疟原虫 Plasmodium

Plasmodium (Malaria Parasite) Species susceptible to human: 1.Plasmodium vivax(Pv): Cause tertian malaria. 2.P.falciparum (Pf): Cause malignant malaria. 3.P.malariae (Pm): Cause quartan malaria. 4.P.ovale (Po): Cause benign malaria.

Prevalence: Malaria is the most important parasitic disease in the world. 300 million cases with one million deaths world wide in 1999; 30 million cases before liberation and 24000 cases reported with 39 death in 2000 in china;

Distribution of Malaria in the World

The vector – female mosquito

Life Cycle

Life Cycle

Life Cycle

Morphology & Life Cycle (Biology Features) 1.Asexual development(in human host): (1)Exo-erythrocytic stage -EE forms (in liver cells), Sporozoite(Tachysporozoite & Bradysporozoite)-schizont-merozoites. One generation results in numerous.

红外期 exo-erythrocytic stage—merozoites in liver cells肝细胞内裂殖体

Morphology Plasmodium is the one-cell parasite, so the basic morphology is a nucleus , cytoplasma and cell membrane Wright or Giemsa stain gives the Cytoplasm – blue; nucleus - red , while the malarial pigments are yellow-brown There are three stages and six main forms of plasmodium in RBC

P.vivax in RBC three stages and six main forms 滋养体期(trophozoites)：ring form and developing trophozoites 裂殖体期(schizonts)：immature and mature schizont-- merozoites 配子体期(gametocyte)： Microgametocytes and macrogametocytes

Ring form of P.v.

Amoeboid form of P.v.

Schizonts Figs.： increasingly mature schizonts

Immature schisont of P.v.

merozoite hemozoin Mature schizont: nucleus divided into 12-24 (16), cytoplasm divided, each nucleus surrounded by a portion of cytoplasm to form merozoites, hemozoin clumped

Female gametocyte of P.v Oval in shape, light blue cytoplasm is abundant compact nucleus, usually at edge of the parasite scattered pigment granules The gametocyte is completely filling its host cell

Male gametocyte of P.v Oval in shape, blue cytoplasm is abundant; Loose and large nucleus (chromatin), central in position Malarial pigments diffuse Infected RBC enlarged and became pale with red Schüffner‘s  dots

Female gametocyte of P.v.

Male gametocyte of P.v.

P.falciparum ring form

P.f ring form Fine ring , smaller,about 1/5 of RBC diameter, Usually multiple infection 1-2 small nucleus Infected RBC is normal,almost no change

P.f. macrogametocyte Compact nucleus, red, usually at the center of the cell Malarial pigments around the nucleus The crescent-shaped gametocytes of P. falciparum are very distinctive, but tend to only appear late in the infection

Pf. microgametocyte Large, diffuse nucleus at the center Sometimes hard to distinguish from the female gametocytes Sausage-shaped with two blunt end

P.f.

The Features of Erythrocytic Stage: a. Repeated generation. b. Synchronous development. c. Definite time duration: Pv 48h; Pf 36h-48. d. The stage responsible for pathogenesis.

Male gametes

ookinetes

Oocysts

Oocysts of P. falciparum in midgut of an infected mosquito Oocysts of P. falciparum in midgut of an infected mosquito. Oocysts appear as circular bodies. Fresh preparation. ×100. Enlarged by 5.4.

Sporozoites

Malarial paroxysm (疟疾发作) An attack occurs because of the sudden liberation of merozoites, malarial pigment and RBC debris into the blood stream.

Clinical features Pathogenesis Typical malaria paroxysm symptom for erythrocytic phase shaking chill （寒战） followed by fever （高热） (2-20 hrs) RBCs rupture releasing merozoites, malarial metabolites, endotoxin in blood, the pyrogens profuse sweating when fever breaks （出汗退热） repeated characteristic cycle for each species

Scanning electron micrograph of Plasmodium-infected red blood cells Scanning electron micrograph of Plasmodium-infected red blood cells. One cell has burst open, releasing merozoites

Recrudescence(再燃) It is a recurrence of symptoms in a patient whose blood stream infection has previously been at such a low level as not to be clinically demonstrable or cause symptoms.

Relapse(复发) It is a recurrence that taken place after complete initial clearing of the erythrocytic infection and implies reinvation of the blood stream by merozoites from activated hypnozoites in liver.

Complications Anemia Splenomegaly Malarious nephrosis Hemolysis of infected erythrocytes Hypersplenism Autoimmunization of uninfected erythrocytes supression of blood production in marrow Splenomegaly Malarious nephrosis fatal malaria-cerebral malaria caused by P.f. (small vessels are plugged)

typical splenomegaly syndrome

Cerebral malaria

Diagnosis Travel history to endemic area & presence of symptoms, e.g., fever and chills Etiological- Microscopic examination of blood Thin and Thick film (Giemsa's stain) To master the morphology of parasites and changes of infected red cells Immune probe-Species McAb based assays. DNA probes- hybridization

实验诊断 Laboratory diagnosis 1．病原检查 （1）Thin film Thick film Question: Which stages are there in the blood film of P.v. or P.f. ?

Epidemiology Distribution: Africa, Asia, Latin America Endemic factors (1)Source of infection: Patients and carriers. (2)Vector host: mosquito (3)Susceptible population (4) resistance of plasmodium to antimalarial drugs. (5) Other transmission mode: by transfusion, congenital transmission

Treatment Antimalarial drugs: (1)Anti-attack drugs: Kill E-forms-Quinine,Chloroquine. (2)Anti-recurrence drugs: Kill EE-forms-Primaquine. (3)Chemoprophylaxis: Kill sporozoite & EE-forms with long shelf life-pyrimethamine 乙胺嘧啶. affect parasite in different ways depending on stage when administered emergence of drug-resistant malaria

Prevention and control Control of the source of infection by chemotherapy Prevention: breaking the human-mosquito-human cycle mosquito control or eradication - not easy Personal protection- netting, repellents, etc. avoidance of infected mosquitoes (bed nets , mosquito repellents)

Insecticide impregnated bednet Permethrinn合成除虫菊脂treated, a synthetic pyrethroid除虫菊素类,合成除虫菊酯, ~ 200 mg/sq m.