Swine Influenza

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SWINE INFLUENZA Nature of the disease Swine influenza (SI) is a virus disease that can cause epidemics of acute respiratory disease in pigs. The disease is due to viruses from the type A of the Orthomyxoviridae family, (there are three types of Orthomyxoviridae, A, B and C). Etiology of SI is complex according to the high genetic variation of the causative viruses, mainly on two glycoprotein : hemagglutin (H) and neuramidase (N). A nomenclature for virus designation has been established by WHO in 1980. The disease causes high morbidity but low mortality. It can also persist as an endemic infection and is a potential zoonosis. Classification SPC List D disease, WHO surveyed disease Susceptible species Pigs are the main host. However, strains of swine influenza virus can also be directly transmissible to humans, and reciprocally. SI was responsible for the human outbreak in 1918-20 that killed more than 20 million people over the world (Spanish flu). A recent strain has also been responsible for an outbreak in 1976. There is increasing evidence of interchange of influenza viruses between pigs, other mammalian (including marine mammals) and avian hosts, either directly or after a process of genetic reassortment or mutation. Distribution Epidemics of swine influenza occur fairly regularly each winter in North America and Europe. Outbreaks have also been reported in many other parts of the world, including South Africa, Kenya, India, China, Hong Kong, Japan, Singapore and South America. Clinical signs There is a very high morbidity rate and most pigs in a herd get the disease almost simultaneously. Outbreaks typically occur colder months but it some cases SI remains endemic. Young pigs are more severely affected. The first signs are: •

Fever

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Anorexia leading to loss of weight,

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Inactivity, prostration and huddling leading to weakness.

Then there is a sudden onset of acute respiratory signs: •

Paroxysmal coughing,

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Sneezing,

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Irregular abdominal breathing,

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Ocular and nasal discharges.

Most pigs recover about six days after the onset of the disease. The mortality rate is generally about 1%, but may be higher in young piglets. SI can precipitate outbreak of more serious respiratory disease causing mortality. In humans the disease is much more severe causing viral pneumonia that is often fatal. Post-mortem findings The lesions are confined to the respiratory system and are not very specific. •

Hyperaemic of the mucosa of the respiratory tract,

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Excess production of mucus,

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Atelectasis and emphysema of the cardiac and apical lobes of the lungs,

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Enlarged bronchial and mediastinal lymph nodes,

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In fatal cases there may be an acute intersticial pneumonia

Differential diagnosis The following diseases must be considered in the differential diagnosis: •

Aujeszky's disease

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Atrophic rhinitis

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Enzootic (mycoplasmal) pneumonia

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Bacterial pneumonia due to Pasteurella or Haemophilus spp.

Specimens required for diagnosis Although the presumptive diagnosis can be based on clinic and epidemiology it is preferable to address samples to reference laboratories. Identification of the virus can be done by by many techniques including immunohistochemical detection, hemagglutination-inhibition coupled to neuramidase inhibition, ELISA and PCR, sometimes several techniques must be combined to identfy (H) and (N) subtypes. Identification tests can be performed from nasal (preferably) or pharyngeal swabs from live animals. Samples must be suspended in glycerol saline and kept at 4°C if they are tested within 48 hours and at 70°C, shipped with dry ice if they are tested after a longer delay. Alternatively lungs from spontaneously dead or sacrificed animals can be sent under similar conditions. For serology, blood samples (about 20 ml each) should be collected from pigs that are in the acute and convalescent stages of the disease (2 to 3 weeks later). Tests are made by hemagglutination inhibition and demonstrate a raise in the antibody level. The interpretation of serological results may be complicated in young pigs because of the persistence of maternal antibodies. Transmission Swine influenza is transmitted by direct contact between pigs. In the acute stages of the disease, high concentrations of virus are found in nasal secretions. Virus is transmitted by aerosols over a short distance. The virus can be shed for 30 days after infection and has been recovered from clinically normal animals.

