**Health Seminar Series - Emerging Diseases**

**March 10, 2000**

Session 5 -- "Emerging Diseases in Tropical Countries" and

"Hepatitis B Virus and Prevention of Primary Cancer of the Liver"

Dr. Arnauld Nicogossian introduced the fifth session in the Health
Seminar Series on Emerging Diseases, the sixth of a series of continuing
education programs sponsored by NASA's Occupational Health Program,
Office of Health Affairs (OHA), in cooperation with the Uniformed
Services University of the Health Sciences (USUHS). He introduced the
speakers for this session: Dr. Larry W. Laughlin, Professor and
Chairman, Department of Preventive Medicine and Biometrics, USUHS; and
Dr. Baruch Blumberg, Director of the Astrobiology Institute, NASA Ames
Research Center.

Dr. Nicogossian noted that these topics are very germane to NASA. The
Agency has dealings on an international level and many employees travel
overseas, both for business and pleasure. We need to be cognizant of the
changes that have occurred in epidemiology and the pathogens in other
countries, which are being introduced to non-native habitats. In the
case of infectious diseases, if we are not careful on how a medical
history is taken and symptoms recognized, we might entirely miss the
diagnosis and the result could be a public health hazard.

Dr. Laughlin discussed emerging infectious diseases in the tropical
countries. Infectious and parasitic diseases still lead the world in
number of deaths (in 1996, 33% were related to infectious disease and
the percentage has remained constant since then). If you focus on
tropical countries, about 50% of deaths are related to infectious and
parasitic diseases. It is an important global issue. Is there any other
evidence to confirm this? An article in *Scientific American* emphasized
recent emerging infectious diseases (viruses) throughout the world. The
largest concentration is in the tropics. This is an issue in the medical
community, but it has extended beyond the medical community into the lay
press. The world is becoming aware of resurgent infectious diseases,
e.g., malaria. It is a public health issue and is of interest all over
the world. The Centers for Disease Control (CDC) conference defined
emerging diseases as infectious diseases whose incidence in humans has
increased in the past two decades. This occurs through change or
evolution of the organism (e.g., part of the HIV issue), an old disease
moving to a new geography or population (e.g., Rift Valley Fever), or a
new disease in a new ecology (e.g., Meningoencephalitis caused by the
Nipah virus). Reemergence is also a category of emerging
diseases---e.g., the pneumococcal organism has become resistant to
penicillin (beginning in South Africa two decades ago), and there is now
drug-resistant tuberculosis. The breakdown in public health measures is
a major factor in re-emergence. The tropical countries have the greatest
history of emergence, the greatest number of diseases, and the greatest
number of cases. These countries are frequently least able to prevent or
cope with epidemics. Epidemics have great impact on the individual who
is already nutritionally compromised. Also, there is great impact on
community health where there is little health infrastructure. Some
examples of emerging diseases in the tropics are malaria; cholera 0139;
Avian flu, Bartonellosis, *Helicobacter pylori*, and HIV. The resurgence
of malaria is directly related to reduced vector control. In the 1950's
and 1960's the World Health Organization supported an attempt to
eradicate malaria by use of DDT. It was applied to the walls of
households in many communities and served as an effective deterrent
(insecticide) to the malaria vector. However, the agricultural community
also resorted to using DDT to help crops. The agricultural community
used DDT in enormous doses, resulting in environmental contamination,
unlike the DDT painted on walls of houses that caused little
environmental exposure. A hasty decision to stop using DDT completely,
and this put much of the world at risk. To a large extent, this has been
responsible for the increase in malaria over the past several decades.
Drug resistant malaria also came of age in the 1970's and had a major
contribution. Certain areas, freed of malaria for a long time, are
seeing it creep back in (e.g., Korea). The new form of cholera began in
the Indian subcontinent in the mid 1990's has now spread to the Middle
East and there are several cases of imported cholera 0139 in different
parts of the world. The Avian (chicken) flu caused a stir in Hong Kong.
Bartonellosis is an interesting disease that is of concern to the USUHS;
it is now qualified as an emerging disease. During this past El Nino
period it broke out of an endemic infection area and moved into a new
area of Peru. *Helicobacter pylori* is much studied in the U.S. and is
now being recognized as a major issue in the tropics as well. HIV is the
prototypic emerging infectious disease that began in the tropics and
still ravages the continent of Africa.

