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| For example, in some parts of the country, Plague (caused by the bacteria Yersinia pestis) can affect dogs (occasionally mild clinical signs) and cats (more severely affected) and can have an appearance similar to a common cat bite abscess or a respiratory illness. |
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Etiological agent = Brucella spp.
Brucella are small, gram (-) coccobacilli. They are facultative intracellular pathogens that survive and replicate in white blood cells. Their virulence is associated with the organism's LPS.
Historically, brucellosis was one of the major public health concerns (along with bovine tuberculosis) for the veterinary profession. In the U.S., the veterinary community can be duly proud of its role in reducing the incidence of human and animal disease caused by Brucella and Mycobacterium bovis through test and slaughter and, in the case of brucellosis, vaccination programs. Because of these efforts, there are now only about 100 cases of human brucellosis per year in the U.S., and many of these are imported. But in developing countries, several hundred thousand cases of human brucellosis still occur each year, due to the continued presence of substantial animal reservoirs of the organisms.
In proximity to the U.S., brucellosis remains one of the most important animal diseases in Latin America. In 1998, there were ~6,500 cases of brucellosis in humans in Mexico alone. Brucellosis is also widespread in portions of the Middle East.
Brucellosis topics
(To view any of these topics, simply click on the appropriate subject.) |
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Etiologic agent = Francisella tularensis
Like Y. pestis, Francisella tularensis is a Gram (-) bipolar rod whose major reservoir is small mammals (especially rabbits and hares ["rabbit fever"], as well as squirrels, voles, muskrats, beavers, and a variety of other species).
Francisella tularensis infection has long been recognized as a direct zoonotic infection of rabbit hunters. They contract the organism while skinning the rabbits.
Tularemia is also an occupational risk for veterinarians handling infected animals, especially cats.
In one study in Alaska, 14% of veterinarians had positive antibody titers to F. tularensis, compared to 1% of the general U.S. population.
7.7% of cases of tularemia in the U.S. between 1977 and 1998 were due to contact (bites/scratches) with infected cats, and during an outbreak in Sweden in 2000, ownership of cats was a specific risk factor for infection.
People may also be exposed by consuming undercooked game meats (infection requires 108 organisms) or inhalation of the organism (infection requires only 101-2 organisms).
Tularemia has also been reported to occur as a waterborne infection in Russia and Italy (The bacteria can survive for weeks to months in water and mud.), and outbreaks may be initiated when environmental conditions favor sudden increases in rodent populations, as happened in post-war Kosovo in 1999-2000.
Like Y. pestis, F. tularensis is transmitted between infected animals in the natural setting via bloodsucking arthropods, especially ticks (Dermacentor and Amblyomma in the U.S.) and biting flies, e.g. deer flies.
The organism passes transovarially in ticks, thereby providing an efficient way of maintaining the organism in nature.
Tick transmission is also a mode of transmission to humans.
Globally, tularemia is found most commonly in the Northern Hemisphere. In the U.S., tularemia in human beings is reported most commonly in Arkansas (23%), Missouri (19%), South Dakota (7%), Oklahoma (7%), Kansas, Montana, and Martha's Vineyard [Massachusetts]. However, during the period from 1990-2000, there were 1,368 cases reported from 44 states.
An outbreak on Martha's Vineyard during the summer of 2000 involved 15 cases, 11 of which were the dangerous pneumonic form. These cases were associated with employment as lawn mower operators/landscapers. A previous pneumonic tularemia outbreak had occurred on the island in 1978. |
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Etiological agent = Bacillus anthracis
The malicious distribution of anthrax spores in the United States during the fall of 2001 (leading to 6 cutaneous and 6 inhalational anthrax cases) acutely heightened awareness of anthrax as a bioterrorist agent. However, anthrax is clearly not a new disease. It has been suggested that the 5th and 6th biblical plagues were systemic and cutaneous anthrax, respectively, Virgil described outbreaks of anthrax-like disease among people and animals in Rome in 70 BC and references were made repeatedly to anthrax in the "Hippokratika," a series of writing about animal health that was produced in the 900s AD. In addition, this disease is famous in the history of science because Koch's postulates in 1876 were defined using anthrax as the model infection.
Bacillus anthracis is a very large, gram (+) rod with characteristic square ends.
The name "anthracis" comes from the Greek word "anthrakis" meaning "coal," referring to the blackened eschar skin lesions that can develop in people with anthrax.
The bacteria commonly grow in long chains in culture.
The bacteria are encapsulated in vivo.
The capsule (D-glutamyl polypeptide) inhibits engulfment by phagocytes.
Extremely resistant spores develop following vegetative growth in the environment.
High CO2 levels in decaying bodies inhibit sporulation, but sporulation occurs as soon as the organism is exposed to O2 outside the body.
Evidence of resistance:
recovered from 200+ year-old remains in archeological digs!
resistant to microwave irradiation at 100C for 30 min!
resistant to conventional pasteurization (will be killed by ultrapasteurization)
Bacillus anthracis is found characteristically in specific regions in the world called "incubator zones" or "anthrax districts" or "cursed fields."
These are areas where infected animals die, contaminate the soils with spores, and these reinfect new animals in a cyclical pattern. Typically these areas also have alkaline, high N2 content soils and often alternating periods of rain and drought.
Anthrax is endemic in tropical and subtropical areas of India, Pakistan, the Middle East, Asia, Africa, South America and Haiti, with an estimated 20,000-100,000 human cases/year globally.
In the U.S., incubator zones remain, and anthrax in animals continues to occur periodically, in the Dakotas, Nebraska, Missouri, Oklahoma, Texas, Arkansas, Louisiana, Mississippi and parts of New Mexico and Minnesota.
Often the incubator zones follow the routes of old cattle drive trails, such as the Sedalia cattle trail in Oklahoma. However, the occurrence of anthrax in cattle in Santa Clara, CA in 2001 points out that anthrax can appear anywhere that local conditions are conducive to perpetuation of the soils.
Pathogenesis of anthrax:
Spores are ingested by macrophages at the site of entry (skin wounds or mucosa) and then germinate to the replicative form of the organism. The organism can spread rapidly via lymphatics and the bloodstream to colonize phagocytic cells (esp. macrophages) throughout the body. Ultimately, a high level bacteremia develops, eventually overcoming the ability of the spleen to filter out the organism.
The lesions of anthrax are caused by the coordinate action of 3 components (edema factor [EF], lethal factor [LF] and protective factor, which serves as a receptor for EF and LF]) that make up a holotoxin.
Edema factor is an adenylate cyclase that increases cAMP levels and ultimately leads to fluid loss from cells.
Lethal factor is a protease that induces macrophage death, with release of massive quantities of inflammatory mediators.
Lethal factor has also been reported to inactivate MAP-kinase-kinase, thereby inhibiting the MAP kinase signal transduction pathway that helps to control cell growth.
Together the effects of these toxins lead to the edema, hemorrhage and necrosis that typify anthrax.
The genes for these toxins and the capsule are carried on plasmids in the bacteria, and relative virulence may depend not only on the presence or absence of the plasmids, but also how many copies of each plasmid a strain carries. |
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Etiological agent = Listeria monocytogenes (a gram [+] rod)
Listeria monocytogenes is a facultative intracellular organism that is able to escape from the phagolysosome and replicate in the cytoplasm of phagocytic cells. Escape from the phagolysosome is aided by expression of listeriolysin O toxin by the bacteria.
Ecology of Listeria:
Listeria monocytogenes is very widely distributed in the environment. It can survive for months to years in the soil.
Listeria monocytogenes is shed in the feces of both clinically ill and subclinically infected animals, particularly ruminants. This is the major source of contamination of the environment, but direct zoonotic transmission between infected animals and humans is relatively uncommon.
Listeria monocytogenes cannot replicate at pH<5. One implication of this is that the organism does not replicate in properly prepared silage. However, poorly fermented silage with pH>5 can be an important source of the organism on the farm.
Listeria monocytogenes is also shed by subclinically-infected humans.
As many as 10-30% of people may be shedding the organism at any given time! |
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Campylobacter" bacteria are the second most frequently reported cause of foodborne illness. A comprehensive farm-to-table approach to food safety is necessary in order to reduce campylobacteriosis. Farmers, industry, food inspectors, retailers, food service workers, and consumers are each critical links in the food safety chain. This document answers common questions about the bacteria "Campylobacter," describes how the Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture (USDA) is addressing the problems of "Campylobacter" contamination on meat and poultry products, and offers guidelines for safe food handling to prevent bacteria, such as "Campylobacter," from causing illness.
Q. What is Campylobacter?
A. Campylobacter [pronounced "kamp-e-lo-back-ter"] is a gram negative, microaerophilic bacterium and is one of the most common bacterial causes of diarrheal illness in the United States. Campylobacter jejuni, the strain associated with most reported human infections, may be present in the body without causing noticeable illness.
Campylobacter organisms can be found everywhere and are commonly found in the intestinal tracts of cats, dogs, poultry, cattle, swine, rodents, monkeys, wild birds, and some humans. The bacteria pass through the body in the feces and cycle through the environment. They are also found in untreated water.
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Q. What harm can Campylobacter bacteria cause?
