Malaria and Sickle-Cell Anemia: Genetic, Physiological, and Cultural Adaptations

1. Malaria and Sickle-Cell Anemia: • Genetic, Physiological, and Cultural Adaptations • Revised by Brad R. Huber, 2/4/2014 10:04:48 AM

2. Malaria and sickle cell anemia are an example of a balanced polymorphism • An equilibrium mixture of homozygotes and heterozygotes maintained by natural selection against both homozygotes

3. Two opposing selective forces: • Malaria selects against • Homozygous Dominant (HbA, HbA) • Sickle-Cell Anemia selects against • Homozygous Recessive (HbS, HbS) • (HbS, HbA) Heterozygous (Sickle Cell Trait) • No anemia & less susceptible to malaria

4. Malaria and Sickle-Cell Anemia Map

5. Malaria Pathogen • Plasmodium is a protozoan parasite that causes malaria • It consumes glucose and enzymes of blood cells, and as a result the cells die. • The cells are destroyed at 2 to 3 day intervals • The release of the waste products causes chills and fever

6. Plasmodium Life Cycle There are sexual and asexual parts of the Plasmodium life cycle

8. Malaria: Vectors • Anopheles gambiae breeds an open sunny pools • Anopheles funestus breeds along shaded river edges and vegetative swamps in undisturbed forest

9. When agriculture was introduced two thousand years ago in sub-Saharan Africa • The forests were cleared & sunny pools of water became more common. • Anopheles gambiae mosquitoes increased • And so did people contracting malaria

11. Malaria: Epidemiological Issues • The current prevalence of malaria is between 300,000,000 - 500,000,000 cases. • Mortality rate: 650,000 people die of malaria each year • Highest among small children • Malaria also causes miscarriage and premature birth.

13. Malaria: Clinical Features • Malaria can lead to kidney failure, anemia, pneumonia • Low birth weight, miscarriage, and stillbirths • It is a strong selective pressure, especially on children • Adults who survive malaria in childhood develop a protective immunity

15. Sickle-Cell Anemia

16. Sickle-Cell Anemia: Genetic Aspects • Hemoglobin is a protein found in red blood cells • It binds with, carries, and releases oxygen to the cells of the body • A hemoglobin molecule is large with a great potential for DNA point mutations to occur

17. Hemoglobin: Genotypes and Phenotypes • Homozygous Dominant (HbA, HbA) • Normal hemoglobin • Homozygous Recessive (HbS, HbS) • Abnormal hemoglobin, Sickle Cell Anemia • Heterozygous (HbA, HbS) • Sickle-Cell Trait • Normal and abnormal hemoglobin, with normal hemoglobin more abundant.

19. Diagnosis of Sickle-Cell Anemia • Amniocentesis of fetal cells can be used in the 16th week of pregnancy • Chorionic villi biopsy can be done at 8 to 10 weeks

20. The Heterozygous Genotype and Malaria • Heterozygous individuals produce red blood cells that live only 2 to 3 weeks instead of 120 days • These red blood cells have both normal and abnormal hemoglobin • They inhibit the reproduction of the malaria parasite • When heterozygous individuals get malaria it is less severe than when homozygous dominant individuals get malaria

21. The Homozygous Recessive Genotype • This Genotype causes Sickle Cell Anemia • Red blood cells with abnormal hemoglobin become sickle shaped. • They clump, blocking blood flow.

23. Clinical Signs and Symptoms • Pain crises • Acute chest syndrome (a life-threatening pneumonia-like illness) • Cerebrovascular accidents • Splenic and renal dysfunction • Chronic anemia • Susceptibility to infections

24. Homozygous recessive individuals who are infected with the malaria parasite die of an anemia crisis • Children with sickle cell anemia must be cautious in play and sports; bruises and scrapes can lead to crises • before modern medical care, the average lifespan was 20 years •  many individuals suffering with sickle cell disease can now live into their mid-40s and beyond

26. Epidemiology • Malaria is found in only a few people in the U.S. • Recent immigrants and tourists • As a result, there is only a selection against the sickling hemoglobin allele (HbS) in the U.S. • For example, HbS allele has decreased in frequency in blacks from about 8.5% to about 1%

27. 70,000 to 100,000 people in the U.S. have sickle cell anemia • 2 million have sickle cell trait. • Sickle cell anemia is more common in certain ethnic groups, including: • People of African descent, including African-Americans • Hispanic–Americans from Central and South America • People of Middle Eastern, Asian, Indian, and Mediterranean descent

28. Cultural and Psychological Adaptation • Teachers and friends of children with sickle cell anemia are often silent; they are uncomfortable talking about serious illness and death • Parents may feel guilty because sickle cell anemia is hereditary. • Adolescents are sometimes pessimistic about getting a job, continuing school, getting married • Adolescents may become depressed

29. Women with sickle cell anemia: • have a 50-50 chance of not surviving after giving birth • there is also a risk of bearing an injured child. • Genetic counseling, sterilization, and abortion are options • However abortion is not acceptable to all. • And it’s difficult to predict how severely a child will be affected by sickle cell anemia. • All newborns in the United States are now tested for the disease.