~3~ The disease is spread to new areas and farms by the movement of infected pigs or carrier people. The virus is easily carried and spread by avian species, particularly waterfowl and turkeys. Outbreak of Asian subtypes of influenza A may involve duck to pig transmission since these animals are traditionally kept together. Care should be taken to prevent spread from and between birds and humans to swine. In endemic areas, while virus is present throughout the year, outbreaks are seasonal, tending to occur in late autumn and early winter. Epidemics are often explosive, with outbreaks occurring on most pig farms in a locality over a short period. Risk of introduction Swine fever is most likely to be introduced through importation of infected pigs. These animals should be screened by serology to determine if they have been exposed to swine influenza. Note that infection from humans to pigs is also possible. Control / vaccines The best way to deal with swine influenza is to prevent the occurrence and spread of the disease. Where the disease does occur, the primary treatment is supportive therapy. Infected pigs require a dry, clean, dust free environment. Antibiotics are also essential to treat and control any secondary bacterial infections that usually develop. Expectorants are commonly used as a herd treatment and are administered in the drinking water. Commercial vaccines are available in Europe and North America. Results from various studies show that vaccinated animal exposed to swine influenza virus have markedly reduced nasal shedding, virus infection in lung tissue, and lung pathology compared to non-vaccinated animals. Studies have also shown than maternally derived antibody in vaccinated sows protected 5 week old pigs from clinical disease, virus infection in the lung, and lung pathology but did not prevent nasal viral shedding. As the passage of swine influenza to humans is a serious threat if suspected, the disease should be diagnosed and notified to Public Health Department.

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Swine Flu History and Overview

Influenza viruses are small RNA viruses that infect many mammals, including humans, birds, and swine. Before 2009, swine influenza predominately affected swine and was not transmitted often or easily to people. Even in the isolated instances in which swine influenza infected people, it had very limited ability to spread from person to person. Most cases were directly linked to contact with swine through farming or at fairs.

~4~ Swine were first noticed to have influenza-like illnesses in 1918 during the human influenza pandemic. The term "pandemic" means that an infection has spread to many countries around the world, causing widespread human disease. Swine influenza did not cause the 1918 pandemic. Rather, pigs apparently acquired the infection from humans or from an undiscovered source. For decades, the swine virus remained relatively unchanged. In the 1990s, however, swine influenza viruses became more diverse and new strains appeared. The reason for this change is not clear but may have been related to overcrowding on large swine farms. Before 2009, there was only one swine influenza outbreak in people that caused public-health concerns. This outbreak occurred in 1979, in soldiers at Fort Dix, New Jersey. One recruit died, and approximately 12 were hospitalized with influenza. Further testing showed that more than 200 recruits had acquired the virus, although most had few or no symptoms. The infecting strain was found to be strongly related to swine influenza virus, raising concerns that a new pandemic might occur. In response, public-health officials began a massive public vaccination program. Up to 25% of people in the United States were vaccinated. Unfortunately, the 1979 vaccine was associated with a small increased risk of Guillain-Barré syndrome, a serious neurological condition, with the risk estimated to be one to nine excess cases per million doses. Importantly, the 1979 strain did not spread easily from person to person and there was no epidemic. Human cases outside of Fort Dix were uncommon. Moreover, the 1979 vaccine was made using an oldfashioned process which is no longer utilized. The lessons learned from the 1979 swine influenza event have been applied in dealing with pandemic threats, including the severe acute respiratory syndrome (SARS) outbreak of 2003 and the 2009 influenza outbreak. Key lessons include ensuring adequate communication with the public, producing a rapid but measured response to potential threats, and ensuring that any new strain fulfills criteria to cause a pandemic before large-scale vaccination is undertaken. The 2009 outbreak of swine influenza (novel H1N1) In March and April 2009, hundreds of cases of human respiratory illness were reported in Mexico that were suspected or confirmed to be caused by a novel swine-type influenza virus. By April, confirmed cases were also reported in the United States. The first reported cases in the U.S. came from San Diego County and Imperial County in California and Guadalupe County in Texas. Reports from other states rapidly followed, and the disease spread rapidly around the globe. The World Health Organization (WHO) has officially declared the 2009 swine flu to be a pandemic. The U.S. Centers for Disease Control and Prevention (CDC) estimates that more than 1 million Americans were infected with swine influenza by June 2009. By August 2009, more than 170 countries and territories reported swine flu cases. By October, 46 U.S. states were reporting widespread outbreaks. By late October, the virus had been confirmed to have caused more than 1,000 deaths in the U.S., with almost 100 of the deaths in children. Approximately 6% of deaths are in pregnant women, although only 1% of the population is pregnant. Physician visits, hospitalizations, and deaths in the fall of 2009 all exceeded seasonal thresholds. On Oct. 25, 2009, President Obama declared a national emergency as a result of the outbreak. This allows public-health officials additional power to allow waive some regulations to facilitate patient care and will allow hospitals to set up separate facilities to isolate sick patients. Swine Flu Cause

Influenza viruses are named according to the types of proteins on the outer surface of the virus. The two main proteins are hemagglutinin (H) and neuraminidase (N). The swine influenza virus

