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History of pathology
The history of pathology can be traced to the earliest application of the scientific method to the field of medicine, a development which occurred in the Middle East during the Islamic Golden Age and in Western Europe during the Italian Renaissance. The first physician known to have made postmortem dissections was the Arabian physician Avenzoar (1091–1161). Rudolf Virchow (1821-1902) is generally recognized to be the father of microscopic pathology. Most early pathologists were also practicing physicians or surgeons.
General pathology
General pathology, also called investigative pathology, experimental pathology or theoretical pathology, is a broad and complex scientific field which seeks to understand the mechanisms of injury to cells and tissues, as well as the body's means of responding to and repairing injury. Areas of study include cellular adaptation to injury, necrosis, inflammation, wound healing and neoplasia. It forms the foundation of pathology, the application of this knowledge to diagnose diseases in humans and animals.
The term "general pathology" is also used to describe the practice of both anatomical and clinical pathology.
Pathology as a medical specialty
Pathologists are physicians who diagnose and characterize disease in living patients by examining biopsies or bodily fluid. The vast majority of cancer diagnoses are made or confirmed by a pathologist. Pathologists may also conduct autopsies to investigate causes of death. Pathology is a core discipline of medical school and many pathologists are also teachers. As managers of medical laboratories, pathologists play an important role in the development of Laboratory information systems. Although the medical practice of pathology grew out the tradition of investigative pathology, most modern pathologists do not perform original research.
Pathology is a unique medical specialty in that pathologists typically do not see patients directly, but rather serve as consultants to other physicians (often referred to as "clinicians" within the pathology community). To be licensed, candidates must complete medical training, an approved residency program and be certified by an appropriate body. In the US, certification is by the American Board of Pathology. The organization of subspecialties within pathology vary between nations but usually include anatomical pathology and clinical pathology.
Anatomical pathology
Anatomical pathology (Commonwealth) or Anatomic pathology (U.S.) is a medical specialty that is concerned with the diagnosis of disease based on the gross, microscopic, and molecular examination of organs, tissues, and whole bodies (autopsy). The anatomical pathologist reports to doctors; he (she) does not usually see patients.
Anatomical pathology is itself divided in subspecialties, the main ones being surgical pathology, cytopathology and forensic pathology. To be licensed to practice anatomical pathology, one has to complete medical school, an approved residency program and be certified. In the U.S., the American board of Pathology certifies pathologists.
Anatomical pathology is one of two branches of pathology, the other being clinical pathology, the diagnosis of disease through the laboratory analysis of bodily fluids. Often, pathologists practice both anatomical and clinical pathology, a combination known as general pathology. Similar specialties exist in veterinary pathology.
Clinical pathology
Clinical pathology is a medical specialty that is concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids such as blood and urine, using the tools of chemistry, microbiology, hematology and molecular pathology. Clinical pathologist work in close collaboration with medical technologists.
Clinical pathology is itself divided in subspecialties, the main ones being clinical chemistry, clinical hematology/blood banking and clinical microbiology.
Clinical pathology is one of the two major divisions of pathology, the other being anatomical pathology. Often, pathologists practice both anatomical and clinical pathology, a combination known as general pathology. Similar specialties exist in veterinary pathology.
Veterinary pathology
Veterinary pathologists are doctors of veterinary medicine who specialise in the diagnosis of diseases through the examination of animal tissue and body fluids. Like for medical pathology, veterinary pathology is divided in two branches, anatomical pathology and clinical pathology. Veterinary pathologists are critical participants in the drug development process.
Plant pathology
For the journal, see Plant Pathology (journal).
Plant pathology (also called phytopathology) is the scientific study of plant diseases caused by pathogens (infectious diseases) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are insects, mites, vertebrate or other pests that affect plant health by consumption of plant tissues. Plant pathology also involves the study of the identification, etiology, disease cycle, economic impact, epidemiology, how plant diseases affect humans and animals, pathosystem genetics and management of plant diseases. </onlyinclude>
Plant pathogens
The "Disease triangle" is a central concept of plant pathology for infectious diseases[1] . It is based on the principle that disease is the result of an interaction between a host, a pathogen, and environment condition.
Fungi
The majority of phytopathogenic fungi belong to the Ascomycetes and the Basidiomycetes.
The fungi reproduce both sexually and asexually via the production of spores. These spores may be spread long distances by air or water, or they may be soil bourne. Many soil bourne spores, normally zoospores and capable of living saprotrophically, carrying out the first part of their lifecycle in the soil.
Fungal diseases can be controlled through the use of fungicides in agriculture, however new races of fungi often evolve that are resistant to various fungicides.
Significant fungal plant pathogens
Ascomycetes
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- Fusarium spp.
- Thielaviopsis spp. (Causal agents of: canker rot, black root rot, Thielaviopsis root rot)
- Verticillium spp.
- Magnaporthe grisea (T.T. Hebert) M.E. Barr; causes blast of rice and gray leaf spot in turfgrasses
Basidiomycetes
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- Rhizoctonia spp.
- Phakospora pachyrhizi Sydow; causes Soybean rust
- Puccinia spp.; causal agents of severe rusts of virtually all cereal grains and cultivated grasses
Oomycetes
The oomycetes are fungal-like organisms that until recently used to be mistaken for fungi. They include some of the most destructive plant pathogens including the genus Phytophthora which includes the casual agents of potato late blight and sudden oak death.
Despite not being closely related to the fungi, the oomycetes have developed very similar infection strategies and so many plant pathologists group them with fungal pathogens.
Significant oomycete plant pathogens
- Pythium spp.
