Introduction

Liver stage-specific antigen 1 (LSA-1) gene is a partial protein-coding gene of 426 nucleotides that belong to strain MAL-T07 of Plasmodium falciparum. It produces 132 amino acids of LSA-1. In P.falciparum strain 3D7 (reference genome of P.falciparum), this gene is found at chromosome 10. Also named as PF10_0356, it is presumed as a protein-coding for external liver stage antigen.

Plasmodium falciparum

Plasmodium genus is the protozoan monocellular parasite that causes Malaria. Among 4 species that human-pathogenic (P.falciparum, P.vivax, P.oval and P.malariae), P.falciparum is the most virulent as it is responsible for the majority of Malaria-caused deaths globally, especially in tropical and subtropical regions. It accounts for 80% of all human malarial infections and 90% of the deaths. Each year, it causes disease in approximately 515 million people and kills between one and three million, most of them young children in Sub-Saharan Africa. In Malaysia, there are 5477 of total cases reported in year 2003, with 21 deaths.

Table shows statistics of Malaria cases reported in Malaysia by states from 2000 to 2003

Do You Know?

Now you know..^_^

Biologic Characteristic

The malaria parasite Plasmodium falciparum belongs to the phylum Apicomplexa, which includes intracellular pathogens such as Toxoplasma, Cryptosporidium, Eimeria, Babesia, and Theileria species. All Apicomplexa are intracellular parasites, with most growing and replicating within a nonphagosomal parasitophorous vacuole, a compartment bound to the membrane and segregated from most intracellular traffic routes.

Some Apicomplexa have a group of organelles (called rhoptries, micronemes, the apical polar ring, and conoids) that form their apical complex. The rhoptries and micronemes are the only secretor organelles that contain products required for mobility, adhesion, host cell invasion, and parasitophorous vacuole formation. The Apicomplexa have another unique structural characteristic, called the apicoplast (similar to a chloroplast), which is an essential organelle for parasite survival. P.falciparum are surrounded by a pellicle, which is a structure formed by the plasma membrane and an internal membrane complex (IMC) found within the cell, intimately associated with several cytoskeleton elements such as actin, myosin, microtubules, and a network of filament-like proteins involved in sporozoite mobilization. Apicomplexan proliferation occurs due to host cell invasion followed by parasite growth and cell division until the host cell is lysed. Parasites become liberated and do not show growth or extracellular division, meaning that they must speedily invade other host cells.

Life cycle of Plasmodium in mosquitoes and humans

All Plasmodium species has a complex life cycle. Infection in humans begins with the bite of an infected female Anopheline mosquito. Sporozoites released from the salivary glands of the mosquito enter the bloodstream during feeding quickly invade liver cells (hepatocytes). Sporozoites are cleared from the circulation within 30-60 minutes.

Some evidence indicates that sporozoites are first trapped by Kupffer cells before it transported to hepatocytes; though, there are other findings suggest that sporozoites home to hepatocytes directly. Circumsporozoite (CS) protein, the primary protein antigen found on the surface of sporozoites, binds to the basolateral domain of hepatocytes. Other sporozoite surface proteins, such as sporozoite surface protein (SSP2), are believed to be involved in hepatocyte invasion.

During the next 14 days in the case of P.falciparum, the liver-stage parasites differentiate and undergo asexual multiplication resulting in tens of thousands of merozoites which burst from the hepatoctye.

-Ring Stage Parasites-
Fig. 1: Normal red cell; Figs. 2-10: Increasingly mature ring stage parasites

-Trophozoites-
Figs. 11-18: Increasingly mature trophozoites

-Schizonts-
Figs. 19-25: Increasingly mature schizonts; Fig. 26: Ruptured schizont

The merozoites are extracellular for only 1-2 minutes before they rapidly invade red blood cells (erythrocytes). Individual merozoites invade erythrocytes and undergo an additional round of multiplication producing as many as 36 merozoites within a schizont. In the erythrocyte the merozoite goes through ring, trophozoite, and schizont stages. The trophozoites are generally ring shaped, 1-2 microns in size, although other forms (ameboid and band) may also exist. The length of this erythrocytic stage of the parasite life cycle depends on the parasite species: 48 hours for P.falciparum, P.vivax, and P.ovale and 72 hours for P.malariae. The clinical manifestations of malaria, fever and chills, are associated with the synchronous rupture of the infected erythrocyte. The released merozoites go on to invade additional erythrocytes.

