Experts from the Centers for Disease Control and Prevetion (CDC) and the National Institutes of Health discussed the status of these threats and outlined current and future preparedness efforts needed in the United States to manage them.
CDC Director Julie L. Gerberding, MD, MPH, noted the public's health will be impacted in the years to come by emerging infectious diseases like SARS. "Although the epidemic appears to be coming under containment now, we have no idea what to expect in the fall. It would not be surprising if we had a resurgence," she predicted.
According to Gerberding, SARS could reappear in the fall much like other respiratory illnesses such as influenza and may be spread by people who don't realize that they are carriers of the virus. Many individuals who have contracted SARS have had mild versions or no symptoms at all.
It is still unknown whether the virus can be transmitted by those who are asymptomatic. Although the future of SARS is uncertain, more information is available regarding the disease that will allow the medical community to act quickly if an outbreak should occur.
Gerberding explained that it is important to be vigilant during these times. "The new normal is emerging infectious diseases," she stated, adding, "Emerging infectious diseases are almost instantaneously a global concern because of the speed with which people, animals and products move around the world."
In order to adapt to these new threats, there is a need for timely identification and reporting, the need to consider health problems from a global perspective, and the need to incorporate practicing physicians in the process as much as possible.
With the discovery of HIV 20 years ago and the demonstration that HIV is the cause of AIDS, it seemed that a vaccine would follow closely behind. That didn't happen.
"While we now have a clearer understanding of the challenges and obstacles in the path to an AIDS vaccine, much work remains to be done," said Gary J. Nabel, M.D., Ph.D., director of the Vaccine Research Center at the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health.
The research community has learned much about the three-dimensional structure of the HIV envelope, he said. Armed with this knowledge, specific targets may be revealed for HIV vaccines that can stimulate a broadly neutralizing antibody immune response. Experts also have a better understanding of how the HIV virus evades the body's normal immune response and how the virus enters target cells, he noted.
Further, at a time when approximately 95 percent of all new HIV infections are occurring in developing countries, scientists more fully appreciate the global nature of HIV genetic diversity, an important consideration in developing a vaccine that can protect against a wide variety of genetically diverse viruses. An early phase clinical trial has recently begun testing of a novel "global" vaccine developed at the Vaccine Research Center.
Unfortunately, said Nabel, HIV is a virus that has evolved to thwart the immune system and will not be easily countered. "It is evident that many more human clinical studies are needed for the development of an effective HIV vaccine," he admitted.
Diarrheal diseases remain among the most common afflictions of mankind. In developing countries, diarrhea remains the second most common cause of death among children. In the United States, it remains a common problem as well, with more than 70 million episodes, 500,000 hospitalizations and some 5,000 deaths occurring each year.
Recognized bacteria and parasites accounted for fewer than 20 percent of all outbreaks and hospitalizations. However, in 1993, norovirus was finally sequenced and molecular diagnostic methods became available. Not only could noroviruses be detected more easily but the sequence of the virus could be determined, making it possible to trace the transmission of a single virus to many different outbreaks.
"Application of these diagnostics has led to an abundance of new studies and increased understanding of the burden of norovirus disease. Noroviruses now appear to be the most common cause of outbreaks of gastroenteritis in Americans of all ages and the most common cause of diarrheal hospitalizations of adults," stated Roger I. Glass, M.D., chief of the Viral Gastroenteritis Section at the Centers for Disease Control and Prevention.
Most recently, studies in the United States, Europe and Japan have identified noroviruses to be the most common cause of hospitalizations of adults for diarrhea, while similar studies in developing countries have identified them as a common cause of severe diarrhea in small children with a disease burden similar to rotavirus, or about 400,000 deaths per year.
West Nile Virus
"In 2002, West Nile virus produced the largest outbreak of arborviral meningo-encephalitis ever reported in North America, with 4,156 cases of West Nile virus infection reported to state and local health departments," revealed Stephen M. Ostroff, M.D., deputy director, Centers for Disease Control and Prevention.
Given an infection ratio of 1 to 150 persons, it can be estimated that more than 500,000 persons were infected with the virus last year. Along with the unprecedented outbreak of human illness, almost 15,000 equine cases were reported.
The virus also continued to expand its range of avian and mosquito hosts. As of early 2003, it had been detected in 37 different mosquito species, 162 species of birds and 18 other types of animals. Since last season, evidence of West Nile virus circulation in the Caribbean basin and Central America is increasing.
Although the vast majority of 2002 West Nile infections were mosquito-transmitted, five unique modes of transmission were reported for the first time. These include 23 episodes of bloodborne transmission, transmission through transplanted organs, an in utero infection, transmission from mother to child via breast feeding, and occupational exposure of laboratory workers.
Efforts continue to develop antiviral therapeutics and a preventative vaccine. However, at present, personal and community prevention activities to reduce exposure to infected mosquitoes remain the mainstays of West Nile interventions. These include integrated pest management efforts to reduce mosquito populations, and personal protective measures including use of insect repellants. "It is impossible to predict the future public health impact of West Nile virus. However, the annual re-emergence of cases in all areas where the virus has been identified along with the large number of avian and mosquito hosts, suggests a need to be prepared for future outbreaks of similar magnitude to the one experienced in 2002," said Ostroff.