Malaria risk factors: Difference between revisions
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{{Malaria}} | {{Malaria}} | ||
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==Overview== | ==Overview== | ||
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Persons who have the [[sickle cell trait]] (heterozygotes for the abnormal hemoglobin gene HbS) are relatively protected against [[P. falciparum malaria]] and thus enjoy a biologic advantage. Because [[P. falciparum]] malaria has been a leading cause of death in Africa since remote times, the sickle cell trait is now more frequently found in Africa and in persons of African ancestry than in other population groups. | Persons who have the [[sickle cell trait]] (heterozygotes for the abnormal hemoglobin gene HbS) are relatively protected against [[P. falciparum malaria]] and thus enjoy a biologic advantage. Because [[P. falciparum]] malaria has been a leading cause of death in Africa since remote times, the sickle cell trait is now more frequently found in Africa and in persons of African ancestry than in other population groups. | ||
In general, the prevalence of hemoglobin-related disorders and other blood cell dyscrasias, such as [[Hemoglobin C]], the [[thalassemia]]s and [[G6PD deficiency]], are more prevalent in malaria endemic areas and are thought to provide protection from malarial disease.<ref name= | In general, the prevalence of hemoglobin-related disorders and other blood cell dyscrasias, such as [[Hemoglobin C]], the [[thalassemia]]s and [[G6PD deficiency]], are more prevalent in malaria endemic areas and are thought to provide protection from malarial disease.<ref name=Factors>Factors. CDC.gov Accessed on 7/24/2014 </ref> | ||
====Duffy Blood Group==== | ====Duffy Blood Group==== | ||
Persons who are negative for the [[Duffy blood group]] have [[red blood cell]]s that are resistant to infection by [[P. vivax]]. Since the majority of Africans are Duffy negative, [[P. vivax]] is rare in Africa south of the Sahara, especially West Africa. In that area, the niche of [[P. vivax]] has been taken over by [[P. ovale]], a very similar parasite that does infect Duffy-negative persons.<ref name= | Persons who are negative for the [[Duffy blood group]] have [[red blood cell]]s that are resistant to infection by [[P. vivax]]. Since the majority of Africans are Duffy negative, [[P. vivax]] is rare in Africa south of the Sahara, especially West Africa. In that area, the niche of [[P. vivax]] has been taken over by [[P. ovale]], a very similar parasite that does infect Duffy-negative persons.<ref name=Factors>Factors. CDC.gov Accessed on 7/24/2014 </ref> | ||
====Other Genetic Factors==== | ====Other Genetic Factors==== | ||
Other genetic factors related to [[red blood cell]]s also influence [[malaria]], but to a lesser extent. Various genetic determinants (such as the "[[HLA complex]]," which plays a role in control of immune responses) may equally influence an individual's risk of developing severe malaria.<ref name= | Other genetic factors related to [[red blood cell]]s also influence [[malaria]], but to a lesser extent. Various genetic determinants (such as the "[[HLA complex]]," which plays a role in control of immune responses) may equally influence an individual's risk of developing severe malaria.<ref name=Factors>Factors. CDC.gov Accessed on 7/24/2014 </ref> | ||
===Children=== | ===Children=== | ||
* In areas with high [[P. falciparum]] transmission (most of Africa south of the Sahara), newborns will be protected during the first few months of life presumably by maternal antibodies transferred to them through the placenta. As these antibodies decrease with time, these young children become vulnerable to disease and death by malaria. If they survive repeated infections to an older age (2-5 years) they will have reached a protective semi-immune status. Thus in high transmission areas, young children are a major risk group and are targeted preferentially by malaria control interventions.<ref name= | * In areas with high [[P. falciparum]] transmission (most of Africa south of the Sahara), newborns will be protected during the first few months of life presumably by maternal antibodies transferred to them through the placenta. As these antibodies decrease with time, these young children become vulnerable to disease and death by malaria. If they survive repeated infections to an older age (2-5 years) they will have reached a protective semi-immune status. Thus in high transmission areas, young children are a major risk group and are targeted preferentially by malaria control interventions.<ref name=Factors>Factors. CDC.gov Accessed on 7/24/2014 </ref> | ||
*In areas with lower transmission (such as Asia and Latin America), infections are less frequent and a larger proportion of the older children and adults have no protective immunity. In such areas, malaria disease can be found in all age groups, and epidemics can occur.<ref name= | *In areas with lower transmission (such as Asia and Latin America), infections are less frequent and a larger proportion of the older children and adults have no protective immunity. In such areas, malaria disease can be found in all age groups, and epidemics can occur.<ref name=Factors>Factors. CDC.gov Accessed on 7/24/2014 </ref> | ||
===Travel=== | ===Travel=== | ||
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===Pregnancy=== | ===Pregnancy=== | ||
[[Pregnancy]] decreases [[immunity]] against many infectious diseases. Women who have developed protective immunity against [[P. falciparum]] tend to lose this protection when they become pregnant (especially during the first and second pregnancies). Malaria during pregnancy is harmful not only to the mothers but also to the unborn children. The latter are at greater risk of being delivered prematurely or with low birth weight, with consequently decreased chances of survival during the early months of life. For this reason pregnant women are also targeted (in addition to young children) for protection by malaria control programs in endemic countries.<ref name= | [[Pregnancy]] decreases [[immunity]] against many infectious diseases. Women who have developed protective immunity against [[P. falciparum]] tend to lose this protection when they become pregnant (especially during the first and second pregnancies). Malaria during pregnancy is harmful not only to the mothers but also to the unborn children. The latter are at greater risk of being delivered prematurely or with low birth weight, with consequently decreased chances of survival during the early months of life. For this reason pregnant women are also targeted (in addition to young children) for protection by malaria control programs in endemic countries.<ref name=Factors>Factors. CDC.gov Accessed on 7/24/2014 </ref> | ||
