Malarial life cycle… Dr.Shelke A.N. Assist.professor Mrs.K.S.K.College,beed

Plasmodium specie which infect humans Plasmodium vivax (tertian) I am giving the old names for these malarias in parentheses to give some historical perspective in case you see these terms again. I will also explain how these old terms relate to the pathogenesis of these respective diseases and the associated fever patterns.

Malaria Life Cycle Life Cycle Sporogony Schizogony Oocyst Sporozoites Mosquito Salivary Gland Zygote Hypnozoites (for P. vivax and P. ovale) Gametocytes Exo- erythrocytic (hepatic) cycle The life cycle of all species that infect humans is basically the same. There is an exogenous asexual phase in the mosquito called sporogony during which the parasite multiplies. There is also an endogenous asexual phase that takes place in the vertebrate or human host that is called schizogeny. This phase includes the parasite development that takes place in the red blood cell, called the erythrocytic cycle and the phase tthat takes place in the parencymal cells in the liver, called the exo-erythrocytic phase. The exo-erthrocytic phase is also called the tissue phase. The schizogeny that takes place here can occur without delay during the primary infection or can be delayed in the case of relapses of malaria. I will focus on the development of the parasite in the human host. Erythrocytic Cycle Schizogony

Malaria Transmission Cycle Exo-erythrocytic (hepatic) Cycle: Sporozoites infect liver cells and develop into schizonts, which release merozoites into the blood Sporozoires injected into human host during blood meal Parasites mature in mosquito midgut and migrate to salivary glands Dormant liver stages (hypnozoites) of P. vivax and P. ovale MOSQUITO HUMAN Erythrocytic Cycle: Merozoites infect red blood cells to form schizonts Some merozoites differentiate into male or female gametocyctes Parasite undergoes sexual reproduction in the mosquito

Components of the Malaria Life Cycle Sporogonic cycle Infective Period Mosquito bites uninfected person Mosquito Vector Parasites visible Human Host Mosquito bites gametocytemic person Symptom onset Prepatent Period Recovery Incubation Period Clinical Illness

Exo-erythrocytic phase Blood is infected with sporozoites about 30 minutes after the mosquito bite The sporozoites are eaten by macrophages or enter the liver cells where they multiply – pre-erythrocytic schizogeny P. vivax sporozoites form parasites in the liver called hypnozoites

Malaria Life Cycle Life Cycle Sporogony Schizogony Oocyst Sporozoites Mosquito Salivary Gland Zygote Hypnozoites (for P. vivax and P. ovale) Gametocytes Exo- erythrocytic (hepatic) cycle The life cycle of all species that infect humans is basically the same. There is an exogenous asexual phase in the mosquito called sporogony during which the parasite multiplies. There is also an endogenous asexual phase that takes place in the vertebrate or human host that is called schizogeny. This phase includes the parasite development that takes place in the red blood cell, called the erythrocytic cycle and the phase tthat takes place in the parencymal cells in the liver, called the exo-erythrocytic phase. The exo-erthrocytic phase is also called the tissue phase. The schizogeny that takes place here can occur without delay during the primary infection or can be delayed in the case of relapses of malaria. I will focus on the development of the parasite in the human host. Erythrocytic Cycle Schizogony

Exo-erythrocytic phase P. vivax and P. ovale hypnozoites remain dormant for months They develop and undergoe pre-erythrocytic sporogeny The schizonts rupture, releasing merozoites and producing clinical relapse

Erythrocytic phase Pre-patent period – interval between date of infection and detection of parasites in peripheral blood Incubation period – time between infection and first appearance of clinical symptoms Merozoites from liver invade peripheral (RBC) and develop causing changes in the RBC There is variability in all 3 of these features depending on species of malaria

Erythrocytic phase stages of parasite in RBC Trophozoites are early stages with ring form the youngest Tropohozoite nucleus and cytoplasm divide forming a schizont Segmentation of schizont’s nucleus and cytoplasm forms merozoites Schizogeny complete when schizont ruptures, releasing merozoites into blood stream, causing fever These are asexual forms

Erythrocytic phase stages of parasite in RBC Merozoites invade other RBCs and schizongeny is repeated Parasite density increases until host’s immune response slows it down Merozoites may develop into gametocytes, the sexual forms of the parasite

Symptoms of malaria Early symptoms Headache Malaise Fatigue Nausea Muscular pains Slight diarrhea Slight fever, usually not intermittent Could mistake for influenza or gastrointestinal infection

Symptoms of malaria Acute febrile illness, may have periodic febrile paroxysms every 48 – 72 hours with Afebrile asymptomatic intervals Tendency to recrudesce or relapse over months to years Anemia, thrombocytopenia, jaundice, hepatosplenomegaly, respiratory distress syndrome, renal dysfunction, hypoglycemia, mental status changes, tropical splenomegaly syndrome

Symptoms of malaria Early symptoms Headache Malaise Fatigue Nausea Muscular pains Slight diarrhea Slight fever, usually not intermittent Could mistake for influenza or gastrointestinal infection

Common features of P.vivax infections Incubation period in non-immunes 12-17 days but can be 8-9 months or longer Some strains from temperate zones show longer incubation periods, 250-637 days First presentation of imported cases – 1 month – over 1 year post return from endemic area Typical prodromal and acute symptoms Can be severe However, acute mortality is very low