-Gametocytes-
Figs. 27, 28: Mature macrogametocytes (female); Fig. 29, 30: Mature microgametocytes (male)

Not all of the merozoites divide into schizonts, some differentiate into sexual forms, male and female gametocytes. This sexual forms are much larger than trophozoites and 7-14 microns in size. P. falciparum is the largest and is banana shaped while others are smaller and round. These gametocytes are taken up by a female Anopheline mosquito during a blood meal.

Within the mosquito midgut, the male gametocyte undergoes a rapid nuclear division, producing 8 flagellated microgametes which fertilize the female macrogamete. The resulting ookinete traverses the mosquito gut wall and encysts on the exterior of the gut wall as a oocyst. Soon the oocyst ruptures, releasing hundreds of sporozoites into the mosquito body cavity where they eventually migrate to the mosquito salivary gland. Then the infectious cycle of malaria continuously repeat itself.

Click here to view animation of the life cycle of P.falciparum.

Reservoir & Transmission

Diagram shows Anopheles mosquito taking its blood meal

Malaria is transmitted from man to man by the female Anopheles mosquito, one of the most capable vectors of human disease. Various species have been found to be the vectors in different parts of the world. However, out of the 380 species of Anopheline mosquito, only 60 can transmit malaria. A.gambiae complex is the chief vector in Africa and A.freeborni in N. America. Nearly 45 species of the mosquito have been found in India and A.culicifacies, A.fluviatilis, A.leucosphyrushave, A.philippinensis, A.stephensi, A.sundaicus, and A.minimus been implicated in the transmission of malaria. The areas of distribution are different for these mosquitoes: A.fluviatilis and A.minimus are found in the foot-hill regions; A.stephensi and A.sundaicus are found in the coastal regions; A.culicifacies and A.philippinensis are found in the plains. Species like A.stephensi are highly adaptable and are found to be very potent vectors of human malaria.

Transmission of Plasmodium falciparum can be reduced by immune factors present in the mosquito blood meal. Specific antibodies and white blood cells (WBCs) can interact with the sexual stages of the parasite inside the mosquito midgut. The relative contribution of serum factors and WBCs on transmission reduction in gametocyte carriers from an endemic area in Cameroon and in travelers with a first malaria experience was studied. Blood from these gametocyte carriers was fed to mosquitoes through membrane feeders after serum replacement, WBC depletion, or both. In most imported malaria cases, serum factors, WBCs, or both showed a significant effect on transmission reduction, while infectiousness of gametocyte carriers from Cameroon was reduced by humoral plasma factors only. In addition, the infectivity of gametocytes from semi immune carriers was significantly lower compared with that of nonimmune carriers, and infectivity was independent of gametocyte density and the presence of WBCs or plasma factors (or both) in the blood meal.Understanding the biology and behavior of Anopheles mosquitoes can help understand how malaria is transmitted and can aid in designing appropriate control strategies. Factors that affect a mosquito's ability to transmit malaria include its innate susceptibility to Plasmodium, its host choice and its longevity. Factors that should be taken into consideration when designing a control program include the susceptibility of malaria vectors to insecticides and the preferred feeding and resting location of adult mosquitoes.

The reemergence of epidemic malaria in the East African highlands (elevation >1,500 m above sea level) is a public health problem. Research indicates that the mechanisms leading to epidemic malaria in the highlands are complex and are probably due to the concerted effects of factors such as topography, hydrology, climate variability, land-use/land-cover change, and drug resistance. Effective disease control calls for a clear understanding of the interaction between these epidemiologic factors.