===Behavioral Factors=== | ===Behavioral Factors=== | ||
Human behavior, often dictated by social and economic reasons, can influence the risk of malaria for individuals and communities. For example:<ref name= | Human behavior, often dictated by social and economic reasons, can influence the risk of malaria for individuals and communities. For example:<ref name=Factors>Factors. CDC.gov Accessed on 7/24/2014 </ref> | ||
* Poor rural populations in malaria-endemic areas often cannot afford the housing and bed nets that would protect them from exposure to mosquitoes. These persons often lack the knowledge to recognize malaria and to treat it promptly and correctly. Often, cultural beliefs result in use of traditional, ineffective methods of treatment. | * Poor rural populations in malaria-endemic areas often cannot afford the housing and bed nets that would protect them from exposure to mosquitoes. These persons often lack the knowledge to recognize malaria and to treat it promptly and correctly. Often, cultural beliefs result in use of traditional, ineffective methods of treatment. | ||
Revision as of 18:27, 24 July 2014
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Rim Halaby, M.D. [2]
Overview
Common risk factors for malaria include thalassemias and Duffy antigen. Sickle cell disease and G6PD deficiency are known to confer protection against malaria and have a particularly high rate of incidence in tropical populations which are at a higher risk for contracting malaria.
Risk Factors
Genetic Factors
Biologic characteristics present from birth can protect against certain types of malaria. Two genetic factors, both associated with human red blood cells, have been shown to be epidemiologically important.
Sickle Cell Trait
Persons who have the sickle cell trait (heterozygotes for the abnormal hemoglobin gene HbS) are relatively protected against P. falciparum malaria and thus enjoy a biologic advantage. Because P. falciparum malaria has been a leading cause of death in Africa since remote times, the sickle cell trait is now more frequently found in Africa and in persons of African ancestry than in other population groups.
In general, the prevalence of hemoglobin-related disorders and other blood cell dyscrasias, such as Hemoglobin C, the thalassemias and G6PD deficiency, are more prevalent in malaria endemic areas and are thought to provide protection from malarial disease.[1]
Duffy Blood Group
Persons who are negative for the Duffy blood group have red blood cells that are resistant to infection by P. vivax. Since the majority of Africans are Duffy negative, P. vivax is rare in Africa south of the Sahara, especially West Africa. In that area, the niche of P. vivax has been taken over by P. ovale, a very similar parasite that does infect Duffy-negative persons.[1]
Other Genetic Factors
Other genetic factors related to red blood cells also influence malaria, but to a lesser extent. Various genetic determinants (such as the "HLA complex," which plays a role in control of immune responses) may equally influence an individual's risk of developing severe malaria.[1]
Children
- In areas with high P. falciparum transmission (most of Africa south of the Sahara), newborns will be protected during the first few months of life presumably by maternal antibodies transferred to them through the placenta. As these antibodies decrease with time, these young children become vulnerable to disease and death by malaria. If they survive repeated infections to an older age (2-5 years) they will have reached a protective semi-immune status. Thus in high transmission areas, young children are a major risk group and are targeted preferentially by malaria control interventions.[1]
- In areas with lower transmission (such as Asia and Latin America), infections are less frequent and a larger proportion of the older children and adults have no protective immunity. In such areas, malaria disease can be found in all age groups, and epidemics can occur.[1]
Travel
Travel to endemic areas is a risk factor for malaria.
Pregnancy
Pregnancy decreases immunity against many infectious diseases. Women who have developed protective immunity against P. falciparum tend to lose this protection when they become pregnant (especially during the first and second pregnancies). Malaria during pregnancy is harmful not only to the mothers but also to the unborn children. The latter are at greater risk of being delivered prematurely or with low birth weight, with consequently decreased chances of survival during the early months of life. For this reason pregnant women are also targeted (in addition to young children) for protection by malaria control programs in endemic countries.[1]
Behavioral Factors
Human behavior, often dictated by social and economic reasons, can influence the risk of malaria for individuals and communities. For example:[1]
- Poor rural populations in malaria-endemic areas often cannot afford the housing and bed nets that would protect them from exposure to mosquitoes. These persons often lack the knowledge to recognize malaria and to treat it promptly and correctly. Often, cultural beliefs result in use of traditional, ineffective methods of treatment.
- Travelers from non-endemic areas may choose not to use insect repellent or medicines to prevent malaria. Reasons may include cost, inconvenience, or a lack of knowledge.
- Human activities can create breeding sites for larvae (standing water in irrigation ditches, burrow pits)
- Agricultural work such as harvesting (also influenced by climate) may force increased nighttime exposure to mosquito bites
- Raising domestic animals near the household may provide alternate sources of blood meals for Anopheles mosquitoes and thus decrease human exposure
- War, migrations (voluntary or forced) and tourism may expose non-immune individuals to an environment with high malaria transmission.