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Vibrio cholerae and Asiatic Cholera (page 1)
(This chapter has 4 pages)
© 2009 Kenneth Todar, PhD
December 9, 2010
Update on cholera outbreak in Haiti from Reuters (unedited, remember Vibrio cholerae is NOT A VIRUS>
From Reuters Health Information
Full Sequence Confirms Haiti Cholera Came From Asia
By Maggie Fox
WASHINGTON (Reuters) Dec 09 - Detailed genetic tests confirm that the cholera strain that has killed more than 2,000 people in Haiti came from south Asia and most closely resembles a strain circulating in Bangladesh, U.S. researchers reported on Thursday.
While they cannot trace who or what precisely carried the cholera to Haiti, the team at Harvard Medical School and Pacific Biosciences of California Inc say their findings show extra measures may be needed to help prevent the spread of cholera from one disaster area to another -- a contentious issue because many Haitians have blamed the outbreak on Nepalese troops sent to help them as part of a United Nations mission.
Aid workers from more than 10,000 organizations all over the world have poured into Haiti to help after the devastating January earthquake.
Writing in the New England Journal of Medicine today, Harvard's Dr. John Mekalanos and colleagues said they also confirmed that Haiti's cholera strain carries a mutation associated with more severe disease.
"Our genome data puts the Haiti strain in the group that is the worst of the worst," Dr. Mekalanos said.
"In the future when people go to work in disaster zones ... they should be screened or just presumptively given a dose of antibiotics or a vaccine so that they will not transfer cholera," Dr. Matthew Waldor of Harvard and Brigham and Women's Hospital added in a telephone interview.
Haiti's health ministry reports more than 93,000 people have been sickened by cholera since it broke out in Haiti in October. Haiti had not had a case of cholera in a century, but the ongoing devastation from January's giant earthquake made conditions perfect for its spread.
In early November the U.S. Centers for Disease Control and Prevention said genetic fingerprinting showed Haiti's cholera strain was part of a 49-year-old global pandemic that began in Indonesia and likely was brought to the Caribbean country in a single instance.
The CDC said it was possible the strain could circulate for years in Haiti and the best options were to try to prevent deaths.
When they got some cholera samples from Haiti in early November, the Harvard team contacted Eric Schadt at Pacific Biosciences, which makes a DNA sequencer. They used this $695,000 sequencer to analyze the Haitian cholera's DNA and compared it to strains from elsewhere.
"We definitely linked it to the recent outbreak strains in Bangladesh," Schadt said in a telephone interview. But it is not identical, he added, which raises the possibility that the virus may have traveled via elsewhere, perhaps West Africa.
What is clear is that the cholera did not originate locally, Dr. Mekalanos said. "Human activity coming from a far-away place brought this strain to Haiti," he said.
"Our work is by no way intended to assign blame here," Dr. Waldor added. "I do think it is important to understand how cholera likely got to Haiti to see if we can prevent it from happening again."
Many in Haiti have blamed the outbreak on Nepalese United Nations troops stationed near a river that is believed to have been the source of the outbreak. Without a sample from Nepal, however, this would be impossible to prove or disprove, the Harvard team said.
The complete report is available online for free on the New England Journal of Medicine website:
N Engl J Med. Posted December 9, 2010
Introduction
The genus Vibrio consists of Gram-negative straight
or
curved rods, motile by means of a single polar flagellum. Vibrios are
capable
of both respiratory and fermentative metabolism. O2 is a
universal
electron acceptor; they do not denitrify. Most species are
oxidase-positive.
In most ways vibrios are related to enteric bacteria, but they share
some
properties with pseudomonads a well. The Family Vibrionaceae is
found in the "Facultatively Anaerobic Gram-negative Rods" in Bergey's
Manual
(1986), on the level with the Family Enterobacteriaceae. In the
revisionist taxonomy of 2001 (Bergey's Manual), based on phylogenetic
analysis,
Vibrionaceae, Pseudomonadaceae and Enterobacteriaceae
are all landed in the Gammaproteobacteria. Vibrios are
distinguished
from enterics by being oxidase-positive and motile by means of polar
flagella.
