Determinants ambientals del virus de la grip aviar (Definitiu)

Afra Boix, Marc Rubio, Jonathan Serrano, Francesc Vidal.

Els determinants ambientals del virus de la grip aviar

1.Introduction   

1.1 Avian flu

The flu or influence is an infectious animal disease caused by viruses that usually they only infect birds. Avian influenza viruses are highly specific birds and on rare occasions have crossed the barrier of species and infected to humans.

The avian influenza was first discovered in free living ducks in 1972. Avian influenza is part of the Orthomyxoviridae group, which is single-stranded RNA virus.

The domestic birds infection causes two main forms of disease. The low pathogenicity, cause mild symptoms (feathers bristling, decreased egg production) and the highly pathogenic form. It spreads very quickly between groups of poultry, causes disease that affects multiple internal organs and has a mortality that can approach 100%, often within 48 hours.

When an infected bird coexist between individuals of the same species, infect its surroundings easily. Then, the virus’ provability to mutate increase and can affect to other species. Then the virus can adopt genetic human and cause serious pathogenic respiratory diseases. That flu person talk, stress or sneeze and expel the virus to the air the flu viruses are transmitted easily from person to person. It can also be infected with touch surfaces virus contaminated and touching the face after (eyes or nose) without washing your hands properly.

There are a vaccine against the flu. That is the better precaution to combate this illness, that is called anti-influenza vaccine, and the effect depends of the person’s age and the risk.

Image 1: Virus propagation between animals and humans.

Source: El País (https://elpais.com/elpais/2004/01/27/media/1075173545_720215.html).

2.Body text

2.1 Origin of the avian flu.

The avian flu epidemic began probably in the meridional Xina as the New Scientist megazine.

The epidemic began in the first semester of 2003, probably in China.

As the megazine wrote, the vaccine in all the chickens allowed the dissemination of H5N1 virus, who is in differents countries in Asia. After the sacrifice of all the chickens in Hong Kong for preparate the advance of the epidemic in 1987 which affected 18 persons, 6 of them died, the chinese products began to vaccinate their animals with a vaccine from the virus H5N1 inactivate.

That could be a mistake. If the vaccine not correspond at the virus, for example the strain of the virus who is propagate from all ASIA, the virus could keep multiplicate no matter if the animals will not show all sintoms.

2.2 Virus structure  

Image 2: Flu virus structure.

Source: Micro Magnet (https://micro.magnet.fsu.edu/cells/viruses/influenzavirus.html).

Ortomixovirus, group of virus what represents the Orthomyxoviridade family, its genome is formed by RNA. Before it’s was known by mixovirus, virus of mucus and all was included at the oromixovirus. However after the study of its structure they have qualified in two families.

The RNA from the viral particle is segmented in 8 fragments that codified the protein presents in her. The nucleocapsid is spiral and his diameter there is between in 80 to 100nm. In the external part of the wrapper lipidic appears for separate two kind of glycoproteins, hemaglutinina (H) and neuraminidasa (N). The first responsable of the agglutination of hematis in the presence of the virus and the second there is a enzim who intervened in the final phase from the virus's freedom.

In fact to have and a RNA fragmented it does that the antigenic combinations been more numerous giving rise a differents virus strains for the people who not presents antibodies.

For these reason, the specific immunity won by a virus strains in particular does not works for the new ones.

The influenza virus type A is the most common cause of pandemics (epidemic of wide extension), the type B causes for the most part local epidemics and that type C, of animal origin rarely is pathogenic.

2.3 Different kind of aviar virus

There are several classifications of avian influenza according to various parameters, such as its virulence or depending on the species that it affects.

Depending on their virulence, they can be classified in highly pathogenic avian influenza (HPAI) or light or non-pathogenic avian influenza (MPAI). They are differentiated because the HA protein from HPAI is synthesized by enzymes found in most cells of the organism, but HA proteins of the MPIA are synthesized exclusively by enzymes found in the respiratory system.

In the other side, the classification based in the vector transmission differences the avian influenza into three types: A, B and C. The type A affects animals like wild and domesticated birds, ducks, gulls, seabirds and mammals (humans, pigs, horses). Types B and C influenzas only affect humans.

2.4 Since they affect the environmental determinants to the virus of the avian flu.  

The avian grip is commonly transmitted by direct contact between infected birds and healthy birds. It can also spread indirectly through contact with surfaces that have been contaminated. The avian flu virus is found in the secretion of the nostrils (nostrils), mouth, eyes and feces of infected birds.

Contact with contaminated feces is the most common means of transmission. The feces of the wild ducks can introduce the avian flu virus into domestic flocks reared in the open air.

Avian flu can be transmitted by contact between and with poultry and their feces, feathers, guts and blood. The greatest risk of infection for people is through the handling and killing of infected live birds.

The virus is spread mainly by the movement of poultry, its products, people and vehicles used for transport. The virus does not spread by air.

The time that the virus lives in the feces varies according to the amount of virus they contain, the temperature and the moisture content. The virus dies more quickly at high temperatures and lower humidity.

2.5 Mutations and effect on vaccination

An important aspect of viruses that possess RNA genome is their high mutation rate because during replication errors are introduced into the genome because of the RNA polymerase correction deficiency. In the case of influenza virus, the introduced mutations are mainly associated with changes in HA and NA proteins; and they can cause that the antibodies produced during the infection do not recognize the new viral variants, reason why it is necessary to update the vaccine annually.

