Tularemia is a highly infectious disease, which affects humans and animals, caused by the bacterium francisella tularensis. The disease affects humans through various means such as skin contact with the infected animal, taking contaminated water, inhaling contaminated dust and aerosols, bites from ticks such as dog ticks, lone star ticks, and wood ticks, bites from deer flies, exposure in the laboratory, and as an act of bioterrorism (CDC). The bacterium is highly contagious, and a small number can cause the disease.
terrorists can use it as a weapon, in form of inhalation, and this would increase the number of people susceptible to the disease. Pneumonic tularemia tends to be more severe. The disease causes severe pain and it could be fatal. Mosquitoes also carry the disease, and they can spread them to humans. The bacteria enter the human body through the skin, mouth, eyes, lungs, or throat. About one hundred animal species can carry the infection (Siderovski 12).
This is in addition to birds, arthropods, and fish, which can also carry the disease. Animals such as rabbits, hares, cats, muskrats, and rodents are more likely to get the infection. In cases of outbreak, the animals die in large numbers. There are no known cases of person-to-person infections. Farmers and hunters are at high risks of getting infections.
Description and Classification
Francisella tularensis is a gram-negative non-molatile bacterium with two biotypes, tularensis (biotype A) and palaearctica (biotype B). It is in capsule form with pleomorphic cells, which appear as short rods.
It is an intracellular pathogen, able to live in ticks for a long time. the bacterium can survive in cool conditions for a long time but the cells are sensitive to heat. The bacterium can survive in water, as well as dry land. It also survives in soil, hay, decaying animal carcasses, and straw. Biotype A is limited to North America and it is highly virulent. Biotype B is found in North America, Europe, Asia and Americas, and it is less virulent. There are four known subspecies, and they include tularensis, holarctica, mediasiatica, and novicida. mediasiatica and novicida have low virulence subspecies tularensis is exclusive to north America, while subspecies holartica is present in Europe and north America (Suckow et al., 341).
Signs and Symptoms
The symptoms of the disease are varied, and they depend on the mode of infection, although all humans affected by the disease experience a high fever. A person infected with the disease normally experiences the symptoms after a period of 3-5 days, although the symptoms can range from 1-21 days. Other than fever, other symptoms include chills, headaches, muscle pain, eye irritation, sweating, diarrhea, dry coughs, weakness, and joint aches among others (CDC). A person with the infection develops a lesion at the site of entry of the bacteria. The sore is often red, with a ribbed rim and a punched-out center (Siderovski 36). The person develops inflammation of the lymph nodes in the affected area (Suckow et al 342). When the bacterium enters the bloodstream, it causes bacteremia, and this enables the infection to spread to other body organs such as kidneys, spleen, and liver (Siderovski 36). Animals infected with the disease often die, but they exhibit symptoms such as depression and anorexia (Suckow et al 342)
Forms of Tularemia
Some of the main forms of the disease include glandular, ocuglandular, oropharyngeal, ulceroglandular, and pneumonic. The bacteria in the ulceroglandular form of disease spreads to the lymph nodes at the point of entry. The ulceroglandular form of the disease is the most common. It occurs when the bacterium affects the person through the skin. A person with ulceroglandular develops a lesion, which develops into an ulcer. The ulcer heals after one week, and it is relatively painless (Oyston 921-930). The location of the ulcer in the body can help to determine the mode of transmission. Ulcers on the upper extremities on the body indicate that the person was in close contact with an infected animal. Ulcers on the lower extremities, abdomen or the back of the body indicate that the person got the infection from arthropods (Goddard 106). Glandular tularemia is similar to ulceroglandular, expect that the infected person does not develop an ulcer.
