It is an RNA virus whose subtypes have been isolated from wild birds. Occasionally, it is transmitted from wild to domestic birds, and this may cause severe disease, outbreaks, or human influenza pandemics.

<span class="mw-page-title-main">Avian influenza</span> Influenza caused by viruses adapted to birds

Avian influenza, also known as avian flu, is a bird flu caused by the influenza A virus, which can infect people. It is similar to other types of animal flu in that it is caused by a virus strain that has adapted to a specific host. The type with the greatest risk is highly pathogenic avian influenza (HPAI).

<span class="mw-page-title-main">Respiratory syncytial virus</span> Species of a virus

Respiratory syncytial virus (RSV), also called human respiratory syncytial virus (hRSV) and human orthopneumovirus, is a common, contagious virus that causes infections of the respiratory tract. It is a negative-sense, single-stranded RNA virus. Its name is derived from the large cells known as syncytia that form when infected cells fuse.

<i>Orthomyxoviridae</i> Family of RNA viruses including the influenza viruses

Orthomyxoviridae is a family of negative-sense RNA viruses. It includes seven genera: Alphainfluenzavirus, Betainfluenzavirus, Gammainfluenzavirus, Deltainfluenzavirus, Isavirus, Thogotovirus, and Quaranjavirus. The first four genera contain viruses that cause influenza in birds and mammals, including humans. Isaviruses infect salmon; the thogotoviruses are arboviruses, infecting vertebrates and invertebrates. The Quaranjaviruses are also arboviruses, infecting vertebrates (birds) and invertebrates (arthropods).

<i>Measles morbillivirus</i> Species of virus

Measles morbillivirus(MeV), also called measles virus (MV), is a single-stranded, negative-sense, enveloped, non-segmented RNA virus of the genus Morbillivirus within the family Paramyxoviridae. It is the cause of measles. Humans are the natural hosts of the virus; no animal reservoirs are known to exist.

<span class="mw-page-title-main">Influenza A virus subtype H5N1</span> Subtype of influenza A virus

Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus which can cause illness in humans and many other species. A bird-adapted strain of H5N1, called HPAI A(H5N1) for highly pathogenic avian influenza virus of type A of subtype H5N1, is the highly pathogenic causative agent of H5N1 flu, commonly known as avian influenza. It is enzootic in many bird populations, especially in Southeast Asia. One strain of HPAI A(H5N1) is spreading globally after first appearing in Asia. It is epizootic and panzootic, killing tens of millions of birds and spurring the culling of hundreds of millions of others to stem its spread. Many references to "bird flu" and H5N1 in the popular media refer to this strain.

<span class="mw-page-title-main">Swine influenza</span> Infection caused by influenza viruses endemic to pigs

Swine influenza is an infection caused by any of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) refers to any strain of the influenza family of viruses that is endemic in pigs. As of 2009, identified SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H2N1, H3N1, H3N2, and H2N3.

<span class="mw-page-title-main">Influenza A virus subtype H1N1</span> Subtype of Influenza A virus

In virology, influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus. Major outbreaks of H1N1 strains in humans include the 1918 Spanish flu pandemic, the 1977 Russian flu pandemic and the 2009 swine flu pandemic. It is an orthomyxovirus that contains the glycoproteins hemagglutinin (H) and neuraminidase (N), antigens whose subtypes are used to classify the strains of the virus as H1N1, H1N2 etc. Hemagglutinin causes red blood cells to clump together and binds the virus to the infected cell. Neuraminidase is a type of glycoside hydrolase enzyme which helps to move the virus particles through the infected cell and assist in budding from the host cells.

<span class="mw-page-title-main">Influenza pandemic</span> Pandemic involving influenza

An influenza pandemic is an epidemic of an influenza virus that spreads across a large region and infects a large proportion of the population. There have been six major influenza epidemics in the last 140 years, with the 1918 flu pandemic being the most severe; this is estimated to have been responsible for the deaths of 50–100 million people. The most recent, the 2009 swine flu pandemic, resulted in under 300,000 deaths and is considered relatively mild. These pandemics occur irregularly.

