|
|
| (23 intermediate revisions by 9 users not shown) |
| Line 1: |
Line 1: |
| | __NOTOC__ |
| {{Allergy}} | | {{Allergy}} |
| {{CMG}} | | {{CMG}} {{AE}} {{MMT}} |
| __NOTOC__
| | |
| ==Overview== | | ==Overview== |
| Allergy causation can be placed in two general categories, namely [[Host (biology)|host]] and environmental factors. Biological factors are strongly familial whereas environmental factors very largely on the type of living environment. More common in industrialized countries than in countries that are more traditional or agricultural, and there is a higher rate of allergic disease in urban populations versus rural populations. | | [[Allergy]] may be caused by genetic, environmental and infectious factors. |
| | |
| | ==Cause[[Allergy]]== |
|
| |
|
| ==Cause==
| | [[Allergy]] may be caused by genetic, environmental and infectious factors. Anaphylaxis is a life-threatening cause of [[Allergy]]. |
| Allergy causation can be placed in two general categories, namely [[Host (biology)|host]] and environmental factors. Host factors include [[heredity]], [[gender|sex]], [[Race (classification of human beings)|race]] and age, with heredity being by far the most important. There are recent increases in the incidence of allergic disorders, however, that cannot be explained by genetic factors alone. The four main candidate environmental factors are alterations in exposure to [[infectious disease]]s during early childhood, environmental pollution, allergen levels, and [[Diet (nutrition)|dietary]] changes.<ref name=Janeway>{{cite book | last = Janeway | first = Charles | authorlink = Charles Janeway | coauthors = Paul Travers, Mark Walport, and Mark Shlomchik | title = Immunobiology; Fifth Edition | publisher = Garland Science | date= 2001 | location = New York and London| pages = e-book | url = http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=imm.TOC&depth=10| doi = | id = ISBN 0-8153-4101-6}}.</ref>
| |
|
| |
|
| ===Genetic basis=== | | ===Common Causes=== |
| Allergic diseases are strongly familial: [[Identical_twins#Identical_twins|identical twins]] are likely to have the same allergic diseases about 70% of the time; the same allergy occurs about 40% of the time in [[twin#Fraternal_twins|non-identical twins]].<ref>{{cite journal |author=Galli SJ |title=Allergy |journal=Curr. Biol. |volume=10 |issue=3 |pages=R93–5 |year=2000 |pmid=10679332 |doi=}}</ref> Allergic parents are more likely to have allergic children,<ref name=DeSwert>{{cite journal |author=De Swert LF |title=Risk factors for allergy |journal=Eur. J. Pediatr. |volume=158 |issue=2 |pages=89–94 |year=1999 |pmid=10048601 |doi=}}</ref> and their allergies are likely to be stronger than those from non-allergic parents. However some allergies are not consistent along [[Genealogy|genealogies]]; parents who are allergic to peanuts, may have children who are allergic to ragweed, or siblings that are allergic to different things. It seems that the likelihood of developing allergies is [[Heredity|inherited]] and due to some irregularity in the way the immune system works, but the specific allergen, which causes the development of an allergy, is not.<ref name=DeSwert/>
| | Common genetic causes of [[allergy]] may include<ref name=Janeway>{{cite book | last = Janeway | first = Charles | authorlink = Charles Janeway | coauthors = Paul Travers, Mark Walport, and Mark Shlomchik | title = Immunobiology; Fifth Edition | publisher = Garland Science | date= 2001 | location = New York and London| pages = e-book | url = http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=imm.TOC&depth=10| doi = | id = ISBN 0-8153-4101-6}}.</ref><ref>{{cite journal |author=Galli SJ |title=Allergy |journal=Curr. Biol. |volume=10 |issue=3 |pages=R93–5 |year=2000 |pmid=10679332 |doi=}}</ref> : |
| | *HLA class 2 genes |
| | *Th2 cytokine genes |
| | *Degranulation and pro-inflammatory responses |
|
| |
|
