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Multiple Sclerosis Clusters
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Clusters have been noted in certain areas that may provide evidence that genetic
or environmental factors are involved. A cluster would typically have an excess
or significantly higher number of cases over the average number of cases in the
area. In this case, there are clusters that are specific to multiple sclerosis
(MS).
Some of the clusters have been the Faroe Islands in the North Atlantic Ocean
which went from no cases of MS to around 25 cases after 1943. A second cluster
is in DePue, Illinois that developed in the early 1970's to the late 1990's
around an area that had a zinc smelter plant leaving traces of metals in the
water and soil. A third cluster in Rochester, New York where zinc was thought to
be a possible factor at a manufacturing plant. A fourth cluster in El Paso,
Texas was identified and concerns raised regarding another metal smelter which
was shown to have contaminated the air and soil with high levels of lead,
arsenic, zinc, and cadmium.
These clusters give support to those who feel that environmental agents have a
large impact on those who are predisposed to MS. Recently, it's been felt by
many that the theory of exposure to heavy metals isn't a cause of MS. This
theory is still worthy of mentioning since it can't be proven with complete
certainty either way and clusters still remain.
A few other facts are that MS is not a contagious disease, nobody can "catch it"
from you. MS is also not directly inherited so you can't blame your parents if
you have it. If your parents moved you directly into a cluster, however, then
you can at least give them a hard time about it, but you can't blame anyone.
Public health departments usually take the lead in investigating and determining
if a cluster exists. If it's determined that a cluster may exist, then typically
they will get the U.S. Centers for Disease Control (CDC) involved.
The Faroe Islands
(Located between Norway, Iceland, & U.K. and not included on the below map)
Some of the earliest and most famous clusters known to MS investigators are a
series of alleged epidemics that occurred on the Faroe Islands, a Danish
possession in the Atlantic between Norway and Iceland. Although the inhabitants
are Nordic and considered a high-risk group for the disease, there were no known
reports of MS prior to 1943 among native-born residents. In the early 1960s a
Washington, D.C. neurologist, Dr. John Kurtzke, became intrigued with a report
by a Danish investigator, K. Hyllested, about 25 cases of MS in the Faroes that
had occurred starting in 1943. It appeared that the disease had been brought
into the Faroes since it hadn’t been reported there before.
The most significant event that had taken place on the Faroes was the British
occupation during World War II. Assuming an incubation period of a few years,
this would tally with the onset of the first alleged epidemic in 1943. When
researchers later grouped the cases of MS with clinical onset from 1943 to 73 by
puberty status at the time of the British occupation, they found three distinct
peaks of MS incidence, corresponding to the three alleged epidemics. The first
consisted of 18 cases, all of whom were past puberty at the time of the
occupation. The second consisted of nine cases who were prepubertal during the
occupation but who reached age 11 between 1941 and 1951, with onset of MS from
1948 to 60. The third comprised five cases who reached age 11 between 1949 and
1963, with onset of MS from 1965 to 73.
Many of the occupation soldiers were from the Scottish Highlands, where the MS
prevalence is quite high: 90 cases per 100,000, comparable to the northern U.S.
In Dr. Kurtzke's view, if MS is triggered by a virus, the disease may have been
brought to the Faroes by the soldiers. Dr. Kurtzke is continuing his studies of
MS in the Faroes, but despite years of intensive investigation, no factor has
yet been identified that can definitively account for the alleged epidemics.
(A) Galion, Ohio
Galion, Ohio, with a population of 12,391, was reported to have 25 cases of MS
in 1986, being about double what might be expected. Nothing in the history of
Galion pointed to any common agent, except that in 1960 a patch of land on part
of an old cemetery was dug up so that a new high school gymnasium could be
built. The loose earth was offered to anyone who would take it away and many
did.
A 1991 analysis published in Neuroepidemiology by a team from the Ohio
Department of Health found that six of the reported cases, or 24%, were not MS,
but a different disease with similar symptoms, a case of misdiagnosis. The
remaining 19 cases had definite or probable MS, however, two of these were not
local residents, and therefore were excluded from the prevalence calculation.
