Epidemiological types of malaria


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Epidemiological types of malaria

  1. 1. Ravi M R PG Dept of Community medicine JSSMC Mysore.
  2. 2. •Introduction •Problem statement •Life cycle of malaria •Human malaria parasites and factors influencing malaria transmision •Epidemiological types • -classification on basis of transmission patterns • - Geographic areas according to intensity of transmision • - defined by WHO • - epidemiological types in india • - other epidemiological types
  3. 3. Introduction  Definition of malaria- A protozoal disease caused by infection with parasites of genus plasmodium and transmitted to man by certain species of infected female Anopheline mosquito.
  4. 4. Mal’ aria= bad air. •Italian word. •The term originally denoted the unwholesome atmosphere caused by the exhalation of marshes, to which the disease was formerly attributed .
  5. 5. Plasmodium, was first identified in 1880 by Charles Laveran The role of mosquitoes  discovered in 1897, winning Ronald Ross the Nobel prize
  6. 6. PROBLEM STATEMENT •Malaria is transmitted in 108 countries containing 3 billion people and causes nearly 1 million deaths each year •In 2008 there were an estimated 243 mllion cases of malaria worldwide. A vast majotity, about 85% were in african region. •In 2008, the reported cause specific mortality rate for malaria was 17 per lac population worldwide. •Out of the 11 countries of the South East Asian Region (SEAR) of WHO, 10 are malaria Endemic.
  7. 7. Malria in India •Malria continues to be a major public health threat in india. •95% of the Indian population lives in malaria risk prone areas •About 27% population lives in malaria high transmission (> 1 case/1000 population) and about 58% in low transmission (0-1 case/1000 population) •Malaria in India is unevenly distributed. In most parts of India about 90% malaria is unstable with relatively low incidence but with a risk of increase in cases in epidemic form every 7 to 10 yrs •The reported incidence is between 2 and 2. 5 million cases annually with some fluctuations every year for last over two decades.
  8. 8. Life cycle of malaria •Asexual cycle- that occurs in man •Sexual cycle( sporogenic cycle) that occurs in mosquitos
  9. 9. Epidemiological types of malaria - Human malaria parasites and factors influencing malaria transmission
  10. 10. Human malaria parasites and factors influencing malaria transmission Malaria species. •Four species of Plasmodium protozoa cause malaria in humans: P.falciparum, P.vivax, P.ovale and P.malariae. The species differ in many ways, some of which have a direct bearing on transmission and distribution patterns. •In P.vivax and P.ovale infections, a non-immune patient will be infectious to mosquitos at or shortly after the onset of clinical symptoms.
  11. 11. •In the case of P.vivax and P.ovale, some parasites remain dormant in the liver for many months. •Relapses caused by these persistent liver forms (hypnozoites) may appear months, and occasionally up to 4 years after exposure, bringing with it the risk of delayed transmission of the infection to others.
  12. 12. Ambient temperature •The length of extrinsic sporogonic cycle depends on the Plasmodium species and the ambient temperature. •The development of P.falciparum in the female adult Anopheles mosquito requires a minimum temperature of 20°C. •Other human malaria species can develop at temperatures down to a minimum of 16°C. •Above the minimum temperature the development of the parasite in the vector accelerates with increasing temperature.
  13. 13. Development. •socio-economic development has reduced malaria transmission through improvements in agriculture, housing construction, land use, etc. •The concomitant development of health services will reduce morbidity and mortality and contribute to a reduction in transmission. •However, uncoordinated development such as in slum areas of rapid urban growth may enhance malaria transmission. •In ill-designed development projects the thoughtless creation of additional mosquito breeding places may combine with large-scale migration to cause malaria epidemics.
  14. 14. Control efforts. •Control efforts aiming to substantially reduce transmission through unsustainable methods may put populations at risk of epidemic malaria when control efforts can no longer be kept up. War •Epidemics can occurred in areas of social and political upheaval or economic distress, where health infrastructure are destroyed, control efforts abandoned, and large populations had to leave their homes in search of security.
  15. 15. Migration. •Migration of non-immunes into endemic areas may lead to malaria epidemics, as may migration of parasite carriers into non-endemic, receptive area. Resistance to drugs. •Ineffective antimalarial drugs will not clear the parasites from the blood, thus potentially prolonging the infective period of patients. •Also, as second line drugs tend to be more expensive, many people may no longer be able to afford a full treatment course
  16. 16. Transmission patterns Stable malaria •Is caused by the presence of a vector with a frequent man-biting habit, with moderate to high longevity, at temperatures favourable to rapid completion of the sporogonic cycle. •Marked fluctuations other than normal seasonal changes are not likely except when due to obvious causes
  17. 17. •Epidemics are very unlikely, except among non-immune populations arriving to the area. •The regularity of transmission is likely to ensure stable immunity, varying in degree from place to place. •The first objective will be to reduce morbidity and mortality through early diagnosis and adequate treatment of malaria disease, especially in children, and through personal protection methods.
