SWINE FLU: AN OVERVIEW

Priyanka Lokwani, Pramod Kumar, Yozana Upadhyay, Stuti Gupta,

Renu Solanki and Nisha Singh

ABSTRACT

Swine flu (swine influenza) is a respiratory disease caused by viruses (influenza viruses
belonging to family Orthomyxoviridae) that infect the respiratory tract of pigs and result in nasal
secretions, a barking-like cough, decreased appetite, and listless behaviour. Oseltamivir (Tamiflu)
and zanamivir (Relenza) is the recommended drug both for prophylaxis and treatment. The best
treatment for influenza infections in humans is prevention by vaccination.

Key words: Swine flu, respiratory tract infection, H1N1 virus, influenza virus

INTRODUCTION
Swine flu (swine influenza) is a respiratory disease caused by viruses (influenza viruses)
that infect the respiratory tract of pigs and result in nasal secretions, a barking-like cough,
decreased appetite (Bouvier et al, 2008). A highly contagious form of influenza seen in swine,
caused by a virus of the family Orthomyxoviridae (Kimura et al, 1997). The infection is
communicable to humans and caused a worldwide epidemic in 1918.The H1N1 virus (swine flu)
is a new flu virus strain that has caused a worldwide pandemic in humans from June 2009 to
August 2010.The Centers for Disease Control and Prevention now call the virus 2009 H1N1, an
acute and highly contagious respiratory disease of swine caused by the orthomyxo virus thought
to be the same virus that caused the 1918 influenza pandemic an acute febrile highly contagious
viral disease. A highly contagious form of human influenza caused by a filterable virus identical
or related to a virus formerly isolated from infected swine. The respiratory infection popularly
known as swine flu is caused by an influenza virus first recognized in spring 2009, near the end
of the usual Northern Hemisphere flu season. The new virus, 2009 H1N1, spreads quickly and
easily (Matsuzaki et al, 2002). A few months after the first cases were reported, rates of
confirmed H1N1-related illness were increasing in almost all parts of the world. As a result, the
World Health Organization declared the infection a global pandemic. That official designation
remained in place for more than a year. Technically, the term "swine flu" refers to influenza in
pigs. Occasionally, pigs transmit influenza viruses to people, mainly hog farm workers and
veterinarians. (Lynch et al, 2007)

Symptoms of Swine Flu

Swine flu produces most of the same symptoms in pigs as human flu produces in people
(Yassine HM, 2007) Swine flu can last about one to two weeks in pigs that survive. In a number of
instances, people have developed the swine flu infection when Shortness of breath or
they are closely associated with pigs (for example, farmers, pork cough Loss of appetite
processors), and likewise, pig populations have occasionally been Aching muscles
infected with the human flu infection. Investigators think the 2009
Swine Flu Symptoms vs. a Cold or Sinus Infection (Haber P
swine flu strain, first seen in Mexico, should be termed novel
H1N1 flu since it is mainly found infecting people and exhibits et al, 2009)
two main surface antigens, H1 (hemagglutinin type 1) and N1 It is important to keep in mind most children with a
(neuraminidase type1). Recent investigations show the eight RNA runny nose or cough will not have swine flu and will not have to
strands from novel H1N1 flu have one strand derived from human see their pediatrician for swine flu testing.
flu strains, two from avian (bird) strains, and five from swine
strains ( Heinen P, 2003).

Fig 1. shows Influenza Virus (Gilchrist MJ, 2007)

Symptoms of swine flu infections include (Antonovics J, 2006):

