Malaria Final
Robert Koch
* "Father of medica lMicrobiology" * Discovered causative agents of anthrax, cholera, and tuberculosis * Nobel prize 1905
Importance of Malaria (1)
* #1 parasitic disease of humans * Causal agent = Plasmodium spp. * Intracelluar Parasite
Importance of Malaria (2)
* #1 vector borne disease of humans * Vector mosquitoes in Genus Anopheles
Hemogoblin Structure
* 4 subunits - 2 alpha - 2 Beta * Each subunit holding iron atom in porphyrin ring
Gametocytes
* A cell that divides by meiosis to form gametes
HW Equilibrium Review
* Assumptions : - Large Population - No Immigration/emigration - No Mutation - Random Mating - No Natural Selection * If valid, allele frequencies are constant * Genotype Frequencies : p^2 + 2pq + q^2
What is needed?
* Basic Science - How does Plasmodium get into cells? - How does immune system respond to plasmodium? -How does Plasmodium reproduce? -How is Plasmodium vectored? -How do mosquitoes interact with Plasmodium? -How do mosquitoes reproduce? -How do mosquitoes find hosts?-Etc., etc.
What drives allele frequency change in a population
* Bottleneck effect * Genetic Drift * Selection * Mutations
HbS
* Extra Valine * Valine more hydrophobic
Canals ...
* Ferdinand du Lesseps •1805-1894 •built Suez Canal •tried building the Panama Canal •twin disease horrors •malaria •yellow fever •mortality of workers in French effort •22,000 dead
How does merozoite move?
* Gliding * Actin - Myosin motor
Crystallization
* Hemezoin (W/ one B-hematin unit outlined)
Summary
* HgC protects against malaria at little cost * HgS protects against malaria at high cost * Why is HgC not more prevalent?
Overview
* High Genetic Load (HbS) * Moderate Genetic Load (HbE,G6PD,thallesmia) * Low Genetic Load (HbC)
What is Plasmodium?
* Protozoan in Apicomplexa •All have similar sets of organelles near anterior end: the apical complex -microneme -rhoptry -dense granules •All parasitic •Examples (other than malaria): - Babesia(babesiosis) - Cryptosporidium(drinking water) -To x o p l a s m a(cats; toxoplasmosis)
Hardy Weinberg
* Review
Merozoites
* Rough surface coat * Apical complex -Microneme -Rhoptry -Dense granules
Merozoite invasion of RBC
1. Initial Contact 2. Reorientation/Deformation 3. Junction Formation 4. Entry
How many times during its life cycle does Plasmodium pass through or invade host cells?
1. Sporozite into liver cells
Detoxifying Heme Groups
1.Sequestration into hemozoin(malarial pigment) in food vacuole 2.Degradation in food vacuole using hydrogen peroxide 3.Degradation outside of food vacuole
Merozoite invasion: summary
1.initial binding: MSP-1 2.reorientation: AMA-1 3.micronemedischarge and junction formation-adhesive proteins, incl. EBA-175, Duffy-binding protein 4.action rhoptryproteins-vacuole formation-clearing of host membrane proteins 5.closure of parasitophorousvesicle * RBC cell membrane not pierced
Evolutionary Implications
Expectations: HgC will eventually replace HgS eventually.
Genetics is a two way street
Glucose 6-phosphate Dehydrogenase Deficiency (G6PD) • G6PD enzyme prevents oxydation of heme group •G6PD absent: more reactive oxygen forms (peroxides, free radicals) •Damage Plasmodium •BUT: P. falciparum strains with their own G6PD
How does Sickle Cell protect from Malaria (2)?
Hypothesis 2: •Sickle cell results in up-regulation of hemeoxygenase (HO-1) - less cell-free heme -less problems •parasitemia might be high, but negative health effects much lower - sickle cell promotes tolerance for Plasmodium
Alternative models for the apicomplexan gliding motor organization.
