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STEALTH VIRUSES AND THEIR RELATIONSHIP TO NEURODEGENERATIVE
DISEASES
Presented at
"Infectious Disease: The Threat and Future Strategies,"
Third Annual Symposium of the
American Association of Clinical Chemists
Anaheim, California, July 15, 1996
"Out of Africa"
In reference to various pathogens, the subtitle of this presentation could be "Out of Africa." But
first, let's make a distinction between two major culprits from Africa. As described in the
previous presentation, Ebola is such an acute illness that within approximately three days of
infection, people were much aware of the virus's presence. With AIDS, progress was not as
quick. It took at least three years to identify the virus that was causing an unusual illness in the
U.S. beginning in the late 1970's. This is still much faster than another type of virus that has taken
more than 30 years to even begin to identify. I am refering to another class of virus -- termed
stealth viruses -- some of which have come out of Africa. In particular, I will review evidence for
the African green monkey as being the origin of certain viruses associated with various neurologic
illnesses. These viruses may have entered humans through live polio virus vaccines. They are
now passing between humans and possibly from humans to animals.
HISTORY OF POLIO
To begin this story, let us first go to Sweden, where in the late 1890s, polio was identified as an
epidemic disease. There had been prior reports of occasional individuals who had a paralytic
illness consistent with polio, but the disease as an epidemic was first described in 1897 by Dr.
Medin, an acute pediatrician from Stockholm. Forty-two cases of an acute paralytic illness were
identified. Epidemics of this illness then began to spread throughout Europe. The next major
development occurred in Vienna, Austria, where Dr. Carl Landsteiner lived. He is the chemist
who described A, B, O blood groups in 1900, and later in the 1940's described the Rhesus (Rh)
blood group. Dr. Landsteiner wanted to see if this new polio illness could be transmitted to
animals. Similar to other investigators, he used mice, rabbits, and guinea pigs; none came down
with an illness. Fortunately at the same time in Vienna, there was a group of psychiatrists
including Dr. Sigmund Freud and others, who had extended the work of Charles Darwin in
showing brain similarities between primates and humans. These psychiatrists were analyzing the
brains of monkeys, and some of these animals were available to Dr. Landsteiner. Specifically, he
took the spinal cord from a 9-year-old child who had died from polio and injected ground up
spinal tissue into two Old World monkeys. One monkey died very quickly. After 17 days the
other monkey, a rhesus monkey, came down with a paralytic illness similar to polio. This
important finding was followed by studies indicating that polio was in fact a viral illness. A very
long gap followed, up to 1948, before Dr. John Enders in Boston showed that polio virus could
be passaged in in vitro cell cultures. This led to immediate interest in making a vaccine. In part,
because rhesus monkeys were known to be susceptible to polio, Dr. Jonas Salk chose kidney cell
cultures from these monkeys to generate large amounts of the three known strains of polio virus.
He used a 1:4000 dilutions for formaldehyde to inactivate the virus for use as a vaccine. In 1954
inactivated polio vaccine was licensed in the United States, leading to a dramatic reduction in the
incidence of polio. Dr. Albert Sabin soon followed Dr. Salk. He chose a difference approach --
using an attenuated, or less-virulent, strain of polio as a live polio vaccine. He too initially chose
rhesus monkeys. Later, it was realized that the formaldehyde technique used to inactivate polio
virus was not successful in inactivating SV-40 virus.
Consequently large numbers, probably millions of people, were inoculated with SV-40 virus. This
type of virus is quite prevalent in rhesus monkeys but less so in African monkeys. This lead to the
rapid shift from rhesus to African green monkey for both the inactivated and the live vaccines.
There was substantial debate about switching from inactivated to live polio vaccine but little
discussion about using African green monkeys in place of rhesus monkeys.
The major advantage of live polio vaccine was the rapid onset of immunity; even a single dose
could essentially interrupt the progress of an epidemic. In addition, this vaccine strain could
spread to individuals who had not actually received the vaccine, and this indirect vaccination
provided more comprehensive immunity within the community. In addition, it was much less
expensive. On the other hand, as with any live virus vaccine, there is the concern that
adventitious or unwanted pathogens might come through the vaccines. There also is the potential
that the vaccine virus, such as polio, could mix with other viruses in the cell substrate, giving rise
to new viruses as a result of the recombinations. We might think there would be hesitation to use
kidney cells straight out of a monkey to start making cell lines than risk using a continuous cell
line that might be oncogenic. Even if a cell were only partially on its way to become malignant,
oncogenic DNA possibly could be transferred. This concern has long since disappeared,
especially with the use of monoclonal antibodies produced in myeloma cells. In other words,
when the vaccines were being developed, it was deemed appropriate to use primary kidney
cultures from African green monkeys to produce a live polio viral vaccine.