Fever, which is usually high, but unlike seasonal flu, Fig 2. shows symptoms of swine Flu (Patterson KD, 1991)
is sometimes absent
Cough High-risk groups (Vellozzi C,2009):
Runny nose or stuffy
nose Sore throat High Risk group includes persons having
Body aches Chronic (long-term) lung
Headache disease Chronic heart disease
Chills Chronic kidney disease
Fatigue or tiredness, which can be extreme Chronic liver disease
Diarrhoea and vomiting, sometimes, but more Chronic neurological disease (neurological
commonly seen than with seasonal flu disorders include chronic fatigue syndrome,
Signs of a more serious swine flu infection might multiple sclerosis and parkinson's disease)
include pneumonia and respiratory failure. Immunosuppression (whether caused by disease
or treatment)
Serious Swine Flu Symptoms (Schmeck , Harold M. 1976)
Diabetes mellitus
More serious symptoms that would indicate that a child
Also at risk are:
with swine flu would need urgent medical attention include:
Fast breathing or trouble breathing Patients who have had drug treatment for asthma within
Bluish or gray skin color the past three years
Not drinking enough fluids Pregnant women
People aged 65 and older (gaydos jc,2006)
Severe or persistent vomiting
Not waking up or not interacting PATHOPHYSIOLOGY OF SWINE FLU
Being so irritable that the child does not want to be held Flu-
like symptoms improve but then return with fever and First, the influenza viruses (types A, B, C) are enveloped
worse cough RNA viruses with a segmented genome; this means the viral RNA
Unusual tiredness genetic code is not a single strand of RNA but exists as eight
Headache different RNA segments in the influenza viruses. A human (or
Runny nose bird) influenza virus can infect a pig respiratory cell at the same
Sore throat time as a swine influenza virus; some of the replicating RNA
strands from the human virus can get mistakenly enclosed inside the been challenged, and the U.S. Centers For Disease Control
enveloped swine influenza virus. For example, one cell could contain and Preventation (CDC) has not completed their comparative
eight swine flu and eight human flu RNA segments. The total number studies of these tests, however, a new test developed by the
of RNA types in one cell would be 16; four swine and four human flu CDC and a commercial company reportedly can detect H1N1
RNA segments could be incorporated into one particle, making a reiably in about one hour; as of October 2009, the test is only
viable eight RNA segmented flu virus from the 16 available segment available to the military.
types. Various combinations of RNA segments can result in a new
Swine flu (H1N1) is definitively diagnosed by identifying the
subtype of virus (known as antigenic shift) that may have the ability to
particular antigens associated with the virus type. In general,
preferentially infect humans but still show characteristics unique to
this test done in a specialized laboratory and is not done by
the swine influenza virus (Figure 3). It is even possible to include
many doctor’s offices or hospital laboratories. However,
RNA strands from birds, swine, and human influenza viruses into one
doctor’s offices are able to send specimens to specialize
virus if a cell becomes infected with all three types of influenza (for
laboratories if necessary. Because of the larger number of
example, two bird flu, three swine flu, and three human flu RNA
novel H1N1 swine flu cases (as of October 2009, the vast
segments to produce a viable eight-segment new type of flu viral
majority of flu cases (about 99%) are due to novel H1N1 flu
genome). Formation of a new viral type is considered to be antigenic
Viruses), the CDC recommends only hospitalizes patient’s flu
shift; small changes in an individual RNA segment in flu viruses are
virus strains be sent to reference labs to be identified.
termed antigenic drift and result in minor changes in the virus.
However, these can accumulate over time to produce enough minor Treatment (Myers KP, 2006)
changes that cumulatively change the virus antigenic makeup over
time (usually years).Second, pigs can play a unique role as an The guiding principles are:
intermediary host to new flu types because pig respiratory cells can be
infected directly with bird, human, and other mammalian flu viruses. Early implementation of infection control precautions to minimize
Consequently, pig respiratory cells are able to be infected with many
A. nosocomical / household spread of disease
types of flu and can function as a "mixing pot" for flu RNA segments
B. Prompt treatment to prevent severe illness & death.
(Figure 3). Bird flu viruses, which usually infect the gastrointestinal
C. Early identification and follow up of persons at risk.
cells of many bird species, are shed in bird faeces. Pigs can pick these
viruses up from the environment and seem to be the major way that 1. Oseltamivir Medication
bird flu virus RNA segments enter the mammalian flu virus
population. (McKinney WP et al, 1990)
Oseltamivir is the recommended drug both for prophylaxis
and treatment.

Dose for treatment is as follows:

By Weight:
‐ For weight <15kg 30 mg BD for 5 days
‐ 15-23kg 45 mg BD for 5 days
‐ 24-<40kg 60 mg BD for 5 days

‐ >40kg 75 mg BD for 5 days93

• For infants:
‐ < 3 months 12 mg BD for 5 days
‐ 3-5 months 20 mg BD for 5 days
‐ 6-11 months 25 mg BD for 5 days
‐ It is also available as syrup (12mg per ml)

‐ If needed dose & duration can be modified as per clinical condition.( Richard E,1978)

