Download pathogenesis of salmonellosis in humans

PATHOGENESIS OF SALMONELLOSIS IN HUMANS
Global Technical Services (2013) - Lohmann Animal Health
Introduction
Salmonella is a bacteria-type bacillus (rod shaped) that causes a very common intestinal
infection in humans and domestic animals, called Salmonellosis. The term Salmonella
refers to a group or family of bacteria that variously cause illness in humans. Salmonella
serotype Typhimurium and Salmonella serotype Enteritidis are the most common
worldwide. During the 1980s, S. Enteritidis emerged as an important cause of human
illness in the United States. In 1976, the incidence of S. Enteritidis was 0.55% per
100.000 inhabitants and represented only 5% of all Salmonella isolates. By 1985, this
proportion reached 10%, and the rate increased to 2.4% per 100.000 inhabitants. During
the same period, total Salmonella infection rates rose from 10.7% per 100.000 in 1976 to
24.3% in 1985.
Etiology
The number of outbreaks of S. Enteritidis infection also increased during the 1980s,
particularly in the northeastern United States. Of the Salmonella outbreaks that occurred
from 1985 through 1999, five hundred
twenty-two (62%) outbreaks of S. Enteritidis
infection were associated with food
prepared at commercial food establishments
(restaurants,
caterers,
delicatessens,
bakeries, cafeteria, or market).
Daniel Elmer Salmon (July 23, 1850 –
August 30, 1914) was a veterinary surgeon.
He earned the first D.V.M. degree awarded
in the United States, and spent his career
studying animal diseases for the U.S.
Department of Agriculture. In 1885, this
pioneering veterinary scientist, together with
Theobald Smith (Dr. Salmon´s researchassistant) discovered the first strain of
Salmonella (Salmonella cholerae suis).
Today the number of known strains of the
bacteria totals over two thousand. Both,
Salmonellosis and the Salmonella genus of
microorganisms derive their names from a
modern Latin coining after Daniel E.
Salmon. The Dr. Daniel E. Salmon Award is Daniel Elmer Salmon, veterinary medical scientist who
pioneered research in bacterial diseases of animals and in
presented annually to recognize outstanding immunology.
contributions and notable service in the public's interest by a veterinarian federally
employed in any human health, environmental health or animal health discipline. This
award is supported through the National Association of Federal Veterinarians in the
United States. Dr. Daniel E. Salmon was a world-renowned veterinary medical scientist
who pioneered research in bacterial diseases of animals and in immunology. His efforts
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led to the development of killed vaccines and to the naming of the bacterial genus
Salmonella in his honor. His work contributed immeasurably to improving the public's
health and to disease control efforts in general.

Pathogenesis
The pathogenesis consists of the mechanism by which the disease is originated, its
development in the body, and type of manifestation, whether it is acute, chronic, or
recurrent. The word comes from the Greek pathos ("disease") and genesis ("creation").
An infectious process can only begin after living Salmonella (not only their toxins) reach
the gastrointestinal tract. Some of the microorganisms are killed in the stomach, while
the surviving Salmonella enter the small intestine and multiply in tissues (localized form).
By the end of the incubation period, the macro-organisms are poisoned by endotoxins
released from the dead Salmonella. The local response to the endotoxins is enteritis and
gastrointestinal disorder. In the generalized form of the disease, Salmonella pass
through the lymphatic system of the intestine into the blood of the patients (typhoid form)
and are carried to various organs (liver, spleen, kidneys) to form secondary foci (septic
form). Endotoxins first act on affected organs' vascular and nervous systems manifested
by increased permeability and decreased tone of the vessels, upset thermal regulation,
vomiting and diarrhea. In severe forms of the disease, enough liquid and electrolytes are
lost to upset the body's water-salt metabolism, to decrease the circulating blood volume
and arterial pressure, and to cause hypovolemic shock. Septic shock also may develop.