When these adjustments were made, the prevalence of MS in Galion was still high,
but it was within "normal" range.
(B) DePue, Illinois
MS clusters sometimes crop up in occupational settings. Dr. Randolph B. Schiffer
and colleagues at the Texas Tech University Health Sciences Center, Lubbock
investigated an industry-based MS cluster in DePue, Ill., in the late 1990s,
results of which were published in the September/October 2001 issue of Archives
of Environmental Health.
The residents of this small town (population 1800) had been exposed to trace
metals in water and soil from a zinc smelter plant that closed in the early
1980's. In conjunction with the Illinois Department of Public Health, the
investigators confirmed the diagnoses of nine people with MS, all of whom had
developed symptoms between 1971 and 1990. Based on expected incidence rates, the
investigators determined that the nine cases far exceeded the number expected to
occur over a two-decade time period in a town of this size. The authors
concluded that exposure to zinc or other trace metals could have been a factor
in the occurrence of this MS cluster, although they had no direct evidence that
zinc or any other metal is, in fact, related to MS.
(C) Rochester, N.Y.
Zinc also was identified as a possible exposure factor in an earlier report by
Drs. E.C. Stein, Schiffer and colleagues, published in the October 1987 issue of
Neurology, describing an MS cluster among employees at a manufacturing plant in
Rochester, N.Y. When the investigators checked workers' records, they found that
11 had developed MS during a 10 year period, 1970 to 79, when two to four cases
would have been expected. Even though the investigators concluded that there was
a significant excess of cases of MS, they could find no differences in exposure
to zinc between the workers who had developed MS and those who had not. However,
genetic susceptibility to MS was not taken into account in the investigation.
(D) El Paso, Texas
In December 1994, a former El Paso, Texas resident with MS contacted the Texas
Department of Health to report an apparent cluster of MS cases among people who
spent their childhoods in the Kern Place/Mission Hills and Smeltertown areas of
El Paso. Early in the investigation, concerns were raised about the possible
impact of a local metal smelter, which was shown to have contaminated the air
and soil with high levels of metals such as lead, arsenic, zinc and cadmium.
The federal Agency for Toxic Substances and Disease Registry (ATSDR) of the CDC
provided a grant to the Texas Department of Health to conduct a study of people
who had attended two elementary schools in the Kern Place/Mission Hills
neighborhood and Smeltertown to determine how many had been diagnosed with MS.
Epidemiologist Judy P. Henry led the study, results of which were presented
publicly in 2001 and may be published in the future.
Students who attended Mesita and E.B. Jones elementary schools from 1948 to 70
were eligible to be included in the study and were sent questionnaires asking
for demographic and medical information. Dr. Randolph B. Schiffer reviewed the
records of those who indicated they had MS to confirm the diagnosis.
The investigators identified and confirmed 14 cases of MS among former Mesita
students. No cases were reported among former E.B. Jones students. The number of
cases among former Mesita students is twice as high as expected, based on
national estimates. This study was not designed to investigate the specific
cause or causes of MS and the results cannot tell us why there is an excess of
MS among the former Mesita students. Based on the findings, the investigators
recommend further investigation of this cluster and possible factors that might
be involved.
Other Clusters
Other MS clusters have been reported over the years, but epidemiologists have
been unable to pinpoint causes. Research into reported clusters continues. In
2002, ATSDR awarded research grants to five investigators to evaluate possible
environmental risk factors for MS and amyotrophic lateral sclerosis (ALS) in
several U.S. communities that are near hazardous waste sites. These studies,
undergoing final analysis, focused on sites in Illinois, Texas, Massachusetts,
eastern Washington and Missouri. While these efforts of ATSDR to understand the
potential health risks of hazardous waste exposure will provide important
information, there is no information to date to suggest a definite link between
hazardous waste and MS.
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