CHALLENGES OF VIRAL DETECTION
The issue of safety from adventitious agents was addressed in various in vitro and in vivo assays
for non-polio viruses. Recently, some of those techniques have been enhanced using molecular
biological techniques, especially to look for evidence of retroviruses such as simian
immunodeficiency virus (SIV) and simian type D viruses. There was also the back-up of looking
for any adverse affect in the early clinical trials. As discussed previously by Dr. Shope, there are
limitations in these techniques. First, molecular probes will not pick up all viruses, especially if
you do not know what sequence you are looking for. Second, the culture tests for viral
pathogens may not pick up slow-growing viruses such as cytomegaloviruses. And probably most
important of all, an epidemiological approach is very limited when dealing with chronic illness of
variable onset. Especially difficult are illnesses that cannot be defined in terms of a clear case
definition, do not develop an acute phase following infection, and may begin to pass between
humans once the virus is introduced into the community. Even greater difficulty arises with an
illness for which there may be multiple causes.
CHRONIC FATIGUE SYNDROME
Probably the most frustrating and the most enigmatic of these diseases is an illness referred to as
chronic fatigue syndrome. But this is only part of a bigger picture that could include an entire
series of psychiatric disorders, neurogenerative diseases, autoimmune diseases, organ
dysfunctions, etc. Although many of these entities have a name -- chronic fatigue syndrome,
schizophrenia, depression, autism, etc. -- giving them a name obscures the fact that we do not
understand the underlying pathophysiology. We really do not know what is happening. Why
does someone change from a normal teenager to a schizophrenic? For many of these illnesses, it
is somewhat glib to simply say the cause is genetic or metabolic; even worse, that it is
psychological, or all in the mind. We need to come to terms with our ignorance about the cause
of many of these common diseases. The also is a notion that many of these diseases are becoming
more prevalent in our society and that we are doing little to understand their causes.
I began my work approximately 10 years ago on chronic fatigue syndrome. In my opinion, there
really is no satisfactory clinical definition of this disease. Suffice it to say that a person changes
from a relatively healthy, energetic individual to someone with an impaired lifestyle. A major
symptom is unexplained severe fatigue. Many of these patients also show symptom overlap with
common illnesses, with some symptoms explained by a lowered pain threshold. These include
diagnoses like fibromyalgia, back pain and pelvic pain syndrome. Other patients show various
mood changes from depression, flat effect, and panic disorders. Others have dementia and
cognitive dysfunction. This also is a series of illnesses generally called psychosomatic, where
there is a dysfunction of the brain's controls over various bodily functions. Again, the names of
these diseases are not very helpful, because if anything, they obscure what is really going on.
CHALLENGES OF VIRAL ASSAYS
I decided to identify a viral cause of some of these unexplained illnesses. Politically, the most
challenging was chronic fatigue syndrome. The conventional approach of trying to culture
something from the blood of affected patients was tired. Interestingly, we observed that in several
of these patients, peripheral blood cells included a mild cytopathic effect on a variety of cell lines.
The effect was not progressive and was hard to define, but it could be transferred. We could not
confirm it using routine serological strains on the cultures, nor could the cause be identified using
high-stringency PCR assays. We switched from cultures to direct testing of the blood sample.
Again using high-stringency PCR, the assays for herpes viruses and retroviruses were essentially
negative. We devised a set of generic herpes viruses primers that could produce weak but
consistent positive results shown by all then-known human herpes viruses. The PCR assays were
run under low-stringency conditions, resulting in multiple produces from some patients and no
responses from several control individuals. In several patients, there were also positive results
using a retroviral primer set against the human T lymphocytotropic virus (HTLV) tax gene.
These PCR findings encouraged efforts to go back to the cultures. We improved the culture
conditions and began to get a stronger cytopathic effect. The first really strong culture came from
a patient with chronic fatigue syndrome. The next was from a patient with acute encephalopathy
following a manic depressive illness. The cytopathic effect could be readily transmitted to cells of
multiple species including human, monkey, mouse, rat, rabbit, and even insect cells. Viruses
could be seen by electron microscopy. Once we had such cultures, we applied the PCR assay to
look for the product that might be generated. If the cultures are maintained and nurtured, we
could see the beginning of syncytia formation followed by a very strong cytopathic effect.
