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- Provide a brief history of this disease.
F. tularensis has been identified as the cause of human outbreaks in ancient Canaan in about 1715 BC and in 1075 BC. A long-lasting epidemic that plagued the eastern Mediterranean in the 14th century BC was also traced back to a focus in Canaan along the Arwad-Euphrates trading route. According to Siro I. Trevisanato, this epidemic contaminated an area stretching from Cyprus to Iraq, and from Palestine to Syria, sparing Egypt (due to a quarantine) and Anatolia (owing to effective political boundaries). Subsequently, wars are believed to have spread the same disease into central Anatolia, from whence it was deliberately introduced into western Anatolia, in acts constituting the first known record of biological warfare. Finally, Aegean soldiers fighting in western Anatolia returned home to their Greek islands, further spreading the same epidemic.
The tularemia bacterium was first isolated by G.W. McCoy of the U.S. Public Health Service plague lab and reported in 1912. Scientists determined tularemia could be dangerous to humans; a human being may catch the infection after contacting an infected animal. The ailment soon became associated with hunters, cooks and agricultural workers.
- Identify cause (both genus/species names)
Tularemia (or tularaemia; also known as Pahvant Valley plague,rabbit fever, deer fly fever, and Ohara's fever) is a serious infectious disease caused by the intracellular bacterium Francisella tularensis. A gram-negative, nonmotile, pleomorphic coccobacillus, the bacterium has several subspecies with varying degrees of virulence. The most important of those is F. tularensis tularensis (Type A), which is found in lagomorphs (rabbits, hares and pikas) in North America, and it is highly virulent in humans and domestic rabbits. F. tularensis palaearctica (Type B) occurs mainly in aquatic rodents (beavers, muskrats) in North America and in hares and small rodents in northern Eurasia. It is less virulent for humans and rabbits.The primary vectors are ticks and deer flies, but the disease can also be spread through other arthropods. The disease is named after Tulare County, California.
-What is the epidemiology of this disease? (when, who, where, etc...)
The disease is endemic in North America and parts of Europe and Asia. The most common mode of transmission is via arthropod vectors. Ticks involved include Amblyomma, Dermacentor, Haemaphysalis, and Ixodes. Rodents, rabbits, and hares often serve as reservoir hosts, but waterborne infection accounts for 5 to 10% of all tularemia in the US. Tularemia can also be transmitted by biting flies, particularly the deer fly Chrysops discalis. Individual flies can remain infective for 14 days and ticks for over two years. Tularemia may also be spread by direct contact with contaminated animals or material, by ingestion of poorly cooked flesh of infected animals or contaminated water, or by inhalation.
In the United States, although records show that tularemia was never particularly common, incidence rates continued to drop over the course of the 20th century, so between 1990 and 2000, the rate was less than 1 per 1,000,000, meaning the disease is extremely rare in the US today.
In Sweden over a period from 1984–2012 a total of 4,830 cases of tularemia occurred (most of the infections were acquired within the country). About 1.86 cases per 100,000 persons occur each year with higher rates in those between 55 and 70.
What is the disease process in the human body? (I want an overview of the overall process, DO NOT provide a list of symptoms)
Depending on the site of infection, tularemia has six characteristic clinical variants: ulceroglandular (the most common type representing 75% of all forms), glandular, oropharyngeal, pneumonic, oculoglandular, and typhoidal.
The incubation period for tularemia is one to 14 days; most human infections become apparent after three to five days. In most susceptible mammals, the clinical signs include fever, lethargy, loss of appetite, signs of sepsis, and possibly death. Nonhuman mammals rarely develop the skin lesions seen in people. Subclinical infections are common, and animals often develop specific antibodies to the organism. Fever is moderate or very high, and tularemia bacilli can be isolated from blood cultures at this stage. The face and eyes redden and become inflamed. Inflammation spreads to the lymph nodes, which enlarge and may suppurate (mimicking bubonic plague). Lymph node involvement is accompanied by a high fever. Death occurs in less than 1% of cases if therapy is initiated promptly.
The bacteria can penetrate into the body through damaged skin and mucous membranes, or through inhalation. Humans are most often infected by tick bite or through handling an infected animal. Ingesting infected water, soil, or food can also cause infection. Tularemia can also be acquired by inhalation; hunters are at a higher risk for this disease because of the potential of inhaling the bacteria during the skinning process. It has been contracted from inhaling particles from an infected rabbit ground up in a lawnmower . Tularemia is not spread directly from person to person.
Francisella tularensis is an intracellular bacterium, meaning it is able to live as a parasite within host cells. It primarily infects macrophages, a type of white blood cell, thus is able to evade the immune system. The course of disease involves the spread of the organism to multiple organ systems, including the lungs, liver, spleen, and lymphatic system. The course of disease is different depending on the route of exposure. Mortality in untreated (before the antibiotic era) patients has been as high as 50% in the pneumoniac and typhoidal forms of the disease, which however account for less than 10% of cases. Overall mortality was 7% for untreated cases, and the disease responds well to antibiotics, with a fatality rate of about 1%. The exact cause of death is unclear, but it is thought to be a combination of multiple organ system failures.
Are there any treatments (provide an overall view, NOT a list of medicine or dosages etc...)
Tularemia is treated with a drug called streptomycin. The drug is given intramuscularly, twice a day, for one to two weeks. Gentamicin is an alternative drug and may be given intravenously. Neither of thesedrugsis effective againstmeningitisbecause they do not penetrate from the bloodstream into the brain. In tularemic meningitis, it may be necessary to put gentamicin directly into the fluid that bathes the brain.
The oral medicationsdoxycycline(Vibramycin) ortetracycline(Sumycin) may work but are less effective than streptomycin. The disease may relapse after treatment with these pills. Other drugs, such asciprofloxacin(Cipro), are effective in the test tube but have not been widely used in patients. However, one outbreak in Spain with 142 patients showed good clinical outcomes with ciprofloxacin; fluoroquinolones may be useful in treating tularemia if additional studies show clinical effectiveness.
Is there a vaccines? (current or in the works...)
There is no vaccine for tularemia currently licensed in the United States. An older vaccine made from a weakened strain ofF. tularensis had many other problems and was withdrawn.
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