Microbe- Human Interactions: Infection and Disease
Infection- a condition in which pathogenic microorganisms penetrate the host defenses, enter the tissues, and multiply. When the cumulative effects of the infection damage or disrupt tissues and organs, the pathologic state that results is known as a disease.
A Disease is defined as any deviation from health. There are hundreds of different diseases caused by such factors as infections, diets, genetics, and aging.
Infectious disease is the disruption of a tissue or organ caused by microbes or their products.
A Disease is defined as any deviation from health. There are hundreds of different diseases caused by such factors as infections, diets, genetics, and aging.
Infectious disease is the disruption of a tissue or organ caused by microbes or their products.
A microbe whose relationship with its host is parasitic and results in infection and disease is termed a pathogen. The type and severity of infection depend both on the pathogenicity of the organism and the condition of the host.
True pathogens (primary pathogens) are capable of causing disease in healthy persons with normal immune defenses. They are generally associated with a specific, recognizable disease, which may vary in severity from mild (colds) to severe (malaria) to fatal (rabies). Examples of true pathogens include influenza virus, plague bacillus, and malarial protozoan.
Opportunistic pathogens cause disease when the host's defenses are compromised or when they become established in a part of the body that is not natural to them. Opportunists are not considered pathogenic to a normal healthy person and, like primary pathogens, do not generally possess well-developed virulence properties. Examples of opportunistic pathogens include Pseudomonas species and Candida albicans.
True pathogens (primary pathogens) are capable of causing disease in healthy persons with normal immune defenses. They are generally associated with a specific, recognizable disease, which may vary in severity from mild (colds) to severe (malaria) to fatal (rabies). Examples of true pathogens include influenza virus, plague bacillus, and malarial protozoan.
Opportunistic pathogens cause disease when the host's defenses are compromised or when they become established in a part of the body that is not natural to them. Opportunists are not considered pathogenic to a normal healthy person and, like primary pathogens, do not generally possess well-developed virulence properties. Examples of opportunistic pathogens include Pseudomonas species and Candida albicans.
Sexually Transmitted Diseases
The urogenital tract is the portal entry for pathogens that are contracted by sexual means (intercourse or intimate direct contact). Sexually transmitted disease (STD) reflects the mode of transmission of these diseases more accurately. STDs account for an estimated 4% of infections worldwide, with approximately 13 million new cases occurring in the United States each year. The microbes of STDs enter the skin or mucosa of the penis, eternal genitalia, vagina, cervix, and urethra. Some can penetrate an unbroken surface; others require a cut or abrasion.
Extracellular Enymes- Many pathogenic bacteria, fungi, protozoa, and worms secrete exoenzymes that break down and inflict damage on tissues. Other enzymes dissolve the host's defense barriers and promote the spread of microbes to deeper tissues.
Examples of enzymes are:
Examples of enzymes are:
- mucinase, which digests the protective coating on mucous membranes and is a factor in amoebic dysentry;
- keratinase, which digests the principal component of skin and hair, and is secreted by fungi that cause ringworm;
- collagenase, which digests the principal fiber of connective tissue and is an invasive factor or Clostridium species and certain worms; and
- hyaluronidase, which digests hyaluronic acid, the ground substance that cements animal cells together. This enzyme is an important virulence factor in staphylococci, clostridia, streptococci, and pneumococci.
Epidemiology- involves the study of the frequency and distribution of disease and other health-related factors in defined human populations. It involves many disciplines- not only microbiology, but anatomy, physiology, immunology, medicine, psychology, sociology, ecology, and statistics- and it considers many diseases other than infectious ones, including heart disease, cancer, drug addiction, and mental illness.
Carriers- an individual who inconspicuously shelters a pathogen and spreads it to others without notice. Although human carriers are occasionally detected through routine screening (blood tests, cultures) and other epidemiological devices, they are unfortunately very difficult to discover and control. As long as a pathogenic reservoir is maintained by the carrier state, the disease will continue to exist in that population, and the potential for epidemics will be a constant threat.