<span class="mw-page-title-main">Canine influenza</span>

Canine influenza is influenza occurring in canine animals. Canine influenza is caused by varieties of influenzavirus A, such as equine influenza virus H3N8, which was discovered to cause disease in canines in 2004. Because of the lack of previous exposure to this virus, dogs have no natural immunity to it. Therefore, the disease is rapidly transmitted between individual dogs. Canine influenza may be endemic in some regional dog populations of the United States. It is a disease with a high morbidity but a low incidence of death.

Pneumococcal pneumonia is a type of bacterial pneumonia that is caused by Streptococcus pneumoniae (pneumococcus). It is the most common bacterial pneumonia found in adults, the most common type of community-acquired pneumonia, and one of the common types of pneumococcal infection. The estimated number of Americans with pneumococcal pneumonia is 900,000 annually, with almost 400,000 cases hospitalized and fatalities accounting for 5-7% of these cases.

Flu is an infectious disease of birds and mammals caused by RNA viruses of the family Orthomyxoviridae, the influenza viruses.

<span class="mw-page-title-main">Transmission and infection of H5N1</span> Spread of an influenza virus

Transmission and infection of H5N1 from infected avian sources to humans has been a concern since the first documented case of human infection in 1997, due to the global spread of H5N1 that constitutes a pandemic threat.

<span class="mw-page-title-main">Equine influenza</span>

Equine influenza is the disease caused by strains of influenza A that are enzootic in horse species. Equine influenza occurs globally, previously caused by two main strains of virus: equine-1 (H7N7) and equine-2 (H3N8). The World Organisation for Animal Health now considers H7N7 strains likely to be extinct since these strains have not been isolated for over 20 years. Predominant international circulating H3N8 strains are Florida sublineage of the American lineage; clade 1 predominates in the Americas and clade 2 in Europe.. The disease has a nearly 100% infection rate in an unvaccinated horse population with no prior exposure to the virus.

<span class="mw-page-title-main">H5N1 genetic structure</span>

H5N1 genetic structure is the molecular structure of the H5N1 virus's RNA.

Bovine alphaherpesvirus 1 (BoHV-1) is a virus of the family Herpesviridae and the subfamily Alphaherpesvirinae, known to cause several diseases worldwide in cattle, including rhinotracheitis, vaginitis, balanoposthitis, abortion, conjunctivitis, and enteritis. BoHV-1 is also a contributing factor in shipping fever, also known as bovine respiratory disease (BRD). It is spread horizontally through sexual contact, artificial insemination, and aerosol transmission and it may also be transmitted vertically across the placenta. BoHV-1 can cause both clinical and subclinical infections, depending on the virulence of the strain. Although these symptoms are mainly non-life-threatening it is an economically important disease as infection may cause a drop in production and affect trade restrictions. Like other herpesviruses, BoHV-1 causes a lifelong latent infection and sporadic shedding of the virus. The sciatic nerve and trigeminal nerve are the sites of latency. A reactivated latent carrier is normally the source of infection in a herd. The clinical signs displayed are dependent on the virulence of the strain. There is a vaccine available which reduces the severity and incidence of disease. Some countries in Europe have successfully eradicated the disease by applying a strict culling policy.

Equine viral arteritis (EVA) is a disease of horses caused by a virus of the species Alphaarterivirus equid, an RNA virus. It is the only species in the genus Alphaarterivirus, and that is the only genus in the Equarterivirinae subfamily. The virus which causes EVA was first isolated in 1953, but the disease has afflicted equine animals worldwide for centuries. It has been more common in some breeds of horses in the United States, but there is no breed "immunity". In the UK, it is a notifiable disease. There is no known human hazard.

