Lecture2 Zoonoses Diseases Bacterial infection Anthrax Anthrax Anthrax

ﺑﺴﻢ ﺍﻟﻠﻪ ﺍﻟﺮﺣﻤﻦ ﺍﻟﺮﺣﻴﻢ Lecture-2 Zoonoses Diseases (Bacterial infection) Anthrax

Anthrax , Anthrax is a serious zoonotic disease that can affect most mammals and several species of birds, but is particularly important in herbivores. The word anthrax is derived from a Greek word meaning charcoal or carbuncle. Anthrax, the disease, likely originated 6, 000 to 7, 000 years ago in Mesopotamia and Egypt, where agricultural civilization was first recorded. . Common names include: Malignant Pustule, Malignant Edema, Woolsorters’ Disease, Ragpickers’ Disease, and Maladi Charbon.

Etiology Anthrax agent : Bacillus anthracis : is a gram-positive rod that exists in two forms: the vegetative bacillus and the spore. Within an infected host, spores germinate to produce the vegetative forms which eventually kill the host. These bacilli are released by the dying or dead animal into the environment (usually soil under the carcass). There they sporulate, ready to be taken up by another animal. Although vegetative forms of B. anthracis grow and multiply readily in normal laboratory nutrient agars or broths, they are more "fragile" than the vegetative forms of other Bacillus species, dying in simple environments such as water or milk. B. anthracis is dependent on sporulation for species survival making it an obligate pathogen. Anthrax can be found nearly worldwide and has roughly 1, 200 various strains.

When conditions are not conducive to growth and multiplication of vegetative bacilli, B. anthracis tends to form spores. Sporulation requires a nutrient poor environment and the presence of free oxygen. The spore form is the predominant phase in the environment, can survive for decades in soil, and it is through the uptake of spores that anthrax is contracted. . (red)

Heavy rains, alternating with dry periods, may concentrate the spores and result in outbreaks among grazing animals. The spore form of anthrax is markedly resistant to biological extremes of heat, cold, p. H, desiccation, and chemicals (and thus to disinfection). Spores are not produced in the unopened carcass (within the anaerobic environment of an infected host the organism is in the vegetative form). It is estimated that 2, 500 to 55, 000 spores represent the lethal inhalation dose for humans Bacillus anthracis in a lesion

Hosts, including humans, are susceptible to anthrax infection to some degree. Ruminants such as cattle, sheep, and goats are most commonly infected because they are grazing animals and may graze on grass growing in infected soil. Other herbivores like horses and pigs may also be infected. Anthrax has been reported in dogs and cats but is rare in these

Transmission Humans are infected by : 1 -ingestion of anthrax. 2 - inhalation of anthrax spores. 3 - by handling contaminated carcasses, wool, or hair. When a person is infected through handling a contaminated object, the spores enter through skin cuts or abrasions. . 4 - Direct person-to-person spread of anthrax is extremely rare

Transmission. In animals, the most common form of transmission is: 1 - ingestion of anthrax spores. The spores in the soil are ingested when environmental conditions are right, when animals grazing in these areas ingest the spores. Drought conditions, in which pastures have little plant growth, can also be a contributing factor. Animals graze closer to the ground than they normally would and may ingest spores. 2 - Biting flies can, but rarely do, transmit B. anthracis from one animal to another. 3 -Wild animals or other scavengers become infected by feeding on infected dead animals.

Transmission

Virulence Factors All virulent strains of B. anthracis form : 1 -a nontoxic capsule that functions to protect the organism against the bactericidal components of plasma and phagocytes and against destruction by gastric juices. 2 -An exotoxin plays a major role in the pathogenesis of anthrax. One component of the anthrax toxin has a lethal mode of action that is not understood at this time. Death is apparently due to oxygen depletion, secondary shock, and respiratory and cardiac failure. Death from anthrax in humans or animals frequently occurs suddenly and unexpectedly.

