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Zoonotic diseases-Anthrax-الأمراض المشتركة/الجمرة الخبيثة

الكلية كلية الطب     القسم  الاحياء المجهرية     المرحلة 3
أستاذ المادة حبيب صاحب نهر المزيداوي       4/28/2011 9:27:11 PM

ZOONOTIC DISEASES: لأمراض المشتركة/كلية الطب البيطري/المرحلة الرابعة 

   Zoonotic diseases are diseases caused by infectious agents that can be transmitted between (or are shared by) animals and humans.

Anthrax:
Etiological agent = Bacillus anthracis
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".
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. All around the world, incubator zones remain, and anthrax in animals continues to occur periodically. 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, 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.

 Anthrax in humans:
Animals play a critical role in the epidemiology of infection in humans, and virtually all cases of human anthrax can be directly or indirectly linked to an infected animal. Specific people at risk include anyone working outdoors in an incubator region, veterinarians, abattoir workers, animal herders and those who work processing animal products. Humans can be infected via: direct contact with infected animals (e.g., farmers, abattoir workers, veterinarians) occupational exposure with contaminated animal products (e.g., those working with sheep and goat hides = "wool sorter s disease") ingestion of meat from infected animals (Milk can also contain the organism in the end stages of disease, but milk is rarely considered a significant risk factor for human infection because, at this point, the animals appear so sick that most people would not consider drinking the milk) contact with soils that were contaminated by an infected animal.

Clinical forms of anthrax in humans:
Cutaneous anthrax:
lesions are unique, beginning as a pruritic papule, progressing through an ulcer stage with surrounding vesicles, and ultimately resulting in a black, necrotic "eschar." There may also be fever, lymphadenopathy and malaise along with the cutaneous lesions. The case fatality rate, even with cutaneous anthrax, is 20% without antibiotic therapy (typically penicillins or ciprofloxacin).

Inhalational anthrax:
a flu-like presentation initially, followed by acute respiratory distress and hypotension ………shock and death. Anthrax is NOT very contagious from person-to-person via aerosols. Massive mediastinal lymphadenopathy, mediastinal hemorrhage and radiographic evidence of mediastinal widening are classic findings in humans with inhalational anthrax (not true pneumonia).

Gastrointestinal anthrax:
oropharyngeal edema (ulcerative lesions of the oropharyngeal mucosa and tonsils, cervical lymphadenopathy) hematemesis (gastric ulcers) bloody diarrhea (ulceration in the intestines [ileum and cecum])hemorrhagic mesenteric lymphadenitis ascites shock and death highly fatal. There is currently only one human anthrax vaccine licensed in the U.S., anthrax vaccine adsorbed (AVA). This is a mixture of B. anthracis proteins, but the PA protein is thought to be the most important immunogen. Newer vaccines are under development.

Examples of recent outbreaks of anthrax in humans include:
Perhaps the most famous outbreak of anthrax took place in Sverdlovsk, Russia in April-May 1979. This outbreak, involving both people and cattle, has been traced to the release of spores into the air. Direct contact with infected cattle accounted for 10,000 cases of human anthrax in Zimbabwe from 1979-1985 and 716 cases in Chad in 1988. Outbreaks occurred again in Zimbabwe (linked to consumption of meat from 2 cows found dead) and Zambia (70 people and over 200 cows) in 1997, and again in Zimbabwe in 2000 and 2001.
In 1996, 3 people developed cutaneous anthrax from an infected cow in Russia and there have been additional cases in the Republic of Georgia and Azerrbaijan.
In 1997, human cases occurred in Thailand following consumption of meat from the head of an infected cow (12 cases), and one abattoir worker in Australia was infected during what became a large scale outbreak among cattle in Victoria. In 1998, 3 people contracted anthrax in Thailand again following consumption of the meat from cows that had died.
In 1998, outbreaks in the Central Asian republics of Buryatia, Kazakhstan and Tajikistan affected over 300 people.
Also in 1998, B. anthracis was discovered during the repair of walls in King s Cross railroad station in London.
In 1999, at least 20 dairy cattle were infected in Thailand, purportedly following the smuggling of infected cattle into the country from Burma. Owners were infected when they consumed meat from their infected cattle.
A farmer in the Russian Republic of Buryatia died and at least 10 other people became infected in 1999 after consuming contaminated meat from infected cattle. Bacillus anthracis was also isolated from slaughtered pigs in the Seversky district in the Krasnodar region of the country.

Anthrax in animals:
Anthrax in animals most commonly occurs following ingestion of the organism, but can also occur by acquisition of the organism in aerosols or via wounds. Herbivores are the most susceptible to disease, while pigs and carnivores are relatively less susceptible.

Clinical presentations of anthrax in cattle:
Peracute death is a common manifestation. Hemorrhage may or may not be externally evident in these peracute cases. Subacute anthrax can also occur in cattle and small ruminants.Fever and inappetence hematuria, hematochezia, peripheral edema splenomegaly respiratory distress behavioral changes and seizures (reflecting CNS edema and hemorrhage) . Blood in the body typically does not clot. 

Anthrax in horses:
Infection may present initially as colic and enteritis, followed by development of edema, hemorrhage and death in 2-4 days.

Anthrax in pigs and dogs:
Pigs and dogs generally have a more limited course of disease, with gastroenteritis and pharyngeal edema. However, the pharyngeal edema may lead to death by asphyxiation.

In endemic areas in the world, animals can be immunized with a vaccine made from spores of an avirulent strain ("Stern vaccine"). Vaccination is also still commonly practiced today. However, in other areas, vaccination is only by authority of the State Veterinarian.

Diagnosis of anthrax in animals:
A diagnosis is most often made by identification of the organism in blood from an infected animal. Blood smears can be directly stained for the organism, or the organism can be readily cultured.
Necropsies should not be performed because of the risk of inducing sporulation and spreading the organism.
Blood should be collected with as little contact as possible with the carcass (e.g., cutting off the tip of the ear or incising into the coronary band) and then the carcass should be burned thoroughly or buried deep and covered with quick lime (calcium oxide).
Quick lime acts to pull water out of the carcass and thereby speed decomposition. In pigs, unlike cattle, organisms are often difficult to find in peripheral blood smears. There are also fluorescent Ab-, ELISA- and PCR-based laboratory tests available and an immunochromatographic rapid diagnosis field test.

Examples of recent cases of anthrax in North America:
In 1996, a cow died of anthrax in Ontario. Interestingly, the owner reported that cows died of anthrax on the same farm 65 years ago and that recent excavations had been made in that area. A similar series of events occurred on a farm in Nevada in 2000.
In 1997 and 1998, anthrax occurred among cattle in South Dakota, New Mexico (associated with oil company drilling and earth work) and the Northwest Territories of Canada.
In 2000, over 150 livestock animals in North Dakota died of anthrax. (This is a massive increase compared to only 24 cases in N. Dakota between 1989-1999.)
In 2000, over 150 livestock animals in North Dakota and 6 cows in Minnesota died or were euthanized because of anthrax.
In this outbreak, 2 farmers slaughtered and ate one of the affected cows. One of them developed intestinal anthrax and the other cutaneous anthrax.
In 2001-2002, anthrax occurred among animals in Texas, Nebraska and South Dakota. The outbreak in Texas in 2001 killed more than 90% of the deer on one ranch. A South Dakota veterinarian who necropsied a cow in 2002 developed cutaneous anthrax.

 

المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .