The Spanish influenza (flu) outbreak of 1918-1919 killed an estimated 20 to 40 million people worldwide. Although the virus was not especially lethal in terms of number of deaths per total cases (by 1918 standards), the virus infected at least an estimated 500 million people. It was, however, very lethal to otherwise healthy adults aged 20 to 44, as opposed to most flu outbreaks, which kill only the very young, the elderly, and people with weakened immune systems. Scientists and public health officials have been trying to learn more about Spanish flu in the hopes of preventing a similar outbreak.
The Spanish flu virus caused one of the most lethal influenza pandemics in modern history. And while the threats of some diseases, such as smallpox, have been contained by vaccination programs, influenza remains a difficult disease. There are worldwide outbreaks of influenza every year (approximately 300,000-500,000 people die of influenza or influenza complications each year--about 36,000 in the United States alone), and the flu typically reaches pandemic proportions (lethally afflicting an unusually high portion of the population) every 10-40 years. Prior to the declaration of a global pandemic of 2009 A / H1N1 influenza in June 2009, the last influenza pandemic was the Hong Kong flu of 1968-1969, which caused an estimated one million deaths worldwide, and killed approximately 33,000 Americans. The influenza virus is highly mutable, so each year's flu outbreak presents the human body with a slightly different virus. Because of this, people do not build immunity to influenza. Vaccines are successful in protecting people against influenza, but vaccine manufacturers must prepare a new batch each year, based on their best supposition of which particular virus will spread.
Most influenza viruses originate in Asia, and doctors, scientists, and public health officials closely monitor flu cases there in order to make the appropriate vaccine. The two main organizations tracking influenza are the Centers for Disease Control (CDC) and the World Health Organization (WHO). The CDC and other government agencies have been preparing for a flu pandemic on the level of Spanish flu since the early 1990s.
In April 2009, a new virus with a mixture of swine, avian, and human influenza genes emanated from Mexico to sites around the world. Initially classified as a swine flu, the flu was renamed the 2009 H1N1 flu (or 2009 A / H1N1 influenza) because there was no evidence that pigs were involved in the most recent transmission to humans. The virus must have passed through pigs at one time. The 2009 H1N1 flu spread quickly and reached pandemic status within two months, because it was a new and highly transmissible virus to which humans had no natural immunity.
By the end of July 2009, more than 55,867 laboratory-confirmed cases of H1N1 influenza, including 700 deaths, were reported to WHO. Officials at the WHO ceased collecting data on individual case counts, as the epidemic was well established in both the Northern and Southern Hemispheres. In August 2010, WHO officials officially declared an end to the global pandemic.
The 2009 pandemic H1N1 virus proved to be less lethal than many other flu viruses (it is not as lethal as the H5N1, Spanish, or Hong Kong viruses, for example), and infectious disease experts predicted that the 2009 influenza pandemic would not approach the severity of prior pandemics such as the 1918-1919 Spanish flu. Priorities for responding to the pandemic included manufacturing and delivering sufficient quantities of antiviral drugs and vaccine specific to the 2009 H1N1 virus.
The Spanish flu actually did not originate in Spain. The first case was recorded in March 1918, at the army base Camp Funston. It quickly spread across the United States, and then to Europe with American soldiers who were fighting in the last months of World War I (1914-1918). Infected ships brought the outbreak to India, New Zealand, and Alaska. Spanish flu killed quickly. People often died within 48 hours of first feeling symptoms. The disease afflicted the lungs, and caused the tiny air sacs, called alveoli, to fill with fluid. Victims were soon starved of oxygen, and sometimes effectively drowned with the fluid clogging their lungs. Children and old people recovered from the Spanish flu at a much higher rate than young adults. In the United States, the death rate from Spanish flu was several times higher for men aged 25-29 than for men in their seventies.
Social conditions at the time probably contributed to the remarkable power of the disease. The flu struck just at the end of World War I, when thousands of soldiers were moving from America to Europe and across that continent. In a peaceful time, sick people may have gone home to bed, and thus passed the disease only to their immediate family. But in 1918, men with the virus were packed in already crowded hospitals and troop ships. The unrest and devastation left by the war probably hastened the spread of Spanish flu. So it is possible that if a similarly virulent virus were to arise again soon, especially with modern anti-viral medicines, it would not be as deadly.
Researchers are concerned about a return of Spanish flu because little is known about what made it so virulent. The flu virus was not isolated until 1933, and since then, there have been several efforts to collect and study the 1918 virus by exhuming graves in Alaska and Norway, where bodies were preserved in permanently frozen ground. In 1997, a Canadian researcher, Kirsty Duncan, was able to extract tissue samples from the corpses of seven miners who had died of Spanish flu in October 1918 and were buried in frozen ground on a tiny island off Norway. Duncan's work allowed scientists at several laboratories around the world to do genetic work on the Spanish flu virus. It was subsequently determined by researchers that the Spanish flu was a mixture of genes, including avian genes.
The influenza virus is believed to originate in migratory waterfowl, particularly ducks. Ducks carry influenza viruses without becoming ill. They excrete the virus in their feces. When their feces collect in water, other animals can become infected. Domestic turkeys and chickens can easily become infected with influenza virus borne by wild ducks. But most avian (bird-borne) influenza does not pass to humans, or if it does, is not particularly virulent. But other mammals, too, can pick up influenza from either wild birds or domestic fowl. Whales, seals, ferrets, horses, and pigs are all susceptible to bird-borne viruses. When the virus moves between species, it may mutate. Human influenza viruses may sometimes pass from ducks to pigs to humans.
A flu outbreak among chickens in Hong Kong in 1997 eventually killed six people, but the epidemic was stopped by the quick slaughter of millions of chickens in the area. This virus identified was classified as an avian flu (bird flu), H5N1 strain of influenza. H5N1 re-emerged in 2003. Spreading from Asia to Europe and Africa, the WHO reports that the virus has "resulted in millions of poultry infections, several hundred human cases, and many human deaths." So far, only a few cases of human-to-human transmission of H5N1 have been documented. However, because of its lethality, the H5N1 virus is closely monitored by epidemiologists in order to watch for signs that the virus could mutate in such a way that it gains the capacity to transmit easily between humans, a necessary step toward pandemic level outbreaks.
Enacting controls on pig and poultry farms may be an important way to prevent the rise of a new influenza pandemic. Some influenza researchers recommend that pigs and domestic ducks and chickens not be raised together. Separating pigs and fowl at live markets may also be a sensible precaution. With the concentration of poultry and pigs at factory farms, it is important for farmers, veterinarians, and public health officials to monitor for influenza. Any action to control flu of course must be an international effort, because the influenza virus moves rapidly without respect to national borders.
Multiple outbreaks of LPAI (low pathogenic avian influenza) of several serotypes (H7N7, H7N1, H5N2) continue to pose threats to commercial flocks of birds.