A
Brief Review on Swine Flu
Aher
Vaibhav D*, Arjun Patra, Pronobesh Chattopadhyay and Munesh Mani
College of
ABSTRACT:
Swine influenza is caused by those
strains of influenza virus that usually infect pigs and are called swine
influenza virus (SIV). Swine influenza is known to be caused by influenza A
subtypes H1N1,
H1N2, H3N1, H3N2, and H2N3. The main route of transmission
is through direct contact between infected and uninfected animals. Airborne
transmission through the aerosols produced by pigs coughing or sneezing is also
an important means of infection. In pigs influenza infection produces fever,
lethargy, sneezing, coughing, difficulty breathing and decreased appetite and
in human include fever, cough, sore throat, body aches, headache, chills and
fatigue. Risk factors that may
contribute to swine-to-human transmission include smoking and not wearing
gloves when working with sick animals. The principal method of
treatment is vaccination and proper animal management
techniques. The modern pork industry also uses antibiotic, which although they
have no effect against the influenza virus, do help prevent bacterial pneumonia and other secondary infections
in influenza-weakened herds. The U.S. Centers
for Disease Control and Prevention recommends the use of Tamiflu (oseltamivir) or Relenza (zanamivir) in human. Vaccines and antivirals will be crucial to the effort,
but tracking and communications technologies could also play a key role in
monitoring the virus, distributing accurate health information, and quelling
outbreaks. Meanwhile, other Internet tools are helping to track the spread of
the virus geographically.
INTRODUCTION:
Swine
influenza
(also called swine flu, pigfluenza, hog flu, and pig flu)
refers to influenza
caused by those strains of influenza
virus that usually infect pigs and are called swine
influenza virus (SIV). Swine influenza is common in pigs in the
Midwestern United States (and occasionally in other states), Mexico, Canada,
South America, Europe (including the United Kingdom, Sweden, and Italy), Kenya,
Mainland China, Taiwan, Japan and other parts of eastern Asia1.
The 2009 flu outbreak in humans that is widely
known as "swine flu" is due to an apparently virulent
new strain of influenza A virus subtype H1N1
that was produced by reassortment from one strain of human
influenza virus, one strain of avian
influenza virus, and two separate strains of swine influenza. The
origin of this new strain is unknown, and the World Organization for Animal Health
(OIE) reports that this strain has not been isolated in pigs2. It
passes with apparent ease from human to human, an ability attributed to an
as-yet unidentified mutation. This 2009 H1N1 strain causes the normal symptoms
of influenza, such as fever, coughing and headache3.
CLASSIFICATION
Of the three
genera
of influenza viruses that cause human flu, two also cause influenza in pigs,
with Influenzavirus A being common in pigs and Influenzavirus
C being rare.4 Influenzavirus
B has not been reported in pigs. Within Influenzavirus A and
Influenzavirus C, the strains found in pigs and humans are largely distinct,
although due to reassortment there have been transfers of genes
among strains crossing swine, avian, and human species boundaries4.
Influenza C:
Influenza C viruses infect both humans and pigs,
but do not infect birds5. Transmission between pigs and humans have
occurred in the past6. For example, influenza C caused a small
outbreaks of a mild form of influenza amongst children in Japan7,
and California8. Due to its limited host range and the lack of
genetic diversity in influenza C, this form of influenza does not cause
pandemics in humans9.
Swine influenza is known to be caused by
influenza A subtypes H1N1,
H1N210, H3N111, H3N210, and H2N312. In
pigs, three influenza A virus subtypes (H1N1, H3N2, and H1N2) are the most
common strains worldwide. In the United States,
the H1N1 subtype was exclusively prevalent among swine populations before 1998;
however, since late August 1998, H3N2 subtypes have been isolated from pigs. As
of 2004, H3N2 virus isolates in US swine and turkey stocks were triple reassortants,
containing genes from human (HA, NA, and PB1), swine (NS, NP, and M),
and avian (PB2 and PA) lineages.13
TRANSMISSION:
Transmission between pigs:
The main route of transmission is through
direct contact between infected and uninfected animals12. These
close contacts are particularly common during animal transport. The direct
transfer of the virus probably occurs either by pigs touching noses, or through
dried mucus. Airborne transmission through the aerosols produced by pigs
coughing or sneezing is also an important means of infection. The virus usually
spreads quickly through a herd, infecting all the pigs within just a few days1.