Model c •Actin attached to Plasmodiumcell membrane •Myosin more flexibly attached to GAP45 complex
Malaria hypothesis (Haldane)
• Certain polymorphisms of especially erythrocyte proteins have been selected for because they provide protection against malaria * Human genetic make-up may be influenced by parasites
Sickle Cell Anemia
• Clinical symptoms: modified erythrocytes ("sickle-shaped") clog capillaries, low functionality -usually lethal
What is Malaria?
• mal'aria: "bad air" -intermittent fever, benign tertian fever, malignant tertian fever, quartan fever, quotidian fever, ague, palustral (or paludal) fever, pioneer shakes, algid malaria, falciparum malaria, vivax malaria, etc., etc.
How does Sickle Cell protect from Malaria (1)?
•Cells will sickle under lower partial pressure oxygen •Plasmodiumuses oxygen - sickling in RBC's of heterozygotes infected with Plasmodiumin venous system - kills Plasmodium; infected RBC's get destroyed - HgS suppresses Plasmodium
"HbS is fast but costly, while HbC is slow but cheap"
•Explain that statement. Why is HbS fast and HbC slow, and why would we call HbS expensive and HbC cheap?
Plasmodium and Human Interactions
•History of discovery of Plasmodium as cause of malaria •Evolutionary history of Plasmodium •Cell invasion and modification
Malaria and Human History
•old disease of humans (records from 4000 years ago) •wide-spread in Old World (introduced into Americas)
Resistance 1: genetics
* Modififcations of Hemogoblin - Sickle Cell (Hemogoblin S) - Hemogoblin C & E - Thallasemia's * Duffy Negativity * Glucose 6-phosphate Dehydrogenase Deficiency (G6PD) (Favism)
Malaria
* One of the Top 10 diseases in low economic families * 90% of the cases in Sub-sahran Africa * 429,000 fatalities in 2015, mostly small children * 2015 = 212 million new cases
3 invasive stages in Plasmodium
* Ookinete: midgut epithelium (mosquito) - motile * Sporozoites: salivary gland cells (mosquito) , hepatocytes (humans) - motile * merozoites: erythrocytes (humans) - motile
Different Clinicals Need to be Considered
* P. Falc vs P. Vivax * 1st Line Drugs * 2nd Line Drugs * Severe Malaria * Pregnancy - Treatment - Prevention
Summary: possible targets based on Plasmodium-host interactions
•During erythrocyte invasion -MSP-1 -ABA-1 -EBA-175 & Duffy factor •During feeding: detoxification of hemegroups •During sequestration-varfamily proteins (EMP's)
Plasmodium in the cell
•First ring stage •Trophozoite •Schizont(asexual reproduction) •Rupture RBC and release merozoites
Human Evolution and Malaria
•Glucose 6-phosphate Dehydrogenase Deficiency (G6PD) •Duffy negativity •Modifications of hemoglobin -Thallassemia's -Sickle Cell (hemoglobin S) -Hemoglobin C & E
Are Plasmodium Host Specific?
......
1c: formation apical junction, Microneme proteins
* Microneme secretion * Junction Formation
Symptoms (2)
* A combination of: • chills • fever • sweats • headaches • nausea and vomiting • body aches • general malaise -may be mis-diagnosed
Rationle for antimalarial combination therapy (ACT)
* Advantages for combining 2 or more antimalarial drugs - Cure rates are usually increased. - In the rare event that a mutant parasite which is resistant to one of the drugs arises de-novo during the course of the infection, it will be killed by the other drug. This mutual protection prevents the emergence of resistance. But: both partner drugs in a combination most be independently effective. Risks : increased side effects and increased risks
Why is our immune system not destroying these invaders?
