On the Importance of Health Monitoring of Swine Workers

This is an article I wrote for a producers group newsletter on February 21, 2008. Unfortunately it was never published because the administrators of the newsletter thought it was too "controversial". I'm not sure what the controversy was. Perhaps it was the fact that I was advocating a review of their employee health policies or biosecurity protocols? Maybe they felt workers might be too scared to come to work? Who knows, but those were the facts and they remain salient today - although the anecdotes may be a bit dated. I ended up submitting piece on swine mange detection and control, which they found more agreeable. My original article follows:

I am sitting here at my computer, surrounded by NyQuil® capsules and
Kleenex®. I feel terrible but these flu symptoms are making me think
about a couple of recently published studies that focused on swine influenza
and its impact on swine workers.

A research group from the University of Alberta recently isolated a strain of Influenza A virus of probable swine origin (H3N2) from a 7-month old infant who lived on a communal farm in Canada. Another research group from the University of Iowa tested nearly 400 swine workers, including farmers, veterinarians, and
meat processing workers for exposure to strains of swine influenza. Their findings showed that occupational exposure to pigs greatly increases these workers' risk of
swine influenza virus infection. Why are these two studies important? It is well known that humans, pigs, and birds are linked in influenza transmission. During
the 1918 pandemic, a concurrent outbreak of swine influenza spread across the US Midwest. Numerous anecdotal accounts from that time period described flu-like illnesses developing in farmers and their families after contact with ill swine and of swine developing symptoms of swine influenza after contact with ill farmers. Since the 1918 pandemic, human influenza viruses have infected swine and swine influenza viruses have occasionally caused recognized disease among humans. The details of
the influenza virus are quite intricate however, it is important to know that Influenza A virus can infect people, pigs, and birds. Influenza A/H3N2 viruses occur commonly in humans; therefore most people have some antibody to these viruses. Two important swine flu virus strains are H1N1 and H3N2. H1N1 viruses do not commonly occur in people, however a high proportion of people occupationally exposed to pigs have been shown in several studies to have antibody evidence of prior swine H1N1 flu infection. For swine H1N1 viruses, only rare person to person
transmission has been documented in the past. Thus, human infections with swine H1N1 viruses should be investigated particularly when they are detected among non-occupationally exposed persons to ensure that human to human transmission is not occurring and to monitor for changes in circulating viruses and the emergence of novel viruses. Since the swine and human H3N2 viruses are similar, a swine H3N2
virus infection in humans would not represent a possible pandemic threat.

So what does this mean for the swine workers of today? Because of their potential bridging role in exposing humans to swine diseases, swine workers are an important risk group in a potential pandemic. Protecting swine workers from influenza viruses will also benefit those with whom they have contact, namely family members, as well as the swine herds for which they care. Encouraging swine workers to receive annual influenza vaccines will reduce their potential role in the genesis of novel influenza strains. You can read more about swine influenza and its importance in swine workers at the Centers for Disease Control and Prevention website: www.cdc.gov/flu/swine.

Heightened Biosecurity Measures

In light of the discovery of the circulating H1N1 influenza virus in a group of pigs on a farm in Alberta, now would be a great time for producers to review or initiate a clear biosecurity policy for their farms. Pigs are susceptible to many human flu viruses, therefore steps must be taken to minimize the introduction of a virus onto a farm, by people, by vehicles, and by wildlife such as birds, or other livestock.

The following are heightened biosecurity protocols that may be initiated during this outbreak:

• Ensure all biosecurity protocols are strictly followed
• People should avoid going into pig barns if they have influenza like symptoms (fever, sore throat, cough, runny nose, achy or tired) or if someone in their family has influenza like symptoms
• People who work in pig barns should visit their doctor if they develop influenza like symptoms
• Visitors should not be allowed into pig barns, especially if they have recently been to areas where people have been affected by this virus
• If symptoms of swine influenza occur in a herd (coughing, fever, depression, runny nose, off feed) contact your veterinarian promptly for diagnosis and advice.

The pork industry reminds the public that type A H1N1 influenza is not a food safety concern. People cannot catch type A H1N1 influenza from consuming pork or pork products and Canadian pork continues to be safe to eat.

