Introduction

Malaria is an infectious disease caused by a protozoa which infects red blood cells(erythrocytes), Plasmodium sp. transmitted by an infective female Anopheles mosquito vector. It is commonly characterized by typical features such as febrile paroxysms, anaemia and splenomegaly. Historical records suggest malaria has infected humans since the beginning of mankind. The name "mala aria" (meaning "bad air" in Italian) was first used in English in 1740 by H. Walpole when describing the disease. The term was shortened to "malaria" in the 20th century. C. Laveran in 1880 was the first to identify the parasites in human blood. In 1889, R. Ross discovered that mosquitoes transmitted malaria.

Female Anopheles mosquito

The 4 Plasmodium species known to cause malaria :

i)                    Plasmodium falciparum

ii)                  Plasmodium vivax

iii)                Plasmodium ovale

iv)                Plasmodium malariae.

*A fifth species, Plasmodium knowlesi, has recently been identified as a clinically    significant pathogen in humans.

Most of the malaria cases reported are due to single infection (infection by a single species) while some individuals may be infected with multiple Plasmodium species. P. falciparum is the most common cause of infection and is responsible for about 80% of all malaria cases, and is also responsible for about 90% of the deaths from malaria. Parasitic Plasmodium species also infect birds, reptiles, monkeys, chimpanzees and rodents.

Life Cycle of Malarial Parasites

Life Cycle of Malarial Parasites

• Sporozoites are injected into human dermis through the bite of infected Anopheles mosquito.
• After inoculation, sporozoites migrate to liver cells to establish the first intracellular replicative stage.
• Merozoites generated from this exoerythrocytic phase then invade erythrocytes (RBCs), and it is during this erythrocytic stage that severe conditions of malaria occur.
• The life cycle is completed when sexual stages (gametocytes) are ingested by a mosquito.
• Sporozoites deposited in the skin migrate rapidly through the region of the bite. Some eventually penetrate capillaries or lymph vessels.
• Those entering the lymph vessels will penetrate lymph vascular endothelial cells in lymph nodes to establish a lymph node form, which appears not to continue the life cycle—but may be significant in priming an immune response.

Epidemiology

Malaysia

Since Malaria Eradication Program which was initiated in 1967 in Peninsular Malaysia there was a reduction in the number of reported malaria cases from 160,385 in 1966 to 9,110 cases in 1980.  However, the anti-malaria activities have remained the same although the concept of eradication has changed to one of control in the 1980.

In 1990:

·        50,500 cases of malaria were reported

·        69.7% (35,190) were from Sabah

·        27.8% (14,066) from Peninsular Malaysia

·        2.5% (1,244) from Sarawak

·        Plasmodium falciparum continues to be the predominant species, contributing to 69.6% of the parasites involved.

·        The case fatality rate for 1990 was 0.09%

·        There were 43 deaths all of which were attributed to cerebral malaria

Until June 1991 a total of 18,306 cases were reported for the country. The main problems faced in the prevention and control of malaria include problems associated with the opening of land for agriculture, mobility of the Orang Asli of Peninsular and inaccessibility of malaria problem areas.

During the speech by YB Dato’ Sri Liow Tiong Lai, Malaysian Minister of Health in The 63^rd World Health Assembly on (21/5/2010), he stated that Malaysia has achieved the Millennium Devolepment Goals(MDG) target for malaria by halving the malaria incidence from 29 per 10,000 in 1990 to 12.3 in 1997 to 2.5 in 2009. We are now moving towards MDG – plus target of completely eliminating Malaria infection by 2020.

Worldwide

 It is estimates that malaria causes 250 million cases of malaria and approximately one million deaths annually. The majority of cases occur in children under 5 years old and pregnant women. Precise statistics are unknown because many cases occur in rural areas where people do not have access to hospitals or the means to afford health care. As a consequence, the majority of cases are undocumented.

Malaria is presently endemic in areas of the Americas, many parts of Asia, and much of Africa; however, it is in sub-Saharan Africa where 85– 90% of malaria fatalities occur. In drier areas, outbreaks of malaria can be predicted with reasonable accuracy by mapping rainfall.Malaria is more common in rural areas than in cities; this is in contrast to dengue fever where urban areas present the greater risk.

Pathogenesis

Individuals with malaria typically acquired the infection in an endemic area following a mosquito bite. Cases of airport malaria and infection secondary to transfusion of infected blood are extremely rare. The risk of infection depends on the intensity of malaria transmission and the use of precautions such as bed nets, diethyl-meta-toluamide (DEET), and malaria prophylaxis. Pathogenesis of Malaria can be divided into 2 cycles in human which are exo-erythrocytic and erythrocytic schizogony.

i) Exo-erythrocytic schizogony: 

Sporozoites are injected into the subcutaneous tissue

travel to the liver either directly or through lymphatic channels. 