* Antigenic Variability * Plasmodioum has multiple pfEMPS variants - Only one expressed at given time, but can switch to a different one [up to 2% / generation (w/o selection)]
Ideas
* Applications of basic population genetics - Hardy Weinberg - Inheritance Patterns (HbC) * Different ways mutations protect against disease
Microneme Proteins
* Erythrocyte Binding Antigen 175 in P. falciparum -binds to glycophorin A on erythrocyte • Duffy-binding protein in P. vivax, P. knowlesi -binds to .... Duffy surface antigen on erythrocyte PLUS •TRAP family (Thrombospondin-Related Anonymous Proteins) -SSP2: sporozoitesurface protein-2 -CTRP (Circumsporozoite-and TRAP-related Protein) in ookinete - similar proteins in all studied Apicomplexa
Erythrocytic Stage
* Erythrocytic stages, during which the organisms enter red blood cells (as merozoites), transform into the feeding stages (trophozoites), and then divide asexually into multiple new merozoites (schizont stage). During the schizont stage, some parasites differentiate into the reproductive forms (gametocytes) rather than the invasive merozoites. Gametocytes are classified as microgametocytes (that will become male gametes) and macrogametocytes (that will become female gametes). The gametocytes must mature through five stages before they become infective to the mosquito.
Exoerythrocytic stage
* Exoerythrocytic stage, in which the sporozoite undergoes multiple rounds of asexual divisions (merogony or schizongony) and matures into merozoites.
Combination Drugs (ACT)
* Fansidar: sulfadoxine+ pyrimethamine(or SP): most used-cheap, effective, efficient-prone to rapid emergence of resistance (already obvious in Asia, Africa) •Malarone: atovaquone+ proguanil -atovaquone inhibits parasite mitochondrial electron transport - Expensive
Heterozygous Advantage
* Homozygous (AA) Wild Type Malaria * Homozygous (SS) Sickle Cell Anemia * Heterozygous (AS) less malaria, low symptoms sickle cell anemia * Balanced polymorphism = is a situation in which two different versions of a gene are maintained in a population of organisms because individuals carrying both versions are better able to survive than those who have two copies of either version alone. When carriers have advantages that allow a detrimental allele to persist in a population, balanced polymorphism is at work. This form of polymorphism often entails heterozygosity for an inherited illness that protects against an infectious illness.
Why is P. falciparum so much more pathogenic than P. vivax, P. ovale, P. malariae?
* Hypothesis 1: P. falciparum is a recent transfer from birds * Te s t : d o s y s t e m a t i c a n a l y s i s , s e e i f P. falciparum groups with bird Plasmodium or with other human Plasmodium
Does it matter if a parasite has been associated with a given host lineage for a long time or if it is a "new" parasite?
* Immediately after host switch parasite is often highly virulent, over time it often becomes less virulen
Sporozoite
* In malaria, the sporozoites are the forms of the plasmodium that are liberated from the oocysts in the mosquito, that accumulate in the salivary glands, and that are transferred to humans when the mosquito feeds.
More Terminolgy
* In parasitological terms, humans are intermediate hosts, mosquitos are definitive hosts
Infective Stages
* Infective stage, when the parasite enters the vertebrate host with a vector bite. This life stage is known as sporozoite.
How to Control Malaria
* Kill plasmodium in human : drugs * make the human resistant : vaccines * prevent mosquito from making contact : bednets * Kill mosquito : insecticide * Make mosquito resistant : CRISPER-CAS 9
Characteristics different Plasmodium?
* P. malariae: quartan fever, other tertian * P. ovale, P. v i v a x form hypnozoites * P. f a l c i p a r u m most virulent * P. knowlesi clearly recent transfer from macaques (host switching!) highly virulent
Why is our immune system not destroy these invaders?
* Plasmodium falciparum parasites express variant antigens on the surface of infected erythrocytes (IEs), which act as targets for natural protection.1 The immunodominant surface antigen P falciparum erythrocyte membrane protein 1 (PfEMP1) is involved in several adhesive interactions resulting in parasite sequestration. PfEMP1 is encoded by members of a multigene family, the var genes, which are responsible for antigenic variation.2 Adhesion to host cells is essential for parasite survival because it prevents destruction in the spleen. These surface antigens also play a role in severe malaria and the observed acquisition of immunity makes these antigens prime candidates for the development of new intervention strategies, specifically aimed at preventing adhesion and protecting against disease. For example, IE sequestration in the placenta mediated by binding of the duffy binding-like (DBL)-γ3 domain of PfEMP1CSAto the chondroitin sulfate A (CSA) receptor, is correlated with maternal morbidity, premature delivery, spontaneous abortion, and low birth weight in first pregnancies in African women.