~5~ in the 2009 outbreak is an H1N1 virus. In fact, although the term swine flu is often used to describe the outbreak, the official term for the virus is novel H1N1 influenza. It is important to realize that the influenza virus changes (mutates) constantly so that there are many strains of H1N1 that differ subtly from each other. Swine flu is caused by one strain of H1N1, but there are many other strains. Some H1N1 strains only infect pigs. Others infect humans, pigs, and birds. These subtle differences matter because the human body makes antibodies that are tailored to a single strain of influenza. If a person recovers from novel H1N1 (swine) flu, they are probably protected against infection from the same swine flu strain but are not protected against infections from variations on the strain or from other strains of influenza. The 2009 novel H1N1 swine influenza strain appears to be a result of genetic "reassortment," meaning that it contains pieces of influenza from many different sources. The 2009 virus includes genes that come from bird influenza viruses, swine influenza viruses, and human influenza viruses. This strain has not previously caused infections in humans or pigs. Thus, it is unlikely that humans will have preexisting immunity to this new strain Swine Flu Transmission

Swine influenza (novel H1N1) spreads from person to person, either by inhaling the virus or touching surfaces contaminated with the virus, then touching the mouth or nose. Infected droplets are expelled into the air through coughing or sneezing. Early information suggests that swine influenza is about as contagious as the usual human influenza. If one person in a household gets swine flu, anywhere from 8%-19% of household contacts will get infected. Reports from the southern hemisphere suggest that swine influenza is causing slightly more infections than would be normal for an influenza season Swine Flu Symptoms

Swine flu is a respiratory infection. The CDC recommends that swine influenza be considered in people who have fever and respiratory symptoms, especially cough or a sore throat. Ill people may also have fatigue, chills, headache, or body aches. Nausea, vomiting, or diarrhea has also occurred in people with swine flu. Very young children may not complain of fever or have a cough but rather have listlessness or shortness of breath as their main symptom. Children and young adults (ages 0-24 years) have the highest rate of infection. Older adults (>65 years) are less likely to have infections, leading some to speculate that older individuals might have "partial immunity." Partial immunity occurs when people make antibodies against one virus that have some effect on another virus. Thus, older people who were exposed to a similar virus may be partly protected against swine flu. The key words here are may and partly. There is no guarantee that an older person is protected, and if they do get infected, they are at risk for complications requiring hospitalization. One recent study showed that 33% of people over age 59 have antibodies that might help protect against novel H1N1. However, if older people do get infected, the disease may be more severe, as is true of most influenza infections. Although the infection is usually mild, some people with swine flu have experienced serious respiratory illness, including pneumonia or respiratory failure leading to death. Pregnant women are at high risk for severe disease. Of concern, most deaths have occurred in adults under age 65, including people under age 25. This is the opposite of what happens in a normal influenza season when most deaths occur in the elderly. People with chronic medical conditions are always at higher risk for complications from influenza and this is also true of swine flu. These chronic medical conditions include asthma,

~6~ chronic lung disease, heart disease, diabetes, suppressed immune systems (including from chemotherapy), and kidney failure. People with swine influenza are assumed to be contagious from one day before getting sick until at least 24 hours after symptoms resolve. Children and people with weak immune systems may be infectious for longer periods (for example, 10 days). When to Seek Medical Care

People with fever and mild respiratory symptoms should call their physician for guidance. If you live in an area that is not currently reporting any cases of swine influenza, your physician may direct you to come into the clinic to be evaluated. If you live in an area where swine influenza is circulating already, your physician may decide to treat you over the phone. The CDC recommends this approach to minimize the number of sick people who go out into the community or into a clinic once cases have been confirmed. People who are seriously ill should seek medical attention immediately through an emergency room or other setting. This includes people with shortness of breath, confusion, dizziness, or alterations in consciousness. Small children may not be able to describe their symptoms, and parents should look for signs of rapid breathing, bluish skin, or reduced level of responsiveness, which should prompt immediate medical attention Exams and Tests

Swine influenza can be confirmed by culturing respiratory secretions such as sputum or nasal/throat secretions, but this is expensive and not often done. Rapid tests are available to give a general idea if an influenza strain is present, but they are far from perfect and may not pick up swine influenza or even regular seasonal influenza. In fact, the CDC does not recommend the use of rapid tests because the results are often inaccurate. Specific testing for the genetic material of the virus, such as a test called a polymerase chain reaction or PCR, may be done at state health departments or at the CDC. Your local laboratory will have a procedure in place to send specimens to the health department when necessary. It is not possible or economically feasible to test every symptomatic patient for swine flu once a community has multiple cases. If there are large numbers of cases of swine flu present in the community, the laboratory will usually stop doing specific tests for swine flu and will simply recommend that patients with symptoms be assumed to have the infection. Swine Flu Treatment

Laboratory testing has shown that the 2009 swine influenza strain is sensitive to two antiviral medicines that are used to treat human influenza. They are oseltamivir (Tamiflu) and zanamivir (Relenza). Oseltamivir is given in pill form. Zanamivir is an inhaled medication. Both medications require a prescription. A few drug-resistant strains have been reported, but most swine flu strains remain sensitive. Older drugs like amantadine (Symmetrel) are not effective. The government has released some of its stockpile of Tamiflu, but the drug may be in short supply in local pharmacies. Not everyone with swine flu needs to be treated. However, the drug should be given to people who appear to have swine influenza if they have chronic medical conditions that put them at risk for complications (see above) or if they are unusually ill.