Perennial malaria transmission in the lowlands has been attributed to high vector densities throughout the year. For example inhabitants of the basin region of Lake Victoria, western Kenya, experienced up to 300 infective bites per year. Vector density and transmission intensity in the highlands are much lower than in the lowlands. For example, a transect study from lowland (300 m elevation) to highland (1,700 m elevation) in the Usambara Mountains in Tanzania found a >1,000-fold reduction in transmission intensity between the holoendemic lowland and the hypoendemic highland plateau. At high altitudes in the highlands and on hilltops, where malaria transmission intensity is low, human populations have poorly developed immunity to malaria because exposures are infrequent, and persons are vulnerable to severe clinical illness and complications from Plasmodium infection. High risk for severe malaria is seen in persons living in areas with low-to-moderate transmission intensities . In such areas, the proportion of asymptomatic persons is usually lower than in high-transmission areas, where P.falciparum prevalence and parasite density varies little between seasons.

Do You Know?

Do you know that only female Mosquito, (we're talking about Anopheles mosquito) bite human and transmit what we called Plasmodium? Why female? Female mosquitoes,(most of the species) need nutrients from blood to develop & lay their egg and not for survival.

Picture shows Anopheles mosquito taking its blood meal

Picture shows Anopheles mosquito in more detail

Now you know..^_^

Virulence Factors

Heterogeneity in parasite virulence is one of several factors that have been proposed to contribute to the wide spectrum of disease severity in Plasmodium falciparum malaria.

Virulence factor : PfEMP1 (key adhesive ligand mediating sequestration)
Mechanism : antigenic variation process where different versions of PfEMP1 that expressed mediate adherence to different receptors on endothelial cells
Effect : avoid antibody-mediated clearance

Virulence factor : rifins (proteins of the repetitive interspersed family)
Mechanism : expressed at the surface of infected red blood cells
Effect : undergo antigenic variation

Pathogenesis

Plasmodium falciparum develop diseases in human body by infecting both circulatory and lymphatic system.

The pathogenesis of P.falciparum starts at the stage where the parasites leave liver cells and attack host’s red blood cells (RBSc). Before it leave the liver cell, the parasites wrapping itself in the cell membrane of the infected host liver cell, thus immune system can’t detect it while it in the bloodstream.

Rug et al. (2004) suggested that, prior to invasion of human erythrocytes, the parasites exports proteins beyond its own plasma membrane to modify the properties of the host red cell membrane. These modifications are critical to the pathogenesis of malaria. In order to establish infection in the host, the malaria parasites export remodeling and virulence proteins into the RBCs. These proteins can traverse a series of membranes, including the parasite membrane, the parasitophorous vacuole membrane, and the erythrocyte membrane (Marti et al. 2004). Another research done by Harrison and co-investigators that written by Crown (2003) found that G proteins in the RBCs may be used by the parasites. This is supported by a research by Haldar and co-investigators that found a G protein subunit, called Gs, concentrates around the malaria parasite during infection of the red blood cell.

According to McKerrow et al. (1993), parasites proteases produced by P.falciparum are likely required during both the invasion of RBCs by merozoites and the rupture of RBCs by mature schizonts. It is because in both events, the RBCs cytoskeletal proteins must be hydrolyzed as it is serves as an important barrier to malaria parasites other than erythrocyte plasma membrane. Multiple proteins of mature schizonts and merozoites are proteolytically processed immediately before or during erythrocyte rupture and invasion, suggesting that proteolytic fragments have roles in these processes. Hemoglobin degradation is found occurs predominantly in trophozoites and early schizonts of P.falciparum, the stages at which the parasites are most metabolically active. Trophozoites ingest RBCs cytoplasm via pinocytosis or use the cytostome, a specialized organelle, and then transport the cytoplasm within vesicles to a large central food vacuole. The hemoglobin is then broken down into heme, which is a major component of malarial pigment; while globin is hydrolyzed to its constituent free amino acids.