Ecology of Malaria
* Plasmodium is a parasite which is widely distributed all over the world. Because it requires warm, humid environments for replication in the insect vector, malaria-generating species of Plasmodium are generally limited to tropical and sub-tropical locations. Global warming and population migrations do have a bearing on Plasmodium's distribution. Plasmodium falciparum is the most widespread in tropical and sub-tropical areas. Plasmodium ovale is most prevalent in the west coast region of Africa. Plasmodium malariae has a widespread distribution area but is fairly scattered within this area. Plasmodium vivax, like falciparum, ranges over a wide area, but in relatively rare in African countries. A number of methods of control have been tested and some, including use of DDT, have proved worthwhile, but drug resistance and other health concerns make some of these methods undesirable.
Host Cell Modification
* Plasmodium secretes proteins to: •Make erythrocyte cell membrane more permeable •Make erythrocyte "sticky". Allows infected cell to hang onto wall small blood vessels -cells develops "knobs" due to parasite proteins -process called sequestration •Knobs include Erythrocyte Membrane Proteins (PfEMP's), members of varprotein family •All with large extracellular N-terminal, including several Duffy-binding like domains-Major targets for immune system (also for vaccines)
Plasmodium In-Depth
* Plasmodium, the parasite responsible for human malaria, is among the most researched genera of parasites in the world. Despite extensive studies on possible control methods, infection in humans continues to grow in tropic and sub-tropic areas. Currently there are an estimated 500,000,000 infected persons, with 1-2 million dying annually. There are four types of Plasmodium which cause human malaria: Plasmodium falciparum, Plasmodium ovale, Plasmodium vivax, and Plasmodium malariae. All of these are transmitted to human hosts solely by way of Anophele mosquito vectors. Plasmodium is one of the oldest known parasites; its long history suggests a long, adaptive relationship with the human host. Today cases of the disease are increasing in non-malarious countries as more people travel to Africa, India, Brazil, and some Asian nations, where the mosquito vectors are most prevalent. Symptoms of the disease may go unnoticed or misdiagnosed; clinical signs include fever, chills, weakness, headache, vomiting, diarrhea, anemia, pulmonary and renal dysfunction, neurologic changes. Untreated malaria may result in death.
Exam Review
* Relate symptoms to plasmodium * Life cycle will be on exam * Understand what the people did * Gorgas reogranzied the canal zone * Koch's postulates * Muller found out DDT was a fantastic insecticide * Allision found out being heterozygote for sickle cell was an advantage to malaria * Orgin = It often does, it becomes less virulent. IF it is too virulent and disrupts its transmission. less virulent strands will have an advantage. * Why does P. Falc kill you, not the others? - It came from a bird = no - it came from a chimpanzee = maybe - it came from a gorilla = yeah * Human - mosquito interactions - cell invasion = really good to getting into cells - What do these different forms do? * Merozoite Invasion - most of this was done for P. Falc - They bang into a rbc and then hold on and reoriention = better attachment - junction formation = necessary for a good bond - Duffy is a absolute for Vivax - P. Falc unique for having alternative methods to getting around - O is less likely to get severe malaria, more difficult for Plasmodium to get in * Plasmodium feeding - free heme groups are toxic, and most be processed * Host cell modification - spleen will destroy any cells that dont belong - there is pressure for the plasmodium to avoid spleen * The immune system cant recognize them * Different adhesion preferences for the different emps we have. * Duffy negativity = useful against vivax only * Genetic load = is the cost involved, sickle cell is costly * Drugs - Quin, Chlro, artemisinin - what do they do? _ What is the effect of them? - Why would antibiotics work against Plasmodium ? They target the apical complex, which orginated from chloroplasts. Apical complex is a modified protozoan - Combination drugs. Why? Resistance is the main problem. We are developing resistance against all are drugs. Combination drugs are used to slow down resistance. * How to develop new drugs? - Drug Action = useful because it shows all the different parts of cell that can be attacked by drugs. Do not memorize everything on the sheet. * Drug resistance * Natural Immune Response = just because it works here, doesnt mean it works anywhere else * Immunity = no immunity means high mortality * Vaccines = * Zika Vaccines * Vaccine = it does make a difference Protozoan = not all targets are visible * pre-erthryotic = they go after sprozoites and go after liver * Gametocytes : it doesnt help the first person, but it helps everybodoyelse
Reproductive Stage
* Reproductive stages, these begin when the vector takes a blood meal from the vertebrate host that contains mature gametocytes. In the vector the gametocytes transform into male and female gametes and merge to become a zygote (the only diploid stage in the organism's life-cycle). The zygote becomes an ookinate which invades the tissues of the vector midgut to become an oocyst. When the oocyst ruptures thousands of sporozoites emerge and travel to the vector's salivary glands, as it is through the saliva that they will enter the next vertebrate host.