| The risk of allergic sensitization and the development of allergies varies with age, with young children most at risk.<ref name=Croner>{{cite journal |author=Croner S |title=Prediction and detection of allergy development: influence of genetic and environmental factors |journal=J. Pediatr. |volume=121 |issue=5 Pt 2 |pages=S58–63 |year=1992 |pmid=1447635 |doi=}}</ref> Several studies have shown that IgE levels are highest in childhood and fall rapidly between the ages of 10 and 30 years.<ref name=Croner/> The peak prevalence of hay fever is highest in children and young adults and the incidence of asthma is highest in children under 10.<ref>Jarvis D, Burney P (1997) Epidemiology of atopy and atopic disease In: Kay AB (ed) Allergy and allergic diseases, vol 2. Blackwell Science London, pp 1208–1224</ref> Overall, boys have a higher risk of developing allergy than girls,<ref name=DeSwert/> although for some diseases, namely asthma in young adults, females are more likely to be affected.<ref>{{cite journal |author=Anderson HR, Pottier AC, Strachan DP |title=Asthma from birth to age 23: incidence and relation to prior and concurrent atopic disease |journal=Thorax |volume=47 |issue=7 |pages=537–42 |year=1992 |pmid=1412098 |doi=}}</ref> Sex differences tend to decrease in adulthood.<ref name=DeSwert/> Ethnicity may play a role in some allergies, however racial factors have been difficult to separate from environmental influences and changes due to migration.<ref name=DeSwert/> Interestingly, with regards to asthma, it has been suggested that different [[Locus (genetics)|genetic loci]] are responsible for asthma in people of Caucasian, Hispanic, Asian, and African origins.<ref>{{cite journal |author=Barnes KC, Grant AV, Hansel NN, Gao P, Dunston GM |title=African Americans with asthma: genetic insights |url= http://pats.atsjournals.org/cgi/content/full/4/1/58 |journal=Proc Am Thorac Soc |volume=4 |issue=1 |pages=58–68 |year=2007 |pmid=17202293 |doi=10.1513/pats.200607-146JG}}</ref>
| | Common environmental causes of [[allergy]] may include<ref name = cooper04>{{cite journal |author=Cooper PJ |title=Intestinal worms and human allergy |journal=Parasite Immunol. |volume=26 |issue=11-12 |pages=455–67 |year=2004 |pmid=15771681 |doi=10.1111/j.0141-9838.2004.00728.x}}</ref>: |
| | *Exposure to allergen: |
| | **Foods( Peanut, soy, eggs, shellfish), Drugs (Antibiotics, NSAIDS, Aspirin, Sulfur containing medications etc), Insects(honeybee, bumblebee, Hornet, fire ant etc), Contrast allergy, Latex, Exercise, vaccinations |
| | *Environmental pollution |
| | *Alteration of microbiota |
| | *Agricultural etiology |
|
| |
|
| ===Environmental factors===
| |
| International differences have been associated with the number of individuals within a population that suffer from allergy. Allergic diseases are more common in industrialized countries than in countries that are more traditional or agricultural, and there is a higher rate of allergic disease in urban populations versus rural populations, although these differences are becoming less defined.<ref name = cooper04>{{cite journal |author=Cooper PJ |title=Intestinal worms and human allergy |journal=Parasite Immunol. |volume=26 |issue=11-12 |pages=455–67 |year=2004 |pmid=15771681 |doi=10.1111/j.0141-9838.2004.00728.x}}</ref>
| |
|
| |
|
| Exposure to allergens, especially in early life, is an important [[Risk factor|risk factor]] for allergy. Alterations in exposure to [[microorganism]]s is the most plausible explanation, at present, for the increase in [[Atopy|atopic allergy]].<ref name= Janeway/> Since children that live in large families or overcrowded households, or attend day care, have a reduced incidence of allergic disease, a relationship has been proposed between exposures to [[bacteria]] and [[virus]]es during childhood, and protection against the development of allergy, which has been called – the "[[hygiene hypothesis]]".<ref name = cooper04/> Exposure to [[endotoxin]] and other components of bacteria may reduce atopic diseases.<ref name="pmid12063508">{{cite journal |author=von Mutius E |title=Environmental factors influencing the development and progression of pediatric asthma |journal=J. Allergy Clin. Immunol. |volume=109 |issue=6 Suppl |pages=S525–32 |year=2002 |pmid=12063508 |doi=}}</ref> Endotoxin exposure reduces release of inflammatory [[cytokine]]s such as [[tumor necrosis factor alpha|TNF-α]], [[interferon-gamma|IFNγ]], [[interleukin-10]], and [[interleukin-12]] from white blood cells ([[leukocytes]]) that circulate in the [[blood]].<ref name="pmid12239255">{{cite journal |author=Braun-Fahrländer C, Riedler J, Herz U, ''et al'' |title=Environmental exposure to endotoxin and its relation to asthma in school-age children |journal=N. Engl. J. Med. |volume=347 |issue=12 |pages=869–77 |year=2002 |pmid=12239255 |doi=10.1056/NEJMoa020057}}</ref> Certain microbe-sensing [[protein]]s, known as [[Toll-like receptor]]s, found on the surface of cells in the body are also thought to be involved in these processes.<ref>{{cite journal |author=Garn H, Renz H |title=Epidemiological and immunological evidence for the hygiene hypothesis |journal=Immunobiology |volume=212 |issue=6 |pages=441–52 |year=2007 |pmid=17544829 |doi=10.1016/j.imbio.2007.03.006}}</ref>
