How is tularemia manifested in humans

Tularemia Infectious Disease

There are many infectious diseases affecting humans that can be contracted from infected animals. Tularemia is one of them. This infectious disease is known under several more names such as rabbit fever, deer fly fever and Pahvant Valley plague. It develops after the person contracts the bacterium Francisella tularensis, a Gram-negative coccobacillus. Transmission develops after direct contact with the infected animal or its products or indirect when Francisella tularensis is transferred via vectors, predominantly ticks.

There are two types of the bacterium. Type A is known to affect rabbits and humans while type B is generally a cause of infection of aquatic rodents such as beavers and muskrats. Type B may also be contracted by humans although it is not that virulent. How is Tularemia Manifested?

Tularemia can develop in several different forms which practically depends on the site of infection. The most common type, however, is ulceroglandular form. Apart from this there are glandular form of the disease, oropharyngeal tularemia, pneumonic tularemia, oculoglandular and typhoidal form of the disease.

The first symptoms develop after an incubation period (1-14 days). In the majority of cases the initial symptoms develop after 3-5 days. Typical symptoms and signs associated with tularemia infection include fever with chills, lethargy and anorexia (loss of appetite accompanied by weight loss). Fever is usually moderate or can be rather high. While experiencing high fever it is possible to isolate the bacterium from blood cultures.

Ulceroglandular tularemia is characterized by skin ulcers that typically develop at the site of infection i.e. the lesions affect the part of the skin bitten by an animal/ insect. Such patients also have enlarged and painful regional lymph nodes. Headache and fatigue occur as well. Furthermore, patients with glandular tularemia practically develop the same symptoms and signs as those suffering from ulceroglandular form of the disease. The only difference is that there are no skin ulcers. Oculoglandular tularemia affects the eyes and leads to eye redness and pain, swelling of the eyelids and discharge. Patients may also develop an ulcer on the inner surface of the eyelid.

In case of oropharyngeal tularemia patients develop symptoms and signs soon after they have ingested poorly cooked infected wild meat or drunk contaminated water. Infection of this type leads to sore throat, nausea and vomiting, and diarrhea. Pneumonic tularemia is the form characterized by chest pain, cough and breathing difficulty (shortness of breath). And finally, there is typhoid tularemia, a rare and rather severe form of the disease. Apart from high fever and extreme exhaustion, such patients are also affected by hepatomegaly (enlarged liver), splenomegaly (enlarged spleen) and pneumonia. Vomiting and diarrhea may occur as well.

In certain cases one develops septicemia which may be a cause of lethal outcome.Treatment for Tularemia

This bacterial infection is easily treated with several antibiotics. Francisella tularensis is sensitive to streptomycin and gentamycin. These antibiotics are administered intramuscularly or intravenously. It is also possible to eradicate infectious agents with oral tetracycline. Patients who have developed complications such as meningitis or pneumonia will receive several more drugs that will take care of these health issues. Even though many people develop immunity after being infected, it is possible to experience disease recurrence or reinfection if there is repeated contact with the bacterium.

Relevant Data

The bacterium Francisella tularensis was first isolated in 1912. Later, research revealed that the bacterium may be contracted from wild animals and that is actually quite harmful to humans. Scientists have also confirmed that many times the infection affects specific professionals such as hunters, cooks and agricultural workers, all those who might come in contact with infected wild animals and their raw products as well as those who have been bitten by ticks.

The disease is endemic in North America, some parts of the Europe and Asia. Today the most common way of disease transmission is via tick bites. Natural hosts of the bacterium are wild rabbits and hares. Still, in spite of proper protection we still have cases of infection that have developed after a close contact with the infected animal, after ingestion of poorly cooked meat or by drinking contaminated water. The infection additionally develops after inhaling bacteria.

According to the available data the number of new cases has significantly dropped. In the period between 1990 and 2000 the infection used to affect less than a person per 1,000,000. This drives to conclusion that in the US this infectious disease is fortunately rare. In the majority of case (70-80%) patients develop ulceroglandular form of the disease. Oculoglandular form is rare affecting 1% of all patients. One of the most severe forms, pneumonic tularemia may develop after inhaling only 10-50 microorganisms. Still, even this form is not so common accounting only for 15% of all cases. Finally, typhoid tularemia affects between 10 and 15 % of patients.