  18. 18. Unstable malaria • occurs where malaria is transmitted by a vector which feeds on humans only infrequently. •Endemicity and the immunity status of the population will differ markedly by area and over time, depending on the presence of other factors favourable for propagation of mosquitos and thus malaria transmission . •When conditions for transmission become favourable, epidemics may occur.
  19. 19. Geographic areas according to intensity of transmision Holoendemic : •Areas of intense transmission with continuing high EIR’s. •Transmission occurs all year long •Virtually every one infected with malaria parasites all time •Under 5 children Spleen rate>75% •Under 5 children Parasitaemia > 60-70%
  20. 20. Hyperendemic : •Regions with intense, but with periods of no transmission during dry season •Under 5 children Spleen rate>50 <70 •Under 5 children Parasitaemia>50 <70
  21. 21. Mesoendemic •Regular seasonal transmission. But at much lower levels •Danger in these ares is occasional epidemics involving those with little immunity . •Under 5 children Spleen rate 20 % <50% •Under 5 children Parasitaemia <20%
  22. 22. Hypoendemic : •Areas with limited malaria transmission . •Population will have little or no immunity •These areas too can have severe malaria epidemics •Under 5 children Spleen rate 0 -<10% •Under 5 ChildrenParasitaemia 0 -<10%.
  23. 23. Further classification schemes have been devised •In efforts to simplify the complexity of epidemiological factors of malaria. •To improve the targeting of stratergies for nalaria control. An expert group brought together by WHO, used an epidemiological approach in 1990 to define a set of eight major epidemiological types of malaria., intended to •Categorize typical transmission to facilitate discussion. •Efficient planning of control efforts.
  24. 24. Malaria of African Savanna •80% of worlds malaria cases and 90% of the mortalty occur in subsaharan africa •The principle vectors are An. Gambiae complex, An. Funestus.
  25. 25. •All breed in aboundance and are highly efficient transmitters of malaria. •All people get infected early in life and have high rates of infant and child mortality. •The survivors gradually develop immunity sufficient to prevent death from malaria by the age of four or five.
  26. 26. •Malaria transmission is typically intense, regular, long, according to the rainfall pattern and presence of water bodies arroung the human communities •Attempts at interruption of transmission or effective control of malaria was unsuccessfull. •Excluded from the world campaign for the eradication of malaria 19551969. •Therefore only few countries were able to develop IRS on national scale
  27. 27. Forest malaria •Is common in many parts of the world, particularly in south east asia and the amazon basin of south america. •Forests and settlements in deforested area harbour very efficent malaria vector. •Regular forest activity was a strong risk-factor for malaria infection
  28. 28. •An. Gambiae, An.moucheti in tropical africa, An.dirus, and An.fluvitalis in south east asia are the efficent vectors. •New comers who enter the forest become heavily infected. •Workers, when staying in the forest overnight, do not usually sleep under insecticide-treated bed nets (ITN) and are therefore exposed to infection. •Moreover, due to the behaviour of the main vector Anopheles dirus (early biting, exophagy and exophily), neither ITNs nor indoor spraying seem to be suitable control measures
  29. 29. Malaria associated with irrigated agriculture Occurs where breeding sites for the mosquitoes become established in the irrigation schemes. •An. culicifacies was found to breed extensively in the smaller irrigation channels (watercourses), especially where vegetation along the edges reduced water velocity.
  30. 30. • when DDT and other potent insecticides became available chemicalbased vector control became the dominating strategy, and engineeringbased interventions lost their importance. • The renewed interest in environmental-management approaches for the control of malaria follows -the rapid development of resistance to the insecticides by mosquitoes, -the increasing cost of developing new chemicals -the logistical constraints involved in the operation of chemical vector control programs. -environmental concerns raised over the use of persistent organic Pollutants.
  31. 31. Highland fringe malaria •Occurs in population settled in high altitudes such as highland plateau of Madgascar, Ethiopia etc. •cyclic epidemic with a period of five to eight years occurs in most parts of the country like ethiopia following climatic changes.
  32. 32. •Plasmodium falciparum and Plasmodium vivax are the dominant species responsible for frequent morbidity and mortality cases. •Anopheles arabiensis and Anopheles quadriannulatus spp B are the two major species of Anopheles gambiae complex that are causing for most malaria transmission. •An. christyi acts as a secondary vector in the highlands •A cyclic epidemic with a period of five to eight years occurs in most parts of the countries of ethiopia , butajira of Africa following climatic changes.
