Pandemic describes the sudden and widespread development of a disease that causes serious illness or death among an exceptionally high proportion of the population. Such an occurrence is referred to as pandemic outbreak, or more colloquially as a pandemic.
True pandemic outbreaks are global events caused by bacteria and viruses that are highly contagious in human populations. Such outbreaks have been documented since the 16th century, and each subsequent century has experienced numerous occurrences. In contrast, an EPIDEMIC outbreak is a disease outbreak that occurs in a specific region during a given period of time and affects a disproportionately large number of people.
The features of pandemics are distinctive: they can spread rapidly across the globe, often within less than a year, and an average of one-quarter of the human population contracts the illness. Pandemics typically start abruptly, peak rapidly and subside fairly quickly. However, they also tend to recur in waves that begin simultaneously in different regions. These waves, which may include second and third waves, often cause even more serious disease.
The first pandemic known to human history is the plague, an infectious disease caused by bacteria called Yersinia pestis, which are found in rodents, especially rats, and in the fleas that feed on them. Plagues have occurred since at least the 1st century AD, but possibly the most well-known plague was the pandemic that began in the early 14th century in Asia and was subsequently introduced into Europe. This bubonic plague, known as the "Black Death," eventually killed more than one-third of the European population. (Bubonic plague is highly contagious and characterized by fever, delirium and swollen lymph nodes, called buboes.) The Black Death was transmitted to humans from rodents via fleas. Fleas served as vectors, or carriers of the infection, for the disease in humans. The discovery of bacteria that cause different types of plagues resulted in the introduction of effective antibiotics as treatments in the 20th century. Nonetheless, infections of different types of plagues, including bubonic, septicemic and pneumonic plagues, still occur often in parts of Africa.
Spanish Influenza 1918-1920
Spanish INFLUENZA developed at the end of World War I; the Spanish flu pandemic first developed in Asia, but the first known patient appeared at a United States military base in Kansas. The first outbreaks of the disease occurred in the spring of 1918. The infection travelled back and forth between Europe and North America on the ships carrying troops fighting in World War I. These troops then introduced the disease into Asia and Africa. The Spanish flu was caused by a viral infection that became deadly, eventually killing an estimated 50 million people worldwide. In Canada more than 50 000 people died and all parts of the country were affected.
The timing of the development of the Spanish flu was critical to the eventual success of the virus because there were many people travelling from one part of the world to another. The Spanish flu is recognized as being the most devastating pandemic in recorded world history. The name derived from media censorship by the military in Allied countries, which prevented the reporting of the viral infection and death of soldiers. Spain was neutral during World War I and the Spanish media widely reported the high incidence of death from the illness. The name of the virus became synonymous with Spain as a result.
One of the features of the Spanish flu was the occurrence of rapid infection in people in the prime of life. This is in contrast to other deaths from influenza, which tend to occur at the extreme ends of the human lifespan, among the very young and the elderly. The Spanish flu caused death by pneumonia in both primary viral infections and secondary bacterial infections. The disease could kill healthy and fit adults within 48 hours. Because antibiotics were not yet available, the secondary bacterial pneumonia could not be treated. There were no vaccines either. It was not until 1933 that human influenza viruses were isolated, which is an initial step in the development of a vaccine that can be used to prevent the disease.
Canada was hit hard by the illness. The spread of the infection included urban areas and even the most remote communities. Canada had a population of about 8.7 million in 1918, based on data from the 1921 census. The death rate from Spanish flu was therefore about 4.5% of the population. More than 1000 people died in Toronto alone, with a total of 8700 deaths in Ontario. There were 4000 deaths in both Alberta and Manitoba and 5000 in Saskatchewan. Some aboriginal communities lost almost the entire population to the illness.
Most Canadian communities adopted measures to attempt to contain the spread of the virus. In Alberta people were required to wear face masks in public. In Regina people could be fined for public coughing or sneezing. Some towns imposed quarantines where people could not enter or leave without being arrested. Canada first established the Department of Health in 1919 in response to Spanish flu.
