Malaria basics Paul R. Earl Facultad de Ciencias Biológicas Universidad Autónoma de Nuevo León San Nicolás, NL, Mexico

1. Malaria basicsPaul R. EarlFacultad de Ciencias BiológicasUniversidad Autónoma de Nuevo LeónSan Nicolás, NL, Mexico

2. The main points.The protozoan genus Plasmodium is responsible for malaria and has four medically important species: Plasmodium falciparum, P. vivax, P. malariae and P. ovale. The most vicious of these is P. falciparum because it is rapidly fatal and is responsible for most malaria related deaths. Mosquito-transmitted malaria is the greatest public health problem in large parts of the world with more than 500 million clinical cases and over 3 million deaths every year, mostly in African children under five years.

3. Malaria occurs in most of the tropics of the world with P. falciparum predominating in subSaharan Africa through to New Guinea. P. vivax is more common on the Indian subcontinent, in Mexico & in Central America with the prevalence of falciparum and vivax malarias being about the same in Asia, Oceania and South America. Infrequent P. malariae is found in most endemic areas, especially subSaharan Africa that has also 90 % of the deaths. P. ovale is unusual outside Africa, although it can be found in southern India. Also, malaria can be a traveler’s disease and imported into any country.

4. By 1970 malaria eradication had succeeded with DDT in all Europe. Malaria used to be prevalent in Russia, USA & Canada. It was prevalent around the Mediterranean, Italy, Greece, Yugoslavia, Bulgaria, Turkey and southern Britain. It had also been eradicated in USSR, North America, several middle eastern countries, large parts of South America, the Caribbean, Australia, Japan and Taiwan. See the map.

5. In India 75 million cases in 1950 were down to 100,000 cases by 1970. Transmission rates in Africa and India were severely reduced. Malaria had been almost eliminated in Sri-Lanka. All of this progress was lost because of DDT hysteria. The enormous penalty for hysteria and mendacity includes losing control of filariasis. Still, the WHO did know what would happen if DDT was suspended. Mendacity is exhibited by crying about drug resistance, while not honestly discussing or otherwise even mentioning lifesaving DDT. Affluent countries without malaria decided to ban DDT whose main features are low cost and efficient residual effect.

6. Clinical symptomsinclude the following: cough, fatigue, malaise, arthralgia, myalgia, and paroxysm of shaking chills and sweats. The classic paroxysm begins with a period of shivering and chills, which lasts for 1-2 hours followed by high fever. Paroxyms of varying 48 hours belong to vivax, ovale and falciparum malaria, whereas 72 hours belongs to malariae infections.

7. As many as 30% of nonimmune adults infected with P falciparum suffer acute renal failure, some with seizures. Blackwater fever is hemoglobinuria with the passage of dark-colored urine Noncardiogenic pulmonary edema is most common in pregnant women and results in death in 80% of patients. Profound hypoglycemia often occurs in young children and pregnant women. The most prominent symptoms all relate to loss of RBCs: a) tachycardia, b) anemia, c) fever, d) hypotension and e) splenomegaly.

8. Malaria has always had a greater impact on humans than any other parasite or infectious agent. Malaria is a rural disease due to the presence of the female Anopheles mosquito vector. Can mosquito vector transmission be lowered? How? In 1956 the World Health Organization (WHO) began a global malaria eradication program, mainly because of the effectiveness of DTT in killing the mosquito vectors. This is an incredibly good pesticide, cheap to make, long-lasting and apparently harmless to humans.

9. One biological reason for the defeat was the development of some resistance to pesticides by the vectors, and another was the development of some drug resistance by the parasite itself. But . . . When health authorities do not have the money or have the will to spend it on vector control, they often lie and promote underestimates of the threat.Transgenic mosquitoes incompetent to transmit the sporozoites are a bright shiny hope.

10. How is global malaria to be managed? Who pays the bill? Political will, public health education and similar social factors sometimes centering on poverty shape the WHO campaign for eradication. Global eradication as an ideal may be impossible for fault of gigantic financing, yet the eradication of malaria is long overdue in countries like Mexico that have fallen very far behind the position they had in their DDT days, not willing to spend the money. Many populations across the world have no idea of the health threats that they live under.

11. What does relapse mean? An infected person who has recovered functions normally for a long time then becomes ill, i. e., has a relapse. Let us say that his town is malaria-free. By 2-3 weeks an outbreak of malaria occurs and public health officials face a new series of infection cycles in local mosquitoes. Universally, the mosquito vectors are not infected as a rule. A single case of relapse is likely to cause a disaster. Before relapse, transmission was not occurring. Acute hospitalized cases display many parasites in red blood cells (RBC), whereas cases in recovery do not, therefore some way has to be found to concentrate RBCs, especially in vivax malaria. This is the thick.