Dr. Laughlin focused on some specific examples of emerging virus. There
are a group of viruses identified as myxoviruses and they include the
Hendra and Nipah viruses. This was a new disease, identified in
Southeast Asia. Another arboviral infection is Rift Valley Fever (RVF).
It has been evolving over the last several decades. Epidemic
Meningoencephalitis (recently identified in Malaysia and Singapore) is a
prime example of a frightening emerging infectious disease from the
topical countries. Beginning the September and October 1998, there began
to be clustering of cases of Meningoencephalitis in Singapore and
Malaysia. These were centered around swine farms in Malaysia and around
abattoirs in Singapore. Every case was identified with some exposure to
swine. In retrospect, there was some disease in the swine as well. While
the farmers had observed this, it had not been translated to any public
health authorities. As the epidemic continued and cases were
investigated, it was discovered that there was a paramyxovirus
associated with this highly fatal infection. It was called a Nipah
virus, very closely related to the Hendra virus. The transmission seemed
to be associated with swine contact, although the exact method of
transmission was not clear. There were no secondary infections. The
incubation period was about 10 days and patients presented fever,
headache, and decreased level of consciousness. Within 24 to 48 hours,
they progressed to coma. Many died; however, if death did not occur,
there was recovery with no neurological residual. Clinical pathological
studies showed central nervous system microinfarction. The mortality
rate was 48%. Once this was recognized and public health officials
became involved, very effective control methods were established. Swine
were destroyed if they were ill or in the area of epidemics. This
stopped the spread of the disease. Hendra virus was very similar to the
Nipah virus. Six years ago, there was an epidemic of horse pneumonia in
Australia. It affected 20 horses (most died) and three humans (one
died). This was a new disease transmitted to humans. The natural host of
this virus was the fruit bat, located in northern Australia and Papua
New Guinea, but a connection could not be made between the fruit bats
and the two epidemics in Australia. Both the Hendra and Nipah viruses
are paramyxoviruses. This is a category of disease that may cause many
of us to be uncomfortable. The myxoviruses have two subgroups: the
othomysxoviruses (e.g., influenza) and the paramyxoviruses
(traditionally, mumps and New Castle disease). Now we have new zoonotic
diseases that have extended to humans with fatal outcomes. The
transmission mechanism remains unknown, but both of these were
respiratory diseases in animals. If this evolves to the state where it
can be transmitted by the respiratory system, is will become a
frightening phenomena. Luckily, both of these epidemics were easily
contained. However, we need to worry about whether these myxoviruses are
on the move.

Another group of viral diseases are arthropod-borne viral diseases and
several have shown elements of emergence over the last couple of
decades. Dengue fever has returned Central America, South America, and
the Caribbean, having been absent for the last twenty or thirty years.
West Nile Fever (a viral encephalitis) showed up in New York City this
past year. Macupo virus is an authentic emerging disease in South
America, but is not arthropod borne. Oropouche is an arthropod disease,
probably transmitted by the sand fly in South America. It has been
moving to other areas. Dr. Laughlin focuses on RVF in Africa. This
disease has been evolving throughout the past century. In 1931, in the
Great Rift Valley of Kenya, there was an epidemic disease among ruminant
animals, particularly sheep. Humans associated with the aborted delivery
of these sheep developed what was thought to be a benign human disease.
It was so benign that researchers gave it to each other to examine the
clinical manifestations of the disease. Then the disease went silent; it
next showed up in the late 40's and early 50's in the Transvaal of South
Africa. There, it became an agricultural issue---it moved into other
ruminants (cattle) and was associated with human disease. However, it
was rarely fatal, the complications seemed manageable, and the cases
were small. In 1977, there was an epidemic of RVF (the largest ever
identified) in the Egypt delta. There were over 600 human deaths and
more than 200,000 people were infected. It broke out of East Africa and
moved to West Africa. In 1997, it moved back to the Rift Valley of Kenya
where more than 400 people were associated with a hemorrhagic death.
This is a serious disease that has evolved from being a mild veterinary
disease to one that has enormous impact on large populations.