H1N1 Diagnosed at Alberta Farm

A worrisome discovery was made when 220 pigs at a 2,200 head unit were diagnosed with the same strain of H1N1 currently spreading through the world's human population. It appears that a farm worker who had recently returned to work after a trip to Mexico may have been the point source for the infection. While it is common that humans can infect pigs and pigs can infect humans with so-called common strains of H3N2 influenza virus, this movement between species gives the virus an opportunity to mutate along the way. This may make it more likely for this virus to become more virulent although this is not a given. Another concern would be for the virus to become seeded in swine populations, especially on smaller farms that may not have the level of biosecurity as larger operations.

The herd has been quarantined and all pigs are recovering or have recovered. The farm worker has recovered as well. Read the story here: http://www.google.com/hostednews/canadianpress/article/ALeqM5jOCNS_KUIXJQ6YeBf31nkGFvTrNQ.

UPENN Actively Monitoring H1N1 Flu Activity

The Office of University Communications at the University of Pennsylvania has just launched a website to monitor and inform the university community about any developments relating to flu cases on Penn's campus.

For additional health updates and information for the Penn community, visit the Student Health Service website.

Egypt to Slaughter Entire Swine Herd

The Associated Press is reporting that Egypt has begun slaughtering their entire swine herd in order as a preventative measure to curb the spread of the H1N1 virus. No cases of the flu have been reported in the country although it was hard hit by an unrelated bird flu outbreak that claimed three lives in recent weeks. The move illustrates the global panic seen as the virus spreads across the world, especially into poorer nations with under-developed public health systems. It remains unclear whether farmers will be compensated for the loss of their herds although the agriculture minister claims that compensation will not be needed since the pig meat will still be allowed to be sold.

Meanwhile in the US, the CEO of the AVMA, Ron DeHaven issued a statement echoing National Pork Producers Council's assurances that the pork supply continues to remain a safe food option.

Potential Source of Swine Flu Discovered?

The Guardian is reporting that Mexican public health officials have confirmed a case of H1N1 swine flu or "North American Flu" in a four-year old boy from a village in south-eastern Mexico where 60% of residents fell ill to a widespread respiratory disease in February. The boy's illness came amid an outbreak of severe respiratory disease in the village of La Gloria in which over 400 residents reported symptoms of high fever, muscle aches, respiratory distress, and vomiting and diarrhea. Virginia-based Smithfield, the largest pork producer in the world, has a production facility approximately 12 miles from the village of La Gloria. In a statement released by the company they stressed that neither their pigs nor their employees had signs or symptoms of the disease. The company is cooperating with Mexican health officials and will be submitting samples from the facility at Granjas Carroll for testing at the University of Mexico.

You can read the entire article from the Guardian here.

North American Flu Update

It has come to my attention that my previous posts may not have been very reader friendly. So I have decided to update information.

Swine influenza is a respiratory disease of pigs caused by type A influenza viruses. Outbreaks of swine flu happen regularly in pigs. Before the current outbreak, people rarely got swine flu, and usually only if they were in very close proximity to infected pigs. However, during the current outbreak, the virus is able to spread from person-to-person.
Symptoms of swine flu in people are similar to those of regular or seasonal flu and include fever, lethargy, lack of appetite and coughing. Some with swine flu also have reported runny nose, sore throat, nausea, vomiting and diarrhea. Although winter is over, there is still a low level of seasonal influenza occurring in Pennsylvania.
There is no vaccine available for people at this time, but the swine flu can be treated with two antiviral drugs. Persons with swine flu are contagious for up to seven days or longer after the onset of illness, so it is important to take the following steps to prevent spreading the virus to others:
· Stay home when you are sick to avoid spreading illness to others;
· Cough or sneeze into the bend of your elbow or a tissue and properly dispose of used tissues;
· Wash your hands frequently and thoroughly with soap and warm water or use an alcohol-based hand sanitizer;
· Avoid touching your eyes, nose and mouth;
· Stay healthy by eating a balanced diet, drinking plenty of water and getting plenty of rest and exercise; and
· Seek care if you have influenza-like illness.

The public is instrumental in preventing the spread of any disease outbreak. Please use common sense when you are ill in order to reduce the risk of spreading your illness.