| |
|
| |
|
| Gutworms and similar parasites are present in untreated drinking water in developing countries, and were present in the water of developed countries until the routine [[chlorination]] and purification of drinking water supplies.<ref>{{cite journal |author=Macpherson CN, Gottstein B, Geerts S |title=Parasitic food-borne and water-borne zoonoses |journal=Rev. - Off. Int. Epizoot. |volume=19 |issue=1 |pages=240–58 |year=2000 |pmid=11189719 |doi=}}</ref> Recent research has shown that some common [[parasite]]s, such as [[Intestinal parasite|intestinal worm]]s (e.g. [[hookworm]]s), secrete chemicals into the gut wall (and hence the bloodstream) that [[immunosuppressant|suppress]] the immune system and prevent the body from attacking the parasite.<ref>{{cite journal |author=Carvalho EM, Bastos LS, Araújo MI |title=Worms and allergy |journal=Parasite Immunol. |volume=28 |issue=10 |pages=525–34 |year=2006 |pmid=16965288 |doi=10.1111/j.1365-3024.2006.00894.x}}</ref> This gives rise to a new slant on the hygiene hypothesis theory — that co-evolution of man and parasites has led to an immune system that only functions correctly in the presence of the parasites. Without them, the immune system becomes unbalanced and oversensitive.<ref>{{cite journal |author=Yazdanbakhsh M, Kremsner PG, van Ree R |title=Allergy, parasites, and the hygiene hypothesis |journal=Science |volume=296 |issue=5567 |pages=490–4 |year=2002 |pmid=11964470 |doi=10.1126/science.296.5567.490}}</ref> In particular, research suggests that allergies may coincide with the delayed establishment of [[gut flora]] in [[infant]]s.<ref name="pmid17382394">{{cite journal |author=Emanuelsson C, Spangfort MD |title=Allergens as eukaryotic proteins lacking bacterial homologues |journal=Mol. Immunol. |volume=44 |issue=12 |pages=3256–60 |year=2007 |pmid=17382394 |doi=10.1016/j.molimm.2007.01.019}}</ref> However, the research to support this theory is conflicting, with some studies performed in China and Ethiopia showing an increase in allergy in people infected with intestinal worms.<ref name = cooper04/> Clinical trials have been initiated to test the effectiveness of certain worms in treating some allergies.<ref name = falcone05>{{cite journal |author=Falcone FH, Pritchard DI |title=Parasite role reversal: worms on trial |journal=Trends Parasitol. |volume=21 |issue=4 |pages=157–60 |year=2005 |pmid=15780835 |doi=10.1016/j.pt.2005.02.002}}</ref> It may be that the term 'parasite' could turn out to be inappropriate, and in fact a hitherto unsuspected [[symbiosis]] is at work.<ref name = falcone05/>
| | |
| For more information on this topic, see [[Helminthic therapy]].
| | Common infectious causes of [[allergy]] may include<ref>{{cite journal |author=Macpherson CN, Gottstein B, Geerts S |title=Parasitic food-borne and water-borne zoonoses |journal=Rev. - Off. Int. Epizoot. |volume=19 |issue=1 |pages=240–58 |year=2000 |pmid=11189719 |doi=}}</ref><ref>{{cite journal |author=Carvalho EM, Bastos LS, Araújo MI |title=Worms and allergy |journal=Parasite Immunol. |volume=28 |issue=10 |pages=525–34 |year=2006 |pmid=16965288 |doi=10.1111/j.1365-3024.2006.00894.x}}</ref>: |
| | *Intestinal parasites |
| | |
| | ===Less Common Causes=== |
| | Less common causes of [[allergy]] include: |
| | *[[PRR]] Genes |
| | *[[Th]] differentiation |
| | *[[Hormonal imbalance]] |
| | *[[Emotional]] stress |
| | *Chronic disease flare up |
| | *Excessive hygiene |
| | *Nutritional deficiencies |
|
| |
|
| ==References== | | ==References== |
| {{reflist|2}} | | {{Reflist|2}} |
|
| |
|
| [[Category:Allergology]] | | [[Category:Dermatology]] |
| | [[Category:Emergency medicine]] |
| [[Category:Immunology]] | | [[Category:Immunology]] |
| [[Category:Dermatology]] | | [[Category:Otolaryngology]] |
| | [[Category:Pediatrics]] |
| | [[Category:Disease]] |
| [[Category:Pulmonology]] | | [[Category:Pulmonology]] |
| | [[Category:Allergology]] |
| | [[Category:Ophthalmology]] |
| [[Category:Immune system]] | | [[Category:Immune system]] |
|
| |
| {{WikiDoc Help Menu}}
| |
| {{WikiDoc Sources}}
| |