Skin infection begins as a raised itchy bump that resembles an insect bite but within 1—2 days develops into a vesicle and then a painless ulcer, usually 1—3 cm in diameter, with a characteristic black necrotic dying area in the center. Lymph glands in the adjacent area may swell. Deaths are rare with appropriate antimicrobial therapy. Inhalation: Initial symptoms are like cold or flu symptoms and can include a sore throat, mild fever, and muscle aches. After several days, the symptoms may progress to cough, chest discomfort, severe breathing problems and shock.
Inhalation anthrax is often fatal. Intestinal: Initial signs of nausea, loss of appetite, vomiting, and fever are followed by abdominal pain, vomiting of blood, and severe diarrhea. While most human cases of anthrax result from contact with infected animals or contaminated animal products, anthrax also can be used as a biologic weapon.
In , dozens of residents of Sverdlovsk in the former Soviet Union are thought to have died of inhalation anthrax after an unintentional release of an aerosol from a biologic weapons facility.
In , 22 cases of anthrax occurred in the United States from letters containing anthrax spores that were mailed to members of Congress, television networks, and newspaper companies. Anthrax is caused by the bacterium Bacillus anthracis.
The anthrax bacterium forms a protective shell called a spore. Anthrax is diagnosed by isolating B. Antibiotics are used to treat all three types of anthrax. Treatment should be initiated early because the disease is more likely to be fatal if treatment is delayed or not given at all.
When anthrax affects humans, it is usually the result of an occupational exposure to infected animals or their products. Naturally occurring anthrax is rare in the United States 28 reported cases between and , but 22 mail-related cases were identified in Infections occur most commonly in wild and domestic lower vertebrates cattle, sheep, goats, camels, antelopes, and other herbivores , but it can also occur in humans when they are exposed to infected animals or tissue from infected animals.
Anthrax can infect a person in three ways: by anthrax spores entering through a break in the skin, by inhaling anthrax spores, or by eating contaminate, undercooked meat.
Anthrax is not spread from person to person. The inhalation form is from breathing in spores from the same sources. Anthrax can also be spread as a bioterrorist agent. Susceptibility to anthrax is universal. Most naturally occurring anthrax affects people whose work brings them into contact with livestock or products from livestock. Such occupations include veterinarians, animal handlers, abattoir workers, and laboratorians.
Soldiers and other potential targets of bioterrorist anthrax attacks might also be considered at increased risk. In countries where anthrax is common and vaccination levels of animal herds are low, humans should avoid contact with livestock and animal products and avoid eating meat that has not been properly slaughtered and cooked.
Also, an anthrax vaccine has been licensed for use in humans. It is used by veterinarians, laboratorians, soldiers, and others who may be at increased risk of exposure, but is not available to the general public at this time.
For a person who has been exposed to anthrax but is not yet sick, antibiotics combined with anthrax vaccine are used to prevent illness. Atlanta: Anthrax. Description: One model shows agent, host, and environment as having equal influence. The other model shows agent and host as variables that are dependent on each other and on the environment. Return to text. Description: Causal pies are pie charts with each component cause as a slice.
Slice A is in each pie. Slice B is only in pies 1 and 2. Slice C is only in pies 1 and 3. Skip directly to site content Skip directly to page options Skip directly to A-Z link. For example, persons with sickle cell trait seem to be at least partially protected from a particular type of malaria. Specific immunity refers to protective antibodies that are directed against a specific agent.
Such antibodies may develop in response to infection, vaccine, or toxoid toxin that has been deactivated but retains its capacity to stimulate production of toxin antibodies or may be acquired by transplacental transfer from mother to fetus or by injection of antitoxin or immune globulin. Nonspecific factors that defend against infection include the skin, mucous membranes, gastric acidity, cilia in the respiratory tract, the cough reflex, and nonspecific immune response.
Factors that may increase susceptibility to infection by disrupting host defenses include malnutrition, alcoholism, and disease or therapy that impairs the nonspecific immune response. Knowledge of the portals of exit and entry and modes of transmission provides a basis for determining appropriate control measures. In general, control measures are usually directed against the segment in the infection chain that is most susceptible to intervention, unless practical issues dictate otherwise.
For some diseases, the most appropriate intervention may be directed at controlling or eliminating the agent at its source. A patient sick with a communicable disease may be treated with antibiotics to eliminate the infection. An asymptomatic but infected person may be treated both to clear the infection and to reduce the risk of transmission to others.
In the community, soil may be decontaminated or covered to prevent escape of the agent. Some interventions are directed at the mode of transmission. Interruption of direct transmission may be accomplished by isolation of someone with infection, or counseling persons to avoid the specific type of contact associated with transmission. Vehicleborne transmission may be interrupted by elimination or decontamination of the vehicle. To prevent fecal-oral transmission, efforts often focus on rearranging the environment to reduce the risk of contamination in the future and on changing behaviors, such as promoting handwashing.