Dr. Laughlin discussed the epidemic in Egypt. There was a small outbreak
of what appeared to be Dengue fever, which was rare in Egypt. Dr.
Laughlin and his colleagues tried to isolate the Dengue virus, but
discovered that the virus could not be identified (over 200 viruses were
screened). Virologists finally identified it as the RVF virus. More
extensive questions were then asked to a broader community. Sheep
abortions had been occurring for the past several months; however, the
agricultural community and the medical community had not connected.
About this time, another issue arose that is representative of emerging
diseases throughout the world, especially in the tropics. The U.S.
medical group was no longer invited to participate in the investigation
after the first seven to ten days, and the Egyptian government demanded
all the samples. What happened was that someone thought this might be a
biological warfare event. This stopped the diagnostic work-up of this
disease for a period of time. Politics also entered into the control of
this disease. There was an established effective animal vaccine (a good
way to interrupt the transmission of this disease to humans), but all of
the vaccine was made and owned by South Africa and this caused a
political problem because of alliances during the 1973 war. The vaccine
had to be sold to different countries two or three times before it could
be purchased by Egypt; however, it did arrive and played a meaningful
role in the control of this epidemic.

RVF is a zoonotic disease. It is an unpredictable epizootic throughout
Africa. The manifestation among ruminant animals is most often abortion.
This has profound impact on families and countries in the tropical
world. This was an economic disaster in the delta area of Egypt and put
many families in great distress. The fatal cases in animals resulted
from a fulminant liver necrosis. The way it was transmitted to humans
(in Egypt) was a spillover phenomenon. The disease had been circulating
in the sheep population for several months. As the number of animals
infected increased and the mosquitoes increased during the winter
season, the spillover effect broke out in humans and caused a large
number of human infections. The human is a dead-end host. The mosquito,
most often the Culex species, vectored transmission. Another experience
was aerosolization of infected blood. The clinical disease of RVF comes
in four forms: (1) the uncomplicated form presents as an alphvirus
syndrome, lasting 3-4 days and recovery is complete in 7-10 days; (2)
hemorrhagic complications (the syndrome deteriorates with massive liver
necrosis with death from hemorrhagic diathesis), uncommon but highly
fatal; (3) retinitis (onset after acute disease with central visual
loss, foveal hemorrhage and scarring, and permanent visual loss in some
patients), which was a sentinel marker in Egypt in 1997; and (4)
encephalitis (manifesting 7-15 days after acute disease, with
astronomical levels of RVF antibodies in the cerebrospinal fluid), with
profound neurological sequelae in about 50% of the survivors. Both
humans and animals have an enormous viral load and aerosolization in the
lab is a significant danger. The virus can be isolated fairly easily,
but is hazardous in a normal lab. There are vaccines against this
disease, but the human vaccine is not FDA approved and has limited
availability. There is now a new recombinant RVF vaccine in development.
The animal vaccine is available and quite effective. Vector control is
important in an epidemic like this, particularly in human cases. The
other issue that should be raised is the fact that remotely sensed
forecast factors have been used to predict the epidemics of Rift Valley
Fever. Satellite images, in connection with climate markers and
vegetation index have been used to predict an epidemic five months
before it happened. This could be used before the next epidemic and
timely animal vaccines could be put into play.

In summary, the tropics are important in the evolution of emerging
infectious diseases. The tropics are a cauldron of infectious disease
(large numbers of cases, large numbers of diseases). Disease
surveillance systems are poor, allowing these emerging infections to get
out of control before they are detected. The human misery index is very
high and the response resources are limited. The economic impact is
profound and the effect on the developed world is real, e.g., the
outbreak of West Nile Fever in New York City. As a global medical
community, we should invest in disease surveillance and disease control
research.

Questions:

Dr. Nicogossian: In the 1980's, in a four-year period, I saw five
patients with malaria in northern Virginia. Why don't we introduce
malaria control in places like California and Florida? In order to
prevent malaria during World War II, airports were being cleared to
ensure that mosquitoes would not reach airports. Today, you can pass by
an airport and get malaria from airline carriers being refueled, etc.