<span class="mw-page-title-main">Influenza</span> Infectious disease, often just "the flu"

Influenza, commonly known as "the flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin from one to four days after exposure to the virus and last for about 2–8 days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia, which can be caused by the virus or by a subsequent bacterial infection. Other complications of infection include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease.

<span class="mw-page-title-main">Host switch</span> Evolutionary change of the host specificity of a parasite or pathogen

In parasitology and epidemiology, a host switch is an evolutionary change of the host specificity of a parasite or pathogen. For example, the human immunodeficiency virus used to infect and circulate in non-human primates in West-central Africa, but switched to humans in the early 20th century.

<i>Influenza D virus</i> Species of virus

Influenza D virus is a species in the virus genus Deltainfluenzavirus, in the family Orthomyxoviridae, that causes influenza.

References

  1. ↑ McGrath, Matt (31 July 2012). "New flu virus found in seals concerns scientists". BBC News. Retrieved 2012-07-31.
  2. ↑ Su S, Wang L, Fu X, et al. (December 2014). "Equine influenza A(H3N8) virus infection in cats". Emerging Infectious Diseases. 20 (12): 2096–2099. doi:10.3201/eid2012.140867. PMC   4257791 . PMID   25417790.
  3. 1 2 "China reports first death from H3N8 bird flu". BNO News. 10 April 2023. Retrieved 10 April 2023.
  4. ↑ "First H3N8 bird flu death reported in China, says WHO". WION. Retrieved 2023-04-12.
  5. ↑ Patton, Dominique (2022-04-27). "China reports first human case of H3N8 bird flu". Reuters. Retrieved 2023-05-09.
  6. 1 2 Equine influenza virus by Wilson et al doi : 10.1053/j.ctep.2006.03.013
  7. ↑ Sharp, GB; Kawaoka, Y; Jones, DJ; et al. (August 1997). "Coinfection of wild ducks by influenza A viruses: distribution patterns and biological significance". J. Virol. 71 (8): 6128–35. doi:10.1128/JVI.71.8.6128-6135.1997. PMC   191873 . PMID   9223507.
  8. ↑ Valleron, Alain-Jacques; Cori, Anne; Valtat, Sophie; Meurisse, Sofia; Carrat, Fabrice; Boëlle, Pierre-Yves (May 11, 2010). "Transmissibility and geographic spread of the 1889 influenza pandemic". PNAS . 107 (19): 8778–8781. Bibcode:2010PNAS..107.8778V. doi: 10.1073/pnas.1000886107 . PMC   2889325 . PMID   20421481.
  9. ↑ Salmon, Roland, Swine Flu: what next? (PDF), National Public Health Service for Wales, Communicable Disease Surveillance Centre
  10. ↑ Hilleman MR (19 August 2002). "Realities and enigmas of human viral influenza: pathogenesis, epidemiology and control". Vaccine. 20 (25–26): 3068–3087. doi:10.1016/s0264-410x(02)00254-2. PMID   12163258.
  11. ↑ "pilva.com".
  12. ↑ Alexis Madrigal (April 26, 2010). "1889 Pandemic Didn't Need Planes to Circle Globe in 4 Months". Wired.
  13. ↑ Didier Raoult; Michel Drancourt, eds. (2008-01-24), Paleomicrobiology: Past Human Infections, Springer, ISBN   9783540758556
  14. 1 2 3 "equidblog.com". ww38.equidblog.com. Retrieved 2023-05-09.
  15. 1 2 Equine influenza virus by Wilson et al. doi : 10.1053/j.ctep.2006.03.013
  16. ↑ Farmnote on Equine Influenza by Karen Yurisich, Veterinary Officer, Perth ISSN   0726-934X.
  17. ↑ Daly, JM; Newton, JR; Mumford, JA (2004). "Current perspectives on control of equine influenza" (PDF). Vet. Res. 35 (4): 411–23. doi:10.1051/vetres:2004023. PMID   15236674. S2CID   11346318.
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