 They reach the liver in 30-40 minutes by brisk motility conferred by 

Circum Sporozoite Protein (CSP)

 

Approximately 8-15 (up to 100) sporozoites are injected 

and thus only a few hepatocytes are infected, 

therefore this stage of the infection causes no symptoms 

The co-receptor on the sporozoites which involve for invasion are the 

thrombospondin domains on the circumsporozoite protein 

and on thrombospondin-related adhesive protein (TRAP). 

These domains bind specifically to heparin sulfate proteoglycans on hepatocytes in the region in apposition to sinusoidal endothelium and Kuppfer cells. 

Within the hepatocyte, each sporozoite divides into

10000-30000 merozoites. 

This phase is called pre-erythrocytic schizogony (development of schizoint 

forms of the parasite before reaching the red blood cells) 

and takes about 10 - 15 days in P. vivax malaria 

and about 7-10 days in P. falciparum malaria.

 Following rupture of their host cells, escape into the blood and infect red blood cells, thus beginning the erythrocytic stage of the life cycle. The parasite escapes from the liver undetected by wrapping itself in the cell membrane of the infected host liver cell

Some P. vivax and P. ovale sporozoites produce hypnozoites that remain dormant for periods ranging from several months (6–12 months is typical) to as long as three years. After a period of dormancy, they reactivate and produce merozoites. Hypnozoites are responsible for long incubation and late relapses in these two species 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, circulating infected blood cells are destroyed in the spleen. 

To avoid this fate, the P. falciparum parasite displays 

• adhesive proteins on the surface of the infected blood cells, causing the blood cells to stick to the walls of small blood vessels, thereby sequestering the parasite from passage through the general circulation and the spleen. 
• This "stickiness" is the main factor giving rise to hemorrhagic complications of malaria. 
• High endothelial venules (the smallest branches of the circulatory system) can be blocked by the attachment of masses of these infected red blood cells. 
• The blockage of these vessels causes symptoms such as icerebral malaria. In cerebral malaria the sequestrated red blood cells can breach the blood brain barrier possibly leading to coma.

ii) Erythrocytic schizogony:

 

At the completion of the pre-erythrocytic schizogony, 

the mature schizonts rupture the liver cells 

and millions of mature merozoites escape into the blood, 

wherein they infect the red blood cells. 

These merozoites continue to multiply within the red blood cells 

and mature into trophozoite and then erythrocytic schizont.

The matured schizonts will rupture and release millions of merozoites.

Haemolysis of the RBCs will lead to anaemia. 

Besides that, the release of the merozoites, parasites debris 

and endogenous pyrogens into the blood circulation 

will cause the malarial fever

Some merozoites turn into male and female gametocytes. 

Since the gametocytes are formed in the blood of the vertebrate host,

the vertebrate host is the definitive host of the disease

If a mosquito pierces the skin of an infected person, 

it potentially picks up gametocytes within the blood. 

Fertilization and sexual recombination of the parasite

occurs in the mosquito's gut

New sporozoites develop and travel to the mosquito's salivary gland, 

completing the cycle 

 Immunological basis of Malarial infections

 

Clinical Manifestation

·   Symptoms of malaria usually start to appear 10-15 days after the bite of an infected mosquito. 

· The typical prepatent and incubation periods following sporozoite inoculation vary according to species. 

·  The prepatent period is defined as the time between sporozoite inoculation and the appearance of parasites in the blood and represents the duration of the liver stage and the number of merozoites produced. 

·   Incubation periods tend to be a little longer and are defined as the time between sporozoite inoculation and the onset of symptoms.

·   All four species can exhibit non-specific prodromal symptoms a few days before the first febril attack. 

·   These prodromal symptoms are generally described as 'flu-like' and include: headache, slight fever, muscle pain, anorexia, nausea and lassitude. The symptoms tend to correlate with increasing numbers of parasites.

 

·   These prodromal symptoms will be followed by febrile attacks also known as the malarial paroxysms. 

·   These paroxysms will exhibit periodicities of 48 hours(benign tertian) for P. vivax, P. ovale, and P. falciparum, 36-48 hours fever(malignant tertian) for P. falciparum and a 72-hour periodicity(quartan fever) for P. malariae.

 

·  Patients may also exhibit splenomegaly, hepatomegaly (slight jaundice), and hemolytic anemia during the period in which the malaria paroxysms occur.