Picture shows 2 ruptured RBCs surrounded by fresh RBCs

In the RBCs, the multiplying process continue, rupture of host cell to invade fresh RBCs.The amplification cycle occur. The symptoms of Malaria such as fever, chills, headache, muscle aches, joint pain, vomitting, and fatigue occur when infected red blood cells that are “incubating” thousands of P.falciparum literally explode and release more parasites into the blood stream during the “blood stage” of malaria.

The parasite is relatively protected from attack by the body's immune system because for most of its human life cycle it resides within the liver and blood cells and is relatively invisible to immune surveillance. However, usually infected RBCs will be destroyed in the spleen. To avoid from destruction in the spleen, the adhesive proteins (PfEMP1) display on the surface of the circulating infected blood cells by these parasites. This causes the blood cells and the wall of small blood vessels stick together. Furthermore, this action avoid the parasite of being destroyed in spleen’s circulation. Although PfEMP1 is exposed to the immune system, it can’t be detected as there are at least 60 variation of the protein (PfEMP1). The “stickness” may induces hemorrhagic complication of malaria. Attachment of masses of the infected RBCs block the high endothelial venules and give rises to some symptoms, for example, placental and cerebral malaria. The sequestrated red blood cells can ruptures the blood brain barrier and possess possibility to cause coma in cerebral malaria.

Diagnosis

A) Clinical Diagnosis

• Confusion, coma, neurological focal signs, severe anemia, and respiratory difficulties are more striking and may increase the suspicion index for malaria.
• Is usually sufficient to warrant treatment.
• Not typical and need to be confirmed by a laboratory test.

B) Microscopic Diagnosis

• Detection of parasites(P. falciparum) in stained blood films.
• This method used to differentiate between different parasite species and stages of the life cycle.
• The specimen is stained with the Giemsa stain to give to the parasites a distinctive appearance.
• Thick blood films are used in routine diagnosis and as few as one parasite per 200 μl bloods can be detected.
• In this additional laboratory findings may include mild anemia, mild decrease in blood platelets (thrombocytopenia), elevation of bilirubin, aminotransferases, albuminuria, and the presence of abnormal bodies in the urine.
• From the microscopic diagnosis, we can diagnose that the person is infected with malaria and the Blood Stage Parasites in thin blood smears and thick blood smears. Here are some images about the Stages of P. falciparum found in blood.

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  Blood smear stained with Giemsa. Showing a white blood cell (on left side) and several red blood cells, two of which are infected with P. falciparum (on right side).
  

C) Rapid Diagnostic Test:

The picture above demonstrates a positive test for P.falciparum.

• An alternate way of quickly establishing the diagnosis of malaria infection by detecting specific malaria antigens in a person's blood.
  
• It is recommended that all RDTs are followed-up with microscopy to confirm the results and to quantify the proportion of red blood cells that are infected.
  

Advantages:

※ Decrease the amount of time that it takes to determine that a patient is infected with malaria

Disadvantages:

※ May not be able to detect some infections with lower numbers of malaria parasites circulating in the patient’s bloodstream.

※ The currently approved DT detects 2 different malaria antigens; one is specific
for P. falciparum and the other is found in all 4 human species of malaria.

※ Thus, microscop is needed to determine the species of malaria .


D) Serology :

• Detects antibodies against malaria parasites using either indirect
  immunofluorescence (IFA) or enzyme-linked immunosorbent assay (ELISA).
  
• Used to assess past malaria experience but not current infection by malaria parasites.
  

Indirect immunofluorescence (IFA):

-> Used to determine if a patient has been infected with Plasmodium via the time required for development of antibody and also the persistence of antibodies.

-> Blood stage Plasmodium species schizonts (meronts) are used as antigen. The patient's
serum is exposed to the organisms; homologous antibody.

-> It will attaches to the antigen, forming an antigen-antibody complex if it present.

-> Fluorescein- labeled anti-human antibody is then added, which attaches to the patient's malaria-specific antibodies.

-> When examined with a fluorescence microscope, a positive reaction
is when the parasites fluoresce an apple green color.