Conclusion of Origins of P. Falciparum
* Resulting from a host switch from gorillas * Timing of switch unknown, perhaps as little as 4,000 years * falciparum-like Plasmodiumin chimpansee/ gorilla may be quite old
Terms, malaria
* Sporozite * Merozite * Gametocyte * Ookinete * Oocyst * Erythrocytic - Exo-erythrocytic cell
Sequestration
* The adherence of infected erythrocytes containing late development stages of the parasite (trophozoites and schzionts) to endothelium of capillaries and venules * Sequestration favors the development of the parasite by protecting it from the filtering action of the spleen (9); it is also responsible for the severe clinical forms of cerebraL malaria in which brain capillaries are obstructed by sequestered parasites. Means of inhibiting sequestration may therefore hinder parasite development and alleviate the clinical severity of the disease.
What is a species concept?
* The biological species concept is the most widely accepted species concept. It defines species in terms of interbreeding. For instance, Ernst Mayr defined a species as follows: * "species are groups of interbreeding natural populations that are reproductively isolated from other such groups." * The biological species concept explains why the members of a species resemble one another, i.e. form phenetic clusters, and differ from other species. * When two organisms breed within a species, their genes pass into their combined offspring. As this process is repeated, the genes of different organisms are constantly shuffled around the species gene pool. The shared gene pool gives the species its identity. By contrast, genes are not (by definition) transferred to other species, and different species therefore take on a different appearance.
History
* The first apparent mention of malaria-like symptoms was recorded in the ancient Nei Ching (The Canon of Medicine) about 4700 BCE. These writings also included many malaria treatments, among them the use of the Qinghao plant to reduce fever (1). Writings can also be found in cuneiform script on clay tablets and ancient Indian, Sumerian and Egyptian texts (2). Hippocrates recorded manifestations of malaria in the 4th century BCE as well as the time of year and place where the victim fell ill. Hippocrates was apparently the first to distinguish the intermittent fever of malaria from the continual fever of other infectious diseases. Malaria was long known to be associated with swamps. It was thought to be transmitted by wind, and its modern name in English is derived from the Italian mal'aria from mala aria, literally "bad air." The name was possibly first used by an Italian physician Francisco Torti (1658-1741). In 1880, Charles Louis Alphonse Laveran, a French physician, discovered the parasite that causes malaria in humans, receiving the Nobel Prize for Medicine and Physiology in 1907. Later, Laveran went on to investigate the existence of the parasites outside the human body. He deduced that "the marsh fever parasite must undergo one phase of its development in mosquitoes, and be inoculated into humans by their bites" (3). In 1886 Camillo Golgi, who won the Nobel prize in 1906 for his discoveries in neurophysiology also studied malaria and found that there are at least two forms of malaria. One form produced a fever every other day and was called tertian. The other produced a fever every third day and was called quartan. In 1890, Giovanni Batista Grassi and Raimondo Filetti, Italian investigators, introduced the names Plasmodium vivax and P. malariae ' for the two of the four malaria parasites which are now known to affect humans. In 1897, American William H. Welch revisited Laveran's work and named a third malaria parasite P. falciparum. Finally in 1922, John W. W. Stephens found a fourth malaria parasite affecting humans, P. ovale. Ronald Ross, a British officer, discovered in 1897 that humans are able to pass the malaria parasite into mosquitoes by releasing malaria-free mosquitoes into the rooms of malaria patients. The actual life or sporogonic cycle of the parasites was first described in 1899 by Giovanni Batista Grassi (4).