- Phytophthora spp.; including the causal agent of the Great Irish Famine (1845-1849)
Rice blast is hemibiotrophic
Bacteria
Most bacteria that are associated with plants are actually saprotrophic, and do no harm to the plant itself. However, a small number, around 100 species, are able to cause disease. Bacterial diseases are much more prevalent in sub-tropical and tropical regions of the world.
Most plant pathogenic bacteria are rod shaped (bacilli). In order to be able to colonise the plant they have specific pathogenicity factors. There are 4 main bacterial pathogenicity factors:
1. Cell wall degrading enzymes - used to break down the plant cell wall in order to release the nutrients inside. Used by pathogens such as Erwinia to cause soft rot.
2. Toxins These can be non-host specific, and damage all plants, or host specific and only cause damage on a host plant.
3. Phytohormones - for example Agrobacterium changes the level of Auxin to cause tumours.
4. Exopolysaccharides - these are produced by bacteria and block xylem vessels, often leading to the death of the plant.
Bacteria control the production of pathogenicity factors via quorum sensing.
Significant bacterial plant pathogens
- Proteobacteria
- Xanthomonas spp.
- Pseudomonas spp.
Phytoplasmas ('Mycoplasma-like organisms') and spiroplasmas
Phytoplasma and Spiroplasma are a genre of bacteria that lack cell walls, and are related to the mycoplasmas which are human pathogens. Together they are referred to as the mollicutes. They also tend to have smaller genomes than true bacteria. They are normally transmitted by sap-sucking insects, being transferred into the plants phloem where it reproduces.
Viruses, viroids and virus-like organisms
There are many types of plant virus, and some are even asymptomatic. Normally plant viruses only cause a loss of yield. Therefore it is not economically viable to try to control them, the exception being when they infect perennial species, such as fruit trees.
Most plant viruses have small, single stranded RNA genomes. These genomes may only encode 3 or 4 proteins: a replicase, a coat protein, a movement protein to allow cell to cell movement and sometimes a protein that allows transmission by a vector.
Plant viruses must be transmitted from plant to plant by a vector. This is normally an insect, but some fungi, nematodes and protozoa have been shown to be viral vectors.
Nematodes
Nematodes are small, multicelluar wormlike creatures. Many live freely in the soil, but there are some species which parasitize plant roots. They are mostly a problem in tropical and subtropical regions of the world, where they may infect crops. Root knot nematodes have quite a large host range, whereas cyst nematodes tend to only be able to infect a few species. Nematodes are able to cause radical changes in root cells in order to facilitate their lifestyle.
Protozoa
There are a few examples of plant diseases caused by protozoa. They are transmitted as zoospores which are very durable, and may be able to survive in a resting state in the soil for many years. They have also been shown to transmit plant viruses.
When the motile zoospores come into contact with a root hair they produce a plasmodium and invade the roots.
Parasitic plants
Parasitic plants such as mistletoe and dodder are included in the study of phytopathology. Dodder, for example, is used as a conduit for the transmission of virues or virus-like agents from a host plant to either a plant that is not typically a host or for an agent that is not graft-transmissible.
Physiological plant disorders
Significant abiotic disorders can be caused by:
- Natural
- Man-made (arguably not abiotic, but usually regarded as such)
Epidemiology
Management
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Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion. (January 2007) |
- Quarantine
- Cultural
- Plant resistance
- Chemical
- Biological
- Integrated
See also
- American Phytopathological Society
- Biological Control
- British Society for Plant Pathology
- burl
- Common names of plant diseases
- Fungicides
- Gene-for-gene relationship
- Global Plant Clinic
- Herbivory
- List of phytopathology journals
- Mycology
- Pesticide
- Plant disease forecasting
- QoI
- Phytoplasma
- Plant virus
- Strobilurins
- Stunt
References
- ^ George N. Agrios (1997) Plant Pathology fourth edition, Academic Press. New York.
Further reading
| Part of a series on Horticulture and Gardening |
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| Gardening |
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Gardening • Garden • Botanical garden • Arboretum • Botany • Plant |
| Horticulture |
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Horticulture • Agriculture • Urban agriculture • City farm • Organic farming • Herb farm • Hobby farm • Intercropping • Farm |
| Customs |
| Plant protection |
External links
- American Phytopathological Society
- British Society for Plant Pathology
- Plant Health Progress, Online journal of applied plant pathology
- Pacific Northwest Fungi, online mycology journal with papers on fungal plant pathogens
- Rothamsted Plant Pathogen Interactions Department
- Grape Virology
Notes
See also
External links
- Association of Clinical Biochemistry (UK)
- American Society for Investigative Pathology
- American Society of Cytopathology
- British Neuropathological Society
- Case Records of the Massachusetts General Hospital - Clinicopathological Conference
- College of American Pathologists
- Flickr group: Pathology and Lab Medicine: numerous photos illustrating the work of pathologists.
- HistoPathology Atlas
- humpath.com (Atlas in Human Pathology)
- Immunohistochemistry protocols and troubleshooting
- Mybiopsy.org
- Pathological Society of Great Britain and Ireland
- Royal College of Pathologists (UK)
- Royal College of Pathologists of Australasia (Australia & Oceania)
- Sullivan Nicolaides Pathology - Leading Australian Pathology Laboratory.
- United States and Canadian Academy of Pathology
- WebPath: The Internet Pathology Laboratory for Medical Education
- Pathtalk.org - A community weblog about pathology-related topics.
- What is a Pathologist? - a perspective from UK pathologist Fraser Charlton.
- Pathologypics - an interactive community-driven histology atlas
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