The Malarial Paroxysm

cold stage hot stage sweating stage feeling of intense cold vigorous shivering lasts 15-60 minutes intense heat dry burning skin throbbing headache lasts 2-6 hours profuse sweating declining temperature exhausted and weak → sleep lasts 2-4 hours

·  The malarial paroxysm usually last 4-8 hours and begins with a sudden onset of chills(cold stage). 

·  Immediately following this cold stage is the hot stage. The patient feels an intense heat accompanied by severe headache. fatigue, dizziness, anorexia, myalgia, and nausea will often be associated with the hot stage. 

·   Next a period of profuse sweating will ensue and the fever will start to decline. The patient is exhausted and weak and will usually fall asleep.

·  After awake the patient usually feels well, other than being tired, and does not exhibit symptoms until the onset of the next paroxysm.

	A typical pattern of temperature (fever) in relation to blood-stage schizogony for the human malarial parasites. The fever paroxysm corresponds to the period of infected erythrocyte rupture and merozoite invasion. (Figure modified from Neva and Brown, Basic Clinical Parasitology, 6th ed., 1994.

Prognosis

                 Most of the people who become infected with P. malariae, ovale, or vivax do well and the fevers abate after about 96 hours. Yet, in endemic areas, reinfection is common. Malaria caused by P. falciparum orP. Knowlesi have outcomes ranging from fair to poor, even when treated. 


                 This is because it depends on how the parasites react to treatment. Untreated people often die from these infections. In general, patients who are infants, children under the age of 5 (especially in sub-Saharan countries), and those immunocompromised patients (for example, AIDS or cancer patients) have a more guarded prognosis.

                 Cerebral malaria carries a mortality of around 20% in adults and 15% in children. Residual deficits are unusual in adults (<3%). About 10% of the children (particularly those with recurrent hypoglycemia, severe anemia, repeated seizures and deep coma), who survive cerebral malaria may have persistent neurological deficits.

Effect and Complication

The list of complications that have been mentioned in various sources for Malaria includes:

• Cerebral malaria
• Death
• Mother-infant transmission - pregnant mother can infect the fetus.
• Low birth weight
• Anemia
• Jaundice
• Kidney failure
• Fluid imbalance
• Enlarged spleen
• Enlarged liver
• Blackwater fever
• Hematuria
• Liver complications 
• Brain complications 
• Hypoglycemia

Read more at http://www.wrongdiagnosis.com/m/malaria/complic.htm?ktrack=kcplink

Diagnosis

The main method of malaria diagnosis has been the microscopic examination of blood. Besides blood, both saliva and urine have been investigated as alternative, less invasive specimens.

a) Blood films

The most economic, preferred, and reliable diagnosis of malaria is microscopic examination of blood films because each of the four major parasite species has distinguishing characteristics. Two sorts of blood film are traditionally used:

1. Thin film

• allow species identification because the parasite's appearance is best preserved in this preparation. 

     2.  Thick film

• allow the microscopist to screen a larger volume of blood and are about eleven times more sensitive than the thin film, so picking up low levels of infection is easier on the thick film, but the appearance of the parasite is much more distorted and therefore distinguishing between the different species can be much more difficult.  
• Diagnosis of species can be difficult because the early trophozoites ("ring form") of all four species look identical which is a single ring form.  

Thick and thin blood blood films

 

b) Antigen tests

•  Immunochromatographic tests (also called Malaria Rapid Diagnostic Tests, Antigen-Capture Assay or "Dipsticks") use finger-stick or venous blood and the completed test takes a total of 15–20 minutes
• results are read visually as the presence or absence of colored stripes on the dipstick, so they are suitable for use in the field. 
• The threshold of detection  is in the range of 100 parasites/µl of blood  
• One disadvantage is that dipstick tests are qualitative but not quantitative - they can determine if parasites are present in the blood, but not how many.
• The first rapid diagnostic tests were using P. falciparum glutamate dehydrogenase as antigen.
• PGluDH was soon replaced by P.falciparum lactate dehydrogenase, a 33 kDa oxidoreductase [EC 1.1.1.27].
• It is the last enzyme of the glycolytic pathway, essential for ATP generation and one of the most abundant enzymes expressed by P.falciparum. 
• PLDH does not persist in the blood but clears about the same time as the parasites following successful treatment. 
• The lack of antigen persistence after treatment makes the pLDH test useful in predicting treatment failure. In this respect, pLDH is similar to pGluDH. 

c) Molecular methods

• PCR (and other molecular methods) is more accurate than microscopy. 
• However, it is expensive, and requires a specialized laboratory.
• Levels of parasitemia are not necessarily correlative with the progression of disease, particularly when the parasite is able to adhere to blood vessel walls.