infectious disease

Also found in: Dictionary, Thesaurus, Medical, Legal, Financial, Acronyms, Wikipedia.

Infectious disease

A pathological condition spread among biological species. Infectious diseases, although varied in their effects, are always associated with viruses, bacteria, fungi, protozoa, multicellular parasites and aberrant proteins known as prions. A complex series of steps, mediated by factors contributed by both the infectious agent and the host, is required for microorganisms or prions to establish an infection or disease. Worldwide, infectious diseases are the third leading cause of human death.

The most common relationship between a host and a microorganism is a commensal one, in which advantages exist for both organisms. For example, hundreds of billions of bacteria of many genera live in the human gastrointestinal tract, coexisting in ecological balance without causing disease. These bacteria help prevent the invasion of the host by more virulent organisms. In exchange, the host provides an environment in which harmless bacteria can readily receive nutrients. There are very few microorganisms that cause disease every time they encounter a host. Instead, many factors of both host and microbial origin are involved in infectious disease. These factors include the general health of the host, previous exposure of the host to the microorganism, and the complement of molecules produced by the bacteria.

Spread of a pathogenic microorganism among individual hosts is the hallmark of an infectious disease. This process, known as transmission, may occur through four major pathways: contact with the microorganism, airborne inhalation, through a common vehicle such as blood, or by vector-borne spread.

The manner in which an infectious disease develops, or its pathogenesis, usually follows a consistent pattern. To initiate an infection, there must be a physical encounter as which the microorganism enters the host. The most frequent portals of entry are the respiratory, gastrointestinal, and genitourinary tracts as well as breaks in the skin. Surface components on the invading organism determine its ability to adhere and establish a primary site of infection. The cellular specificity of adherence of microorganisms often limits the range of susceptible hosts. For example, although measles and distemper viruses are closely related, dogs do not get measles and humans do not get distemper. From the initial site of infection, microorganisms may directly invade further into tissues or travel through the blood or lymphatic system to other organs.

Microorganisms produce toxins that can cause tissue destruction at the site of infection, can damage cells throughout the host, or can interfere with the normal metabolism of the host. The damage that microorganisms cause is directly related to the toxins they produce. Toxins are varied in their mechanism of action and host targets. See Cholera, Staphylococcus

The host's reaction to an infecting organism is the inflammatory response, the body's most important internal defense mechanism. Although the inflammatory response is also seen as secondary to physical injury and nonspecific immune reactions, it is a reliable indicator of the presence of pathogenic microorganisms. Immune cells known as lymphocytes and granulocytes are carried by the blood to the site of infection. These cells either engulf and kill, or secrete substances which inhibit and neutralize, microorganisms. Other white blood cells, primarily monocytes, recognize foreign organisms and transmit chemical signals to other cells of the host's immune system, triggering the production of specific antibodies or specialized killer cells, both of which are lethal to the infecting microorganism. Any influence that reduces the immune system's ability to respond to foreign invasion, such as radiation therapy, chemotherapy, or destruction of immune cells by an immunodeficiency virus such as HIV, increases the likelihood that a organism will cause disease within the host.

Chemical compounds that are more toxic to microorganisms than to the host are commonly employed in the prevention and treatment of infectious disease; however, the emergence of drug-resistant organisms has led to increases in the morbidity and mortality associated with some infections. Other methods for controlling the spread of infectious diseases are accomplished by breaking a link in the chain of transmission between the host, microorganism, and mode of spread by altering the defensive capability of the host. Overall, the three most important advances to extend human life are clean water, vaccination, and antibiotics (in that order of importance).

Water-borne infections are controlled by filtration and chlorination of municipal water supplies. Checking food handlers for disease, refrigeration, proper cooking, and eliminating rodent and insect infestation have markedly reduced the level of food poisonings. The transmission of vector-borne diseases can be controlled by eradication of the vector. Blood-borne infections are reduced by screening donated blood for antibodies specific for HIV and other viruses and by rejecting donations from high-risk donors. For diseases such as tuberculosis, the airborne spread of the causative agent, Mycobacterium tuberculosis, can be reduced by quarantining infected individuals. The spread of sexually transmitted diseases, including AIDS, syphilis, and herpes simplex, can be prevented by inhibiting direct contact between the pathogenic microorganism and uninfected hosts. See Acquired immune deficiency syndrome (AIDS), Food poisoning, Vaccination, Water-borne disease

infectious disease

[in′fek·shəs di′zēz]
Any disease caused by invasion by a pathogen which subsequently grows and multiplies in the body.
References in periodicals archive ?
His research interests include vaccine-preventable diseases antimicrobial drug resistance, emerging infectious diseases, microbial ecology, and emergency preparedness planning and response.
Finally, lessons for building resilience against unpredictable catastrophes are emerging from the recent tragic tsunami in the Indian Ocean that, at last report, has killed upwards of 150,000 people, with many more injured or at risk of infectious diseases.
The report also discusses that counterfeiting drugs and medical treatment devices is emerging as a universal concern in the Global Infectious Disease Treatment market.
pylori Testing OTC - Home Use Testing For Infectious Disease Molecular HIV Testing Molecular Hepatitis Testing Molecular GC/Chlamydia Testing Molecular Hospital Acquired Infection Testing Molecular Respiratory Testing Organism ID Testing Blood Bank, Immunoassays Blood Bank, Molecular ID/AST Panels ID/AST Chromogenetic Media Parasitology Sepsis Testing Others
The current 992-page 27th edition has newly added sections, including key developments in combination vaccines, the 2006 AAP standards for child and adolescent immunization practices, parental refusal to vaccinate, updates on prevention of mosquitoborne infections, and updated information on emerging infectious diseases and pathogens, including Baylisascaris, metapneumovirus, West Nile virus, coronaviruses, pertussis, tuberculosis, and pneumococcal, meningococcal, and varicella infections.
The report, drafted by a 19-member panel of physicians and scientists, asserts that the United States lacks the ability to mobilize quickly against emerging infectious diseases.
Quick TAT is especially relevant to infectious disease testing, as fast diagnosis increases treatment options and patient prognosis.
To order this report: In_Vitro_Diagnostic Industry : European Blood Typing, Grouping and Infectious Disease Screening Market 2013: France, Germany, Italy, Spain, UK-- Sales Forecasts, Supplier Shares, Competitive Strategies
As strategies to deal with emerging infectious disease threats are developed, a key component is consideration of special populations, including pregnant women (1).
More general information related to emerging infectious diseases can be found at the bottom of the main page.
eIuResearch in RNA-loaded dendritic cell immunotherapies for HIV treatment may provide the next important and effective treatment option for infectious disease,eIN stated Dr.
Its broad-based content would mirror the complex microbial, demographic, genetic, economic, technologic, behavioral, social, and other factors (including nefarious ones) that contribute to infectious disease emergence.

Full browser ?