1. A microbial pathogen can be defined as: "An organism capable of causing disease". How good is this definition?

1. A microbial pathogen can be defined as: "An organism capable of causing disease". How good is this definition?

(Answered by Tracey Archer)

microbial pathogen is an organism capable of causing disease however The word organisms in this text must include pathogenic bacteria that contributes to causing diseases such as plague, tuberculosis and anthrax for example protozoa, causing diseases such as malaria, sleeping sickness and toxoplasmosis; and also fungi causing diseases such as ringworm, candidiasis or histoplasmosis. However, other diseases such as influenza, yellow fever or AIDS are caused by pathogenic viruses, which are not living organisms and are not therefore microorganisms. So it could be said that the definition itself is not correct but only one aspect of the correct definition. A microbial pathogen can be defined as: "An organism capable of causing disease" however it is not the only and maybe not the most important disease causing factor.As of 2007, no clear examples of archaean pathogens are known although a relationship has been proposed between the presence of some methanogens and human periodontal disease.so how good is this definition following are 4 disease that are considered extremely relevent to the human species by looking at each example we can deside weather or not each disease falls into this category.

Malaria is one of the most common infectious diseases and an enormous public health problem. is a vector-borne infectious disease caused by protozoan parasites. It is widespread in tropical and subtropical regions, including parts of the Americas, Asia, and Africa. Each year, there are approximately 515 million cases of malaria, killing between one and three million people, the majority of whom are young children in Sub-Saharan Africa the most serious forms of the disease are caused by Plasmodium falciparum and Plasmodium vivax, but other related species (Plasmodium ovale, Plasmodium malariae) can also affect humans. This group of human-pathogenic Plasmodium species is usually referred to as malaria parasites. Only Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken on an infected person. When a mosquito bites an infected person, a small amount of blood is taken which contains microscopic malaria parasites. About 1 week later, when the mosquito takes its next blood meal, these parasites mix with the mosquito's saliva and are injected into the person being bitten. The parasites multiply within red blood cells, causing symptoms that include symptoms of anemia (light headedness, shortness of breath, tachycardia etc.), as well as other general symptoms such as fever, chills, nausea, flu-like illness, and, in severe cases, coma and death Although some are under development, no vaccine is currently available for malaria; preventive drugs must be taken continuously to reduce the risk of infection. These prophylactic drug treatments are often too expensive for most people living in endemic areas. Most adults from endemic areas have a degree of long-term infection which tends to recur, and also possess partial immunity (resistance); the resistance reduces with time and such adults may become susceptible to severe malaria if they have spent a significant amount of time in non-endemic areas. They are strongly recommended to take full precautions if they return to an endemic area. Malaria infections are treated through the use of antimalarial drugs, such as quinine or artemisinin derivatives, although drug resistance is increasingly common.

Sleeping sickness or human African trypanosomiasis is a parasitic disease of people and animals, caused by protozoa of species Trypanosoma brucei and transmitted by the tsetse flySymptoms begin with fever, headaches, and joint pains. As the parasites enter through both the blood and lymph systems, lymph nodes often swell up to tremendous sizes. Winterbottom's sign, the telltale swollen lymph nodes along the back of the neck may appear. If untreated, the disease slowly overcomes the defenses of the infected person, and symptoms spread to include anemia, endocrine, cardiac, and kidney diseases and disorders. The disease then enters a neurological phase when the parasite passes through the blood-brain barrier. The symptoms of the second phase give the disease its name; besides confusion and reduced coordination, the sleep cycle is disturbed with bouts of fatigue punctuated with manic periods progressing to daytime slumber and nighttime insomnia. Without treatment, the disease is invariably fatal, with progressive mental deterioration leading to coma and death. Damage caused in the neurological phase can be irreversible. In addition to the bite of the tsetse fly, the disease is contractible in the following ways:

* Mother to child infection: the trypanosome can cross the placenta and infect the fetus, causing prenatal death.
* Laboratories: accidental infections, for example, through the handling of blood of an infected person and organ transplantation, although this is uncommon.
* Blood transfusion

The disease is found in two forms, depending on the parasite, either Trypanosoma brucei gambiense or Trypanosoma brucei rhodesiense. T. b. gambiense is found in central and western Africa; it causes a chronic condition that can extend in a passive phase for months or years before symptoms emerge. T. b. rhodesiense, is the acute form of the disease but has a much more limited range. It is found in southern and eastern Africa; its infection emerges in a few weeks and is more virulent and faster developing. According to recent estimates, the disability adjusted life years (9 to 10 years) (DALYs) lost due to sleeping sickness are 2.0 milliondiagnosis rests upon demonstrating trypanosomes by microscopic examination of chancre fluid, lymph node aspirates, blood, bone marrow, or, in the late stages of infection, cerebrospinal fluid. A wet preparation should be examined for the motile trypanosomes, and in addition a smear should be fixed, stained with Giemsa (or Field), Concentration techniques can be used prior to microscopic examinationblood samples, include centrifugation followed by examination of the buffy coat; mini anion-exchange/centrifugation; and the Quantitative Buffy Coat (QBC) technique. For other samples such as spinal fluid, concentration techniques include centrifugation followed by examination of the sediment. Isolation of the parasite by inoculation of rats or mice is a sensitive method, but its use is limited to T. b. rhodesiense. Antibody detection has sensitivity and specificity that are too variable for clinical decisions. In addition, in infections with T. b. rhodesiense, seroconversion occurs after the onset of clinical symptoms and thus is of limited use.