People who work with poultry and swine,
especially people with intense exposures, are at increased risk of zoonotic
infection with influenza virus endemic in these animals, and constitute a
population of human hosts in which zoonosis
and reassortment
can co-occur. Transmission of influenza from swine to humans who work with
swine was documented in a small surveillance study performed in 2004 at the
SIGNS
AND SYMPTOMS:
In pigs influenza infection produces fever,
lethargy, sneezing, coughing, difficulty breathing and decreased appetite12.
In some cases the infection can cause abortion. Although mortality is usually
low (around 1-4%) 1, the virus can produce weight loss and poor growth, causing
economic loss to farmers. Infected pigs can lose up to 12 pounds of body weight
over a 3 to 4 week period.12
In
humans:
According to the Centers for Disease Control and
Prevention (CDC), in humans the symptoms of the 2009 "swine
flu" H1N1 virus are similar to those of influenza
and of influenza-like illness in general.
Symptoms include fever, cough, sore throat, body aches, headache, chills and
fatigue. The 2009 outbreak has shown an increased percentage of patients
reporting diarrhea and vomiting. The 2009 H1N1 virus is not zoonotic swine flu,
as it is not transmitted from pigs to humans, but from person to person15.
PREVENTION:
Methods of preventing the spread of
influenza among swine include facility management, herd management, and
vaccination. Because much of the illness and death associated with swine flu
involves secondary infection by other pathogens, control strategies that rely
on vaccination may be insufficient.
Control of swine influenza by vaccination
has become more difficult in recent decades, as the evolution
of the virus
has resulted in inconsistent responses to traditional vaccines. Standard
commercial swine flu vaccines are effective in controlling the infection when
the virus strains match enough to have significant cross-protection, and custom
(autogenous) vaccines made from the specific viruses isolated are created and
used in the more difficult cases.16, 17. Present vaccination
strategies for SIV control and prevention in swine farms; typically include the
use of one of several bivalent SIV vaccines commercially available in the
Prevention
of pig to human transmission (Fig. 1)
Swine can be infected by both avian and
human influenza strains of influenza, and therefore are hosts where the antigenic
shifts can occur that create new influenza strains. The transmission
from swine to human is believed to occur mainly in swine farms where farmers
are in close contact with live pigs. Although strains of swine influenza are
usually not able to infect humans this may occasionally happen, so farmers and
veterinarians are encouraged to use a face mask when dealing with infected
animals. The use of vaccines on swine to prevent their infection is a major
method of limiting swine to human transmission. Risk factors that may
contribute to swine-to-human transmission include smoking and not wearing
gloves when working with sick animals.20
Prevention
of human to human transmission (Fig. 1)
Influenza spreads between humans through
coughing or sneezing and people touching something with the virus on it and
then touching their own nose or mouth.
Swine flu cannot be spread by pork products, since the virus is not
transmitted through food21. The swine flu in humans is most
contagious during the first five days of the illness although some people, most
commonly children, can remain contagious for up to ten days. Diagnosis can be
made by sending a specimen, collected during the first five days for analysis.
Experts agree that hand-washing can help prevent viral infections, including
ordinary influenza and the swine flu virus. Influenza can spread in coughs or
sneezes, but an increasing body of evidence shows small droplets containing the
virus can linger on tabletops, telephones and other surfaces and be transferred
via the fingers to the mouth, nose or eyes. Alcohol-based gel or foam hand
sanitizers work well to destroy viruses and bacteria.
Figure 1: Prevention of swine
flu: Prevention of pig to human
transmission and Prevention of human to human transmission
Anyone with flu-like
symptoms such as a sudden fever, cough or muscle aches should stay away from
work or public transportation and should contact a doctor to be tested.
Social distancing is
another tactic. It means staying away from other people who might be infected
and can include avoiding large gatherings, spreading out a little at work, or
perhaps staying home and lying low if an infection is spreading in a community.
Public health
and other responsible authorities have action plans which social distancing
actions to request or require depending on the severity of the outbreak22.
As swine influenza is not usually fatal to pigs, little treatment is
required. Instead veterinary efforts are focused on preventing the spread of
the virus throughout the farm, or to other farms.12 Vaccination and animal management techniques are most
important in these efforts. The modern pork industry also uses antibiotic,
which although they have no effect against the influenza virus, do help prevent
bacterial pneumonia
and other secondary infections in influenza-weakened
herds23.
