1. Learning Unit 2 Basic malaria epidemiology and transmission dynamics

2. Learning Unit 2: Learning objectives Specify biological and epidemiological features of P. vivax and P. falciparum that are favouring or hindering elimination Specify factors that influence malaria elimination, related to: Vectors Human hosts Eco-geographical factors Define the major parameters of transmission intensity which are used in malaria epidemiology Identify the relationships between vectorial capacity, basic reproductive rate, entomological inoculation rate, and incidence and prevalence of malaria infection Describe how the relationship between vectorial capacity and other concepts of malaria transmission intensity influence the selection of strategies and methods in different epidemiological situations

3. Overview of topics for the day Plenary 1: Biological aspects related to parasites and human hosts Exercise: Exercise 2.1 in class discussion Tuesday morning

4. Biological aspects related to parasites Plasmodium falciparum Plasmodium vivax Plasmodium malariae Plasmodium ovale

5. Life-cycle of human malaria parasites

6. The four processes in the life-cycles of plasmodia in humans Name of the process Host organ Host cellStages involvedDuration Dormancy (for certain species of plasmodia) liverhepatocytehypnozoiteusually 5-18 months Exo-erythrocytic schizogony liverhepatocyte exo-erythrocytic schizont -> merozoite 6-15 days, depending on the species Erythrocytic schizogony blood red blood cell merozoite -> trophozoite -> schizont -> merozoite-> etc. a number of cycles, each of 2 or 3 days duration Gametocytogonyblood red blood cell merozoite -> gametocytes (male and female) Days/weeks

7. Life-cycle of P. falciparum

8. Life-cycle of P. vivax

9. Duration of critical intervals for P. falciparum and P. vivax CharacteristicsP. falciparumP. vivax Prepatency (from inoculation to the appearance of microscopy detectable parasitaemia) 7-10 days11-13 days Incubation: short (from inoculation to the appearance of symptoms) 8-14 days10-18 days Incubation: long (from inoculation to the appearance of symptoms) Not applicable5-18-months Minimum time to appearance of mature gametocytes after the appearance of parasitaemia 12 days0 days Maximum time of disappearance of circulating gametocytes (after treatment with blood schizontocides) 8 weeks< 1 day Asexual cycle in the blood48 hours Typical duration of untreated infectionOne year or less in about 80% of cases 1 - 2 years (exceptionally, up to 5 years)

10. Biological aspects related to human host Susceptibility to malaria is universal in humans. Only exception: People with no Duffy antigen on red cell surfaces are refractory to P. vivax. – This genotype is widespread among Africans (especially West Africa) – Therefore, a sufficient pool of susceptible individuals to vivax do not exist – That’s why vivax transmission is limited in Africa

11. Some haemoglobinopathies (gene polymorphisms) offer some protection: – Haemoglobin S (causing sickle cell disease) – Thalassaemias (alpha-thalassimia): missing genes that affect how the body makes hemoglobin. RBC weak and destroyed – Ovalocytosis (ovale shaped blood cells) – Glycose-6-phosphate dehydrogenase (G6PD) deficiency: the enzyme is important red blood cell metabolismred blood cell Most of these gene polymorphisms are linked to intensity of malaria transmission Biological aspects related to human host

12. Acquired malaria immunity – Clinical immunity develops by age – Offers partial protection – Determines the clinical epidemiology in an area – Strongly dependent on malaria exposure (transmission intensity) throughout life Biological aspects related to human host

13. A. Low endemicity B. Moderate endemicity C. High endemicity D. Hyperendemicity E. Epidemic

14. eco-geographical factors

15. Geographical factors Temperature – The most important factor for mosquito and parasite (in mosquito) development – Mosquitoes less sensitive to low temperatures than parasites – anophelines can breed at temperature above 10  C where the lower threshold of sporogony is 16  C – Lower threshold for P. vivax sporozoite development is 16  C, for P. falciparum it is 18°C – Optimum temperature for mosquito development is 25- 27°C and maximum is 40°C – Optimum temperature for parasite development is 27°C – Extremely high temperature is deleterious to vectors and parasites – Average daily temperature (ADT) is main meteorological indicator

16. Exercise 2.1: Comparing natural history and epidemiology of Pf and Pv a)Analyze biological traits of falciparum and vivax that are responsible for major distinctions in their natural history and epidemiology. b)Which species is easier to eliminate in your area? Organize the information in tabular form.