Adverse reactions
Oseltamivir is generally well tolerated, gastrointestinal side effects
(transient nausea, vomiting) may increase with increasing doses,
particularly above 300 mg/day. Occasionally it may cause
bronchitis, insomnia and vertigo. Less commonly angina, pseudo
membranous colitis and peritonsillar abscess have also been
reported. There have been rare reports of anaphylaxis and skin
Fig 3. Shows Pathophysiology of Swine Flu (Heinen, P. (2003) rashes. In children, most frequently reported side effect is
vomiting. Infrequently, abdominal pain, epistaxis, bronchitis, otitis
DIAGNOSIS (Gray GC, 2009) media, dermatitis and conjunctivitis have also been observed.
A quick test (for example, nasopharyngeal swab sample) is done
to see if the patient is infected with influenza A or B virus. Most
of the tests can distinguish between A and B types. The test can
be negative (no flu infection) or positive for type B, the flu is not
likely to be swine flu (H1N1). If it is positive for type A, the
person could have a conventional flu strain or swine flu (H1N1).
However, the accuracy of these tests has
2. Supportive therapy 3. Discharge Policy
 Adult patients should be discharged 7 days after symptoms
 IV Fluids. have subsided.
 Parentral nutrition.  Children should be discharged 14 days after symptoms
 Oxygen therapy/ ventilatory support. have subsided.
 Antibiotics for secondary infection.  The family of patients discharged earlier should be
 Vasopressors for shock. educated on personal hygiene and infection control
 Paracetamol or ibuprofen is prescribed for fever, myalgia measures at home; children should not attend school
and headache. Patient is advised to drink plenty of fluids. during this period.
Smokers should avoid smoking. For sore throat, short
course of topical decongestants, saline nasal drops, throat 4. Chemo Prophylaxis
lozenges and steam inhalation may be beneficial.
 Salicylate / aspirin is strictly contraindicated in any  All close contacts of suspected, probable and confirmed
influenza patient due to its potential to cause Reye’s cases. Close contacts include household /social contacts,
syndrome. family members, workplace or school contacts, fellow
 The suspected cases would be constantly monitored for travelers etc.
clinical /radiological evidence of lower respiratory tract  All health care personnel coming in contact with suspected,
infection and for hypoxia (respiratory rate, oxygen probable or confirmed cases
saturation, level of consciousness).  Oseltamivir is the drug of choice.
 Patients with signs of tachypnea, dyspnea, respiratory  Prophylaxis should be provided till 10 days after last
distress and oxygen saturation less than 90 per cent should exposure (maximum period of 6 weeks)
be supplemented with oxygen therapy. Types of oxygen  By Weight:
‐ For weight <15kg 30 mg OD
‐ 15-23kg 45 mg OD

devices depend on the severity of hypoxic conditions which ‐

‐
24-<40kg 60 mg OD
>40kg 75 mg OD

can be started from oxygen cannula, simple mask, partial  For infants:
‐ < 3 months not recommended unless situation judged critical
re-breathing mask (mask with reservoir bag) and non due to limited data on use in this age group
rebreathing mask. In children, oxygen hood or head boxes
‐ 3-5 months 20 mg OD
‐ 6-11 months 25 mg OD

can be used. 5. Non-Pharmaceutical Interventions (Lindstrom SE,2004)

 Patients with severe pneumonia and acute respiratory failure
(SpO2 < 90% and PaO2 <60 mmHg with oxygen therapy) Close Contacts of suspected, probable and confirmed cases
must be supported with mechanical ventilation. Invasive should be advised to remain at home (voluntary home quarantine) for
mechanical ventilation is preferred choice. Non invasive at least 7 days after the last contact with the case. Monitoring of fever
ventilation is an option when mechanical ventilation is not should be done for at least 7 days. Prompt testing and hospitalization
available. To reduce spread of infectious aerosols, use of must be done when symptoms are reported. All suspected cases,
HEPA filters on expiratory ports of the ventilator circuit / clusters of ILI/SARI cases need to be notified to the State Health
high flow oxygen masks is recommended. Authorities and the Ministry of Health
 Maintain airway, breathing and circulation (ABC); & Family Welfare, Govt. of India (Director, EMR and NICD). If a
 Maintain hydration, electrolyte balance and nutrition. person becomes sick with swine flu, antiviral drugs can make the
 If the laboratory reports are negative, the patient would be illness milder and make the patient feel better faster. They may
discharged after giving full course of oseltamivir. Even if also prevent serious flu complications. For treatment, antiviral
the test results are negative, all cases with strong drugs work best if started soon after getting sick (within 2 days of
epidemiological criteria need to be followed up. symptoms). Beside antivirals, supportive care at home or in
 Immunomodulating drugs has not been found to be hospital, focuses on controlling fevers, relieving pain and
beneficial in treatment of ARDS or sepsis associated multi maintaining fluid balance, as well as identifying and treating any
organ failure. High dose corticosteroids in particular have secondary infections or other medical problems. The U.S. Centers
no evidence of benefit and there is potential for harm. Low for Disease Control and Prevention recommends the use of
dose corticosteroids (Hydrocortisone 200-400 mg/ day) Tamiflu (oseltamivir) or Relenza (zanamivir) for the treatment
may be useful in persisting septic shock (SBP < 90). and/or prevention of infection with swine influenza viruses;
 Suspected case not having pneumonia do not require
antibiotic therapy. Antibacterial agents should be
administered, if required, as per locally accepted clinical
practice guidelines. Patient on mechanical ventilation
should be administered antibiotic prophylactically to
prevent hospital associated infections.
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