ANTHRAX

Anthrax is an infectious disease due to a type of bacteria called Bacillus anthracis. Infection in humans most often involves the skin, gastrointestinal tract, or lungs.

Anthrax commonly affects hoofed animals such as sheep, cattle, and goats, but humans who come into contact with infected animals can be infected with anthrax, too. In the past, the people who were most at risk for anthrax included farm workers, veterinarians, and tannery and wool workers. In recent years, anthrax has received a great deal of attention as it has become clear that the infection can also be spread by a bioterrorist attack or by biological warfare. Anthrax does not spread from person to person. It was a German physician and scientist, Dr. Robert Koch, who proved that the anthrax bacterium was the cause of a disease that affected farm animals in his community. Under the microscope, the bacteria look like large rods. However, in the soil, anthrax organisms exist in a dormant form called spores. These spores are very hardy and difficult to destroy. The spores have been known to survive in the soil for as long as 48 years. The anthrax bacillus prefers alkaline soils and alternating periods of flooding and drought.

Anthrax can infect humans in three ways:

1. The most common is infection through the skin, which causes an ugly sore that usually goes away without treatment.
2. Humans and animals can ingest anthrax from carcasses of dead animals that have been contaminated with anthrax. Ingestion of anthrax can cause serious, sometimes fatal disease.
3.The most deadly form is inhalation anthrax. If the spores of anthrax are inhaled, they migrate to lymph glands in the chest where they proliferate, spread, and produce toxins that often cause death.

Epidemiology:
-In herbivores, anthrax commonly presents as an acute septicemia with a high fatality rate, often accompanied by hemorrhagic lymphadenitis.

-Underdiagnosis and unreliable reporting make it difficult to estimate the true incidence of anthrax worldwide. However, anthrax has been reported from nearly every continent and is most common in agricultural regions with neutral or alkaline, calcareous soils. In these regions, anthrax periodically emerges as epizootics among susceptible domestic and wild animals. These epizootics are usually associated with drought, flooding, or soil disturbance, and many years may pass between outbreaks. During interepidemic periods, sporadic cases may help maintain soil contamination.

Pathogenesis:

-B anthracis spores have a high affinity for macrophages. After wound inoculation, ingestion, or inhalation, spores infect macrophages, germinate, and proliferate. In cutaneous and GI infection, proliferation can occur at the site of infection and the lymph nodes draining the site of infection. Lethal toxin and edema toxin are produced by B anthracis and respectively cause local necrosis and extensive edema, which is a frequent characteristic of the disease. As the bacteria multiply in the lymph nodes, toxemia progresses and bacteremia may ensue. With the increase in toxin production, the potential for disseminated tissue destruction and organ failure increases. After vegetative bacilli are discharged from an animal following death (by carcass bloating, scavengers, or postmortem examination), the oxygen content of air induces sporulation. Spores are relatively resistant to extremes of temperature, chemical disinfection, and dessication. Necropsy is discouraged because of the potential for vegetative cells to be exposed to air, resulting in large numbers of spores being produced. Because of the rapid pH change following death and decomposition, vegetative cells in an unopened carcass quickly die without sporulating

Symptoms in infected cattle

- Among cattle and sheep, the period of illness is often so short that the affected animals may be found dead without signs of illness having been noticed. Nevertheless, anthrax is not always rapidly fatal to cattle and sheep, and an affected animal may be ill for several days before death occurs. Any of the following symptoms may be observed: high temperature, shivering and twitching, harsh dry coat, fits, bright staring eyes, colicky pains, dejection, refusal of food, and marked decrease or complete loss of milk. Occasionally a small trickle of blood from the nostrils is visible and there may also be blood in the dung.

Treatment

-Treatment is seldom possible for animals infected with anthrax because of the rapid and fatal course of the disease once symptoms become apparent. However, if time permits, antibiotic drugs may be used with good effect. If animals are likely to be continually exposed to infection, for example by grazing over infected pastures, vaccination with anthrax spore vaccine is recommended.

-This vaccine is safe to use and protects the animals for six months or more. Animals remain in a susceptible state, however, for about ten days after vaccination, and should be isolated as far as possible from contact with possible sources of infection during this period.

-When the circumstances appear to warrant treatment with antibiotics or vaccine, a veterinary surgeon should be consulted.