"North American Flu" Update

The following is the latest update on the H1N1 influenza outbreak:

• As of the 1:00pm EDT update, CDC is confirming 40 cases in 5 states (CA, TX, KS, OH & NY). None have any reported direct contact with swine. The outbreak continues to be transmitted human to human.
• According to the World Health Organization (WHO), the virus has been confirmed in 4 countries -- Mexico, U.S., Canada and Spain.
• The World Organization for Animal Health (OIE) is recommending that a more appropriate name for the virus would be "North-American influenza" since there has been no evidence of animal involvement.
• National diagnostic laboratories have received the virus isolated from cases in California and are beginning work to investigate questions associated with: diagnostic testing, swine susceptibility, transmission and pathogenesis, vaccine efficacy, etc.
• They have already determined that the current matrix test available in the National Animal Health Lab Network (NAHLN) labs will detect this virus, but a differential test is still being developed. Serology will be of limited value since the HA component of this virus is common in normal circulating SIV.
• 5 countries (Russia, China, Philippines, Serbia & Kazakhstan) have announced bans on some pork imports from the U.S. and Mexico while the WHO confirms that pork is safe to eat.
• Market hog prices were down the limit today.

Swine Influenza Fact Sheet

This is an excerpt of a Swine Influenza Fact Sheet I wrote for the former Pennsylvania state veterinarian in May 2007. It's a good starting point for a discussion on the current H1N1 swine flu outbreak.

Influenza A:
· Ducks/waterfowl are natural hosts
· All 15 HA and 9 NA virus types circulate among these avian species
· Virus targets the GI tract
· Infections are almost always subclinical in natural hosts

Antigenic Shift: a sudden emergence of antigenically different strains of influenza virus in a species. Can occur through 1 of 3 mechanisms:
· Direct transfer: transfer of a whole virus from one species to another
· Genetic reassortment: 2 different viruses of different species infect the same host at the same time. Gene segments can be exchanged between viruses creating a new virus strain.
· Re-emergence: a virus that may have died down re-emerges, the reasons for the disappearance and subsequent re-emergence are usually unknown
Antigenic Drift: gradual changes in antigenicity of a circulating virus after successive point mutations in the HA molecule until the virus is sufficiently different from earlier strains so that a large proportion of the population is susceptible and cases reach an epidemic level.

Swine Influenza: Clinical signs
· Acute febrile, respiratory disease characterized by apathy, anorexia, labored breathing (+/- coughing in later stages, also sneezing, nasal discharge and conjunctivitis may be seen less frequently).
· Morbidity can be up to 100% in a herd outbreak, mortality is low.
· Recovery is rapid – usually 5 -7 days after onset of clinical signs.
· Secondary bacterial infections can result in pneumonia.
· Gross lung lesions include lesions on apical and cardiac lobes; areas are dark to red-purple, depressed and consolidated. Airways are dilated and filled with blood-tinged fibrinous exudate. Bronchial and mediastinal lymph nodes are usually enlarged.

Swine Influenza: Epizootiology
· Swine influenza is widespread and endemic throughout the world.
· H1N1 and H3N2 infections are responsible for 50% of the cases of acute respiratory disease in pigs.
· SI is related to movement of infected pigs to susceptible herds and clinical disease appears with introduction of new pigs in to a herd.
· In an infected herd the disease persists through production of young susceptible pigs and introduction of new stock.
· Outbreaks peak in colder months.
· Infection is typically subclinical and clinical signs may be seen in 25 – 30% of the herd.
· Disease transmission is direct and occurs via the nasopharyngeal route (aerosols that are formed during sneezing or coughing) or indirectly after physical contact.
· Nasal secretions are laden with virus during the febrile (acute) state. This will last for 5 days.
· Severity of disease is dependent on: maternal immunity, virus strain, route of inoculation and secondary bacterial infections.

Vaccination and Control
Human vaccines:
· Inactivated whole or split or purified preps without adjuvant.
· Increases the chances of antigenic shift.
· Live-attenuated virus vaccine can mimic natural infection and produce local IgA and IgG with intranasal administration. There is a potential risk of reversion to wild-type virus*.
· Anti-virals are an effective means of control/treatment.
Swine vaccines:
· Based on inactivated and disrupted (split) virus suspended in oil adjuvant.
· Chances of antigenic shift are limited due to a shorter lifespan of individual pigs.
· Only injection is practical (intranasal administration is not practical therefore production of IgA is limited).
· No anti-virals are licensed for use in swine.
*Note on vaccination:
· The segmented genome of the virus means that if an individual is vaccinated while infected with an influenza virus, the attenuated virus (vaccine strain) can acquire wild-type gene segments of the other (natural virus strain) and new reassortant viruses can arise.
· This is only a risk related to human vaccination.

Virology: swine viruses currently circulating in North American swine – H1N1, H3N2, H1N2, and recently H3N1.

