Lecture 7: Parasitology III

Plasmodium

a group of parasites that causes malaria

P. vivax, P. falciparum, P. ovale, P. malariae

Hepatocytes

main liver cells that perform metabolic functions

erythrocytes

red blood cells responsible for oxygen transport

Malaria location and reservoir

hepatocytes/erythrocytes and reservoir is humans

Malaria Transmission

spread by vector-borne female anopheles mosquitoes and also congenital & needle transfer

Malaria Epidemiology

affects worldwide, most fatalities in children, most morbidity and mortality due to P. falciparum, and increasing drug and insecticide resistance

Malaria life cycle alternates b/t

2 hosts:

female Anopheles mosquito vector sexual cycle

human host intermediate asexual cycle

Malaria life cycle Mosquito: first step of infection

Mosquito bites an infected human → picks up gametocytes. Gametocyte mature into gametes inside mosquito midgut, and then fertilization of microgamete and macrogamete becomes zygote 

Malaria life cycle Mosquito: gametes fertilize

Zygote transforms into an ookinete that embeds in the outside of midgut wall and forms an oocyst that grows, divide, and produces thousands of sporozoites (sporogony)

Malaria life cycle Mosquito: final step to get ready to infect humans

Oocysts burst releasing sporozoites in mosquito’s body cavity, sporozoites migrate to salivary glands

They are now ready to infect humans

Malaria life cycle Human: mosquito infects humans

Mosquito injects sporozoites into human during blood meal, the sporozoites travel thru bloodstream to liver and inside become a liver schizont that produces thousands of merozoites

Malaria life cycle Human: RBCs invaded by merozoites

Schizonts rupture releasing merozoites into bloodstream, the merozoites invade RBCs, inside the RBC the parasite progresses thru 3 main stages; ring, trophozoite, and schizont

Ring stage

Earliest form inside RBC that looks like a ring and is the beginning of feeding

Trophozoite stage

The feeding and growing stage where the parasite digests hemoglobin and produces hemozoin (brown pigment) and it grows larger

Schizont stage

Sporozoite enters liver cell and become trophozoite that becomes a schizont that divides and forms 8-32 merozoites, when the merozoite mature the liver cell schizont rupture

Malaria life cycle Human: RBC ruptures

releases merozoites causing clinical symptoms such as fever, chills, anemia and then merozoites infect new RBCs

Sporozoite Role

parasites stored in salivary glands of mosquito that are injected into humans and start malaria by invading liver cells

Merozoite Role

Plasmodium parasites invade red blood cells, multiple, and cause symptoms of malaria

Liver to blood and infects RBCs and is asexual

Schizont Role

the asexual replicative stage that produces merozoites and causes RBC rupture, leading to fever and anemia

Trophozoite role

the feeding and growing form in RBCs that digests hemoglobin and matures toward division

Gametocyte Role

the sexual Plasmodium forms in human blood that are taken up by mosquitoes and begin the parasite's sexual cycle, enabling transmission to new hosts (infective to mosquito)

Ookinete  Role

motile form that invades mosquito gut wall and becomes an oocyst

Oocyst role 

In mosquito outside midgut wall that produces thousands of sporozoites

malaria species roles in symptoms

fever cycle with synchronous bursts of merozoites

P. vivax & P. ovale: 48 hr spike

P. malariae: 72 hr spike

P. falciparum: 48 hr broad

Malaria symptoms

chills, fever, splenomegaly, myalgia, headache, and anemia results from erythrocyte destruction

cerebral malaria

extreme result of P. falciparum only disruption of cytokines networks and  IV quinidine for treatment 

latent hepatic forms in

P. vivax & P. ovale

P. falciparum

multiple rings per RBC,  no trophozoites or schizonts, and banana shaped gametocytes

Erythrocytic Stages of Human Malarias signs P. falciparum

Banana -shaped gametocytes, no circulating trophozoites or schizonts, and multiple ring stages per RBC

Malaria Immunity

slow to develop; requires multiple infection, short lived, and easily reinfected

Malaria Treatment

multidrug resistance common, especially chloroquine!

