By the 1950s, scientists were optimistic that advances in disease control would conquer the problem of communicable diseases (Lasker, 1997). Subsequent events, however, awakened a realization that infectious diseases will never be fully controlled (Lederberg J., 1992; CDC, 1998), as the outbreaks we describe next illustrate dramatically.
4.1. Lyme Disease (1975)
In the town of Lyme, Connecticut, in 1975, two children were diagnosed with the same rare disease—juvenile rheumatoid arthritis. Their mothers became aware of other similarly affected children in their community (American Museum of Natural History, 1998) and notified the local health department about this unusual circumstance. The local health department, suspecting the emergence of a new infectious disease, asked Dr. Allen Steere to investigate. His study of the children of Lyme produced several clues: the disease did not appear to spread from one person to another, it occurred most often in the summer when insect-borne disease was more common, and a rash often appeared before children developed arthritic symptoms, suggesting a tick-borne disease. In 1981, entomologist Willy Burgdorfer found the cause by looking at the digestive tracts of Ixodes ticks under a microscope.The bacterium he found, Borrelia burgdorferi, was named in his honor.
We now know that B. burgdorferi, and other closely related organisms, exist on many continents and likely have been causing disease in humans for hundreds of years. One reason for the unusual number of cases in Lyme was the fashionable practice of building new homes in wooded locations. This practice brought mice (a carrier of B. burgdorferi) and deer, which are necessary for tick survival, and humans (tick food) into proximity and created conditions in which the bacteria could infect humans in large numbers.
Lyme disease in humans is an example of a vector-borne disease. Malaria, the most prevalent of the vector-borne diseases, causes 1.5 to 2.7 million deaths annually, mostly in third world countries, and remains a major world health problem (Southwest Foundation for Biomedical Research, n.d.). Biosurveillance for vector-borne diseases is complex and involves monitoring the interactions of humans, animals, and insects.
4.2. Legionnaire's Disease (1976)
One Sunday in 1976, an American Legion official contacted Dr. Lewis D. Polk, director of the Philadelphia Health Department to report the deaths of eight veterans who had participated in a recent American Legion convention in the city (Lewis D. Polk, personal communication). The initial investigation found neither a causative organism nor a common source of exposure, and attendees of the convention continued to die (CDC, 1976). Philadelphia was celebrating the nation's bicentennial, leading to speculation that a chemical or biologic attack had occurred.
The strongest clue available was the Bellevue Stratford Hotel, one of the convention hotels. Many victims visited the hotel during the course of the convention or had walked within a single block of the hotel. However, it was puzzling that individuals who worked at the hotel did not get sick. Investigators compared individuals, both sick and healthy, who had some contact with the hotel. This analysis revealed only that the attack rate was higher in smokers and individuals who spent more time in the hotel lobby.
The cause of this outbreak was not found until 6 months later, when, in January 1977, researchers at the Centers for
Disease Control and Prevention (CDC) discovered a new class of bacteria by examining microscopic slides of guinea pigs injected with lung tissue from deceased patients. They named the bacteria Legionella pneumophila. Investigators believe that the water cooling tower on the roof of the hotel was the source of bacteria for the Philadelphia outbreak. Water from cooling towers sprays into the air as microdroplets, which may enter the body by inhalation. In the end, this outbreak caused an estimated 180 cases and 29 deaths (CDC, 1997).
Subsequent research has demonstrated that L. pneumophila had been causing outbreaks of pneumonia throughout the United States for years. Researchers thawed and tested serum samples saved from earlier outbreaks of pneumonic illness for which a cause had never been found. They found that L. pneu-mophila caused the outbreak of "Pontiac fever'' in Pontiac, Michigan, in 1968 (CDC, 1997).A second large outbreak occurred in 1966 in a psychiatric hospital, causing 94 cases and 15 deaths (CDC, 1997).
Today, we know that L. pneumophila exists in nature as a common colonizer of water systems but rarely infects people. The American Legion convention brought together a large number of people whose lung defenses were weakened by age and the effects of cigarette smoking.
