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Genes & Disease
Emerging infectious diseases
Emerging infectious diseases are commonly defined as those that have newly
appeared in a population or have existed but are rapidly increasing in
incidence or geographic range. Also of interest will be our
'Other important human diseases'
(non-infectious diseases) section.
Some examples of emerging infectious diseases include:
Additonal topics discussed:
Click here for a more comprehensive World Health Organisation report on emerging infectious diseases.
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AIDS
 According to the World Health Organization, an estimated 5.8 million people
worldwide became newly infected with HIV during 1998, and as of December
1998, about 33.4 million people worldwide were living with HIV/AIDS. As
these figures indicate, the AIDS epidemic still rages out of control,
particularly in sub-Saharan Africa and in Asia. However, recent reports
of significant progress in clinical and basic research on HIV disease
have fostered cautious optimism within the AIDS research community.
The arrival
of the protease inhibitor drugs, which were shown to reduce the amount of
HIV in the blood of many infected persons to undetectable levels when used
in combination with other AIDS drugs, has dramatically altered the epidemic
in the United States. Approximately 31,130 deaths attributable to HIV infection
occurred in the United States in 1996. In 1997, the estimated number of HIV-related
deaths (16,685) in the United States was 47 percent lower. This was in large
part due to these new regimens.
Most researchers still believe that development of a vaccine capable of preventing
HIV infection will be critical in stopping the epidemic. Since 1987, NIAID
scientists and grantees have conducted 52 clinical trials involving 27 experimental
vaccines. In early 1999, NIAID opened the first AIDS vaccine trial in Africa, an
important step for global vaccine development. This small study in Uganda will
help determine if it is necessary to tailor-make vaccines for different parts of the world.
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Enterohemorrhagic Escherichia coli
 Within the past few years,
numerous outbreaks of intestinal disease characterised by bloody diarrhoea have been reported in the United
States and abroad. These outbreaks have been largely attributed to the O157:H7 strain of Escherichia coli
(E. coli) bacteria, which was first recognised in 1982. Outbreaks of EHEC have been linked to contaminated
beef, sausages, apple juice and fresh produce, but the bacterium can also be transmitted by contaminated
water and by person-to-person contact. Approximately 10 to 15 percent of persons infected with these organisms
develop hemolytic uremic syndrome (HUS), a serious complication that can lead to kidney failure and death.
Children and the elderly are particularly at risk for developing HUS.
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Hepatitis C
 Discovered in 1989, the
hepatitis C virus causes approximately 20 percent of all cases of acute viral hepatitis each year in the
United States. Recovery from infection is rare, about 85 percent of infected persons become chronic carriers
of the virus. According to estimates from the Centers for Disease Control and Prevention
(CDC), nearly 4 million
Americans are infected with hepatitis C. Chronic liver disease due to hepatitis C causes between 8,000 and
10,000 deaths and leads to about 1,000 liver transplants each year in the United States. Over the next two
decades (2000-2020), the number of annual deaths from hepatitis C is expected to triple if no effective therapy is found.
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Influenza
 In
the United States, approximately 25 percent of the population
has an influenza-associated illness annually, leading
to an average of 20,000 to 40,000 deaths per year. Many
people might not think of flu as an emerging disease,
but influenza viruses change from year to year and virulent
strains have emerged throughout history to cause worldwide,
catastrophic pandemics. Many scientists believe the
next pandemic is long overdue. In addition, recent reports
that people in Hong Kong became infected with avian
influenza (bird flu), the first documented cases of flu virus jumping
directly from birds to humans, emphasises the threat
that influenza viruses pose to human health.
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Lyme Disease
 First
recognised as an infectious disease in 1975, Lyme disease is the most
common tick-borne infection in the United States. More than 112,000 cases
of Lyme disease have been reported in the United States since 1982.
Analyses of the bacterium's various proteins led to the development
of rapid and sensitive blood tests for the disease. NIAID studies of the
immunity-stimulating properties of proteins found on the outer surface of
the Lyme bacterium resulted in the identification of several vaccine candidates,
one of which was recently approved by the Food and Drug Administration. Other
NIAID-supported investigators have identified and isolated several outer surface
proteins that appear to be associated with the bacterium's ability to cause
disease. Scientists are examining whether these antigens might also be potential
vaccine candidates.
Although people with Lyme disease usually are treated successfully with a
two- to four-week course of oral antibiotics, some of them develop chronic
Lyme disease, a condition characterised by persistent musculoskeletal and
peripheral nerve pain, fatigue and memory impairment.
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Malaria
 Malaria, the most deadly of all tropical parasitic diseases, has been undergoing a dramatic
resurgence. The World Health Organization estimates that between 300 and 500 million new
cases of malaria occur each year, and annual deaths from the disease number between 2 and 3 million.