Electron microscopy showed viral particles as well as dense bodies similar to those seen some
cytomegalovirus cultures. These structures provide components that go into the formation of
viruses. Appearances were suggestive of a herpes type virus, yet staining these cultures with
specific antisera against cytomegalovirus, human herpesvirus 6/7 or varicella zoster (Herpes
simplex), gave negative results. In the same way, running PCR assays using primers specific for
those viruses also gave negative results. On the other hand, the HTLV primer produced two
large products that could be cloned and sequenced. Interestingly, both products were generated
with a single HTLV primer, which flanked both ends. The internal secquences of one of the
products showed a significant match to human cytomegalorvirus. These data were published in
The American Journal of Pathology in 1994 ("Cytomegalovirus-related Sequence in an Atypical
Cytopathic Virus, Repeatedly Isolated from a Patient with Chronic Fatigue Syndrome"). Having
obtained sequence data, we were able to perform a high stringency PCR assay that showed the
presence of viral sequences in the patient's blood, confirming the infection. The viral DNA also
was isolated from the culture. It was cloned, allowing for more extended sequencing. Each time
a sequence was obtained, it was compared to sequences listed within GenBank. For moany
animal viruses, only limited sequence data are available. We finally came across sequences that
allowed us to identify the true origin of the virus we had cultured. The sequence is related to
human cytomegalorvirus, more closely related to rhesus, and very highly related to African green
monkey simian cytomegalovirus (SCMV). The same pattern has occured with other origins of the
virus. We have preformed PCR assays based on known sequences of SCMV and the cultured
virus to confirm similarity but non-identity; the cultured virus differs from SCMV in the type of
cytopathic effect, the host range and in vivo pathogenicity studies. But there is sufficient data to
unequivocally establish the original derivation of the virus from the African green monkey. This
takes us to the fact that the African green monkey was the source of much of the polio
vaccination in this country. I don't believe many people have African green monkeys as pets. In
our paper describing these studies, we suggest that attention should be given to live polio
vaccines. It is worthwhile pursuing this topic because polio vaccines are still being produced in
the African green monkey.
I emphasize that the virus is pathogenic for animals. It will induce encephalopathy in cats,
drastically affecting their behavior. Yet looking at the brain histologically, there is no
inflammatory reaction. We can see vacuolated cells and viral particles by electron microscopy.
The effects are quite subtle, however, and ordinarily would receive only minor mention by a
neuropathologist looking primarily for either malignancy or for an inflammatory change. The
acute illness is followed by a chronic illness. Although the virus is widespread in the animal, the
major clinical manifestations are neurologic. In preliminary observations, if animals are
preimmunized with viral infected cells, they do not come down with an illness. This might be
because they have established an antibody barrier to the virus getting to the brain.
STEALTH VIRUSES
The animal studies have produced an impetus for human studies. Historically, we see the same
changes in human brain biopsies as in the cats. We also have cultured virus from biopsies.
Histologically, the most interesting aspect is the failure of vacuolated brain cells to evoke a
significant inflammatory reaction, leading to the designation of "stealth viruses." While these
viruses need to be more fully sequenced, it is known that relatively few components of viruses act
as potent inducers of a cellular inflammatory reaction. Those components appear to be deleted,
or at least, mutated, in stealth viruses. Therefore, they can bypass the cellular immune system,
which does not respond. Stealth viruses take much more effort to grow than a fully intact virus.
They probably don't do much damage in many organs of the body unless there's a secondary
complication such as autoimmunity. But they can disrupt the very complex integrated function of
the brain, such that a small amount of viral damage could cause profound clinical effects.
Inappropriate responses could occur as a result of viral damage.
CLINICAL MANIFESTATIONS
In this presentations, we focused on the origin of stealth viruses and patients who have been
identified. Let me assure you there are many patients now identified by culture as having stealth
virus infections. Some are extremely sick and some have been in vegetative states for the past
several years. A school teacher in Palm Springs, California, has been in a nursing home for the
past several years. She had a brain in 1991 showing typical vacuolated cell change. There is a
girl who is in a vegetative state. She was first diagnosed at Los Angeles County Hospital as
schizophrenic. Her diagnosis was changed to a manic-depressive illness. In 1991, she came into
the County Hospital with what clinically thought to be Herpes simplex encephalitis. But the
cerebrospinal fluid showed no inflammatory reaction. Clinically, the diagnosis shifted to "must be
a drug overdose." There are several medical professionals, some of whom voluntarily gave up
their licences because they could not practice medicine. One has essentially lived the life of a
demented individual for the past several years. There is a dentist who was perfectly normal one
year ago, a jovial fun person. She had an absolute change of character throughout last year, lost
her job and became paranoid. She was admitted to a psychiatric hospital. Her clinicians finally
realized there was something more organic going on. She became comatose and a brain biopsy
was performed. It revealed the same characteristic pattern of minimal inflammation and
widespread minor cellular changes. Her culture was positive for stealth-adapted viruses. Another
case involves an immigrant who died within a year of being admitted with an unexplained
encephalopathy. A series of these cases is now being complied, for which there's no evidence on
brain biopsy and culture for atypical cytopathic viruses. Some, but certainly not all, are
suggestive of an African green monkey origin. In other words, this is only one of a wide variety
of possible sources of stealth-adapted viruses. Of interest, rubella vaccines were first grown in
dog kidney cells and subsequently in duck cells. Other live vaccines are produced in foreign
species. Once such viruses are in humans, they can pass from human to human.
SUMMARY
Stealth viruses can probably produce clinical manifestations beyond chronic fatigue syndrome.
The concept presented here is that chronic fatigue syndrome is part of a spectrum of neurologic
disorders associated with, at least in some cases, a viral infection potentially derived as an
inadvertent consequence of live viral vaccines. The challenge now is for the U.S. Food and Drug
Administration, CDC, and state and county health departments to look at the prevalence of this
kind of an infection.
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