Effective measures to prevent, detect, and treat Legionnaire's disease now exist, so an outbreak from this organism with this degree of mortality is unlikely to occur again. However, outbreaks and sporadic cases secondary to aspiration of drinking water or inhalation of contaminated aerosols continue to occur (Pedro-Botet et al., 2002;Yu, 2002).
4.3. Anthrax Outbreak, Sverdlovsk, Soviet Union (1979)
In April 1979, people, and many animals, were dying in the Soviet city of Sverdlovsk from an unknown illness (Guillemin, 1999). The first clue that the organism causing the illness was Bacillus anthracis came from a pathologist, who found that the brain of a victim showed a cardinal's cap—bleeding at the top of the brain. A cardinal's cap is a pathognomic finding (a finding that allows a physician to conclude a diagnosis with certainty) for the disease anthrax (Mangold and Goldberg, 2000).
Soviet authorities maintained that the cause was consumption of contaminated meat. Although the Soviet Union had signed the Convention on the Prohibition of the Development, Production, and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on their Destruction—effective March 26, 1975 (Goldblat, 1997)—experts in the West remained suspicious of the official explanation.
More than a decade later, a team lead by Mathew Meselson (Meselson et al., 1994) visited Sverdlovsk (then renamed Yekaterinburg), to interview survivors, witnesses, and patholo-gists. They reviewed tissue samples of lung and intestinal tract taken from victims of this outbreak. The tissue samples were more consistent with an inhalational form of anthrax rather than a gastrointestinal form, which would be expected if the infection were acquired by eating contaminated meat. They, therefore, postulated that the cause was airborne release of anthrax. To test this hypothesis, they analyzed the geographical distribution of sick individuals and the known wind conditions, concluding that the outbreak was most likely due to an airborne release of anthrax from a single location.
In 1992, Russian authorities admitted that there had been an accidental release of B. anthracis (Kirov strain) from Soviet Biological Weapons Compound 19. During a shift change, a laboratory technician had removed an air filter from a testing chamber, which the subsequent shift failed to replace (Israelyan, 2002). As a result, this outbreak was caused by an accidental release of material being tested for use in biological weaponry.
This outbreak highlights the difficulties of controlling disease in a world where bureaucratic organizations reward secrecy and restrict information. It is an interesting but unanswered question as to what extent their attempts to cover up the truth affected the morbidity and mortality of this outbreak. Because anthrax is not contagious, secrecy did not result in dissemination of disease outside of Sverdlovsk. However, in the words of Victor Israelyan, former Soviet ambassador, "Such a lack of transparency can have dire consequences in this new era of terrorism'' (Israelyan, 2002).
In 1981, doctors in Los Angeles, San Francisco, and New York City began to encounter homosexual patients with rare infections and diseases, including cytomegalovirus, Pneumocystis carinii, and Kaposi's sarcoma (CDC, 1981a,b; Drew et al., 1981). These rare diseases tend to occur in immunocompromised patients, a clue that pointed investigators to look for an infection or chemical exposure that damaged or interfered with cellular immunity (CDC, 2001).
A CDC team formed in June 1981. They named the disease acquired immunodeficiency syndrome (AIDS) and developed a working case definition. They used the working case definition to find infected individuals to interview and examine. They compared the behaviors and histories of these individuals with those of non-infected individuals, and concluded that AIDS could be contracted from blood transfusion, intravenous drug use, or sexual intercourse or could be passed from mother to child in utero. This information was the basis for the March 1983 recommendations on how to prevent infection, disseminated well before the actual cause of the disease—the human immunodeficiency virus (HIV)—was discovered in 1984 (Srikameswaran, 1999).
Subsequent research has elucidated that HIV existed long before AIDS was first recognized in 1981. The evidence indicates that HIV developed through mutation or recombination in monkeys before crossing over into humans. The earliest known human case, as determined by testing stored serum and tissue, was an adult living in the Democratic Republic of Congo in 1959 (Kanabus and Allen, 2005). In the absence of international travel and high-risk behaviors (multiple sex partners and sharing of needles), which produced clusters of cases in San Francisco and New York City, HIV could have remained undetected for many years, with the resultant deaths blending in with many infectious-disease deaths in areas with little health care.