Shock of mixed character (with signs of both hypovolemic and septic shock) is more
common in severe Salmonellosis. Oliguria and azotemia develop in severe cases as a
result of renal (kidney) involvement due to hypoxia and bacteremia.
Salmonellosis is an infection with Salmonella bacteria. Most people infected with
Salmonella develop diarrhea, fever, vomiting and abdominal 12 to 72 hours after
infection. In most cases, the illness lasts four to seven days, and most people recover
without treatment. In some cases, though, the diarrhea may be so severe, the patient
becomes dangerously dehydrated and must be hospitalized. At the hospital, the patient
may receive intravenous fluids to treat the dehydration, and may be given medications to
provide symptomatic relief, such as fever reduction. In severe cases, the Salmonella
infection may spread from the intestines to the blood stream, and then to other body
sites, and can cause death unless the person is treated promptly with antibiotics.
The elderly, infants, and those with impaired immune systems are more likely to develop
severe illness. Some people afflicted with Salmonellosis later experience reactive
arthritis, which can have long-lasting, disabling effects. The different kinds of Salmonella
include S. bongori and S. enterica.
The type of Salmonella usually associated with infections in humans, non-typhoid
Salmonella, is usually contracted from sources such as:
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Poultry, pork and beef if the meat is prepared incorrectly or is infected with
the bacteria after preparation.
Infected eggs, egg products, and milk when not prepared, handled, or
refrigerated properly.
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Reptiles, such as turtles, lizards and snakes, which may carry the bacteria in
their intestines.
Tainted fruits and vegetables
The typhoidal form of Salmonella can lead to typhoid fever. Typhoid fever is a lifethreatening illness, and about 400 cases are reported each year in the United States,
and 75% of these are acquired while traveling out of the country. It is carried only by
humans and is usually contracted through direct contact with the fecal matter of an
infected person. Typhoid Salmonella is more commonly found in those locations where
unsanitary conditions are more likely to occur, and can affect as many as 21.5 million
persons each year worldwide.
Symptoms in humans
The bacterium induces responses in the person it is infecting, and this typically causes
the symptoms, rather than any direct toxin produced. Symptoms are usually
gastrointestinal, including nausea, vomiting, abdominal cramps, and bloody diarrhea with
mucus. Headache, fatigue, and rose spots are also possible. These symptoms can be
severe, especially in young children and the elderly. Symptoms last generally up to a
week, and can appear 12 to 72 hours after ingesting the bacterium. After bacterial
infections, reactive arthritis (Reiters syndrome) can develop. In sickle-cell anemia,
osteomyelitis due to Salmonella infection is much more common than in the general
population.
Pathophysiology
Pathophysiology is a convergence of pathology with physiology. Pathology is the
medical and veterinary discipline that describes conditions typically observed during a
disease state, whereas physiology is the biological discipline that describes processes or
mechanisms operating within a healthy organism. Pathology describes the abnormal or
undesired condition, whereupon pathophysiology seeks to explain the physiological
processes or mechanisms whereby such condition develops and progresses.
Salmonella lives in the intestinal tracts of humans and other animals, including birds
(especially poultry species). Salmonella are usually transmitted to humans by eating
foods contaminated with animal feces. Contaminated foods usually look and smell
normal. Contaminated foods are often of animal origin, such as beef, poultry, milk, or
eggs, but all foods, including vegetables may become contaminated. Many raw foods of
animal origin are frequently contaminated, but fortunately, thorough cooking kills
Salmonella. Food may also become contaminated by the unwashed hands of an
infected food handler, who forgot to wash his or her hands with soap after using the
bathroom. Salmonella may also be found in the feces of some pets, especially those
with diarrhea, and people can become infected if they do not wash their hands after
contact with these feces. Reptiles are particularly likely to harbor Salmonella and people
should always wash their hands immediately after handling a reptile, even if the reptile is
healthy. Adults should also be careful that children wash their hands after handling a
reptile. Among all the sources of contamination it has been demonstrated that poultry
meat and eggs are especially important.
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