The natural history of involves cyclical infection of humans and female Anopheles mosquitoes.
In humans, the parasites grow and multiply first in the liver cells and then in the red cells of the blood. The blood stage are those that cause the symptoms of malaria.
When certain forms of blood stage parasites gametocytes, which occur in male and female forms are ingested during blood feeding by a female Anopheles mosquito, they mate in the gut of the mosquito and begin a cycle of growth and multiplication in the mosquito.
When the Anopheles mosquito takes a blood meal on another human, anticoagulant saliva is injected together with the sporozoites, which migrate to the liver, thereby beginning a new cycle. The malaria parasite life cycle involves two hosts. During a
Asexual life cycle of plasmodium falciparum macrogametocyte meal, a malaria-infected female Anopheles mosquito inoculates sporozoites into the human host. Sporozoites infect liver cells and mature into schizontswhich rupture and release merozoites.
Of note, in P. After this initial replication in the liver exo-erythrocytic schizogonythe parasites undergo asexual multiplication in the erythrocytes erythrocytic schizogony. Merozoites infect red blood cells.
The ring stage trophozoites mature into schizonts, which rupture releasing merozoites. Some parasites differentiate into sexual erythrocytic stages gametocytes. Blood stage parasites are responsible for the clinical manifestations of the disease. The gametocytes, male microgametocytes and female macrogametocytesare ingested by an Asexual life cycle of plasmodium falciparum macrogametocyte mosquito during a blood meal.
The zygotes in turn become motile and elongated ookinetes which invade the midgut wall of the mosquito where they develop into oocysts. Inoculation of the sporozoites into a Asexual life cycle of plasmodium falciparum macrogametocyte human host perpetuates the malaria life cycle.
Human Factors and Malaria. Factors that determine the occurrence of malaria are those that influence the three components of the malaria life cycle:. In rare cases malaria parasites can be transmitted from one person to another without requiring passage through a mosquito from mother child in "congenital malaria" or through transfusion, organ transplantation, or shared needles.
Climate can influence all three components of the life cycle. It is thus a key in the geographic distribution and the seasonality of malaria. Such breeding sites may dry up prematurely in the absence of further rainfall, or conversely they can be flushed and destroyed by excessive rains.
Once adult mosquitoes have emerged, the ambient temperature, humidity, and rains will determine their chances of survival. Warmer ambient temperatures shorten the duration of the extrinsic cycle, thus increasing the chances of transmission.
This explains in part why malaria transmission is greater in warmer areas of the globe tropical and semitropical areas and lower altitudesparticularly Asexual life cycle of plasmodium falciparum macrogametocyte P.
Climate also determines human
Asexual life cycle of plasmodium falciparum macrogametocyte that may increase contact with Anopheles mosquitoes between dusk and dawn, when the Anopheles are most active. Hot weather may encourage people to sleep outdoors or discourage them from using bed nets. During harvest seasons, agricultural workers might sleep in the fields or nearby locales, without protection against mosquito bites. The types species of Anopheles present in an area at a given time will influence the intensity of malaria transmission.
Some species are biologically unable to carry human malaria parasites, while others are readily infected Asexual life cycle of plasmodium falciparum macrogametocyte produce large numbers of sporozoites the parasite stage that is infective to humans.
Different Anopheles species may differ in selected behavior Asexual life cycle of plasmodium falciparum macrogametocyte, with important consequences on their abilities as malaria vectors. All other factors being equal, the anthropophilic, endophagic species will have more frequent contacts with humans and thus will be more effective malaria vectors.
The anthropophilic Anopheles gambiae is an extremely effective vector and is one of the reasons why malaria is so prevalent in Africa. An important biologic factor is insecticide resistance. If the mosquitoes are resistant to the insecticide s used locally for spraying or for treating bed nets, these measures will be ineffective in curtailing transmission. Human Factors And Malaria. Characteristics of the malaria parasite can influence occurrence of malaria and its impact on human populations:.
Plasmodium falciparum predominates in Africa south of the Sahara, one reason why malaria is so severe in that area. A certain species of malaria called P. Humans living in close proximity to populations of these macaques may be
Asexual life cycle of plasmodium falciparum macrogametocyte risk of infection with this zoonotic parasite. Malaria transmission has been eliminated in many countries of the Asexual life cycle of plasmodium falciparum macrogametocyte, including the United States.