12. Symptoms.Malaria is characterized by severe undulating fever (paroxyms) occurring every 48 or 72 hours, depending on the species, varying from 48 hours in P.vivax, P. ovale, and P. falciparum malaria, to 72 hours in P. malariae infections. The 48 hour fever is called tertian because it occurs every third day: fever on day 1, no fever on day 2, fever on day 3 and so on. The 72 hour fever is called quartan, because it returns on every fourth day.The erythrocytic schizogony cycle (vegetative) becomes synchronized, and the febrile paroxysms become consistent.

13. Table1. Clinical Features of MalariaP. vivax, P. falciparum P. MalariaeP. ovale . Incubation 8-24 d 8-24 d 15-30 daysType of fever Tertian Aperiodic Quartan quotidianExoerythrocytic cycle Yes No No Relapse Common Recrudescence Recrudescence

14. The principal signs of cerebral malaria are seizures and unconsciousness, usually preceded by a severe headache. Neurologic examination may include contracted or unequal pupils, a Babinski sign, and absent or exaggerated deep tendon reflexes. Cerebrospinal fluid examination shows increased pressure, increased protein, and minimal or no pleocytosis. High fever, 41° to 42°C (106° to 108°F), with hot, dry skin may occur.

15. Often fatal, acute pulmonary edema can develop rapidly and is associated with excessive intravenous fluid therapy. Fast, labored respiration, with shortness of breath, a non-productive cough, and physical findings of moist rales and rhonchi are usually present. Chest X-rays usually show increased bronchovascular markings. Most patients with falciparum malaria complain of loss of appetite and nausea. However, in some patients (especially young children), additional symptoms including vomiting, abdominal pain, watery diarrhea, and jaundice.

16. Treatment of Malaria.1) P. vivax, P. ovale: Oral chloroquine 10 mg/kg (max. 600 mg) followed by 5 mg/kg (max. 300 mg) after 6, 24 and 48 hours Oral primaquine 15 mg/kg / day x 14 days to prevent relapse 2) P. falciparum:Chloroquine sensitive – As above. Chloroquine resistant - Pyrimethamine 25 mg + sulphadoxine 500 mg tablets - 3 tablets single dose for adults OR - Quinine sulphate 650 mg (10 mg/kg) salt orally TDS times 7 days, plus Tetracycline 250 mg QDS times 7 days - Multidrug resistant - Mefloquine 15-25 mg/kg (max 1.5 g) single dose orally OR - Artesunate 200 mg on first day followed by 100 mg daily times 4 days.

17. The vector life cycle. All four species are transmitted through the bite of an infected female Anopheles species mosquito. Malaria also can be transmitted via a blood transfusion or congenitally between mother and fetus. Malaria-carrying Anopheles mosquitoes tend to bite only near dusk and dawn. The vector, the Anopheles species mosquito, passes plasmodia, which are contained in its saliva, into its host while obtaining a blood meal. Plasmodia enter circulating RBCs and feed on the hemoglobin, other proteins and glucose within the cells.

18. Insect life cycles are well known: eggs, pupas, larvas and adults. Anopheles mosquitoes feeding on infected hosts ingest sexual forms developing in RBCs. The female macrogametocytes and male microgametocytes mature in the mosquito’s stomach and combine forming a zygote. The products of this fertilization are ookinetes, which force themselves between the epithelial cells to the outer surface of the mosquito stomach, and form into small spheres called oocysts. The oocysts enlarge as the nucleus divides, eventually rupturing and releasing thousands of motile sporozoites into the body cavity. The sporozoites migrate to the salivary glands, making the female mosquito infective. The vector phase of the life cycle, called sporogony, is complete in 8 to 35 days depending on species and environmental conditions.

19. The mammalian life cycle.Plasmodia replicate inside the RBC. This replication induces RBC cytolysis and causes the release of toxic metabolic byproducts into the bloodstream. These symptoms include chills, headache, myalgias and malaise, occurring in cycles. The parasite also may cause splenomegaly, jaundice and anemia. The symptoms relate to blood cell destruction. P falciparum may induce kidney failure, coma and death.

20. The sexual cycle.Fertilization of the macro- by the microgamete to form a karyosome called a sporogonia in the mosquito stomach is a good place to start the life cycle, but by tradition it starts with the mosquito bite of the mammal, bird or other vertebrate host. The injection of sporozooites caused infection. Sporo-zoites, the infective stage of plasmodia, are injected from the salivary glands of mosquitoes during a blood meal. The sporozoites disappear from the blood within a half hour, most destroyed by white blood cells, but some enter liver cells. Sporozoites that enter liver cells multiply asexually in a process called exoerythrocytic schizogony.

21. Merozoite is the traditional term for vegetative or nonsexual state = trophozoite = schizont. A hepatic schizont contains many thousands of tiny, invasive merozo-ites, created in a single segmentation. These asexual merozoites are the smallest and shortest lived form of the life cycle. Within a few minutes, they invade RBCs. The apical complex of the merozite is specialized to recognise and attach to epitopes on the RBCsOver 5-10 hours, the zygote in the mosquito differentiates into a cigar-shaped invasive ookinete. During the differentiation of the ookinete the diploid set of chromosomes divides as the first step in a two stage meiosis, the second stage takes place at the start of sporogony.