The eye is a possible route of infection, and when this happens, the person develops ocuglandular tularemia. A person with this form of disease has swollen eyelids, and he or she develops conjunctivitis. Oropharyngeal tularemia develops when a person eats infected meat or drinks contaminated water (Oyston 921-930). It can also develop when a person puts infected fingers in the mouth (Siderovski 41). This form is also known as gastrointestinal tularemia. A person with this form of disease develops pharyngitis, swollen cervical lymph nodes, and ulcers. Diarrhea is a common symptom in this form of disease, and it ranges from mild and persistent diarrhea to acute diarrhea, which is often fatal. The infected person develops an ulceration of the bowel. He or she experiences nausea and vomiting. A person develops pneumonic or respiratory diarrhea through inhalation. A person with this form of the disease becomes delirious. He or she develops a non-productive cough, chest pain, and dyspenea. The bacteria replicates quickly once a person inhales it. The person might require assistance in breathing.
Testing and Diagnosis
Tularemia is a rare disease, and doctors find it hard to diagnose the disease. This is because the disease symptoms resemble symptoms of other diseases. Doctors look for symptoms such as swelling lymph nodes and ulcers on the skin to make their diagnosis (Siderovski 48). The patient can help the doctor, by pointing out any chance of exposure with an infected animal. Physicians can identify the disease by examining secretions and biopsy specimen using gram stain or direct fluorescent antibody. Examination using the fluorescent antibodies is quick, and the physician gets the report after a few hours but it is not always possible to guarantee the accuracy of the results (Dennis et al 2763-2773). When testing for the disease, it is important to alert those working in the laboratory, so that they can take the correct preventive measures. There have been several cases of people getting infections because of laboratory exposure. The most efficient way of confirming the disease is by growing it in culture, although it is often difficult to do so. One can grow culture using sputum or pharyngeal washing. For a person with inhalation tularemia, the physician grows the culture from fasting gastric aspirates. The culture has to contain cysteine, and the physician places it in an environment rich in carbon dioxide. It takes about four to six days for the culture to grow (Hepburn & Simpson 231-240)
Prevention and Treatment
People can minimize their chances of infection by adopting several measures such as not handling carcasses since one does not know whether the animal had the diseases, and using gloves when handling infected animals and carcasses. People should not take water if they are not sure of its safety. Contaminated water is one of the easiest ways of acquiring the disease. People who take wild meat should ensure that they cook it thoroughly. Tularemia often affects wild animals, and people should be careful when consuming such meat. People in endemic areas should use repellants to get rid of arthropods, and reduce their chances of infection. They should treat their clothes with repellants, as this will help them to avoid insect bites. Worry about terrorists using the bacterium as a possible weapon has compelled researchers to develop a vaccine. There have been several attempts at this, and the live vaccine strain (LVS) seems to have been the most successful. The vaccine is successful in providing protection against small doses of a virulent strain. Governments have not licensed the vaccine because of its reversion to virulence, variable immunogenicity, and mixed colony morphology (Oyston 921-930). The disease can be fatal in humans, if not treated. The mortality rate for untreated tularemia is 30%. Treating the disease reduces this rate to 1% (Goddard 106). Doctors use antibiotics to treat the disease in human beings. Doctors use antibiotics such as streptomycin, gentamicin, doxycycline, and ciprofloxacin to treat the disease (CDC). These are the most common antibiotics, although other antibiotics such as tetracycline and chloramphenicol are in use (Goddard 106). Treatment depends on the type of medication used and stage of the disease, though it takes 10-21 days. The use of antibiotics has increased the chances of the patients’ recovery, and most patients treated usually recover from their illness.
CDC. Tularemia. Centers for Disease Control and Prevention. 2011. Web. 12 July 2012
Dennis, T. David et al. “Tularemia as a Biological Weapon.” The Journal of American Medical Association 285.21 (2001): 2763-2773
Goddard, Jerome. Infectious Diseases and Arthropods. New York, NY: Springer, 2008. Print
Hepburn, J. Matthew and JH Simpson. Tularemia: Current Diagnosis and Treatment Options. 2008. Web. 12 July 2012
Oyston, C. F. Petra. “Francisella Tularensis: Unravelling the Secrets of an Intracellular Pathogen.” Journal of Medical Microbiology 57.8 (2008): 921-930. Print
Siderovski, H. Susan. Tularemia. Infobase Publishing, 2006. Print
Suckow, A, Mark et al. The Laboratory Rabbit, Guinea Pig, Hamster, and Other Rodents. Waltham, MA: Academic Press, 2012. Print