Malaria Research in the Real World Sarah Kaslow skaslow@gmail.com

Malaria: A Brief Introduction Life-threatening disease caused by a parasite, transmitted by bites of infected mosquitoes In 2010, malaria caused an estimated 655,000 deaths (mostly among Sub-Saharan African children). Several species infect humans: Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, Plasmodium ovale, Plasmodium knowlesi Malaria is preventable and curable. Complex life cycle complicates eradication/control efforts.

The Malaria Life Cycle is Complicated Haploid Blood stream Meiosis Midgut Salivary Glands Dormant liver stage (hypnozoites) causes disease relapses Liver C JHSPH

vivax and falciparum Are Different Relapses of disease - hypnozoites Highest morbidity 70 – 300 million people annually (most under age of 5) No in vitro culture method 1st line Treatment: Chloroquine/Artemisinin Combination + Primaquine Baird K, 2009 Broad range of clinical outcome despite relatively low parasitemia

Chloroquine 4-aminoquinoline drug used in the treatment/prevention of malaria The antimalarial treatment of choice since 1950s. Inexpensive, widely available Low toxicity Standard pediatric dose is 25 mg/kg over three days. Half-life of ~42 days.

Mutations in pfcrt and CQR in P. falciparum Resistance first reported in the 1950s; since spread through Asia and into Africa K76T mutation of PfCRT connected to chloroquine resistance Ortholog gene in P. vivax is pvcrt-o; no mutations associated to CQR Marker has enabled typing of parasites from endemic areas Distribution of PfCRT K76T Mutation K: CQS T: CQR Adapted from Sá et al, 2011 PfCRT is a transmembrane protein found in the digestive vacuole of the parasite A genetic marker has enabled typing of the pfcrt gene. With a genetic marker we can map the distribution of resistance, come up with resistance containment strategies, and alter treatment policies. Genetic mapping is a public health tool.

Molecular Mechanism of CQR in P. vivax is Unknown CQ Resistance (CQR) in P. vivax was first reported in 1989 and has spread from the South Pacific Islands. Molecular mechanism and genetic basis of CQR in P. vivax remains unknown. Baird K, 2009

Hypotheses and Experimental Approach CQR is an inheritable trait Generate a genetic cross between a CQ-R and a CQ-S parasite CQ selects mutations in genes involved in its transport or mode of action Search for a common genetic marker in CQ-R progeny

Approach: Genetic Cross Drug Sensitive Drug Resistant Chimpanzee CQ-S x CQ-R Recombinant Oocysts Cryopreserved Recombinant Sporozoites Drug pressure CQ-R Progeny Mosquitoes Multiple Aotus Cure Aotus Recombinant Progeny Map Genetic Determinants: Linkage Group Selection (LGS)

Approach: Linkage Group Selection Sensitive Parasite Resistant Parasite Recombinant Progeny Selection Pressure Two haploid parasites that differ in their sensitivity to a particular selection pressure are genetically crossed. In this example, resistance to the selection pressure is conferred by a gene at the brown square. The resulting recombinant progeny population will consist of thousands of parasites. This uncloned population is then subjected to selection pressure, and the resulting selected population will consist solely of parasites that possess the resistant allele of the gene that controls the phenotype of interest. We look for markers of the sensitive parent that are removed or reduced by the selection pressure; the greater the reduction in the intensity of a sensitive marker, the closer it is linked to the allele removed by the selection pressure. Culleton et al. 2005

My Path Claremont McKenna College Philosophy, Politics, and Economics University of Maryland School of Medicine Johns Hopkins University Post-Baccalaureate Pre-Medical Johns Hopkins Bloomberg School of Public Health Masters in Public Health Laboratory of Malaria and Vector Research #ILookLikeASurgeon