Increasing resistance of the malaria parasite (Plasmodium falciparum) to inexpensive and
effective drugs presents problems for the treatment of active infections. At the same time,
increasing resistance of mosquitoes to standard insecticides makes control of transmission
difficult to achieve.
Studies sponsored
by the National Institute of Allergy and Infectious Diseases
(NIAID) include
identifying biochemical targets for new drugs; determining how existing drugs work; analysing how Plasmodium
falciparum, the parasite causing the most severe form of malaria, develops resistance to drugs; and assessing
the effectiveness of new malaria therapies in clinical trials. Other NIAID-supported scientists characterise
how the parasite survives in its human host and how infection produces disease. A team of researchers
supported in part by NIAID recently determined the complete genetic sequence of a chromosome of P.
falciparum (2002). This advance may help identify new targets for anti-malaria drugs and vaccines.
Research aimed at developing effective vaccines against malaria is a high priority. To find potential
vaccine candidates, scientists study how the immune system responds when exposed to the malaria parasite
and to its various molecular components. Such analyses should lead to the development of vaccines that
will protect humans from infection or disease. Researchers are also developing vaccines that will block
transmission of malaria parasites from infected humans to mosquitoes.
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MRSA
 MRSA is the term given to Methicillin resistant strains of the bacteria
Staphylococcus Aureus, it is also used as a description for
any strain of Staphylococcus bacteria which is resistant to one or
more conventional antibiotic. It is an infection that is now endemic in almost
every hospital in the UK. In 2004 100,000 of those who went into hospital
contracted an infection there. Of those, 5,000 died and a very high proportion
of these instances were related to MRSA infection.
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Mumps
 The Department of Health in the UK had urged that all children and
young adults be fully immunised against mumps even if they are
older than the recommended age range. This is due to the rapid
rise in the incidence of mumps in the UK in recent years.
The Health Protection Agency (HPA) in the UK said 28,470 cases were
notified in the first four months of this year (2005), almost all
of which were expected to be confirmed as true cases of mumps.
This is compared to 1,529 confirmed cases in England and Wales
last year, which was three times the figure in 2002, and double
the number in 2001.
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SARS
 SARS
is a new disease, first recognised in late February
2003. It has spread along the routes of international
air travel. As of 22nd April 2003, a cumulative total
of 3947 cases had been reported from 25 countries on
five continents.
Precautionary measures aim to reduce
the impact of SARS and contain the disease while it
is still in a relatively early stage. The SARS situation
is assessed on a daily basis to determine whether other
areas need to be included in the travel advice and if
additional precautionary measures are required.
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Tuberculosis
 Nearly 2 billion people, one-third of the
world's population, are infected with the tuberculosis (TB) bacterium. This includes between 10 and 15 million people
in the United States. TB is the world's leading cause of death from a single infectious organism, killing more adults
each year than AIDS and malaria combined.
The TB crisis is intensified by the emergence of disease caused by multidrug-resistant organisms. Infections
caused by these organisms may result in an incurable form of the disease. The World Health Organization
estimates that more than 50 million people worldwide may be infected with drug-resistant strains of TB.
The TB genome sequence will open new avenues of research. The findings will allow scientists to
understand and predict how certain strains of M. tuberculosis become drug-resistant.
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Other Emerging Viral Diseases
In 1993, an outbreak of a mysterious, often fatal illness occurred in
the Southwestern United States. Scientists quickly determined that the
illness, characterised by fever, chills and muscle pain followed by acute
respiratory distress, was caused by a previously unrecognised strain of
hantavirus, a family of disease-causing viruses that occurs naturally in
mice and other rodents. Now known as hantavirus pulmonary syndrome (HPS),
the disease has been diagnosed in 211 people as of March 1999. Almost half
of all reported cases have resulted in death.
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Technologies to Combat Emerging Diseases
Genetic immunisation, which involves injecting DNA encoding a pathogen protein directly into muscle tissue,
is a new approach that may have important implications for controlling emerging disease outbreaks. DNA vaccines,
as they are known, have shown promise in several disease models. NIAID-supported investigators have shown that
DNA vaccines can protect mice from infection with TB and Lyme disease bacteria.
The genetic immunisation approach uses so-called "gene libraries," containing all of an infectious
organism's DNA which could be used in a vaccine. The researchers showed that a vaccine made from a partial
library of DNA from a microorganism that infects rodents, protected rats against infection with the pathogen.
Gene library immunisation could provide a rapid technique for identifying DNA vaccine candidates once an emerging
pathogen has been identified.
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