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Many scientists believe it is only a matter of time until the next influenza pandemic occurs. The severity of the next pandemic cannot be predicted, but modeling studies suggest that the impact of a pandemic on the United States could be substantial. In the absence of any control measures (vaccination or drugs), it has been estimated that in the United States a “medium–level” pandemic could affect between 15% and 35% of the U.S. population, and the economic impact could range between $71.3 and $166.5 billion.
Influenza pandemics are different from many of the threats for which public health and health-care systems are currently planning:
Once a fully contagious virus emerges, its global spread is considered inevitable. Countries might, through measures such as border closures and travel restrictions, delay arrival of the virus, but cannot stop it. The pandemics of the previous century encircled the globe in 6 to 9 months, even when most international travel was by ship. Given the speed and volume of international air travel today, the virus could spread more rapidly, possibly reaching all continents in less than 3 months.
On March 1 2006, the New Zealand Herald reported: “The first case of bird flu has been detected in the Far North province”. Cameroon’s government reported that the virus was found on a duck farm. Nigeria, Egypt and Niger have already reported cases of the highly pathogenic H5N1 avian flu strain in poultry flocks. Cameroon’s Far North province borders Nigeria, where Africa’s first H5N1 bird flu outbreak was confirmed on February 8. Suspected poultry outbreaks in Gabon (which borders Cameroon to the north) Ethiopia, Gambia and Sierra Leone are also under investigation. According to Reuters, Greece confirmed in Feb. that dead swans tested positively for H5NI. It is spreading - no question about it! As of this writing (May 2006), there are 225 confirmed deaths from H5N1.
High rates of illness and worker absenteeism are expected, and these will contribute to social and economic disruption. Past pandemics have spread globally in two and sometimes three waves. Not all parts of the world would have simultaneous outbreaks; that is, it would affect different areas more severely than others at the same time. Social and economic disruptions could be temporary, but may be amplified in today’s closely interrelated and interdependent systems of trade and commerce. Social disruption may be greatest when rates of absenteeism impair essential services: power, transportation distribution of goods/services and communications. It is overwhelming to fathom the economic implications of a deadly outbreak and the cascading ramifications.
Today, an intensive care unit requires the price of a small used car to keep one patient in one bed for one 24-hour period. Three nurses are required to provide the one-on-one nursing care that is required over the day’s three shifts.
In desperate times bought on by a pandemic, 14-hour shifts would probably become necessary, if nurses are willing and able. Hospitals would have a finite supply of beds, respirators, meds, and staff. Who would pay?
Would the insurance industry be able to support all the care required, or will they also be preparing to avoid coverage of an individual’s costs should a pandemic strike. Who would then pay for care? This writer does not believe the question has been answered and that careful planning is needed to address this growing concern.
People have been worrying about surge capacity in case of terrorism but that is a small number compared to the masses involved in a full-scale pandemic. This is why preparation is so important. Think about your current hospital census. What if it doubles? Triples? Quadruples? Can this be managed?
The reality is that the lack of ICU beds available is only the tip of the iceberg. Shortages of trained medical staff are already severe, after years of deliberate attrition, and cannot simply be fixed quickly, certainly not in crisis unless, collectively, we begin now. A plan needs to be established in each community to accommodate the possible surges in hospital bed/nurse ratios.
Supplies of vaccines and antiviral drugs will be inadequate in all countries at the start of a pandemic and for many months thereafter. Inadequate supplies of vaccines are of particular concern, as vaccines are considered the first line of defense for protecting populations. Speaking of vaccines, we’ve already surmised that there are no vaccines as of yet, because the actual “shift” has not happened.
Historically, the number of deaths during a pandemic has varied greatly. Death rates are largely determined by four factors: the number of people who become infected, the virulence of the virus, the underlying characteristics and vulnerability of affected populations, and the effectiveness of preventive measures. Accurate predictions of mortality cannot be made before the pandemic virus emerges and begins to spread. All estimates of the number of deaths are purely speculative.
The WHO has used a relatively conservative estimate – from 2 million to 7.4 million deaths – because it provides a useful and plausible planning target. This estimate is based on the comparatively mild 1957 pandemic. Estimates based on a more virulent virus, closer to the one seen in 1918, have been made and are much higher. However, the 1918 pandemic was considered exceptional. Other estimates are in the 200 to 400 million. Perhaps this is just sensationalism, perhaps it is not: let the reader decide.
It is feared that a pandemic can occur as a result of the swine flu or the bird flu. Swine flu will be discussed in this chapter and the next chapter will be devoted to the avian or bird flu.
Swine Influenza is an acute, febrile respiratory disease of swine with high morbidity and low mortality. It is commonly known as swine flu, hog flu, or pig flu.
The causative agent is an H1N1 influenza A virus possibly derived from a common ancestor. These viruses have remained largely endemic in pig populations worldwide and have been responsible for one of the most prevalent respiratory diseases in pigs. The etiology of hog flu is a Type A Influenza virus that, as you might recall, belongs to the Orthomyxoviridae family and is an enveloped RNA virus.
Given the worldwide interaction between humans, pigs, birds and other mammalian species there is cross-species transmission of influenza viruses in nature. Pigs are an important host in influenza virus ecology since they are susceptible to infection with both avian and human influenza. Influenza generally appears with the introduction of infected pigs into a herd, either through movement or mixing of infected pigs with susceptible animals.
Transmission from humans to pigs occurs occasionally, but rarely from avian species. Once a herd is infected with a virus that is able to replicate, the virus persists through the production of young susceptible pigs and the introduction of new stock, often leading to the herd becoming infected endemically.
Swine influenza (SI) was first observed in 1918 in the United States, Hungary and China. It coincided with the Spanish Flu, which accounted for at least 20 million deaths worldwide. Those who first noticed the disease in pigs, recognized similarities between the porcine and human disease and suggested they had a common etiology. Later retrospective serological investigations confirmed that the disease in humans and pigs had been caused by closely related influenza A viruses in both cases.
Since 1979 the dominant H1N1 viruses in European pigs have been “avian-like”. More recently an independent introduction of H1N1 virus from birds to pigs has occurred in southern China and these viruses have been detected in pigs in South East Asia since 1993 where they are currently co-circulating with classical H1N1 viruses.
Swine husbandry practices directly influence the evolution of influenza viruses in pigs leading generally to reduced genetic drift, particularly in the genes encoding HA and neuraminidase (NA), compared to those of similar viruses in the human population. SI generally appears with the introduction of new pigs into a herd, thereby being related to the movement of animals from infected to susceptible herds.
Influenza is transmitted primarily pig-to-pig by the nasopharyngeal route. The incubation period is 1 to 3 days, and can be as short as 4 hours. Nasal secretions are laden with virus during the acute febrile stage. The virus is easily carried and spread by avian species, particularly waterfowl, and humans. Care should be taken to prevent spread from and between birds and humans to swine. The virus can be shed for 30 days post-inoculation and has been recovered from clinically normal animals.
The clinical signs of Swine Influenza are typical flu-like symptoms. The pigs will develop a fever, (40.5oC - 41.7oC), nasal and ocular discharge, and severe spasms of coughing. They will appear lethargic and become anorectic. These signs will appear very suddenly, spread rapidly throughout the entire barn, and persist for about 7 days.
Diagnosis of Swine Influenza can be based on clinical signs, virus isolation, and historical pathological confirmation of lesions, paired serology, and antigen detection.