Intro to Parasites: Metazoan Worms:!Metazoa: multi-celled animals!Types of Parasitic Worms:!1) Nematodes (roundworms): cylindrical, unsegmented!" -many are saprophytic: eat dead organic matter!" -live in soil or water!" -most nematodes are NOT parasites!2) Trematodes (flatworms): flat unsegmented, external, suckers!" -aka "flukes"!" -incomplete digestive system (take in food through the mouth and expel waste back out through the mouth)!" -eggs emit larvae!" -no distinction between males and females (unisex)!3) Cestodes (flatworms): ribbonlike segmented external suckers!" -aka tapeworms!" -absorb pre-digested food through their outer covering!" -eggs emit larvae!" -also unisex like trematodes!!Protozoan Parasites Trypanosomiasis: several diseases from the genus Trypanosoma!" -all caused by protozoan parasite: flagellate protozoa!"-primary host: tsetse fly (also known as the definitive host)!"-secondary host: human: humans and other animals!Trypanosomiasis!" Trypanosomiasis is biggest problem in Africa!" " -often called the "sleeping sickness"!" Two forms:!""1) Gambian (less severe but long term, may last years) West/central Africa!""2) Rhodesian (very severe; lasts weeks to months instead of years) East Africa!" Humans get sleeping sickness from infected tsetse fly.!" " -incubation of tryp. is 2 weeks before chancre appears!""-first symptom is local chancre: hard, painless nodule!""-next: chancre area becomes red, swollen!" Tryptanosomes then spread to nearby lymph glands!" Rhodesian Form: 2 Courses 1st Course symptoms:!" " " -high temperature (up to 106 degrees F ← near the brain damaging temp point)!" " " -convulsions!" " " -coma and death follow quickly!"" 2nd Course = classic sleeping sickness!" " " -high temperature (up to 106 F) for weeks!" " " -apathetic & sleepy!" " " -slurred speech!" " " -deep coma!" " " -death from heart failure, malnutrition, infection!Societal Impact of Trypanosomiasis: " " -livestock are affected more than people!" Five tryp. types exist all together:!" " -three only affect animals!" " -two affect both animals and people!" " -different fly vectors for each types!" " -fly vectors adapted to slightly different environments!!Trypanosomiasis & Society!" T.gambiense: likes humid forests of West & Central Africa!" " -only infect humans and pigs!" " -infection rate is low because the Western form cannot reproduce in mature flies which limits the " " " " " " " population of mature flies that might bite and infect a person (trypanosome cannot reproduce in mature ""flies)!!!" T.rhodesiense: likes dry savannah woodlands of East Africa!" " -primarily affects antelope!" " -humans are incidental victims (souvenir)!" " -introduced cattle have not evolved with the disease and die from the disease!Pre-Coloinal Africa:!" -Rhodesian form of Tryp. had a limited range!" -mostly woodland savanna!" " -herding got economically viable where disease existed!Trypanosomiasis limited range of herders in past! Zimbabwe (AD 350): influenced most by the ABSENSE of the tsetse fly!" -Shona people move to high plateau region!" -Shona are pastoralists!" -elevation was too high for tsetse fly, so livestock prospered!Zimbabwe (AD 1250):!" -largest pre-Contact civilization in subsaharan Africa !" -10-20,000 people population (large enough to be a complex society )!-no tsetse fly!" -Were able to monopolize the trade in gold Malaria - Protozoan Parasite!" Malaria is common in the tropical areas of the world!"-Estimated 500,000,000 disease episodes per year !" " -1 million deaths -mostly children!" " -90% of cases in sub-saharan Africa!" " -170 different forms (birds, mammals, etc.)!" " -vector- Anopheles mosquitos (20 common types)!Malaria: Two most important types:!" Plasmodium vivax (less severe)!" -oldest form of human malaria (50 thousand years ago-300 thousand years ago)!" -SE Asia (from macaques)!" -only reproduces in immature RBCs!" -usually not fatal!" -can survive in liver for 3-5 years (may stay dormant for awhile, but under times of stress may infect RBCs)!" Plasmodium falciparum (more severe)!" -recent - (3000-7500 years ago) - after agriculture becomes important for societies!" -Africa - probably from gorilla form!" -most deadly form - reproduction can take place inside both immature and mature RBC's!" -children may have 2-3 episodes per year!" -1% survival rate after infection!" -probably doesn't get stored in the liver (as in vivax strain)!" Malaria: Tow other types:!" Plasmodium malariae & ovale!" -less widespread, less dangerous!"-P.malariae - in blood many years!"-P.ovale - West African form!" -All except falciparum cause cyclic fever (fever comes and goes often)!" Malaria- Life Cycle!" " -female Anopheles mosquito bites human!" " -malaria sporozites enter blood!" " -travel to liver, invades liver cels!" " -first phase of reproduction - merozoites form!" " -leave liver about the same time!" " -merozoites enter blood, invade RBCs!" " -reproduction continues in second stage - merozoites divide until RBCs are full → then burst!" " -cyclical fever!" " Some merozoites from gametocytes. Another mosquito bites infected individual!!!Malaria and Natural Selection!" Malaria is strongest known selective pressure in recent human history!" " -hyperendemic areas = 20% child death rate!" At least eight genetic mutations linked to malaria!" " -HbS - sickle cell allele - affects hemoglobin - 10 times less likely to get severe malaria!" " -Duffy antigen absences - creates immunity to P. vivax. Vivax uses Duffy antigen on RBCs to invade!" Another genetic mutation that helps to protect people from malaria:!" G6PD enzyme - X Chromosome!" G6PD controls oxidative stress!" " " -too many free radicals can damage RBCs!" " G6PD keeps # of free radicals under control!" Free Radicals damage RBCs → anemia!" Sensitive to fava beans, develop anemia from eating them!" Common in Africa and