H3N8
Encyclopedia
H3N8 is a subtype of the species Influenza A virus
that is endemic in birds, horses and dogs.
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 to humans has
not occurred during outbreaks of the disease in horses.
Equine influenza poses no threat to people.
in either 1889 or 1900. Sources differ; some say the 1889 pandemic was caused by H2N2. The experts also differ on exactly how sure we can be if either were even involved.
A 1997 study found H3N8 was responsible for over one quarter of the influenza infections in wild ducks. In 1963, the H3N8 (A/equine/2/Miami/63) subtype created
an epidemic of equine influenza in Miami6 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 USA 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.
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 The virus is delicate
within the environment and easily killed by heat, cold, desiccation
,
and disinfectants. 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
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
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.
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
Influenzavirus A
Influenza A virus causes influenza in birds and some mammals and is the only species of Influenzavirus A. Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon...
that is endemic in birds, horses and dogs.
Introduction
Equine influenza (EI) is a highly contagious respiratorydisease 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
Orthomyxoviridae
The Orthomyxoviridae are a family of RNA viruses that includes five genera: Influenzavirus A, Influenzavirus B, Influenzavirus C, Isavirus and Thogotovirus. A sixth has recently been described...
(genus Influenzavirus) Transmission of the equine influenza virus to humans has
not occurred during outbreaks of the disease in horses.
Equine influenza poses no threat to people.
History
H3N8 was suspected of causing a human influenza pandemicInfluenza pandemic
An influenza pandemic is an epidemic of an influenza virus that spreads on a worldwide scale and infects a large proportion of the human population. In contrast to the regular seasonal epidemics of influenza, these pandemics occur irregularly, with the 1918 Spanish flu the most serious pandemic in...
in either 1889 or 1900. Sources differ; some say the 1889 pandemic was caused by H2N2. The experts also differ on exactly how sure we can be if either were even involved.
A 1997 study found H3N8 was responsible for over one quarter of the influenza infections in wild ducks. In 1963, the H3N8 (A/equine/2/Miami/63) subtype created
an epidemic of equine influenza in Miami6 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 USA 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.
Route of transmission
EIV can be spread by a few different routes. The ultimate source of the virus is respiratory tractRespiratory tract
In humans the respiratory tract is the part of the anatomy involved with the process of respiration.The respiratory tract is divided into 3 segments:*Upper respiratory tract: nose and nasal passages, paranasal sinuses, and throat or pharynx...
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 The virus is delicate
within the environment and easily killed by heat, cold, desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
,
and disinfectants. The virus Multiplies in epithelial cells of upper respiratory tract. Dispersed by aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...
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
Biosecurity
Biosecurity is a set of preventive measures designed to reduce the risk of transmission of infectious diseases, quarantined pests, invasive alien species, living modified organisms...
procedures have not been followed
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
Incubation period
This is the time from when a horse gets exposed to the time when it gets sick. It's quite short for equine influenza: usually 1–3 days (although it might be as long as 7 days in some circumstances). That's actually a good thing from a control standpoint, because you know sooner rather than later if exposed horses have really been infected (and are infectious). Diseases that have very long incubation periods can be more difficult to control.Diagnosis
Fever of 102.5- 105.0 F, 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 antibodyAntibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
titer in equine-1 or 2 serum
Serum
Serum may refer to:*Blood serum, a component of blood which is collected after coagulation.**Antiserum, blood serum with specific antibodies for passive immunity*Serous fluid, any clear bodily fluid*any drug derived from an animal's blood or serous fluid...
can be used as diagnosis
Diagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...
in horses.
Other
clinical findings may include a serous or light mucoid nasal
discharge, epiphora
Epiphora
Epiphora may refer to:* Epiphora , an excessive tear production usually a result from an irritation of the eye* Epistrophe, the repetition of the same word or words at the end of successive phrases, clauses or sentences...
, tender but rarely swollen submandibular
lymph nodes, hyperemia of nasal and conjunctival mucosa,
tachypnea
Tachypnea
Tachypnea means rapid breathing. Any rate between 12-20 breaths per minute is normal. Tachypnea is a respiration rate greater than 20 breaths per minute. - Distinction from other breathing terms :...
, tachycardia
Tachycardia
Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...
, limb edema, muscle soreness
and stiffness.
Period of infectivity
This is 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.Pathophysiology
Aerosolized influenza virus is inhaled and embeds in therespiratory 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
Neuraminidase
Neuraminidase enzymes are glycoside hydrolase enzymes that cleave the glycosidic linkages of neuraminic acids. Neuraminidase enzymes are a large family, found in a range of organisms. The most commonly known neuraminidase is the viral neuraminidase, a drug target for the prevention of the spread...
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
Hemagglutinin
Influenza hemagglutinin or haemagglutinin is a type of hemagglutinin found on the surface of the influenza viruses. It is an antigenic glycoprotein. It is responsible for binding the virus to the cell that is being infected...
spike to the N-acetylneuraminic
acid receptor on the cell. The virus then enters the cell
by endocytosis
Endocytosis
Endocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...
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
Viremia
Viremia is a medical condition where viruses enter the bloodstream and hence have access to the rest of the body. It is similar to bacteremia, a condition where bacteria enter the bloodstream.- Primary versus Secondary :...
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