For airborne diseases, strategies may be directed at modifying ventilation or air pressure, and filtering or treating the air. To interrupt vectorborne transmission, measures may be directed toward controlling the vector population, such as spraying to reduce the mosquito population. Some strategies that protect portals of entry are simple and effective.
For example, bed nets are used to protect sleeping persons from being bitten by mosquitoes that may transmit malaria. Wearing of long pants and sleeves and use of insect repellent are recommended to reduce the risk of Lyme disease and West Nile virus infection, which are transmitted by the bite of ticks and mosquitoes, respectively.
Vaccinations promote development of specific antibodies that protect against infection. On the other hand, prophylactic use of antimalarial drugs, recommended for visitors to malaria-endemic areas, does not prevent exposure through mosquito bites, but does prevent infection from taking root.
Finally, some interventions attempt to prevent a pathogen from encountering a susceptible host. The degree of herd immunity necessary to prevent or interrupt an outbreak varies by disease. In theory, herd immunity means that not everyone in a community needs to be resistant immune to prevent disease spread and occurrence of an outbreak.
One problem is that, in highly immunized populations, the relatively few susceptible persons are often clustered in subgroups defined by socioeconomic or cultural factors. If the pathogen is introduced into one of these subgroups, an outbreak may occur. Information about dengue fever is provided on the following pages. After studying this information, outline the chain of infection by identifying the reservoir s , portal s of exit, mode s of transmission, portal s of entry, and factors in host susceptibility.
Check your answer. Dengue is an acute infectious disease that comes in two forms: dengue and dengue hemorrhagic fever. The principal symptoms of dengue are high fever, severe headache, backache, joint pains, nausea and vomiting, eye pain, and rash.
Generally, younger children have a milder illness than older children and adults. Dengue hemorrhagic fever is a more severe form of dengue. It is characterized by a fever that lasts from 2 to 7 days, with general signs and symptoms that could occur with many other illnesses e. This stage is followed by hemorrhagic manifestations, tendency to bruise easily or other types of skin hemorrhages, bleeding nose or gums, and possibly internal bleeding.
This may lead to failure of the circulatory system and shock, followed by death, if circulatory failure is not corrected. Diagnosis of dengue infection requires laboratory confirmation, either by isolating the virus from serum within 5 days after onset of symptoms, or by detecting convalescent-phase specific antibodies obtained at least 6 days after onset of symptoms.
There is no specific medication for treatment of a dengue infection. Persons who think they have dengue should use analgesics pain relievers with acetaminophen and avoid those containing aspirin. They should also rest, drink plenty of fluids, and consult a physician. Persons with dengue hemorrhagic fever can be effectively treated by fluid replacement therapy if an early clinical diagnosis is made, but hospitalization is often required.
Dengue is endemic in many tropical countries in Asia and Latin America, most countries in Africa, and much of the Caribbean, including Puerto Rico. Cases have occurred sporadically in Texas. Epidemics occur periodically. Globally, an estimated 50 to million cases of dengue and several hundred thousand cases of dengue hemorrhagic fever occur each year, depending on epidemic activity.
Between and suspected cases are introduced into the United States each year by travelers. Dengue is transmitted to people by the bite of an Aedes mosquito that is infected with a dengue virus.
The mosquito becomes infected with dengue virus when it bites a person who has dengue or DHF and after about a week can transmit the virus while biting a healthy person. Monkeys may serve as a reservoir in some parts of Asia and Africa.
Dengue cannot be spread directly from person to person. Susceptibility to dengue is universal. Residents of or visitors to tropical urban areas and other areas where dengue is endemic are at highest risk of becoming infected.
While a person who survives a bout of dengue caused by one serotype develops lifelong immunity to that serotype, there is no cross-protection against the three other serotypes. There is no vaccine for preventing dengue. The best preventive measure for residents living in areas infested with Aedes aegypti is to eliminate the places where the mosquito lays her eggs, primarily artificial containers that hold water.
Factors that increase the susceptibility of a host to the development of a communicable disease are called risk factors. Some risk factors arise from outside the individual — for example, poor personal hygiene, or poor control of reservoirs of infection in the environment.
Factors such as these increase the exposure of susceptible hosts to infectious agents, which makes the disease more likely to develop. Additionally, some people in a community are more likely to develop the disease than others, even though they all have the same exposure to infectious agents. This is due to a low level of immunity within the more susceptible individuals.
Immunity refers to the resistance of an individual to communicable diseases, because their white blood cells and antibodies defensive proteins are able to fight the infectious agents successfully. Low levels of immunity could be due to:. In general terms, in what two ways could the risk of developing a communicable disease be reduced? For further information, take a look at our frequently asked questions which may give you the support you need.
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