Malaria prevention

2 vaccines, avoid mosquitoes, and drugs like doxycicline

Phylum Platyhelminthes AKA flatworms

a diverse group of soft-bodied invertebrates that includes free-living and parasitic species

Phylum Platyhelminthes classes:

Cestoda and Trematoda

Class Cestoda

Tapeworms; flattened segmented bodies, no internal digestive system; nutrients absorbed across cuticle

Class Cestoda adult attach

by the anterior end (scolex) to the gut wall of definitive host

Class Cestoda transmission

ingestion of larval cysticerci (bad) or eggs (very bad), and their segments (proglottids) grow anterior to posterior

Class Trematoda

Flukes of the lungs, liver and blood and broad flattened bodies with a simple digestive system; a single opening serves as mouth and anus

Class Trematoda transmission

One or more intermediate host, one of which is a snail and transmission can be invasive or ingestive

Phylum nemahelminthes classes

Nematoda

Class Nematoda

Roundworms of the tissues and gut, has cylindrical body; well developed digestive and nervous systems.

Class Nematoda Transmission

Ingestive (no intermediate host) Ascaris, Trichuris, etc

Invasive (no intermediate host) Hookworms

Vector-borne (one intermediate host) Filarial Worms

Class Cestoda species

Taenia saginata (raw beef) and Taenia solium (raw pork) and both found in intestine

Class Nematoda (roundworm) species

Enterobius vermicularis found in lumen of intestinal/anal and transmitted by ingesting direct egg

Beef tapeworm

organism is Taenia saginata found in lumen of jejunum (upper small intestine) and humans are the only definitive host, cattle is intermediate host

Beef tapeworm epidemiology

World-wide and cosmopolitan in beef eating countries causes abdominal discomfort; nausea, vomiting and diarrhea and rarely serious

Beef tapeworm immunity and diagnosis

Humoral response to adults, reinfection is possible, and observation of proglottids or eggs in stool

Beef tapeworm treatment

drugs single dose is effective and prevented by good hygiene and well cooked beef

Egg / Oncosphere

host is cattle and is embryo in feces, eaten by cattle

Cysticercus

Larval stage (infective to humans)and found in cattle muscle

Adult tapeworm

Mature worm producing eggs and found in human intestine

Gravid proglottid

Segment containing thousands of eggs and found in human feces

Life cycle of Beef Tapeworm: Taenia saginata part 1

Adult Taenia saginata lives in the small intestine of humans, releases proglottids containing fertilized eggs passed in human feces, and cattles are infected by contaminated feed/water

Life cycle of Beef Tapeworm: Taenia saginata part 2

in cows intestine the oncosphere hatches and enters bloodstream  to muscle tissue and develop cysticerci, and then humans eat undercooked beef containing cystercerci

Pork tapeworm

organism is Taenia solium, found in lumenal jejunum of adults and cysticeri found in any tissue

Pork tapeworm host

definite host are humans and intermediate host are pigs or humans

Pork tapeworm transmission

- Ingest cysticerci; definitive host (bad)

- Ingest eggs; intermediate host (VERY BAD)

Pork tapeworm lifecycle

like beef tapeworm except eggs are infectious for humans and cysticerci develop in any human tissue

Pork tapeworm diagnosis and prevention

Adults same as beef tapeworm and X-ray, calcified dead larva; CAT/MRI, viable cysticerci, prevented by good hygiene and well cooked pork, and freezing kills cysticerci

Pork tapeworm treatment

multiple treatment to kill cysticerci, consensus is to not treat cysticerci outside of CNS

Pinworm

Organism is Enterobius vermicularis and found in adults in colon

Pinworm transmission

Ingestion of eggs and definitive host is only humans

Pinworm epidemiology

World-wide and cosmopolitan; >20 million in USA and an equal opportunity parasite

Pinworm pathology immunity treatment

Intense perianal pruritis, bacterial infection, no immunity and treatment are drugs or multiple treatment for severe infection

Pinworm life cycle 

infective eggs are ingested through contamination and hatch in the small intestine releasing larvae and mature into adult worms in the large intestine, migrate to perianal area and lay thousands of eggs on skin leading to scratching  where eggs get into fingernails and become infective again

Candiru AKA vampire catfish

organism is Vandellia cirrhosa and are tiny parasitic catfish found only in the amazon/oranoco rivers of south america

Candiru food

Voracious appetite for blood; will parasitize fish, mammals, & HUMANS and it has no enemies

Candiru life cycle

Inserts itself inside the gill flap. Spines pierce the fish and draws blood while anchoring the candiru in place. It feeds on the blood using its mouth as a slurping apparatus and while rasping with the long teeth on its top jaw.