Plasmodium Life Cycle
* The malaria parasite life cycle involves two hosts. During a blood meal, a malaria-infected female Anopheles mosquito inoculates sporozoites into the human host . Sporozoites infect liver cells and mature into schizonts , which rupture and release merozoites . (Of note, in P. vivax and P. ovale a dormant stage [hypnozoites] can persist in the liver and cause relapses by invading the bloodstream weeks, or even years later.) After this initial replication in the liver (exo-erythrocytic schizogony ), the 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 (macrogametocytes), are ingested by an Anopheles mosquito during a blood meal . The parasites' multiplication in the mosquito is known as the sporogonic cycle . While in the mosquito's stomach, the microgametes penetrate the macrogametes generating zygotes . The zygotes in turn become motile and elongated (ookinetes) which invade the midgut wall of the mosquito where they develop into oocysts . The oocysts grow, rupture, and release sporozoites , which make their way to the mosquito's salivary glands. Inoculation of the sporozoites into a new human host perpetuates the malaria life cycle.
Malarial Drugs: Overview
* What drugs are available and how do they act? * Problem - Drug Resistance * Possible Solutions
Merozoite
* a cell developed from a schizont that parasitizes a red blood cell in the host.
Symptoms: classic, uncomplicated malaria
* attack lasting 6-10 hours includes: - a cold stage (sensation of cold, shivering) - a hot stage (fever, headaches, vomiting; seizures in young children) -a sweating stage (sweats, return to normal temperature, tiredness) * attacks occur every second day (tertian fever) or third day (quartan fever)
Koch's Postulate
* criteria for determining disease-causing organisms 1. find the same organism in each diseased individual 2. isolate organism and grow in pure culture 3. induce disease in experimental animals by transferring organism 4. isolate same organism from experimental animals
1a: initial contact, Merozoite Surface Proteins, e.g. MSP-1
* major protein on surface of merozoite * binds "band 3" protein in erythrocytes *proteolytic processing associated with maturation and invasion * Merozoite"coat" gets stripped off
Symptoms (3)
* physical findings •elevated temperature •perspiration •weakness •enlarged spleen *additional possibilities with falciparummalaria •mild jaundice •enlargement of the liver •increased respiratory rate
The system
* the parasite = Plasmodium (Protozoan) * The vector and host 1 = Anopheles (mosquito) * Host 2 = Humans
Plasmodium
*Species-rich group •Species concepts often fuzzy * Many species in lizards and birds •Cause lizard or bird malaria * Five species cause disease in humans •P. malariae •P. ovale •P. v i v a x •P. f a l c i p a r u m •P. knowlesi
Cell Invasion, Cell Modification
- Host Cell Invasion - Processes involved in feeding - Host cell modification/ cell adherence
Antigenic Variation
Plasmodium falciparum employs a strategy of clonal antigenic variation to evade the host immune response during the intraerythrocytic stage of its life cycle. The major variant parasite molecule is the P. falciparum erythrocyte membrane protein (PfEMP)1, which is encoded by the var multigene family. The parasite switches between different PfEMP1 molecules through regulation of var transcription. Recent studies have shed considerable light on this process, but much remains unknown. However, striking parallels between transcriptional control of var and genes in other organisms provide direction for future studies. Protection from falciparum malaria correlates with the acquisition of humoral immunity to variant antigens expressed by the parasite on the surface of the infected red blood cell (iRBC) [1,2]. Conversely, susceptibility to clinical disease is associated with lack of antibody reactive with the specific variant antigens expressed by the infecting parasite [3]. Plasmodium falciparum can maintain a chronic infection due to the sequential immune clearance of parasites, followed by emergence of isogenic parasite populations expressing different variant antigens on the surface of the iRBC [4,5]. Knowledge of the molecular mechanisms regulating antigenic variation has advanced considerably, but many questions
Sickle Anemia
