NEW YORK--An outbreak of tuberculosis (TB) in a stone-age Brazilian
Indian tribe is producing mortality rates 100 times higher than were
reported in New York City at the peak of the multidrug-resistant TB
epidemic in 1994.
"Although an outbreak of TB in our communities is serious, when
this disease emerges for the first time in populations that never
have experienced it, the effects are devastating," said
Alexandra De Sousa, MD, PhD, Howard Hughes Research Associate in the
Department of Microbiology and Immunology, Albert Einstein College of
Medicine, Bronx, NY.
Speaking at the Irvington Institute for Immunological Research, Dr.
De Sousa detailed her studies of the Yanomami Indians, an Amazonian
rain forest tribe, and the TB epidemic currently ravaging this population.
This group of Indians had remained unknown to outsiders until 1920,
when explorers and missionaries first ventured deep into the Amazon
jungle spanning regions of northern Brazil and southern Venezuela,
Dr. De Sousa said.
"As the 20th century progressed, other outside groups went to
the jungle where the Yanomami lived. With the recent influx of over
80,000 miners looking for gold in this region, TB was introduced to
this population between 1985 and 1990," she said, adding that
the epidemic was declared in 1992.
"Among the 9,400 Yanomami alive today, we documented 40 cases of
active TB among the 625 people we studied," Dr. De Sousa said.
This translates to a 6.4% prevalence or about 100 times higher than
that observed in surrounding regions of Brazil. Similarly, the
mortality rate among the Yanomami is 1.28%, about 100 times higher
than the TB death rate recorded at the height of New York Citys
The fact that this population has never before been exposed to the
pathogen is key to why this epidemic has such high mortality rates,
she said. Also, the nomadic lifestyle and 3-week hunts the men must
participate in to obtain food make quarantining and long-term drug
administration very difficult.
Detailed DNA analysis of the bacilli isolated from infected Indians
revealed the presence of two genetic clusters, signifying that in
this region, the epidemic was likely started by two infected people.
Furthermore, despite the fact that the Yanomami were vaccinated with
the bacille Calmette-Guérin (BCG) vaccine 3 years prior to Dr.
De Sousas studies, screening these Indians with the purified
protein derivative (PPD) test showed that most Yanomami were negative
for PPD responses regardless of whether they were previously
vaccinated. Normally, the PPD test is positive if an individual was
vaccinated with BCG or exposed to the TB pathogen.
"We found high rates of mortality and morbidity; low response
rates to PPD; high titers of IgG class 2 and 4 antibodies; and a
negative correlation between cellular (T-cell) and humoral (B-cell)
responses in the Yanomami Indians," Dr. De Sousa said. Notably,
the trends observed among the Yanomami epidemic parallel those
identified in other TB epidemics in populations exposed to TB for the
first time in their history, for example, the Alaskan Eskimos in 1893.
Moreover, historical data confirmed by mathematical modeling indicate
that TB epidemics follow defined epidemio-logic progressions. "TB
epidemics last about 300 years, with the highest mortality rates
occurring at about 50 years and the highest morbidity at 150 years
from the outset," she said. "The Yanomami epidemic is in
its 20th year, so we wont see a decline in mortality for
approximately another 70 years."
The TB epidemic may be overshadowed by out-of-control slash and burn
fires that are destroying the Amazon rain forest and threatening the
existence of this tribe regardless of TB, she lamented. "Although
TB is a killer," she said, "mankind has unleashed its own
epidemic of destruction, taking with it the Amazon jungle and its