H1N1: classical swine influenza virus circulating since “Spanish flu” pandemic of 1918; isolated in 1930; endemic in swine populations.
· H1N1 (classical) is prevalent throughout the world, 25-30% of commercial pigs have evidence of disease
o In the US: the virus is antigenically conserved
o In Europe: virus disappeared and reappeared in 1976; in 1979 avian-like swine H1N1 replaced classical swine H1N1.
H3N2: new virus subtype emerged in swine populations in 1998; triple reassortment containing genes from swine, human, and avian viruses; endemic in swine populations.
· In Europe: in 1970 human H3N2 virus transferred to pigs; human-like swine H3N2 circulated in Europe and Asia with no clinical signs; in 1984 H3N2 (reassortment with avian-like swine H1N1) started causing disease in swine; this reassortant human-like swine H3N2 has replaced the original H3N2 in Europe.
o Recently: human-like swine H3N2 has started to circulate in the US causing serious disease and reproductive losses in sows.
H1N2: emerged in 1999; reassortment between H3N2 and H1N1; caused respiratory disease in swine and continues to circulate in swine populations.

H3N1: Lekcharoensuk et. al. characterized a new SIV subtype that may have arisen from reassortment of H3N2 turkey isolate and human H1N1 isolate and currently circulating swine viruses.

New strains: Recently, wholly avian viruses H4N6, H3N3, H1N1 from waterfowl were isolated from swine in Canada. However, there is no evidence that these viruses can be maintained successfully in swine populations

Public Health Implications:
· Human population has little immunity against animal influenza A viruses.
o If infections do arise the source of infection must be investigated as well as the extent of the spread and evidence of human to human infection.
o Only rare human to human transmission of animal influenza A viruses has been documented.
· Human H1N1 viruses are antigenically very different than swine H1N1 viruses.
o Human infections with human H1N1 viruses are rare.
o Influenza A viruses that are new to the human population (like H1N1) that are able to efficiently transmit from person to person and cause illness may represent a pandemic threat.
o H1N1 virus detection in swine workers may not be very important as antibody evidence of exposure is relatively common in this high risk group.
o H1N1 antibody detection in non-occupationally exposed persons is a possible pandemic threat.
· Most persons have some antibody to H3N2 viruses since they occur commonly in humans, swine H3N2 virus infections in people would not represent a possible pandemic threat.
o H3N2 infections can transmit from humans to pigs.
o Seasonal Flu vaccination will likely help provide partial protection against swine H3N2 virus subtype but not swine H1N1.
o Swine H3N2 viruses typically do not infect humans but persons who work closely with pigs are the majority of cases.

Health Implications - Agricultural Workers:
· There is scientific evidence that persons that are occupationally exposed to swine (farmers>veterinarians>meat processors) have an increased risk of infection with influenza viruses that infect pigs (Meyers et.al.).
o Therefore, there is a need to protect agricultural workers in order to prevent transmission among humans and domestic animals during a pandemic.
· It is likely that swine influenza infections occur in humans, especially in high risk groups, at an unspecified rate. However, due to the fact that symptoms are not only mild but also no different from “human” influenza infections, it is likely that non-fatal cases of swine influenza continue to occur but are not identified.
· Persons who work with swine could be considered for sentinel influenza surveillance and are an important group to include in pandemic planning.
· A policy of vaccinating swine workers annually with human influenza vaccine may decrease the risk of reassortment events.

References:

Lekcharoensuk P, Lager KM, Vemulapalli R, Woodruff M, Vincent AL, Richt JA. Novel swine influenza virus subtype H3N1, United States. Emerging Infectious Diseases [serial on the Internet]. 2006 May. Available from http://www.cdc.gov/ncidod/EID/vol12no05/05-1060.htm

Meyer KP, Olsen CW, Setterquist SF, Capuano AW, Donham KJ, Thacker EL, Merchant JA, and Gray GC. Are swine workers in the United States at increased risk of infection with zoonotic influenza virus? Clinical Infectious Diseases, 42 (2006), 14–20.

http://www.cdc.gov/flu/swine/. Accessed April 30, 2007.

http://www3.niaid.nih.gov/news/newsreleases/2005/swineflu.htm.%20%20Accessed%20April%2030, 2007.

http://www.vetscite.org/publish/articles/000041/print.html. Accessed May 1, 2007.

http://mark.asci.ncsu.edu/HealthyHogs/book1994/woodlief.htm. Accessed May 1, 2007.

Swine Welfare Blog

Blog goes online on April 22, 2009.