Anthrax in Animals Cattle, Sheep, And Goats • Anthrax in ruminants may cause a peracute (very sudden) disease, in which the animals are found dead, having shown no clinical signs before death • . Acute cases of anthrax are associated with sudden illness, characterized by high fever, localized edema, decreased or absent rumination, decreased milk production with blood-tinged or yellow-colored milk, difficult breathing, convulsions, bleeding that does not clot coming from body openings, and death.

Anthrax in Animal Anthrax can cause abortion. The incubation period is 1 to 3 days following exposure, with death usually occurring in 2 to 3 days Horses can become infected with anthrax either through ingestion or through the bite of an insect. Cats and Dogs Anthrax is rarely reported in cats and dogs because they seem to be relatively resistant to infection.

Anthrax in Human Three forms of anthrax are seen in humans. Cutaneous Form The cutaneous form is the most common, accounting for nearly 95% of all human anthrax cases. The incubation period is 1 to 12 days, and the disease is characterized by what initially looks like an insect bite. Localized, painless ulceration with a central black scab; fever; and headache develop rapidly. These symptoms may be followed within a few days by septicemia and meningitis. There is a 20% fatality rate if the disease is left untreated

Anthrax in Human Cutaneous anthrax may occur when handling infected tissues, wool, hides, soil, and products made from contaminated hides or hair, such as drums, rugs, or brushes. Biting flies are also suspected of being mechanical vectors of anthrax to humans under certain conditions.

Pulmonary or Inhalation Form The pulmonary, or inhalation, form (also known • as woolsorter’s disease) is caused by inhalation of spores from contaminated carcasses, wool, or hair. The spores may also be found on brush bristles, after grooming an animal with contaminated fur. The incubation period is 1 to 5 days, up to a month and a half. The disease may initially present as a cold or the flu. It is characterized by fever, sore throat, cough, difficulty breathing, muscle aches, respiratory failure, and usually death within 24 hours. Mortality can reach 95% if

Intestinal or Gastrointestinal Form The intestinal or gastrointestinal form • results from ingestion of contaminated meat. The incubation period is 12 hours to 5 days. Fever, anorexia, nausea, vomiting, and diarrhea are followed by intestinal pain and vomiting blood. Mortality averages around 50% if untreated

Diagnosis • A tentative diagnosis in some animals : 1 - primarily ruminants, can be made from the • physical signs found on a carcass; the sudden death, accompanied by bloody discharges that do not clot coming from body openings. 2 - Sputum, blood, or tissue can be Gram stained • to look for gram positive rods. 3 -Culture on blood agar yields nonmotile, • nonhemolytic, bacterial colonies. .

Diagnosis 4 -Antibody titers will be elevated. • 5 - Chest radiographs are taken in people • suspected of having inhalation anthrax.

Treatment The U. S. Food and Drug Administration (FDA) has approved penicillin, ciprofloxacin, and doxycycline for treatment of anthrax in humans. Penicillin and tetracycline are used in animals.

Prevention An anthrax vaccine is available for • livestock, but none has been approved for use in cats and dogs. Animal vaccines cannot be used in humans. An anthrax vaccine has been licensed for use in risk humans. The. Pregnant women should be vaccinated only if absolutely necessary.

Control If an animal is found dead or dies following treatment and anthrax is suspected, leave the carcass alone. Do not touch it, and do not open it for a necropsy. Doing so will release vegetative B. anthracis that will convert to spores when exposed to the air and contaminate the immediate environment. In humans, this may result in an inhalation or cutaneous anthrax infection. Notify a veterinarian who will dispose of the carcass. 2 -Carcasses will be burned where they are found and/or buried at least 4 feet deep (some states require burying 10 feet deep) and covered with lime.

The soil directly under the carcass will be burned and buried also. 34 If an animal is diagnosed with anthrax, the herd from which it came will be quarantined. 5 -Exposed animals that look healthy will be vaccinated. 6 -Animals that appear sick will be isolated and treated. 7 -The pasture where the animals are feeding will be abandoned if possible. Animals that have recently left the herd will be located, and the premises where they currently reside quarantined. 8 -When the disease is under control, the premises need to be cleaned. 9 -Preventing cats and dogs from scavenging on carcasses, especially if the cause of death is unknown, will

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