Dr. Laughlin: Your concerns are real. There have been three confirmed
transmissions of malaria within the U.S., e.g., someone came into the
country, transmitted it to the vectors, and passed it to an American
here. Fortunately, we have enough development that the mosquito does not
flourish in a huge way and there is enough tracking and reporting that
we are able to pick up on these events. Before the 1940's, malaria was a
real disease in the U.S. The airport issue is fascinating. There were a
couple of cases from the Paris airport. It is possible to transmit an
infected vector in this manner, and then infect people at the airport.

Dr. Nicogossian: You don't have to travel to get tropical diseases; you
can get it by purchasing exotic pets (e.g., parakeets).

Dr. Laughlin: That is true. The issue will become more evident in the
food supply---we get much of our food supply from the tropical countries
and there is potential for spread of diseases throughout North America
and South America. For example, animal hides brought into the U.S can
transmit anthrax. Illegal importation of animals, particularly birds, is
a way to quietly introduce diseases into the U.S.

Dr. Nicogossian: People bring back diarrhea (mostly *e. coli*) from the
topical areas, but people from the tropical areas also develop diarrhea
when they travel to the temperate zones.

Dr. Laughlin: While living in the tropics, you reach equilibrium. The
diarrhea is the result of a readjustment of the flora within the
intestine. It is a common phenomena---if you have been overseas long
enough, you have to adjust to your new bacterial environment upon your
return.

HQ: Regarding the investment in disease surveillance, do you have a
recommendation on how best to make use of satellite systems that could
do this kind of prediction and how to get that information out to a
customer?

Dr. Laughlin: This sort of imagery will be most useful to vector-borne
diseases. Vegetation index can be easily measured from satellite images;
the vector index relates directly to the amount of water and the burden
of vectors that are there. Strong correlations have been shown with
malaria in Central America. In the best of circumstances, you would
develop some sort of surveillance index where someone is monitoring the
vegetation index throughout the world, and then notify public health
systems when things start to move into a negative alignment, e.g.,
certain circumstances leading to high vectors. I can imagine a global
surveillance system that would have a powerful arm using one of these
indices from the remotely sensed satellite images.

Dr. Blumberg discussed the Hepatitis B virus and the vaccination
programs that have been in place for about 10-15 years which have had a
profound effect on the incidence and prevalence of this disease, and
subsequently on the incidence of primary cancer of the liver. This could
be a model for other preventative programs in cancer, since there are
other cancers that have viruses as part of their etiology. Dr. Blumberg
showed a list of most of the named hepatitis viruses. The Hepatitis A
virus (HAV) is an RNA virus, associated with acute hepatitis; there is
only rarely a chronic form of it. The Hepatitis B virus (HBV) is a DNA
virus, associated with both acute hepatitis and chronic forms of
infection as well as primary cancer of the liver. The Hepatitis C virus
(HCV), an RNA virus, occurs both in acute and chronic form and is also
associated with the etiology of primary cancer of the liver. Hepatitis D
virus (HDV) is a very small virus that has the unusual characteristic of
infecting only people who are already chronically infected with HBV.
This is also associated with chronic forms of hepatitis, very often
quite severe. Hepatitis E virus (HEV) is an RNA virus that is spread by
the fecal-oral route, as is HAV, and is associated with large epidemics
of hepatitis and often with large numbers of fatalities, common in south
Asia and other parts of the world. The methods of transmission differ.
The fecal-oral route transmits the HAV and HEV. HBV, HCV, and HDV are
transmitted primarily from transmission of blood from an infected person
to a non-infected person. In addition, there is the Hepatitis G virus
(HGV), whose role in pathology is not clear.

The top infectious disease killers are acute respiratory infections,
diarrheal diseases, tuberculosis, malaria, Hepatitis B, and HIV/AIDS.
Hepatitis B kills about the same as number of people per year as
HIV/AIDS. Dr. Blumberg showed the electron microscopy of the HBV
isolated from the blood of a carrier. The unusual particles containing
the surface antigen are present in very high concentrations in the
blood. When it was discovered, HBV formed a new class of viruses
(hapagnovirus type 1). A great deal is known about the molecular biology
of the virus. It uses reverse transcription in replication. In addition
to the whole virus, there are smaller and elongated particles that are
made up entirely of the surface antigen. They do not contain DNA, do not
replicate, and are not pathogenic, but they occur in large numbers in
people who carry the virus. Based on the availability of the surface
antigen particles, Dr. Millman and Dr. Blumberg invented a method for
producing a vaccine from the surface antigen particles in the blood of
carriers. The small particles are isolated and treated to kill any
possible virus that may remain in the blood. The vaccine was invented in
1969; by the mid-1970's there had been a large amount of testing and a
field trial in the late 1970's. It proved to be a good vaccine and was
approved by the FDA and tens of millions of doses have been used. A
recombinant vaccine has largely replaced this vaccine.

Dr. Blumberg showed an illustration of the four reading frames that are
present in the genome of the HBV---an S gene (a surface antigen gene), a
C gene that produces a core surrounding the nucleic acid, a P gene
responsible for enzymes required for replication, and an X gene
associated with the development of cancer and other phases of
replication of the virus. It is an extremely simple virus and it is
remarkably well adapted to its environment. The S gene was introduced
into various cells to produce a recombinant vaccine in the 1980's. It
was the first recombinant vaccine produced. The vaccines were initially
made from the entire genome; now, it is made by combinations of the
Pre-S1, the Pre-S2 and the S. A large amount of this vaccine has been
produced, and it has been administered to over 1 billion people. Dr.
Blumberg showed a diagram of the C gene, illustrating the complexity in
a small number of genes. The gene can produce both the core antigen and
the e-antigen. It is thought that the e-antigen serves a role in
maintaining the chronicity of the HBV and it tolerizes the host against
the c-antigen. The tolerization of the host decreases the probability of
the host to eliminate the liver cell containing the virus. This is a
remarkable adaptation to keep the virus in chronic form. Dr. Blumberg
showed a diagram on what happens in acute HBV infection. Most people who
get an infection develop antibodies, and they have lifelong immunity. In
many cases people will develop an acute infection, but there is usually
complete recovery. The first serological event is the appearance of HBV
surface antigen in the blood (before there are symptoms). The surface
antigen begins to decrease by the time the jaundice becomes apparent.
Within a few weeks the surface antigen decreases to undetectable levels
and antibodies against the core antigen begins to increase. Later in the
infection the anit-HBe will appear. These people usually recover in a
few weeks. The serological test allows one to diagnose the disease
specifically before symptoms and continuing well into the life of the
individual. About 5% of people in North America who develop acute
infection will go on to a chronic infection. The surface antigens don't
decrease as they do in the acute case. The HBe antigen may be detectable
in the blood. That chronicity may last for the lifetime of the
individual, although usually the surface antigens decrease as the person
ages. The chronic form of HBV infection can happen without any obvious
effect on the individual. The effects of the chronic infection may not
manifest for decades after the initial infection.

Dr. Blumberg showed the global distribution of chronic HBV infection.
There is good data available on this because blood banks test for HBV
all over the world. The major areas for infection are East Asia (China
and the Pacific Islands), Africa (particularly sub-Saharan Africa), the
Amazon basin, and the Innuit in the Arctic region. There is an
intermediate level in parts of Europe, particularly eastern and southern
Europe. The temperate zones of North America have lower frequencies.
Overall, there are about 350 million people in the world infected with
HBV. It is a common, serious illness in many parts of the world. This
high infection rate occurs in about 45% of the world's population. From
a public health point of view, the acute infection is a nasty illness,
but it not as important as the chronic hepatitis state. There are a
number of factors in determining whether an individual will become a
chronic carrier. Age of infection is an important factor. Neonates
infected by mothers at the time of birth have a very high probability of
chronic infection. Infants also have a high probability (50%). Adults
are much less likely to become chronically infected. Family studies have
been done to determine the probabilities of transmission. Transmissions
from mothers to children are the highest; between siblings is next
highest; from father to children is less likely. From an epidemiological
point of view, the maternal/neonatal transmission is the most important;
the other is sexual transmission. If a mother is a carrier of the HBV
and is replicating the virus, there is 95% probability that the newborn
will be chronically infected. If the mother isn't replicating, there is
still a high probability (about 20%). If the mother has acute hepatitis
in the third trimester, there is a high probability of transmission but
this is much less likely to occur. The transmission from chronically
infected individuals to the newborn is an extremely important method of
transmission. Males are much more likely to become chronically infected
than females. The female becomes a carrier and can infect her newborn
child; all are subject to increased risk of developing primary cancer of
the liver.