However, in many Asexual life cycle of plasmodium falciparum macrogametocyte these countries including the United States Anopheles mosquitoes are still present. Thus the potential for reintroduction of active transmission of malaria exists in many non-endemic parts of the world.
All patients must be diagnosed and treated promptly for their own benefit but also to prevent the reintroduction of malaria. 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.
Persons who have the sickle cell trait heterozygotes
Asexual life cycle of plasmodium falciparum macrogametocyte the abnormal hemoglobin gene HbS are relatively protected against P. 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. Persons who are negative for the Duffy blood group have red blood cells that are resistant to infection by P.
Since the majority of Africans are Duffy negative, P. In that area, the niche of P. Other genetic factors related to red blood cells also influence malaria, but to a lesser extent. Sickle Cell and Malaria. Acquired immunity greatly influences how malaria affects an individual and a community. After repeated attacks of malaria a person may develop a partially protective immunity.
In areas with high P. 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 Asexual life cycle of plasmodium falciparum macrogametocyte 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. In areas with lower transmission such as Asia and Latin Americainfections 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.
Asexual life cycle of plasmodium falciparum macrogametocyte in young children in Asembo Bay, a highly endemic area in western Kenya. Anemia occurs most between the ages of 6 and 24 months. After 24 months, it decreases because the children have built up their acquired immunity against malaria and its consequence, anemia.
The mother had malaria, with infection of the placenta. Pregnancy decreases immunity against many infectious diseases. Women who have developed protective immunity against P. 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.
Human behavior, often dictated by social and economic reasons, can influence the risk of malaria for individuals and communities. Human behavior in endemic countries also determines in part how successful malaria control activities will be in their efforts to decrease transmission. The governments of malaria-endemic countries often lack financial resources.
As a consequence, health workers in the public sector are often underpaid and overworked. They lack equipment, drugs, training, and supervision. The local populations are aware of such Asexual life cycle of plasmodium falciparum macrogametocyte when they occur, and cease relying on the public sector health facilities.
Conversely, the private sector suffers
Correcting this situation is a tremendous challenge that must be addressed if malaria control and ultimately elimination is to be successful. Only in some individuals do malaria episodes progress to severe life-threatening disease, while in the majority the episodes are self-limiting. This is partly because of host genetic factors such the sickle cell gene. The sickle cell gene is caused by a single amino acid mutation valine instead of glutamate at the 6th position in the beta chain of the hemoglobin gene.
Inheritance of this mutated gene from both parents leads to sickle cell disease and people with this disease have shorter life expectancy. On the contrary, individuals who are carriers for the sickle cell disease with one sickle gene and one Asexual life cycle of plasmodium falciparum macrogametocyte hemoglobin gene, also known as sickle cell trait have some protective advantage against malaria.
As a result, the frequencies of sickle cell carriers are high in malaria-endemic areas. Most earlier studies of the relationship between sickle cell trait and malaria were cross-sectional, and therefore some important data relevant to the protective effects of sickle cell trait were missing.
Most of this protection occurs between months of life, before the
Asexual life cycle of plasmodium falciparum macrogametocyte of clinical immunity in areas with intense transmission of malaria. Those who had the sickle cell trait HbAS had a slight survival advantage over those without any sickle cell genes HbAAwith children with sickle cell disease HbSS faring the worst. Malaria is transmitted among humans by female mosquitoes of the genus Anopheles.
Female mosquitoes take blood meals to carry out egg production, and such blood meals are the link between the human and the mosquito hosts in the parasite life cycle. Differently from the human host, the mosquito host does not suffer noticeably from the Asexual life cycle of plasmodium falciparum macrogametocyte of the parasites.
Map of the world showing the distribution of predominant malaria vectors. Anopheles freeborni mosquito pumping blood Larger Picture. Sequential images of the mosquito taking its blood meal. Like all mosquitoes, anophelines go through four stages in their life cycle: The first three stages are aquatic and last days, depending on the species and the ambient temperature. The adult stage is when the female Anopheles mosquito acts as malaria vector.