Epidemiology of malaria

Epidemiology of malaria

1. Epidemiology of Malaria Dr. Kunadoddi Archana Assistant Professor Community Medicine Department Rama Medical College and Research Centre, Hapur

2. Malaria Malaria is a protozoal disease caused by infection with parasites of the genus Plasmodium and transmitted to man by certain species of infected female Anopheline mosquito.

3. The clinical features of malaria vary from mild to severe, and complicated, according to the species of parasite present, the patient's state of immunity, the intensity of the infection and also the presence of concomitant conditions such as malnutrition or other diseases.

4. Problem statement WORLD: About 198 million (124-283 million) cases of malaria in the year 2013 and an estimated 584,000 deaths (367,000-755,000). Malaria mortality rates have fallen by 4 7 per cent globally since year 2000, and by 54 per cent in the WHO African Region. Most deaths occur among children living in Africa, where a child dies every minute from malaria.

5. The specific risk groups for malaria includes the following population: young children non-immune pregnant women people with HIV/AIDS international travellers immigrants and their children

6. INDIA Malaria is a major public health threat in India, particularly due to Plasmodium falciparum which is prone to complications. In India about 21.98 per cent population lives in malaria high transmission(2: 1 case/1000 population) areas and about 67 per cent in low transmission (0-1 case/1000 population) areas.

7. About 92 per cent of malaria cases and 97 per cent of deaths due to malaria is reported from North-eastern states, Chhattisgarh, Jharkhand, Madhya Pradesh, Orissa, Andhra Pradesh, Maharashtra, Gujarat, Rajasthan, West Bengal and Karnataka.

8. India is predominantly characterized by unstable malaria transmission. Transmission is seasonal with increased intensity related to rains. Due to the low and unstable transmission dynamics, most of the population has no or little immunity toward malaria. As a result, the majority of Indians living in malarious areas are at risk of infection with all age groups affected.

9. There are six primary vectors of malaria in India 1)An. Culicifacies (P. Vivax and P. falciparum )- rural and peri -urban areas 2)An. Stephensi - is responsible for malaria in urban and industrial areas. 3) An. Fluviatilis - vector in hilly areas, forests and forest. 4) An. Minimus - vector in hilly areas 5) An. dirus - important forest vector in the North-East. 6) An. Epiroticus - Andaman and Nicobar Islands.

10. Epidemiological determinants AGENT: In India, about 50 per cent of the infections are reported to be due to P. falciparum and 4-8 per cent due to mixed infection. Life history: The malaria parasite undergoes 2 cycles of development the human cycle ( asexual cycle ) and the mosquito cycle ( sexual cycle ). Man is the intermediate host and mosquito the definitive host.

11. RESERVOIR OF INFECTION A human reservoir is one who harbours the sexual forms (gametocytes) of the parasite. A patient can be a carrier of several plasmodial species at the same time. Children are more likely to be gametocyte carriers than adults. The child is thus epidemiologically a better reservoir than the adult.

12. PERIOD OF COMMUNICABILITY In vivax infections, gametocytes appear in blood 4-5 days after the appearance of the asexual parasites; In falcipanim infections, they do not appear until 10-12 days after the first appearance of asexual parasites.

13. RELAPSES It is usual for vivax and ovale malaria to relapse more than 3 years after the patient's first attack. Recurrences of falciparum malaria usually disappear within 1-2 years.

14. Host factors AGE SEX RACE: Individuals with AS haemoglobin (sickle-cell trait) have a milder illness with falciparum infection than do those with normal (AA) haemoglobin . Persons whose red blood cells are "Duffy negative" (a genetic trait) are resistant to P. vivax infection.

15. PREGNANCY: Pregnancy increases the risk of malaria in women. Malaria during pregnancy may cause intrauterine death of the foetus ; it may also cause premature labour or abortion. Primigravid women are at greatest risk. SOCIO-ECONOMIC DEVELOPMENT HOUSING POPULATION MOBILITY: People migrate for one reason or other from one country to another or from one part of a country to another. Labourers connected with various engineering, irrigation, agricultural and other projects and periodic migration of nomads and wandering tribes are outstanding examples of internal migration.