Vibrios are distinguished from pseudomonads by being fermentative as
well
as oxidative in their metabolism. Of the vibrios that are clinically
significant
to humans, Vibrio cholerae,the agent of cholera, is the most
important.
Most vibrios have relatively simple growth factor requirements and
will
grow in synthetic media with glucose as a sole source of carbon and
energy.
However, since vibrios are typically marine organisms, most species
require
2-3% NaCl or a sea water base for optimal growth. Vibrios vary in their
nutritional versatility, but some species will grow on more than 150
different
organic compounds as carbon and energy sources, occupying the same
level
of metabolic versatility as Pseudomonas. In liquid media
vibrios
are motile by polar flagella that are enclosed in a sheath continuous
with
the outer membrane of the cell wall. On solid media they may synthesize
numerous lateral flagella which are not sheathed.
Vibrios are one of the most common organisms in surface waters of
the
world. They occur in both marine and freshwater habitats and in
associations
with aquatic animals. Some species are bioluminescent and live in
mutualistic
associations with fish and other marine life. Other species are
pathogenic
for fish, eels, and frogs, as well as other vertebrates and
invertebrates.
V. cholerae and V. parahaemolyticus are pathogens of
humans.
Both produce diarrhea, but in ways that are entirely different. V.
parahaemolyticus
is an invasive organism affecting primarily the colon; V. cholerae
is noninvasive, affecting the small intestine through secretion of an
enterotoxin.
Vibrio vulnificus is an emerging pathogen of humans. This
organism
causes wound infections, gastroenteritis, or a syndrome known as
"primary
septicemia."
Campylobacter jejuni (formerly Vibrio fetus), is now
moved
to the class Epsilonproteobacteria in the the family Campylobacteraceae.
Campylobacter
jejuni has been associated with dysentery-like gastroenteritis, as
well as with other types of infection, including bacteremic and central
nervous system infections in humans. Another vibrio-like organism, Helicobacter
pylori causes duodenal and gastric ulcers and gastric
cancer.
It is also reclassified into the class Epsilonproteobacteria
family
Helicobacteraceae.
Vibrio cholerae
Cholera
Cholera (frequently called Asiatic cholera or epidemic
cholera) is a severe diarrheal disease caused by the bacterium Vibrio
cholerae. Transmission to humans is by water or food. The
natural
reservoir of the organism is not known. It was long assumed to be
humans,
but some evidence suggests that it is the aquatic environment.
V. cholerae produces cholera toxin, the model for
enterotoxins,
whose action on the mucosal epithelium is responsible for the
characteristic
diarrhea of the disease cholera. In its extreme manifestation, cholera
is one of the most rapidly fatal illnesses known. A healthy person may
become hypotensive within an hour of the onset of symptoms and may die
within 2-3 hours if no treatment is provided. More commonly, the
disease
progresses from the first liquid stool to shock in 4-12 hours, with
death
following in 18 hours to several days.
The clinical description of cholera begins with sudden
onset
of massive diarrhea. The patient may lose gallons of protein-free fluid
and associated electrolytes, bicarbonates and ions within a day or two.
This results from the activity of the cholera enterotoxin which
activates
the adenylate cyclase enzyme in the intestinal cells, converting them
into
pumps which extract water and electrolytes from blood and tissues and
pump
it into the lumen of the intestine. This loss of fluid leads to
dehydration,
anuria, acidosis and shock. The watery diarrhea is speckled with flakes
of mucus and epithelial cells ("rice-water stool") and contains
enormous
numbers of vibrios. The loss of potassium ions may result in cardiac
complications
and circulatory failure. Untreated cholera frequently results in high
(50-60%)
mortality rates.
Treatment of cholera involves the rapid intravenous
replacement
of the lost fluid and ions. Following this replacement, administration
of isotonic maintenance solution should continue until the diarrhea
ceases.
If glucose is added to the maintenance solution it may be administered
orally, thereby eliminating the need for sterility and iv.
administration.
By this simple treatment regimen, patients on the brink of death seem
to
be miraculously cured and the mortality rate of cholera can be reduced
more than ten-fold. Most antibiotics and chemotherapeutic agents have
no
value in cholera therapy, although a few (e.g. tetracyclines) may
shorten
the duration of diarrhea and reduce fluid loss.
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