The fluorescence indicates that the patient serum being tested contains antibodies that are reacting with the antigen preparation (P.falciparum).

Enzyme-linked immunosorbent assay:

-> Screen blood donors, but have limited sensitivity due to use of only Plasmodium
falciparium antigen instead of antigens of all four human species.

E) Molecular Diagnosis

• Detection of parasite genetic material through polymerase-chain reaction (PCR)
  techniques.
• Detection and speciation of Plasmodium is done with a two step nested PCR using the primers of Snounou et al 1993. Specific primers have been developed for each of the four species of human malaria.

The steps are:
~ In the first step (PCR1), 1 µl of extracted DNA is amplified using genus specific primers.1 µl of PCR1 amplification product is further amplified using primers specific.

~ Ten microliters of each PCR2 amplified DNA product is electrophoretically resolved on a 2% agarose gel then stained for 15 min with ethidium bromide and visualized by UV illumination for analysis of result.

Disadvantages:

※ High cost, high degree of training required.

※ Need for special equipment, absolute requirement for electricity

※ Potential for cross-contamination between samples.

Prevention

• As we know, malaria disease has taken millions of people's life since 60's.

• Prevention infection is especially important because resistance to anti-malarial drugs is a growing problem and as far as we concern, no effective vaccine has been developed, yet researchers has never giving up for the sake of human's health.

• People belief that prevention is always better than cure. So here are some tips on how we can practice prevention act in our daily life. Remember, its never too late to start.

• In general:
• avoid mosquito bites especially at dawn and dusk -> mosquito tend to go out
• For travelers, always take precaution when visiting malaria's area
  (See below map for malaria's location reported)

• When outside:
• Do wear long sleeve and long pants whenever planning to go outside
• It is wise to use insect repellent on exposed skin
• Still, thin clothes not suggested as it can pass through it
• Use an effective repellent-> 20->35% DEET(N,N-diethylmethyltoluamide)

• When inside:
• Sleeping time!! Using bednet in your bedroom might be perfect idea
• Spraying insecticides in living area is necessary specially if you planning to sleep outside

• Anti-malarial drug:
• Taking drug dependent on what type of country you're in
• REMEMBER!! Most of it too expensive::Prophylactic->not affordable for many malaria's patients
• There are 5 regimens and each taken based on resistance exist by malaria to various drug::A,B,C,D,E
• Always take proper medication especially traveler,do take before and after visiting endemic area. This is important to cover the incubation period.

For travelers, you might wanna have a look which country for using which regimens, click here to find out more

Treatment

• If you were thinking drug can settle malaria's problem, think again. Each Plasmodium species has different resistance towards drug and patients are need to take based on which resistance they have.
• Having fever, your body chills, and sweating recently? Those are malaria common symptoms and if you do have, you better take a medication treatment A.S.A.P. You will never know how serious this might be cause you might be diagnose to Malaria fever.
• Here is the list of common drugs used to treat Malaria:
• The ABCD of Malaria treatment

o A: be Aware of the risk of malaria if you are travelling to a foreign country.

o B: avoid mosquito Bites by taking appropriate measures. Reducing the number of Bites reduces the chances of getting malaria.

o C: Comply with the appropriate prophylactic drug regimen for the area you are visiting. This is vitally important since failure to comply places you at great risk. Studies have shown that there is a reduced risk of contracting malaria even if you take the wrong regimen.

o D: early Diagnosis of malaria if symptoms manifest following travel to a malarious region is vital. Malaria can be fatal but early diagnosis and treatment is usually 100% effective.