In the U.S., the major method of transmission is heterosexual activity
(40%). Intravenous drug use also represents a large proportion of
transmissions (20%). Other risk factors are homosexual activity (10%)
and non-sexual household contact (3%). In other parts of the world, the
major method of transmission is from mothers to children; sexual
activity is probably the next important factor unless intravenous drug
use is prevalent in the community. The probability of sexual
transmission of HBV is very high (higher than HIV). There is a very high
field infection rate in several mosquito species; it is extremely high
in bed bugs (more than 50%). However, there isn't any substantial
evidence that insects are a major form of transmission, but the
appropriate studies may not have been done. Tattooing has been a form of
transmission in some cultures. The virus has selected for its main
mechanisms of transmission the most vital processes in the life cycle of
humans, e.g., childbirth, infanthood, and sexual activity. Dr. Blumberg
showed some examples of the hepadnaviruses found in other species---tree
squirrels, woodchuck, ducks, and ground squirrels. The course of the
disease is fairly similar in woodchucks; if the woodchuck is infected,
they have a 90% chance of developing cancer of the liver if they survive
to 4 or 5 years old.

The treatment for liver cancer is very poor; the five-year survival rate
is only about 8%. It is now possible to diagnose cases very early, and
it was thought that this could increase the survival rate. Primary
cancer of the liver is the third most common cause of death from cancer
in males worldwide. It is the seventh most common cause of death from
cancer in females. Males are more likely to develop chronic liver
disease and liver cancer than females. There are about 1 million deaths
per year from primary liver cancer and HBV and HCV account for most of
these cancers.

There is a substantial body of data that links HBV etiologically with
primary cancer of the liver. An interesting study was done in Taiwan in
the 1970's. It was a prospective study of people who carried the HBV
compared with a non-carrier growth. The number of primary hepatocellular
carcinoma cases was vastly different after about a 7-year follow-up. The
incidence of cases was over 400 for the carriers and less than 10-20 for
non-carriers. An important area for study is the molecular biology of
HBV. There is a great deal of research on this issue. Dr. Blumberg
illustrated the complicated nature of the pathogen. Many factors affect
the outcome in the progression from HBV infection to cancer: gender
(males more likely to suffer dire affects), increased iron storage
protein levels (increase the probability that infected people will go on
to develop cancer), other infectious agents, aflatoxin from fungi
(increases the probability of developing cancer), and host genetics (at
least five loci in the human genome relate to the probability becoming a
chronic carrier and of developing cancer). There can be intervention at
several points, e.g., vaccination of the mother, vaccination of the
offspring, etc. Dr. Blumberg discussed the interaction of the aflatoxin
with the HBV, illustrating how two variables (aflatoxin and HBsAg)
interact together. There was a study in the early 1980's on the efficacy
of the HBV vaccine (Heptavax B). If people got all three of the vaccine
doses, the protective efficacy was close to 100%. This led to FDA
approval of the vaccine.

Questions:

JSC: In reference to anyone who has had HAV or HEV, then subsequently
had HBV or HCV, what is the potential for protection from the A/E and
also is there any epidemiology relevant to development of subsequent
cancer in those types of group cases?

Dr. Blumberg: My understanding is that there is no cross-antigenicity or
cross-protection for the anti-HAV antibody. There is a very effective
vaccine against HAV, which is quite widely used. HAV does not increase
the probability of primary cancer of the liver, nor does HEV. They are
not cross protective. The vaccines that are available are for HAV and
HBV; there is no vaccine for HDV or HEV.