16. OCCUPATION HUMAN HABITS: Habits such as sleeping out of doors, refusal to accept spraying of houses, replastering of walls after spraying and not using measures of personal protection (e.g. bed nets) influence man-vector contact, and obviously the choice of control measures. IMMUNITY

17. Environmental factors SEASON : maximum prevalence is from July to November. TEMPERATURE : Temperature affects the life cycle of the malaria parasite. development of the malaria parasite in the insect vector is between 20 deg. to 30 deg.C HUMIDITY : The atmospheric humidity has a direct effect on the length of life of the mosquito, although it has no effect on the parasite. when the relative humidity is high, mosquitoes are more active and they feed more voraciously.

18. Environmental factors cont.. RAINFALL : Rain in general provides opportunities for the breeding of mosquitoes and may give rise to epidemics of malaria. ALTITUDE : Anophelines are not found at altitudes above 2000-2500 metres , due to unfavourable climatic conditions. MAN-MADE MALARIA : Burrow pits, garden pools, irrigation channels and engineering projects like construction of hydroelectric dams, roads, bridges have led to the breeding of mosquitoes and an increase in malaria.

19. Factors which determine the vectorial importance of mosquitoes are DENSITY LIFE SPAN CHOICE OF HOST RESTING HABITS BREEDING HABITS TIME OF BITING RESISTANCE TO INSECTICIDES

20. Mode of transmission VECTOR TRANSMISSION : Malaria is transmitted by the bite of certain species of infected, female, anopheline mosquitoes. A single infected vector, during her life time, may infect several persons. DIRECT TRANSMISSION : Malaria may be induced accidentally by hypodermic intramuscular and intravenous injections of blood or plasma, e.g., blood transfusion, malaria in drug addicts CONGENITAL MALARIA : Congenital infection of the newborn from an infected mother may also occur, but it is comparatively rare.

21. Incubation period The duration of the incubation period varies with the species of the parasite this is 12 (9-14) days for falciparum malaria , 14 (8-17) days for vivax malaria and 17 (16-18) days for ovale malaria. With some strains of P. vivax , the incubation period may be delayed for as long as 9 months.

22. Clinical features The primary fever is marked by paroxysms which correspond to the development of the parasites in the red blood cells. The peaks of the fever coincide with the release into the blood stream of successive broods of merozites . The typical attack comprises three distinct stages:-

23. Clinical features Cont.. COLD STAGE : The onset is with lassitude, headache, nausea and chilly sensation followed in an hour or so by rigors. The temperature rises rapidly to 39-41°C. Headache is often severe and commonly there is vomiting. In early part of this stage, skin feels cold; later it becomes hot. Parasites are usually demonstrable in the blood. The pulse is rapid and may be weak. This stage lasts for 1/4-1 hour.

24. Clinical features Cont.. HOT STAGE : The patient feels burning hot and casts off his clothes. The skin is hot and dry to touch. Headache is intense but nausea commonly diminishes. The pulse is full and respiration rapid. This stage lasts for 2 to 6 hours.

25. Clinical features Cont.. SWEATING STAGE : Fever comes down with profuse sweating. The temperature drops rapidly to normal and skin is cool and moist. The pulse rate becomes slower, patient feels relieved and often falls asleep. This stage lasts for 2-4 hours.

26. Diagnosis Microscopy : (The "thin film" and the "thick film“).The sensitivity is high. It is possible to detect malarial parasite at low densities. It also helps to quantify the parasite load. It is possible to distinguish the various species of malaria parasite and their different stages. Serological test :The malarial fluorescent antibody test usually becomes positive two weeks or more after primary infection. The test is of the greatest value in epidemiological studies and in determining whether a person has had malaria in the past.

27. Diagnosis Cont.. Rapid diagnostic test (RDT) : Rapid Diagnostic Tests are based on the detection of circulating parasite antigens with a simple dipstick format. The latter kits are expensive and temperature sensitive.