• The drug treatment of malaria depends on the type and severity of the attack. Typically, Quinine Sulphate tablets are used and the normal adult dosage is 600mg every twelve
  hours which can also be given by intravenous infusion if the illness is severe.
• Here are some extra tips for you guys:
• if suspected,A.S.A.P treatment under medical supervision
• some medicine are too expensive
  -> prophylactic(not affordable for second/third class people)
  not100% effective, need to change frequently,5 regimens(A,B,C,D)based on resistance that exist by malaria to various drug
  ->quinine(cheap but developing its resistance)
  ->arteminisin derivatives
• always remember drug can give side-effects!!
  ->Proguanil (Paludrine) can cause nausea and simple mouth ulcers.
  ->Chloroquine (Nivaquine or Avloclor) can cause nausea, temporary blurred vision and rashes.
• Patients with a history of psychiatric disturbances (including depression) should not take mefloquine as it may precipitate these conditions. It is now advised that mefloquine be started two and a half weeks before travel.
• Doxycycline does carry some risk of photosensitivation i.e. can make you prone to sunburn.
• Malarone is a relatively new treatment and is virtually free of side effects. It is licensed for use in stays of up to 28 days but there is now experience of it being taken safely for up to three months.
• No other tablets are required with mefloquine or doxycycline or Malaron.

• Why no vaccine, have to change frequent or take different medicine?
• it is because of plasmodia, not the mosquito
• plasmodia has the ability to develop resistance,which has always been challenging factor in developing vaccine and medicine treatment
• since 60s, chloroquine is the best, but throughout years,it efficiency been decline
• its plasmodia survival way->have the ability to develop resistance
• research never stop until now to tackle dis problem,but modifying drug will only increasing the drug cost->malaria affect mostly 3rd world country->unaffordable
• research never stop until now to tackle dis problem, but modifying drug will make more side-effect->different people different gene
• last few years, new drug has taken down plasmodia, but now plasmodia shows resistance to new drugs
• recently, plasmodia develop resistance to mefloquine -> see map below

Map shows area of Mefloquine-resistant Malaria

New Prevention Step

• After some research done, it has been calculated over more than 10 000 travellers were reported to get infected with malaria disease after returning home. But there are some unreported cases which has made the number incerase up to 30 000 people.
• Any idea why such thing could happen?
• never bother how worst malaria could
• simply taking whichever drug they like without prescription from doctor. REMEMBER!!different malaria infected places have different level of resistancy.
• travellers not frequently take drugs->important to those who stays more than 6 months
• most of them are non-immune & often exposed to late or wrong malaria diagnosis when returning to their home country
• FYI,in most cases malaria fever occur within 3 months of leaving a malaria-endemic area->medical emergency treatment is needed
• But no need to worry, follow this steps and you should be safe:
• do some homework on country that you are about to visit
• see your doctor to take some precautions needed
• going out? plan your time, try to avoid dusk and dawn as mosquito are nocturnal (active time->dusk and dawn)
• plan your schedule, not to visit during at the end of the rain season or soon after
  
  
• For those who going to Sabah, below regimens are recommend:
  

• FOLLOW A LARIAM (MEFLOQUINE HYDROCHOLORIDE) REGIMEN:

  Take one tablet of LARIAM 250mg ONCE a week. Start one week before entering the malarious area, continue weekly during your stay and continue for four weeks after leaving. (Lariam should not be taken by persons suffering from cardiac diseases, liver or kidney disorders, epilepsy, psychiatric disorders, pregnant women and children under 30 lbs/15 kg in weight.)

• FOLLOW A MALARONE (ATORVAQUONE + PROGUANIL) REGIMEN

  Take ONE tablet daily (250mg Atorvaquone +100mg Proguanil). Start 1 to 2 days before entering the malarious area, continue daily during your stay, and continue for 7 days after leaving. MALARONE should be taken at the same time every day with food or milk.

• FOLLOW A DOXYCYCLINE (VIBRAMYCIN) REGIMEN

  Take ONE tablet daily of 100mg Doxycycline (Vibramycin). Start one day before entering malarious area, continue daily during your stay, and continue for four weeks after leaving.

  When taking Doxycycline avoid exposure to direct sunlight and use sun screen with protection against long range ultraviolet radiation (UVA) to minimize risk of photosensitive reaction. Drink large amounts of water to avoid esophageal and stomach irritation.

  Doxycycline should not be taken by persons with known intolerance to tetracyclines, pregnant women and children under eight years of age.
  