The outbreaks of severe acute respiratory syndrome (SARS) and Avian flu in the early 21st century renewed interest in the Spanish flu. All of these viral infections originated from mutated animal viruses. Animal viruses are not usually contagious in humans, and a virus must undergo certain changes in genes, or mutations, in order to become infectious. Scientists do not understand the exact mutations involved, but research into historical diseases such as the Spanish flu may help develop new theories and potential treatments.
Avian influenza, also called bird flu, is currently infrequently transmitted to humans but is affecting ever greater numbers of birds all over the world. There are global concerns that avian flu has the potential to become a pandemic if actions are not taken to learn more about the specific virus and contain infection.
Avian flu is caused by influenza A viruses, which occur naturally in wild birds. Wild birds have carried these viruses for many hundreds of years without harm to the populations or to other bird species. However, one type of avian influenza A, the H5N1 virus, crossed the species barrier from wild birds to domesticated birds in Asia in 1997. The virus caused high mortality rates in domesticated birds and could kill chickens in 48 hours. The virus then disappeared from detection until it resurfaced in 2003. Since then the virus has infected domesticated birds in many Asian countries including China, Korea, Vietnam, Thailand, Cambodia and Malaysia. Dramatic cull programs of domesticated birds were widely instituted to try to contain the virus. The outbreaks were contained in relatively small regions. However, there were a small number of people infected with the virus, usually workers in domestic poultry operations that received intense exposure to the virus during culling procedures.
New outbreaks of avian flu in domestic bird populations appeared in 2004. These outbreaks were fairly small, with an estimated one million poultry infected. However, despite the small number of infected birds, there were human cases of infection with H5N1 in numerous Asian countries. There were also cases of cross-species contamination among captive tigers in Thailand that were fed raw chicken carcasses. These cases of cross-species contamination through ingestion of infected birds have caused increasing concern among scientists worldwide. In 2004 the Fraser Valley region of British Columbia experienced a large avian flu outbreak among commercial poultry, of the virus subtype H7N3. Quick response by animal and health professionals controlled the outbreak in a few months. Only 2 people were confirmed as infected with the virus and both had mild symptoms. Because of the province's close relationship with Asia Pacific nations, an enhanced state of surveillance for avian influence H5N1 is maintained.
Besides trade in domestic birds, migratory bird flyways are potential transmission routes of the H5N1 virus into Canada. Wild birds in British Columbia, Québec and Manitoba have been identified as carrying a type of H5 influenza virus, but not the H5N1 subtype. Large numbers of migratory birds use flyways that cross Europe and Asia and then pass into the Arctic regions. Once in the Arctic there are 4 North American flyways that migratory birds can access. The Pacific, Central, Mississippi and Atlantic flyways are the major routes migratory birds use during fall and spring to and from nesting sites in North and South America.
Scientists in Canada and the United States study samples from migratory duck species in order to set up a warning system for the arrival of Avian flu by intercontinental flyways. This research is studying the strains on the continent currently and in what proportion. There are 6 laboratories across the nation mapping the kinds of birds and types of viruses that are circulating.
Study of Pandemics and Potential Treatments
EPIDEMIOLOGY is the study of disease in human populations, including the causes, distribution patterns and control of disease. It is an important method used in public health research across the world in the assessment of causal relationships in disease. Canada and many other countries, in cooperation with the World Health Organization, is engaged in learning more about the transmission of H5N1 from one species to another and about diseases with the potential to become pandemic.
Canada began planning for pandemic influenza viruses in 1983. The Public Health Agency of Canada coordinates planning along with the provincial and territorial ministries of health to identify the roles and responsibilities involved in responding to a potential pandemic. Immunization is an essential aspect of preparation for any viral infection. There are a number of influenza vaccines available and it is believed that annual immunization will help to reduce the risk of infection. Interaction between federal, provincial, territorial and municipal governments to implement the planning is important to ensure that Canadians receive the proper vaccinations to help prevent future pandemics.