  33. 33. Dessert fringe and oasis malaria •Desert fringe areas are located on warm low land area. •Malaria transmission is dependent on availability of surface water and associated increase in humidity. •AN. Arabiensis are the main vectors which are more adaptable to dry conditions.
  34. 34. •Abnormally heavy rainfall causing flooding almost always gives rise to malaria epidemic in desert fringe areas •Oasis malaria ius characterized by transmission of malaria limited to spring and autumn season when both temperature and humidity are suitable •Transmission usually occurs in abnormal years with very long warm periods or heavy rain fall.
  35. 35. Urban malaria There are two basic types of urban malaria. 1) that transmitted by vectors such as An. Stephensi in south asia, which have adapted to city water sources. 2) In areas of town encroachment into malarious areas such as semi urban African vilages
  36. 36. •Practically all cities of malaria endemic areas accumulate a considerable number of imported malaria cases. •As city dwellers often be infected elsewhere, and medical services of the city attract people in search of treatment. •This accumulation of imported cases tends to be biased towards severe and drug resistant cases, since city hospitals tends to be main referral centres for neighbouring areas.
  37. 37. Plains malaria: •Associated with traditional agriculture in south asia and central america •It is in such areas with relatively stable agricultural economy , that the main success of global eradication campaign, based on IRS were achieved. •Malaria control was not successful in areas where, -Transformation of agricultural infrastructure ( irrigation, transformation of land ownership, road construction etc..) took place -Rural urban migration with rapid development of periurban areas -Modification of agricultural practices, introduction of cash crops. -Increased use of migrant temporary laborers.
  38. 38. Seashore malaria: •Costal areas arround the world offer particularly favourable conditions for malaria transmission. •Efficent vector species often thrive in brackish waters or wetland habitats nad costal areas are often attractive to variety of human activities. •An, labranchiae, An,sacharovi in europe, An.subpictus complex, An. Sudaicus complex in south east asia are the main vctors of seashore or costal malaria.
  39. 39. Epidemiological types of malaria in India Tribal malaria: •the population of tribal areas of Andhra Pradesh, madhya pradesh, Chattisagarh, gujarat, Maharastra, Bihar, Jharkhand , Rajasthan, Orissa and North eastern states are contributing about 50 percent p.falciparum cases of the country. •Infants, young children, pregnant women have been identified as malaria high risk groups followed by mobile tribal population engaged in forest related activities. •Limited health infrastructure and lack of drugs at village level are the factors responsible for high morbidity due to malaria.
  40. 40. Rural malaria: •These include irrigated areas of arid and semiarid plains of Haryana, Pujab, Western Uttar pradesh, parts of Rajasthan, Madhya pradesh, plain desert areas and plain costal areas of Orissa, Andhra Pradesh and Tamil Nadu. •Malaria is moderate to low endemicity. •An. Culcifacies is the main vector and P. vivax is prdominant during lean period and P. falciparum during periodic exacerbation •In these health infrastructure is moderately developed.
  41. 41. Urban malaria: •15 major cities including 4 metropolitans account for nearly 80% of malaria cases covered under urban malria control scheme. •The cities are, Delhi, Mumbai, Chennai, Kolkata, Hyderabad, Bangalore, Ahmedabad, Bhopal, Jaipur, Lucknow, Chandigarh, Vadodara, Vishakapatnam, Vijaywada and Kanpur
  42. 42. •Important features of malaria are modearate to low endemicity with P. vivax predominance and focal P. falciparum transmission. •An. Stephensi is the main vector. •The health infrastructure is well developed.
  43. 43. Malria in Project areas: •Project areas are those areas where construction and developmental activities are taken up. •Temporary tropical agregation of laborers takes place bringing in different strains of malaria parasite and non immune population. •One or more major vectors are involved in malaria transmission.
  44. 44. •These pockets contribute a large number of malaria cases which are highly disproportionate to the relatively small population groups inhabitating the area •Limited health facilites for prompt treatment is invariably associated with chloroquine resistant malaria parasite
  45. 45. Border malaria •These are high malaria transmission belts along the international borders and state borders. •These have there own problems in regard to malaria control because of mixing of population and poor administrative control.
  46. 46. Other epidemiological types of Malaria •Induced malaria: Malaria infection due to medical interference, such as transmission by contaminated blood transfusion or deliberate transmission •Sporadic malaria: case of malaria occurring, sporadically, in areas wjere malaria is not endemic
  47. 47. •Imported malaria: A case of malaria resulting from the bite of a mosquito in a non malaria region that was carried into non malaria region through any means of transportation. •Autochthonous malaria: A case of malaria resulting from the bite of a mosquito in a malariaendemic region