influenza Influenza, commonly known as the flu, is an infectious disease of birds and mammals caused by RNA viruses of the family Orthomyxoviridae (the influenza viruses). The name influenza comes from the Italian: influenza, meaning "influence", (Latin: influentia). In humans, common symptoms of the disease are chills and fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort. In more serious cases, influenza causes pneumonia, which can be fatal, particularly in young children and the elderly. Although it is sometimes confused with the common cold, influenza is a much more severe disease and is caused by a different type of virus.[2] Influenza can produce nausea and vomiting, especially in children,[1] but these symptoms are more characteristic of the unrelated gastroenteritis, which is sometimes called "stomach flu" or "24-hour flu"

Typically, influenza is transmitted from infected mammals through the air by coughs or sneezes, creating aerosols containing the virus, and from infected birds through their droppings. Influenza can also be transmitted by saliva, nasal secretions, feces and blood. Infections also occur through contact with these body fluids or with contaminated surfaces. Flu viruses can remain infectious for about one week at human body temperature, over 30 days at 0 °C (32 °F), and for much longer periods at very low temperatures. Most influenza strains can be inactivated easily by disinfectants and detergents

Flu spreads around the world in seasonal epidemics, resulting in the deaths of hundreds of thousands annually — millions in pandemic years . Three influenza pandemics occurred in the 20th century and killed tens of millions of people, with each of these pandemics being caused by the appearance of a new strain of the virus in humans. Often, these new strains result from the spread of an existing flu virus to humans from other animal species. A deadly avian strain named H5N1 has posed the greatest risk for a new influenza pandemic since it first killed humans in Asia in the 1990s. Fortunately, this virus has not mutated to a form that spreads easily between people.

Vaccinations against influenza are usually given to people in developed countries with a high risk of contracting the disease and to farmed poultry. The most common human vaccine is the trivalent influenza vaccine that contains purified and inactivated material from three viral strains. Typically, this vaccine includes material from two influenza A virus subtypes and one influenza B virus strain. A vaccine formulated for one year may be ineffective in the following year, since the influenza virus changes rapidly over time, and different strains become dominant. Antiviral drugs can be used to treat influenza, with neuraminidase inhibitors being particularly effective.

The first significant step towards preventing influenza was the development in 1944 of a killed-virus vaccine for influenza by Thomas Francis, Jr.. This built on work by Frank Macfarlane Burnet, who showed that the virus lost virulence when it was cultured in fertilized hen's eggs Application of this observation by Francis allowed his group of researchers at the University of Michigan to develop the first influenza vaccine, with support from the U.S. Army.[27] The Army was deeply involved in this research due to its experience of influenza in World War I, when thousands of troops were killed by the virus in a matter of months.

AIDS Acquired immune deficiency syndrome or acquired immunodeficiency syndrome (AIDS or Aids) is a set of symptoms and infections resulting from the damage to the human immune system caused by the human immunodeficiency virus (HIV).[1] This condition progressively reduces the effectiveness of the immune system and leaves individuals susceptible to opportunistic infections and tumors. HIV is transmitted through direct contact of a mucous membrane or the bloodstream with a bodily fluid containing HIV, such as blood, semen, vaginal fluid, preseminal fluid, and breast milk.[2][3] This transmission can involve anal, vaginal or oral sex, blood transfusion, contaminated hypodermic needles, exchange between mother and baby during pregnancy, childbirth, or breastfeeding, or other exposure to one of the above bodily fluids.

AIDS is now a pandemic.[4] In 2007, an estimated 33.2 million people lived with the disease worldwide, and it killed an estimated 2.1 million people, including 330,000 children.[5] Over three-quarters of these deaths occurred in sub-Saharan Africa,[5] retarding economic growth and destroying human capital.[6] Most researchers believe that HIV originated in sub-Saharan Africa during the twentieth century.[7] AIDS was first recognized by the U.S. Centers for Disease Control and Prevention in 1981 and its cause, HIV, identified by American and French scientists in the early 1980s.[8]

Although treatments for AIDS and HIV can slow the course of the disease, there is currently no vaccine or cure. Antiretroviral treatment reduces both the mortality and the morbidity of HIV infection, but these drugs are expensive and routine access to antiretroviral medication is not available in all countries.[9] Due to the difficulty in treating HIV infection, preventing infection is a key aim in controlling the AIDS epidemic, with health organizations promoting safe sex and needle-exchange programmes in attempts to slow the spread of the virus.

The symptoms of AIDS are primarily the result of conditions that do not normally develop in individuals with healthy immune systems. Most of these conditions are infections caused by bacteria, viruses, fungi and parasites that are normally controlled by the elements of the immune system that HIV damages. Opportunistic infections are common in people with AIDS. HIV affects nearly every organ system. People with AIDS also have an increased risk of developing various cancers such as Kaposi's sarcoma, cervical cancer and cancers of the immune system known as lymphomas. Additionally, people with AIDS often have systemic symptoms of infection like fevers, sweats (particularly at night), swollen glands, chills, weakness, and weight loss. The specific opportunistic infections that AIDS patients develop depend in part on the prevalence of these infections in the geographic area in which the patient lives

The first two diseases acturally fit into the discription quite well however the 2nd two do not as they are infact pathogenic viruses.Where as you could say that microbial pathogens can be defined as “an organism that can cause disease this infact is not a good definition because noty all pathogens that cause disease are micriobes , not all microes cause disease and some pathogenic microes do not cause disease at all.