• ANTI-MALARIAL REGIMEN FOR PERSONS WHO CANNOT FOLLOW ONE OF THE ABOVE REGIMEN

  Take Chloroquine (Aralen) in weekly doses of 500mg (300mg base). Start one week before entering malarious area, continue weekly during your stay and continue for four weeks after leaving. It is imperative to use a mosquito bed net to avoid the bite of the nocturnal Anopheles mosquito. Use repellents and insecticides.

  Persons following a Chloroquine regimen must be aware these drugs are much less effective than Lariam, Malarone or Doxycycline. They must seek immediate medical attention in case of flu-like symptoms - fever, headache, nausea, general malaise - appearing about seven days or later after entering malarious area.

  Persons traveling to or working in remote areas where medical attention cannot be sought within 24 hours should consult with a specialist before leaving their home country for advice on possible self-treatment regimen in case of a malaria breakthrough attack.

• For people who live at endemic area such as Sabah and Sarawak, they are advised to possess and use insecticide-treated nets, and use intermittent preventive treatment (IPT) among pregnant women (PW) where national policy indicates. Other than that, don't go out of house when it is dawn and dusk (time where mosquitoes actively looking for blood).
  

New Diagnostic Strategy

The recent evolution of diagnostic technologies has added a new dimension to malaria control efforts. The recent evolution of diagnostic technologies has added a new dimension to malaria control efforts. The most widely used diagnostic approach for malaria is clinical diagnosis. It is unreliable because the symptoms of malaria are non-specific and overlap with other febrile diseases, while technical and logistic requirements make microscopic confirmation difficult at the peripheral level.

Thus, the introduction of rapid diagnostic tests for malaria is of considerable interest. Rapid immunochromatographic dipstick tests have been developed that detect parasite antigens from a fingerprick blood sample. These tests are simple to use, require minimal training, and show reasonable sensitivity and specificity.

Before malaria RDTs can be widely adopted, several issues remain to be addressed, including improving their accuracy, lowering their cost, and ensuring their adequate performance under adverse field conditions.

Diagram shows component of Rapid Malaria Test and examples of its result

Laboratory diagnosis of malaria can be made through microscopic examination of thick blood smears than thin blood smears. Thick blood smears are more sensitive in detecting malaria parasites because the blood is more concentrated allowing for a greater volume of blood to be examined.

In addition, improved PCR techniques could prove useful for conducting molecular epidemiological investigations of malaria clusters or epidemics.

Vaccination & Eradication

Malaria eradication has been a priority for the World Health Organization (WHO). The discovery of the insecticide DDT in 1942 has been successfully lowered malaria rates in many parts of the world. However, it was discontinued to be use due to environmental toxicity. Hence, the current measures that protect against infection are still mosquito-focused. For example, protective clothing, repellents, bed nets, and mosquito control programs.

Since Plasmodium falciparum causes disease on human cardiovascular and lymphatic system, hormones that regulate cardiovascular function and drugs that control blood pressure could be use as a tool to control malaria infection. These findings, has been published in article in the Sept. 19, 2003 issue of the journal Science by Kasturi Haldar, Jon Lomasney, Travis Harrison and colleagues at the Feinberg School of Medicine at Northwestern University .

As a consequence, beta-blockers, which are safe, inexpensive and commonly prescribed drugs used worldwide to treat high blood pressure, are proposed to use against the deadliest and most drug-resistant strain of malaria parasites.

In fact, there is also research done in other approach which focused on identifying and blocking the process by which red blood cells allow parasite entry. Charles E. and Emma H. Morrison Professor in Pathology and professor of microbiology-immunology at the Feinberg School are putting their effort into this study.

Overall, there is still hope for vaccination and eradication to be continuously developed in the near future.