A. Infection caused by Campylobacter bacteria is called campylobacteriosis and is usually caused by consuming unpasteurized milk, raw or undercooked meat or poultry, or other contaminated foods and water, and contact with feces from infected animals. While the bacteria can exist in the intestinal tracts of people and animals without causing any symptoms or illness, studies show that consuming as little as 500 Campylobacter cells can cause the illness.
Symptoms of Campylobacter infection, which usually occur within 2 to 10 days after the bacteria are ingested, include fever, abdominal cramps, and diarrhea (often bloody). In some cases, physicians prescribe antibiotics when diarrhea is severe. The illness can last about a week.
Complications can include meningitis, urinary tract infections, and possibly reactive arthritis (rare and almost always short-term), and rarely, Guillain-Barre syndrome, an unusual type of paralysis. While most people who contract campylobacteriosis recover completely within 2 to 5 days, some Campylobacter infections can be fatal, resulting in an estimated 124 deaths each year.
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Q. Are more people becoming ill from campylobacteriosis?
A. The Foodborne Diseases Active Surveillance Network (FoodNet) found a decline, in the rates of infection in 2009 for Campylobacter (30% decrease), in comparison with the previous three years of surveillance (1996 to 1998). Still, according to the Centers for Disease Control and Prevention (CDC), campylobacteriosis causes an incidence of about 13 cases per 100,000 population diagnosed in the United States annually.
FoodNet is a collaborative project among CDC, the 10 Emerging Infections Program sites (EPIs), USDA, and the U.S. Food and Drug Administration (FDA). One of the objectives of FoodNet is to measure effectiveness of a variety of preventive measures in reducing the incidence of foodborne illness attributable to the consumption of meat, poultry, and other foods.
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Q. Who is most susceptible?
A. Anyone may become ill from Campylobacter. However, infants and young children, pregnant women and their unborn babies, and older adults, are at a higher risk for foodborne illness, as are people with weakened immune systems (such as those with HIV/AIDS, cancer, diabetes, kidney disease, and transplant patients).
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Q. How can Campylobacter be controlled?
A. Campylobacter can be controlled at a number of different points in the food production and marketing chain.
On the farm:
Good sanitary practices on farms, as recommended by USDA, minimize the opportunity for the bacteria to spread among animals and birds.
Pasteurization of milk and treatment of municipal water supplies eliminate another route of transmission for Campylobacter and other bacteria.
In the plant:
Raw foods are not sterile, and there are no requirements that they be sterile. Food processing companies are accountable for following good, up-to-date manufacturing practices that minimize the opportunity for the spread of Campylobacter and other bacteria.
At retail:
A food recall is a voluntary action by a manufacturer or distributor to protect the public from products that may cause health problems or possible death. FSIS conducts a sufficient number of effectiveness checks to verify the recalling firm has contacted the distributor or retailer.
Individuals:
Reporting the problem is another way to control these bacteria and prevent others from becoming exposed to the source of contamination. Any individual that experiences symptoms of campylobacteriosis should contact a physician. Physicians who diagnose campylobacteriosis and clinical laboratories that identify this organism should report their findings to the local health department.
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Q. What is FSIS doing to prevent Campylobacter infections?
A. In its commitment to ensure that the public has a safe, wholesome food supply, FSIS is constantly working to improve the level of safety and reduce contaminants in the meat and poultry supply.
In 1998, FSIS began enforcing a combination of Hazard Analysis and Critical Control Points (HACCP) based process control, microbial testing, pathogen reduction performance standards, and sanitation standard operating procedures which significantly reduce contamination of meat and poultry with harmful bacteria and reduce the risk of foodborne illness. Establishments can choose to include Campylobacter in their HACCP analysis. If Campylobacter is identified by the establishment as being reasonably likely to occur or if it becomes evident that it is an emerging problem in their process, FSIS would expect the establishment to have controls in place designed to address this microbial food safety hazard.
HACCP clarifies the responsibilities of industry and FSIS in the production of safe meat and poultry products. The role of FSIS is to set appropriate food safety standards and maintain vigorous inspection oversight to ensure that those standards are met.
USDA is supporting research to learn more about Campylobacter in food and how to control it.
Finally, FSIS maintains extensive safe food handling education programs to help individuals prevent and reduce the risks of foodborne illness.
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Q. What is the best way to prevent Campylobacter infections?
A. Meat and poultry can contain Campylobacter. However, the bacteria can be found in almost all raw poultry because it lives in the intestinal track of healthy birds. Improving safe food handling practices in kitchens will reduce the number of Campylobacter illnesses. Campylobacter bacteria are extremely fragile and are easily destroyed by cooking to a safe minimum internal temperature. They are also destroyed through typical water treatment systems. Freezing cannot be relied on to destroy the bacteria. Home freezers are generally not cold enough to destroy bacteria. |
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