The AIDS pandemic is an example of an outbreak that has never been brought under control. The Joint United Nations Program on HIV/AIDS estimates that 20 million people have died from AIDS, and an additional 38 million people are living with HIV. During 2003—19 years after the virus was isolated— an estimated five million people were newly infected with HIV (UNAIDS, 2004).
Two highly prevalent human infectious diseases—HIV and hepatitis C (Koop, 1998)—pose difficult biosurveillance problems because they have a long period of infectivity before the onset of symptoms. It is hoped that future advances in biotechnology will yield better methods for detecting infections during their asymptomatic periods.
4.5. Mad Cow Disease and Variant Creutzfeldt-Jakob Disease (1986)
In 1986, veterinary pathologists at the Central Veterinary Laboratory in Weybridge, United Kingdom, became suspicious that a new disease was killing cattle (Donnelly et al., 1999; Matravers et al., 2000).Their suspicions were aroused by the microscopic appearance of the brain from a cow that died after exhibiting progressive abnormalities of behavior and movement that resembled those of sheep affected with the disease scrapie. Because of the unnerving signs of this disease, it came to be known as mad cow disease.
When pathologists saw similar microscopic findings in two more cattle, they feared that a scrapie-type disease had emerged in cattle. The head veterinary epidemiologist for the United Kingdom, John Wilesmith, commissioned studies to find the origin of this new disease. As a starting point, investigators assumed the new disease was caused by an organism similar to the one that causes scrapie in sheep. Moreover, they hypothesized that an unusual transmission pathway—the eating of brains from infected animals—caused the spread of the disease. In the cattle industry, carcasses of livestock that are not fit for human consumption were rendered (cooked) into meat-and-bone meal, which was fed to animals as a protein supplement.
Their methods involved a series of observational studies and computer simulations. These studies suggested that a mass exposure of the cattle population to a new organism was occurring—most likely beginning in winter 1981/1982. They found that the risk of exposure was 30 times greater for one-month-old dairy calves than for adult cattle. This discovery, coupled with knowledge that dairy farmers remove calves from their mothers at one day of age and feed them powdered milk and high-protein supplements based on meat-and-bone meal, confirmed their conjecture about the route of exposure. The incidence of affected dairy herds also increased as herd size increased. Larger herds require more supplement feeds than do smaller herds, thereby increasing the risk of exposure.
Although cattle had been resistant previously to scrapie, it is now believed that a cow became infected with a mutant strain of the scrapie agent some time during the 1970s. The sick cow was recycled into meat-and-bone meal, resulting in the exposure of a large number of animals to the newly adapted scrapie agent.
Mad cow disease (more properly referred to as bovine spongiform encephalopathy) remained undetected for many years after the initial mutation in the 1970s. The delay in detection allowed the disease to establish within the cattle population. The conditions for disease transmission were broken in 1988, when regulators banned the use of animal protein sources for animal feeds, and the epidemic in cattle gradually abated.
For many years, however, cattle that were infected, but not yet symptomatic, entered the human food supply, resulting in a mass exposure of the human population to this new agent. This exposure set up conditions that allowed the disease to cross from cattle into humans. The public were aware of possible exposure to the agent through consumption of contaminated beef; therefore, when a new variant of Creutzfeldt-Jakob disease (vCJD) first appeared in humans in the United Kingdom during the 1990s, people saw the similarity to mad cow disease in cattle (Nathanson et al., 1997).
The total number of confirmed cases of human vCJD, from first identification to 2005, now approaches 150. The exact number of humans who will develop the disease is unknown. Additional routes of disease transmission (e.g., person to person through blood transfusion) are contributing to uncertainty in disease projections. Figure 2.4 shows a bovine spongi-form encephalopathy epidemic curve.
The story of mad cow disease and vCJD demonstrates the need for better methods of biosurveillance of animals for the protection of humans. Although the investigation of mad cow disease occurred at breathtaking speed, the initiation of this
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