Idea vaccine for malaria today

Possess 3 important charactheristics:

• multi-stage : incorporating antigenic characteristics at multiple stages of P. falciparum’s life cycle.
• multi-valent : possess multiple epitopes restricted by different MHC molecules
• multi-immune : inducing more than one type of immune response

Genome Information

Referred to 3D7 strains of P.falciparum that has been mapped as reference genome, P.falciparum has 23Mb of 14 chromosomes that high AT content. The chromosomes are haploid throughout majority of its life cycle in human, and distributed among sequencing centers.

P.falciparum also has 5.9kb of mitochodrial DNA and 35kb of plastid-like circular DNA. By analysing mitochodrial DNA sequence polymorphism of P.falciparum, we are able to know its origin and geographical spread. A research by Conway et al. (2000) shown that P. falciparum originated in Africa and colonised Southeast Asia and South America separately by mitochondrial DNA analysis. While the plastid-like DNA molecule, it encoding almost exclusively components involved in gene expression. Other parasitic protists of the Phylum Apicomplexa also have a plastid-like genome with less sequence complexity.

Other than 3D7 strain, so far already 11 other strains of genome are sequenced by Broad Institute of MIT and Harvard in order to enable comparative genome studies. For example, among P.falciparum strains, P.falciparum Dd2 has a high tendency to acquire drug resistance, thus it is used to genetically map drug-resistance determinants by means of microsatellite markers. This comparative study of similarities and differences in genome between strains of P.falciparum enable studies to formulate effective antimalarial drugs and vaccines using gene or siRNA (short interfering RNA) etc. in order to eradicate Malaria globally.

There are several Plasmodium species that closely related to P.falciparum which are Plasmodium reichenowi, Plasmodium gallinaceu, and Plasmodium berghei. Although these species don’t infect human, they are served as a relevant model organism to study and define the genetic pathways involved in parasite development. Their genome data also useful for malaria vaccine development.

Genomic Evolution

Comparative genomics allows inferences to be drawn about the coding potential of related genomes, and the evolutionary forces that have influenced genome organization. In 2 researches that compare the genome of Plasmodium falciparum with Plasmodium berghei and Plasmodium yoelii yoelii by Thompson et al. (2001) and Carlton et al. (2005) respectively, which both are malaria parasites of rodents, both indicate there are striking conservation of gene synteny (conserved physical association of genes) between malaria species within conserved chromosome cores. They also found that genes that elicit a host immune response are frequently found to be species-specific, although a large variant multigene family is common to many rodent malaria species and Plasmodium vivax.

Broad Institute currently conduct a project that compare between Dd2 and HB3 strains of Plasmodium falciparum for better understanding their polymorphism. These 2 strains are the parents of a widely used genetic cross and differ in the frequency of acquisition of drug resistance. Polymorphism in P. falciparum is known to be concentrated in genes that are involved in immune system evasion and pathogenicity. Generating data on polymorphism in P. falciparum can thus not only speed identification of these key loci but also provide important insight into the evolutionary pressures shaping their function. So far the research found that Dd2 strain has a high propensity to acquire drug resistance whereas HB3 does not. Thus, the complete genomic sequences will make it possible to identify the mutations responsible for this important predisposition to acquiring drug resistance.

References

1. Allan, B 2007, ‘Malaria’s multiple infection and evasion capabilities must be countered to create an effective vaccine’, The Walter and Eliza Hall Institute of Medical Research
2. BBC News 2004, Hopes of malaria vaccine by 2010
3. Broad Institute 2007, Plasmodium falciparum: Project Info
4. Carlton, J, Silva, J & Hall N 2005, ‘The genome of model malaria parasites, and comparative genomics’, Current Issues in Molecular Biology, vol.7, no.1, pp. 23-37
5. Conway, DJ, Fanello, C, Lloyd, JM, Al-Joubori, BM, Baloch, AH, Somanath, SD, Roper, C, Oduola, AM, Mulder, B, Povoa, MM, Singh & B, Thomas, AW 2000, ‘Origin of Plasmodium falciparum malaria is traced by mitochondrial DNA’, Molecular & Biochemical Parasitology
   
6. Cross, C 2004, Diagnosis of Malaria, Welcome Trust

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