If a person becomes sick with swine flu, antiviral drugs can make the
illness milder and make the patient feel better faster. They may also prevent
serious flu complications. For treatment, antiviral drugs work best if started
soon after getting sick (within 2 days of symptoms). Beside antivirals, palliative
care, at home or in the hospitals, focuses on controlling fevers and
maintaining fluid balance. The U.S. Centers for Disease Control and
Prevention recommends the use of Tamiflu (oseltamivir)
or Relenza (zanamivir)
for the treatment and/or prevention of infection with swine influenza viruses,
however, the majority of people infected with the virus make a full recovery
without requiring medical attention or antiviral drugs.24
The virus isolates in the 2009 outbreak have been found resistant to amantadine
and rimantadine.25
In the U.S., on April 27, 2009, the FDA issued Emergency Use Authorizations to make
available Relenza
and Tamiflu
antiviral
drugs to treat the swine influenza virus in cases for which they are
currently unapproved26.
According to the
CDC: Influenza vaccination is the primary method for preventing influenza and
its severe complications. Vaccination is associated with reductions in
influenza-related respiratory illness and physician visits among all age
groups, hospitalization and death among persons at high risk, otitis media
among children, and work absenteeism among adults. Although influenza
vaccination levels increased substantially during the 1990s, further
improvements in vaccine coverage levels are needed.27
Influenza research includes molecular virology, molecular evolution, pathogenesis,
host immune responses, genomics,
and epidemiology.
These help in developing influenza countermeasures such as vaccines,
therapies and diagnostic tools. Improved influenza countermeasures require
basic research on how viruses enter cells, replicate, mutate, evolve into new
strains and induce an immune response. The Influenza Genome Sequencing Project
is creating a library of influenza sequences that will help us understand what
makes one strain more lethal than another, what genetic determinants most
affect immunogenicity, and how the virus evolves over
time. Solutions to limitations in current vaccine methods are being researched28.
The Influenza Genome Sequencing Project
(IGSP) is an American-based genome
project aimed at improving the availability of genomic
sequence data from influenza
viruses and related information. The project is funded by the National
Institute of Allergy and Infectious Diseases (NIAID), a division of
the National Institutes of Health (NIH), and
has been operating out of the NIAID Microbial Sequencing Center at The Institute for Genomic Research
(TIGR). Sequence information generated by the project has been placed into public domain
through Gene Bank.
The project completed its first genomes in March 2005 and has rapidly
accelerated since, with over 1800 genomes now in the public domain. As of
January 2007, 1813 isolates had been completely sequenced from influenza
viruses that are endemic in human (human flu) avian (bird flu) and swine (swine
flu) populations, including many strains of H3N2 (human), H1N1 (human), and H5N1 (avian)29.
Variants
of Influenza virus A
Variants are
sometimes named according to the species (host) the strain is endemic in or
adapted to some variants named using this convention are
·
Bird flu
·
Dog Flu
Avian variants have
also sometimes been named according to their deadliness in poultry, especially
chickens:
·
Low Pathogenic Avian Influenza (LPAI)
·
Highly Pathogenic Avian Influenza (HPAI), also called deadly
flu or death flu Influenza A viruses are negative sense, single-stranded, segmented RNA viruses.
There are 16 different HA antigens (H1 to H16) and nine different NA antigens
(N1 to N9) for influenza A. Until recently, 15 HA types had been recognized,
but a new type (H16) was isolated from black-headed
gulls caught in Sweden and the Netherlands
in 1999 and reported in the literature in 200530.
CONCLUSION:
Swine flu is a dreaded disease and its
treatment is not certain. So its important to gather information on the
outbreak, spreading and fighting of the so-called swine flu; and we have to see the increasing transmission,
particularly human-to-human across the world as it's going to be increasingly difficult
for us to prevent this disease. This review focuses on what is known about the
basic concept of swine flu: its sources, classification, transmission,
symptoms, prevention and treatment in swine and human. Also current status of
pathogenicity and spread of influenza A virus in species other than man, with
particular emphasis on the wild bird reservoir. A drug development programme
should be undertaken to develop modern drugs for the treatment of the disease.
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A
Received on 21.09.2009
Accepted on 18.11.2009
© A&V Publication all right reserved
Research J. Pharmacology and
Pharmacodynamics 2(2): March April 2010: 126-130