Aympstomatic carriers- are infected, but as perviously indicated, they show no symptoms. A few asymptotic infections (gonorrhea and genital warts, for instance) can carry out their entire course without overt manifestations.
Passive carriers- state of great concern during patient care. Medical and dental personnel who must constantly handle materials that are heavily contaminated with patient secretions and blood rid picking up pathogens mechanically and accidentally transferring them to other patients. Proper hand washing, handling of contaminated materials, and aseptic techniques greatly reduce this likelihood.
Vector is used by epidemiologists to indicate a live animal that transmits an infectious agent from one host to another. The majority of vectors are arthropods such as fleas, mosquitos, flies, and ticks, although larger animals can also spread infection- for example, mammals (rabies), birds (psittacosis), or lower vertebrates (salmonellosis).
Biological Vector- Actively participates in a pathogen's life cycle, serving as a site in which it can multiply or complete its life cycle. A biological vector communicates the infectious agent to the human host of biting, aerosol formation, or touch. In the case of biting vectors, the animal can
Mechanical Vector- are not necessary to the life cycle of an infectious agent and merely transport it without being infected.
A disease is communicable when an infected host can transmit the infectious agent to another host and establish infection in that host. The transmission of the agent can be direct or indirect, and the ease with which the disease is transmitted varies considerably from one agent to another. If the agent is highly communicable, especially through direct contact, the disease is contagious. Influenza and measles move readily from host to host and thus are contagious, whereas leprosy is only weakly communicable.
In contrast, a non-communicable infectious disease does not arise through transmission of the infectious agent from host to host. The infection an disease are acquired through some other, special circumstance. Non-communicable infections occur primarily when a compromised person is invaded by his or her own microflora (as with certain pneumonias, for example) or when an individual has accidental contact with a facultative parasite that exists in a nonliving reservoir such as soil.
Aympstomatic carriers- are infected, but as perviously indicated, they show no symptoms. A few asymptotic infections (gonorrhea and genital warts, for instance) can carry out their entire course without overt manifestations.
Passive carriers- state of great concern during patient care. Medical and dental personnel who must constantly handle materials that are heavily contaminated with patient secretions and blood rid picking up pathogens mechanically and accidentally transferring them to other patients. Proper hand washing, handling of contaminated materials, and aseptic techniques greatly reduce this likelihood.
Vector is used by epidemiologists to indicate a live animal that transmits an infectious agent from one host to another. The majority of vectors are arthropods such as fleas, mosquitos, flies, and ticks, although larger animals can also spread infection- for example, mammals (rabies), birds (psittacosis), or lower vertebrates (salmonellosis).
Biological Vector- Actively participates in a pathogen's life cycle, serving as a site in which it can multiply or complete its life cycle. A biological vector communicates the infectious agent to the human host of biting, aerosol formation, or touch. In the case of biting vectors, the animal can
- inject infected saliva into the blood (the mosquito)
- defecate around the bite wound (the flea), or
- regurgitate blood into the wound (the tsetse fly).
Mechanical Vector- are not necessary to the life cycle of an infectious agent and merely transport it without being infected.
A disease is communicable when an infected host can transmit the infectious agent to another host and establish infection in that host. The transmission of the agent can be direct or indirect, and the ease with which the disease is transmitted varies considerably from one agent to another. If the agent is highly communicable, especially through direct contact, the disease is contagious. Influenza and measles move readily from host to host and thus are contagious, whereas leprosy is only weakly communicable.
In contrast, a non-communicable infectious disease does not arise through transmission of the infectious agent from host to host. The infection an disease are acquired through some other, special circumstance. Non-communicable infections occur primarily when a compromised person is invaded by his or her own microflora (as with certain pneumonias, for example) or when an individual has accidental contact with a facultative parasite that exists in a nonliving reservoir such as soil.