These small genetic changes can accumulate over time and become antigenically different viruses (far away in the phylogenetic tree). When this happens, it is possible that the body's immune system does not recognize those viruses.

This process works in the following way: a person infected with a particular influenza virus develops antibodies against that virus. As the antigenic changes accumulate, the antibodies created to fight the previous viruses stop recognizing the "newer" virus and the person can get sick again. The fact that the genetic changes produced by a virus with different antigenic properties explains the reason why people can get influenza more than once. It is also the reason why the composition of the influenza vaccine should be reviewed every year and updated as necessary to deal with evolving viruses.

The other type of change is called "major antigenic change." The major antigenic change is an abrupt and important change in influenza A viruses, which results in new hemagglutinin proteins or new proteins of hemagglutinin and neuraminidase in influenza viruses that cause infection in humans. The change results in a new subtype of influenza A or a virus with hemagglutinin or a combination of hemagglutinin or neuraminidase that arose from an animal population that is so different from the same subtype in humans that most people do not have immunity to the new virus .

2.6. Propagation

The flu propagation occurs when an infected person talk, stress or sneeze and expel the virus to the air the flu viruses are transmitted easily around people. It can also be infected with touch surfaces virus contaminated and touching the face after without washing your hands properly.

The mother virus generates more virus using human cells or avian cells.

It is important to analyze the eggs, it’s not enough analyze the ducks to find the virus.

Image 3. Avian Influenza Transmission.

2.7. How to propagate the virus in different species

The avian flu called too avian influenza virus has infected a lot a different animals, including chicken, pics, horses. Nevertheless, some subtypes of the virus are specifics per a especie, except for the avian, who have the all types known from influenza virus A. The avian influenza virus what normally contagious between animals from the same specie, sometimes can infected another kind of specie.

The avian influenza virus can contagious between animals and people by two methods:

-Directly from the avian or from the contaminate zones by the virus to the people.

-Through in a organism who works like host, as the pic.

The avian influenza virus has 8 segments of gens separated. The genome segmented allow the avian influenza virus from different specie mix it and create a new virus from different species infecting a the same person or animal.  

These change in the aviar influenza virus is called antigenic variation. The variation antigenic is given when the new subtype of influenza A to which the majority of people who doesn’t have enough or nule protection.

It’s possible what the process of genetic redistribution can appears in a person who is coinfected from the avian influenza virus A and human influenza virus. The genetic information of both virus can recombination for made a new influenza virus A with hemaglutinina form the aviar virus and other gens from the human virus. The influenza virus A with hemagglutinin (H), against the humans has little or not immunization, who has recombined with a human influenza virus, they are more likely to cause a epidemic between humans.

Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: the hemagglutinin (H) and the neuraminidase (N). There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes. All known subtypes of influenza A viruses have been found among birds, except subtype H17N10 and H18N11 which have only been found in bats. Below is a table showing the different hemagglutinin and neuraminidase subtypes and the species in which they have been detected.     

Image 4: Influenza virus structure.

2.8. Control and diagnosis of avian influenza

The main measure that is being carried out to stop the spread of the epidemic is the sacrifice of the entire population of infected poultry and the surveillance of closed groups or linked to infected groups, the quarantine of the exposed groups and the subsequent eradication, if the disease is detected.

The personnel involved in this task and in others, such as the elimination of poultry waste and excreta, must use suitable clothes and material for each case and follow a strict hygiene of hand washing, material and facilities.

On the other hand, they have to receive antiviral treatment as a preventive measure. It is also important to establish a vigilance of workers (go to the doctor in case having respiratory symptoms, fever and conjunctivitis) and animals (if they are sick or dead).

Image 5. Methods of prevention of avian influenza proposed by Shetland Islands Council’s Environmental Health Team.

In order to determine the presence of the virus in birds that may be infected, laboratory techniques are used to establish a diagnosis. The most used techniques are the following:

• Molecular techniques (r-PCR or reverse polymerase chain reaction): routine methods of early diagnosis. They allow detecting the presence of the virus in minimal quantities from tracheal exudates or faeces, with several days before the definitive diagnosis by isolation.

• Isolation and identification of the virus: necessary for a definitive diagnosis. Chicken embryo culture (embryonated chicken eggs 9-11 days old) from samples of trachea and cloaca (or feces) of live birds, or from different organs and faeces of dead birds.

• Detection of antibodies: from blood samples. They have no diagnostic value, since they only indicate that the animal has had contact with the virus and its organism has reacted to the agent.

3. Conclusion

In conclusion, bird flu is an infectious disease of birds caused by type A strains of influenza virus. In birds, the infection can manifest itself in various forms, from mild symptoms that can go unnoticed, to a disease that quickly leads to death and can cause a serious epidemic.

Image 6. Cases of avian flu between 2014 and 2016 collected by the World Animal Health Information System (WAHIS).

Bird flu viruses do not normally infect humans. However, there have been cases of hyperpathogenic strains (A (H5N1) and A (H7N9)) that have caused serious respiratory diseases in humans. In most cases, the infected persons had been in direct contact with infected poultry or objects contaminated by their feces. However, there is concern that the virus could mutate and acquire the ability to transmit easily between humans, which would increase the risk of a flu pandemic.

Therefore, in order to reduce the risk to human health, it is essential to control and monitor the disease in animals and people.

4.Webgrafia

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