Sickle Cell disease is an autosomal recessive disorder that causes anemia, joint pain, a swollen spleen, and frequent, severe infections. It illustrates balanced polymorphism because carriers are resistant to malaria, an infection by the parasite Plasmodium falciparum that causes cycles of chills and fever. The parasite spends the first stage of its life cycle in the salivary glands of the mosquito Anopheles gambiae. When an infected mosquito bites a human, the malaria parasite enters the red blood cells, which transport it to the liver. The red blood cells burst, releasing the parasite throughout the body. In 1949, British geneticist Anthony Allison found that the frequency of sickle cell carriers in tropical Africa was higher in regions where malaria raged all year long. Blood tests from children hospitalized with malaria found that nearly all were homozygous for the wild type of sickle cell allele. The few sickle cell carriers among them had the mildest cases of malaria. Was the presence of malaria somehow selecting for the sickle cell allele by felling people who did not inherit it? The fact that sickle cell disease is far less common in the United States, where malaria is rare, supports the idea that sickle cell heterozygosity provides a protective effect. Further evidence of a sickle cell carrier's advantage in a malaria-ridden environment is the fact that the rise of sickle cell disease parallels the cultivation of crops that provide breeding grounds for Anopheles mosquitoes. About 1,000 B.C., Malayo-Polynesian sailors from southeast Asia traveled in canoes to East Africa, bringing new crops of bananas, yams, taros, and coconuts. When the jungle was cleared to grow these crops, the open space provided breeding ground for mosquitoes. The insects, in turn, offered a habitat for part of the life cycle of the malaria parasite. The sickle cell gene may have been brought to Africa by people migrating from Southern Arabia and India, or it may have arisen by mutation directly in East Africa. However it happened, people who inherited one copy of the sickle cell allele had red blood cell membranes that did not admit the parasite. Carriers had more children and passed the protective allele to approximately half of them. Gradually, the frequency of the sickle cell allele in East Africa rose from 0.1 percent to a spectacular 45 percent in thirty-five generations. Carriers paid the price for this genetic protection, whenever two produced a child with sickle cell disease. A cycle set in. Settlements with large numbers of sickle cell carriers escaped debilitating malaria. They were therefore strong enough to clear even more land to grow food- and support the disease-bearing mosquitoes. Even today, sickle cell disease is more prevalent in agricultural societies than among people who hunt and gather their food.
Duffy Negativity and P. Vivax
• Single nucleotide substitution in promotor of gene for Duffy antigen - no expresssion - no entry by merozoite - no malaria • Duffy negative individuals have: -Good resistance to vivax malaria as homozygotes -Mutation almost to fixation in Western Africa -Very little vivax in Western Africa
Allisons Work In East Africa
• comparison of distribution of endemic malaria with sickle cell allele •experimental infection of humans with falciparum malaria -AS (heterozygotes) more resistant than AA (wild-type) •comparison of genotype with parasitism among children (6 mo-4 years) -AS with lower parasite counts than AA -few SS with cerebral malaria (but very few SS)
Feeding
•95% of RBC protein is hemoglobin •Protein is good, but free hemegroups are toxic to Plasmodium
1d: formation parasitophorous vacuole, Rhoptry proteins
•Clearing of host membrane proteins •Vacuole expands as parasite enters erythrocyte •Junction widens, becomes ring, will close behind parasite
Why do we see different pathologies with same Plasmodiumin different patients?
•Different PfEMP's have different adhesion preferences •CD36 most common receptor protein in endothelium of most of the body (not in brain) •ICAM-1 in brain *different clones bind in different parts body * different pathology
G6PD: Unusual Aspects
•Disease lacking this gene known as favism -Triggered by some foods (e.g. fava beans) -Triggered by many malarial drugs •Gene located on X-chromosome
Statistical Comparison Meaning ?