28. Measurement of malaria PRE-ERADICATION ERA : In the pre-eradication era, the magnitude of the malaria problem in a country used to be determined mostly from the reports of the clinically diagnosed malaria cases. Therefore, the classical malariometric measures may provide the needed information, i.e. the trend of the disease.

29. Measurement of malaria Cont.. ( PRE-ERADICATION ERA ) SPLEEN RATE : It is defined as the percentage of children between 2 and 10 years of age showing enlargement of spleen. Adults are excluded from spleen surveys , because causes other than malaria frequently operate in causing splenic enlargement in them. The spleen rate is widely used for measuring the endemicity of malaria in a community.

30. Measurement of malaria Cont.. ( PRE-ERADICATION ERA ) AVERAGE ENLARGED SPLEEN : It is a useful malariometric index. PARASITE RATE : It is defined as the percentage of children between the ages 2 and 10 years showing malaria parasites in their blood films. PARASITE DENSITY INDEX : It indicates the average degree of parasitaemia in a sample of well-defined group of the population.

31. Measurement of malaria Cont.. ( PRE-ERADICATION ERA ) INFANT PARASITE RATE : It is defined as the percentage of infants below the age of one year showing malaria parasites in their blood films. PROPORTIONAL CASE RATE : It is defined as the number of cases diagnosed as clinical malaria for every 100 patients attending the hospitals and dispensaries.

32. ERADICATION ERA (current incidence levels) 1. Annual parasite incidence ( API ) API= Confirmed cases during one year X1000 Population under surveillance 2. Annual blood examination rate (ABER) ABER = Number of slides examined X100 Population

33. ERADICATION ERA cont.. (current incidence levels) 3. Annual falciparum incidence (AFI) 4. Slide positivity rate (SPR) 5. Slide falciparum rate (SFR).

34. VECTOR INDICES A malaria survey is not complete unless it includes investigations relating to the insect vector. Some of the important vector indices are: 1. HUMAN BLOOD INDEX : It is the proportion of freshly-fed female Anopheline mosquitoes whose stomach contains human blood. It indicates the degree of anthrophilism .

35. VECTOR INDICES Cont.. 2. SPOROZOITE RATE :It is the percentage of female anophelines with sporozoites in their salivary glands. 3. MOSQUITO DENSITY : It is usually expressed as the number of mosquitoes per man-hour-catch. 4. MAN-BITING RATE : It is defined as the average incidence of anopheline bites per day per person.

36. VECTOR INDICES Cont.. INOCULATION RATE : The man-biting rate multiplied by the infective sporozoite rate is called the inoculation rate. Used in building up a epidemiological picture of malaria.

37. APPROACHES AND STRATEGIES OF MALARIA CONTROL Strategic Action Plan for malaria control in India, 2007-2012, and more recently 2012-2017 were developed by Directorate of National Vector Borne Disease Control Programme . The strategies for prevention and control of malaria and its transmission are: Surveillance and case management : Case detection (passive and active) Early diagnosis and complete treatment Sentinel surveillance.

38. APPROACHES AND STRATEGIES OF MALARIA CONTROL Cont.. (B) Integrated vector management : Indoor residual spray (IRS) Insecticide treated bed-nets Antilarval measures including source reduction.

39. APPROACHES AND STRATEGIES OF MALARIA CONTROL Cont.. (C) Epidemic preparedness and early response (d) Supportive interventions: ( 1) Capacity building (2) Behavioural change communication (3) Intersectoral collaboration (4) Monitoring and Evaluation (5) Operational research and applied field research.