22. All infected liver cells parasitized with P. falciparum and P. malariae rupture and release merozoites at about the same time. In contrast, P. vivax and P. ovale have two exoerythrocytic forms. The primary type develops, causes liver cell rupture, and releases merozoites just as in P. falciparum and P. malariae. The other form, which develops concurrently, is known as the hypnozoite. Sporozoites that enter liver cells differentiate into nonsexual hypnozoites that remain dormant for weeks, or even years. The hypnozoites activate and undergo exoerythrocytic schizogony, forming a wave of merozoites that cause a relapse.

23. Anopheles species.North America, from Great Lakes to southern Mexico: A. freeborni, A. quadrimaculatus, A. hermsi Central America, southwestern Mexico, Caribbean islands, north of South American coast: A. albimanus, A. argyritarsis, A. pseudopunctipennis, A. aquasalis, A. darlingiSouth America: A. pseudopunctipennis, A. punctimaculus, A. albimanus, A. albitaris, A. aquasalis, A. darlingi North Eurasia, Europe and west Asia, excluding Mediterranean coast: Mediterrane-an South coast of Europe, North coast of Africa: A. atroparvus, A. labranchiae, A. sacharovi, A. superpictus

24. Defective globin genes.About 250 million people, 4.5 % of the world population,are carriers of a defective globulin gene. Each year about 300,000 homozygotes are born about equally divided between sickle cell disorders and thalassemia syndromes. Malarial parasites feed on RBCs. Then clinical symptoms like plain anemia and just about everything else are strongly affected by RBC destruction. Are there mutant hemoglobin molecules unsuitable to mosquitoes? Yes. One causes sickle cell anemia, and others cause - and -thalassemias.

25. Another associated genetic blood disease is glucose-6-phosphate dehydrogenase deficiency in RBCs. Only men are affected as this is an X-chromosome linked trait. Glucose-6-phosphate dehydrogenase is involved in protecting RBCs from damage by free radicals and in particular reactive oxygen intermediates.

26. In sickle cell anemia, normal hemoglobin is replaced by hemoglobin S (HbS). HbS is much less soluble than normal hemoglobin when in the deoxygenated state and may precipitate, distorting the RBCs. This is caused by a single amino acid substitution where a glutamic acid in the gene sequence is replaced by a valine.

27. A heterozygous person has HbA/HbS. Their blood appears normal unless exposed to low oxygen when reversible sickling occurs. However, the homozygotes with HbS/HbS become ill, and most die in infancy. Children who are heterozygous are more likely to survive than those having normal hemoglobin. Is selection of the fittest in operation?

28. Hemoglobin consists of two subunits, 2- and 2-. In thalassemia, one of the two subunits is not made. The persons lack either the - or -subgroups. This causes abnormal RBCs that again confer resistance to malaria.One homozygote dies of malaria, the other of a globin gene defect, and the heterozygotic person is protected.

29. Laboratory identifications with Giemsa. Again, the heart of an eradication campaign is the thick. Interest focuses on good Geimsa staining. You must be able to identify the gametocytes of the 4 species, but first find out if malaria parasites are present. Examine a thick Giemsa slide, especially if from a field survey. The hospital slide from a patient already diagnosed needs to be identified to the species level.

30. Vaccination and control.In general, vaccination, yet to be truely developed for malaria, prevents high-risk diseases. High risk can relate to lack of vector control, and involves millions of people. Next, the cost of any procedure is paramount. Diagnosis by the polymerase chain reaction (PCR) can become routine in some laboratories, whereas in most the cost is prohibitive. Dipsticks for histidine-rich protein (HRP2) of P. falciparum are accurate, fast and cheap. Other simple immunological highlights may develop. Present rapid dipstick methods stand out.

31. The first requirement for the classic malariologist is to differentiate the 4 malaria species with Giemsa stain at the microscope. Diagnosis, medical treatment, epidemiology, vector control and vaccination (hardly mentioned here) and other concerns all follow the identifications of infections from asymtomatic to fatal. In eradication campaigns, emphasis might be placed on rooting out silent or relapsed cases. The prevalence of malaria in some districts points to the failure of vector control.

32. Roll Back Malaria. The campaign Roll Back Malaria in Africa involving the manufacture of insecticide impregnated sleeping nets began in October 1998, supported by the World Health Organization (WHO). Regardless, the way to rid the world of malaria and some other insect-borne diseases like dengue fever is by spraying residual insecticides like DDT inside houses. The establishment of the Global Fund to Fight AIDS, Tuberculosis and Malaria (GFATM) is providing significant new grants to help countries accelerate implementation of their plans to roll back malaria.

33. Malaria morbidity and mortality a) Hospital deaths due to malaria: the percentage of recorded inpatient deaths that are attributed to malaria; derived from Ministry of Health reports where data are available, b) Malaria admissions: the percentage of recorded health facility admissions that are attributed to malaria, c) Malaria outpatient attendance: the percentage of recorded outpatient visits to health facilities that are attributed to malaria.