•In malarial group fewer individuals with AS (and SS) than predicted, more AA's - HbS protects against malaria (in heterozygote) •In malarial group fewer individuals with AC, and especially CC, than predicted, more AA's - HbC protects against malaria
Thasselmias
•Loss of a or b chain of hemoglobin ~50% reduction in risk for malaria •Common around Mediterranean, Africa, South Asia, Western Pacific
Discovery of Plasmodium
•Louis Alphonse Charles Laveran •army doctor in Algeria •examined fresh blood smears •witnessed exflagellation •"father of protozoology" •Nobel Prize, 1907
Merozoite Invasion
•Merozoite invasion involves specific interactions with the host erythrocyte. •The actively growing parasite places metabolic and other demands on the host cell. •Ultrastructural modifica-tions are evident in the infected erythrocyte.
Hemogoblin E (HbE)
•Mutation in position 26 of the bchain ((HbE; b26GluèLys) •Most effective against P. vivax •S.E. Asia, Western Pacific
severe (complicated) malaria
•cerebral malaria, with abnormal behavior, impairment of consciousness, seizures, coma, or other neurologic abnormalities •severe anemia due to hemolysis (destruction of the red blood cells) •hemoglobinuria (hemoglobin in the urine) due to hemolysis •pulmonary edema (fluid build-up in the lungs) or acute respiratory distress syndrome (ARDS), which may occur even after the parasite counts have decreased in response to treatment •abnormalities in blood coagulation and thrombocytopenia (decrease in blood platelets) •cardiovascular collapse and shock •acute kidney failure •hypoglycemia (low blood glucose)•metabolic acidosis (excessive acidity in the blood and tissue fluids), often in association with hypoglycemia
4-aminoquinlolines
•chloroquine (CQ) -introduced 1944-1945-cheap, non-toxic, active against all species -resistance observed in SE Asia at end of 1950s, in Africa in 1970s •amodiaquine
Quinine
•earliest effective treatment known in western countries •from bark of cinchona tree -group of species from Andes -drug known to Incas -"discovered"in Peru •Countess of Chinchón legend •Jesuit powder•introduced to Europe in 1631 •ground bark ingested •active ingredient extracted in 1817 •until 1940's was drug of choice for treatment of malaria •synthesis possible, but uneconomical •side effects: tinnitis, nausea, blurred vision, headaches, etc.
Modiano et al. (2001)
•hemoglobin C: lysine instead of glutamic acid at 6thamino acid of bchain (mutation in first nucleotide of codon) •no major negative effect of either heterozygote or homozygote •some evidence of fewer cases of malaria than expected in HbCCand HbAC
Distrubtion of Malaria
•historical distribution•widespread in Mediterranean basin•into northern Europe, as far as Arctic Circle•widespread in United States•endemic in South•north to Lake Ontario•present-day distribution•tropics, subtropics•30% of world's population
Sickle Cell Disease Problem
•how to account for high frequency of allele in some parts of the world-several locations in Africa-India-Greece •devastating effects of homozygotes should result in loss of allele through selection (has high genetic load)
Folate Antagonists
•inhibit synthesis of parasite pyrimidines •dihydrofolatereductase inhibitors -pyrimethamine -proguanil •Malarone: proguanil+ atovaquone •dihydropteroatesynthase inhibitors-sulfones, sulfadoxine, sulfonamides •marked synergism-often used in combination -Fansidar: pyrimethamine+ sulfadoxine(or SP)
Quinoline-methanols
•quinine -now used as treatment for difficult cases -intravenous infusion for severe falciparum •mefloquine(Lariam) -longer half-life (14-21 days) -common prophylactic= much resistance -used in combination therapy
1b: Re-Orientation, Apical Membrane Antigen-1 (AMA-1)
•transmembrane protein at apical end merozoite •binds erythrocyte •accompanied by membrane deformation in erythrocyte •Evidence: anti AMA-1 antibodies prevent re-orientation