40. Treatment The aims of the Malaria case management are: To provide prompt and complete treatment to all suspected/ confirmed cases of malaria To prevent progression of mild cases of malaria in to severe or complicated from of malaria To prevent deaths from severe and complicated malaria To prevent transmission of malaria To minimize risk of spread of drug resistant parasites by use of effective drugs in appropriate dosage by everyone

41. Uncomplicated P. Vivax malaria Uncomplicated malaria is defined as symptomatic malaria without signs of severity or evidence (clinical/ laboratory)of vital organ dysfunction. Dosage of CQ (CQ sensitive ) 25 mg/kg (base) divided over 3 days. Day 1 -10mg/kg Day 2- 10 mg/kg Day 3- 5 mg/kg Plus Primaquine 0.25 mg/kg for 14 days along with food after negative G6PD testing

42. Uncomplicated P. Vivax malaria Cont.. In mild to moderate G6PD deficiency, primaquine to be given 0.75 mg/kg once a week for 8 weeks In severe deficiency, it should not be given. Also c o n t r a i ndi ca t ed i n p r eg n a n c y a n d chil d r en <4 yr s CQ resistant: ACT (except AS+SP) along with primaquine . AS+SP not effective and rapidly develop resistance to P. Vivax species.

43. Uncomplicated P. Vivax malaria Cont..  Treatment of mixed infections ( P.vivax + P.falciparum ) cases:  All mixed infections should be treated with full course of ACT and Primaquine 0.25 mg per kg body weight daily for 14 days. Treatment of P. ovale and P. malariae : In India these species are very rarely found in few places. P. ovale should be treated as P. vivax and P. malariae should be treated as P. falciparum . Treatment of mixed infections: All cases of mixed infection are to be treated as Pf plus primaquine for 14 days

44. Uncomplicated P. Falci malaria Dose schedule: Artemisinin based Combination Therapy (ACT- SP) Artesunate 4 mg/kg body weight daily for 3 days Plus Sulfadoxine (25 mg/kg body weight) – Pyrimethamine (1.25 mg/kg body weight) on first day  or Artesunate (4 mg/kg qd for 3 days) plus amodiaquine (10 mg of base/kg qd for 3 days) plus Primaquine : 0.75 mg/kg body weight on day 2.

45. Uncomplicated P. Falci malaria Cont.. Multidrug-resistant P. falciparum malaria: Artemether-lumefantrine c (1.5/9 mg/kg bid for 3 days with food)  or Artesunate c (4 mg/kg qd for 3 days)  plus Mefloquine (25 mg of base/kg—either 8 mg/kg qd for 3 days or 15 mg/kg on day 2 and then 10 mg/kg on day 3)

46. Uncomplicated P. Falci malaria Cont.. Second-line treatment/treatment of imported malaria: Artesunate c (2 mg/kg qd for 7 days)  Or Quinine (10 mg of salt/kg tid for 7 days)  plus 1 of the following 3: 1. Tetracycline e (4 mg/kg qid for 7 days) 2. Doxycycline e (3 mg/kg qd for 7 days) 3. Clindamycin (10 mg/kg bid for 7 days)

47. VECTOR CONTROL STRATEGIES Anti-adult measures : ( i ) Residual spraying : Malathion and fenitrothion are organophosphate insecticides which are being used with increasing frequency for malaria control following the development of vector resistance to DDT . (ii) Space application : It involves the application of pesticides in the form of fog or mist using special equipment.

48. VECTOR CONTROL STRATEGIES Cont.. (iii) Individual protection : use of repellents, protective clothing, bed-nets (b) Anti-larval measures Larvicides : paris green effectively controlled malaria, temephos which confer long effect with low toxicity are more widely used. (ii) Source reduction : drainage or filling, deepening or flushing, management of water level, changing the salt content of water and intermittent irrigation are among the classical methods of malaria control to which attention is being paid again.

49. VECTOR CONTROL STRATEGIES Cont.. (iii) Integrated control : In order to reduce too much dependance on residual insecticides, increasing emphasis is being put on "integrated" vector control methodology which includes bioenvironmental and personal protection measure . This approach is important because there is no single and simple method that would ensure control of transmission.

50. MALARIAL VACCINES Vaccination against malaria is burning issue today. They are under intensive research. The task of developing a preventive vaccine for malaria is a complex process. There are number of consideration to be made concerning what strategy a potential vaccine should be adopt.

51. References: K Park. Textbook of Preventive and Social Medicine. 23rd edition. Diagnosis and treatment of malaria 2013, NVBDCP

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