~7~ Self-Care at Home

People who are suspected of having novel H1N1 (swine) influenza should stay home from work and not go into the community, including attending school or going to work. The CDC recommends that people with influenza-like illness remain at home until at least 24 hours after they are free of fever. Over-the-counter medicines like ibuprofen (Advil) or acetaminophen (Tylenol) may be used to reduce fever or aches. Aspirin or aspirin-containing products should not be given to children 18 years of age or younger, due to the risk of liver damage (Reye syndrome). Always follow the package directions for any over-the-counter cold or flu remedy. Prevention and Vaccines

Simple measures have been shown to reduce the risk of transmission of influenza. These include frequent hand washing with soap and water or disinfection with alcohol. People should try to avoid touching their face or mucous membranes. The influenza virus can live about two hours on surfaces that become contaminated. During coughs and sneezes, the mouth should be covered with a tissue or a sleeve. In areas with large numbers of cases, it is best to minimize nonessential exposure to crowds. Sick people should stay home whenever possible. To reduce the risk of spreading the flu to other family members, everyone in the household should wash their hands frequently. Alcohol-based sanitizing gels are available in stores and may be used instead of soap and water when hands are not visibly soiled. Rarely, if a person has been exposed to a confirmed case of swine influenza, a physician may recommend a course of medications to reduce the risk of disease. This is called "prophylaxis" and is usually reserved for people at very high risk for complications, such as pregnant women. The CDC has issued guidelines for prophylaxis in special circumstances (www.cdc.gov). A vaccine against swine influenza is available, although supplies have been limited initially . There are two types of vaccine: the nasal vaccine and the shot. The nasal vaccine has a weakened ("attenuated") virus and is administered by sniffing. The nasal vaccine is used for people 2-49 years of age. The injection (shot) does not contain living viruses, only inactivated viruses, and may be given to anyone over the age of 6 months. Your doctor can help you decide which vaccine is best for you. People over the age of 9 years should receive a single dose, whereas children aged 6 months to 9 years will receive two doses one month apart. Because vaccine is in short supply, the CDC recommends that the following groups be vaccinated first: pregnant women, caregivers for infants under 6 months of age, health-care workers, people aged 6 months to 24 years of age, and people age 25-64 who have chronic health conditions. When the shortage resolves, the vaccine will be recommended for all people over 6 months of age. It is important to point out that the 2009 novel H1N1 vaccine is not related to the 1976 vaccine. The 2009 vaccine is made using the modern process, and the 2009 virus is very dissimilar to the 1976 virus. Preliminary studies have shown that the 2009 vaccine has similar side effects to our modern seasonal influenza vaccines and that these side effects are usually confined to a sore arm. Less commonly, a person may have generalized aches or a low-grade fever. Severe allergic reactions are very rare, but people who have severe egg allergies or previous severe reactions to influenza vaccines should not receive the 2009 novel H1N1 vaccine. Some people have died from bacterial infections that attack lungs already damaged by influenza. For this reason, the CDC recommends that the pneumococcal vaccine (against Pneumococcus bacteria that may cause pneumonia) be offered to all people with underlying chronic illness and

~8~ all people over 65 years of age. In addition, people who survive novel H1N1 (swine) flu are still at risk for the regular seasonal flu. For this reason, the CDC continues to recommend the seasonal influenza vaccine be used as recommended. Next Steps

The results of ongoing investigations will answer several key questions. Specifically, it will be important to know what proportion of people become severely ill, what puts people at risk for severe illness, and how effective the new vaccine will be. It will also be important to monitor the virus to see if it mutates to become more (or less) dangerous. So far, the virus has not changed much since it first appeared. Outlook

The 2009 influenza pandemic has caused significant economic, social, and health problems. Although the number of deaths is not high for an influenza virus, it is concerning that death rates in pregnant women and otherwise health young people are disproportionately high. Simple infection-control measures (covering coughs, washing hands) will help reduce the risk of infection. Vaccination is an effective method of controlling the disease and should be given whenever indicated and available.