MSB Microbiology 3 Malaria

What is Sequestration?

(hiding) - due to cytoadherence. Infected RBC (particularly schizonts) adhere to the endothelial cells in the microvasculature (venules & capillaries) Hence schizonts of P. falciparum are rarely seen in the peripheral circulation because they hide in the microvasculature of the organs

How is malaria diagnosed?

-Gold standard is microscopy: Examination of Giemsa stained thin & thick blood films under light microscopy -Rapid dipstick tests

What are the recommendations for prevention with drugs and prophylaxis?

1. Early DX and treat 2. IPT - Intermittent preventive treatment in pregnancy - give sulfadoxine-pyrimethamine twice during pregnancy in asymptomatic women 3. Chemoprophylaxis in non-immune travellers based on region visited

What is the duration of treatment and why?

4 weeks - incubation is from 6-40 days

What are the complications of P. falciparum?

Cerebral malaria, Severe anaemia, Severe hypoglycaemia, Poor pregnancy outcome w/increased morbidity and mortality for both baby and mother Rapid & massive intravascular haemolysis (Blackwater fever)- Assoc w/chronic malaria exposure in non-immune patient and in some an Autoimmune reaction

What are the three stages of Malarial Paroxysms?

Cold stage (15-60 min)- Feeling of intense cold, Vigorous shivering Hot stage (2-6 hrs)-Intense heat, Dry burning skin, Throbbing headache Sweating stage (2-4hrs) - Profuse sweating, Declining temperature, Exhaustion

What is Cerebral Malaria?

Complication of severe falciparum malaria usually seen in children and non-immune adults. Gradual or rapid onset. Diffuse encephalopathy w/Loss of Consciousness/Altered levels of consciouness: stupor to coma Seizures, Unresponsive to pain, visual, and verbal stimuli . Survivors may have learning impairment & cognitive damage

What are the consequences of Sequestration?

Consequences of sequestration -by hiding in the microvasculature: able to evade the immune mechanism low oxygen tension = better growth condition development of complications

What do Rapid dipstick tests detect?

Detection of malaria antigens HRP-2 (Histidine rich protein) -specific for P. falciparum pLDH (Lactate dehydrogenase); Aldolase- Seen in all Very useful in areas non-endemic areas where they may not have the expertise to correctly identify the parasite on microscopy

Why is immunity and a vaccine difficult?

Different developmental stages Live in different environments Express different antigens and Antigenic switching Susceptible to different immune mechanisms - intracellular = CMI and extracellular = Humoral

Why is immunity partial?

Due to antigenic switching Immunity can be lost after prolonged non-exposure e.g. if patient lives outside the malarious region for a long time

What is the initial stage of malarial infection

During a blood meal, a malaria-infected female Anopheles mosquito inoculates sporozoites into the human host. Sporozoites go to liver cells

What are the receptors involved?

Endothelial cells receptors: CD36, ICAM-1, E-selectin Placental binding receptor: Chondroitin sulfate A

Identify

Erythrocytic forms: Young ring forms in P. falciparum If you see two ring forms or one ring form with two dots within one RBC that is falciparum

Malaria Clinical infection

Febrile attacks-malarial paroxysms (reoccurrences); continuous or periodic fever, Nausea, vomiting, diarrhea Splenomegaly, Hepatomegaly, Anaemia

Identify

Gametocytes: P. falciparum

What would you need to treat for when you see this?

Hypnozoites P vivax: Trophozoite showing amoeboid appearance

What is the relationship of immunity and disease tolerance with endemicity?

Immunity and disease tolerance correlate with endemicity. Epidemics unlikely with high endemicity

Immunity to malaria in endemic areas

Infant immunity from maternal antibodies (~3 mo); Presence of HbF (Fetal hemoglobin) Repeated infections = partial immunity usually achieved by age 5yrs. Keeps parasitaemia low; reduces occurrence of severe infection

What is cerebral malaria assoc with and what are the cytokines?

Infected RBC sequestration in cerebral microvasculature -Cytokines (TNF-a, IL1, IL6, Nitric oxide)

What are the Consequences of invasion of erythocytes of all ages?

Large number of merozoites produced = higher parasitaemia More RBC destruction

Identify

Mixed stages (P. falciparum )

How is malaria transmitted?

Natural - mosquitoes Mechanical-transfusion/sharing syringes Congenital - rare

What complication is associated with P. malariae?

Nephrotic syndrome

Identify

Neutrophils (large cells) surrounded by parasites RBC are hemolyzed in thick smears; Only leukocytes & malaria parasites present are detectable. -Thick smears are used to detect infection & estimate parasite concentration

What is done to control?

No standing water Insecticide/larvicide Sterilization

Increased morbidity and mortality in P. falciparum: Why?

P. falciparum: Erythrocytes of all ages invaded P. vivax & ovale prefer young RBC (reticulocytes) P. malariae prefer old RBC

The most severe form of malaria is caused by what organism and where is it found? What is the most dangerous complication?

Plasmodium falciparum Malignant tertian Tropical Africa, Asia, Latin America Most dangerous comp is cerebral malaria w/ convulsions->coma

Identify

Plasmodium malariae Band form of P. malariae trophozoite. Nephrotic syndrome peridocity is 72 hrs

The mildest malaria

Plasmodium malariae - Quartan malaria Worldwide but very patchy

Identify

Plasmodium vivax

What are the tertian malaria organisms?

Plasmodium vivax- Worldwide Plasmodium ovale - West Africa

Severe hypoglycaemia a marker of what? What is the cause?

Poor outcome-Common in pregnant women and children. Close monitoring of glucose levels essential. Causes: Increased glucose utilization; large requirements of the malaria parasites. Drug induced- Quinine-induced insulinaemia

Vaccines under development

Pre Erythorcytic Vaccine -Inhibit development in liver Erythrocytic or blood-stage vaccine - Prevent multiplication in RBC and diminish severe disease Sexual stage Vaccine- Does not protect infected person, but interrupts transmission

What causes innate resistance to malaria?

Pt w/ hemoglobinopathies - HbS, HbC, thalassaemias & RBC enzyme deficiencies e.g. G6PD deficiency Internal milieu of the RBC is not supportive of optimal parasite growth. Protective effect seen in carrier HbAS (sickle cell trait)-have less severe malaria compared to HbAA & HbSS patients. HbSS (full sickle cell anaemia) patient are likely to have a fatal outcome due to complications -increased sickling, severe anaemia

What can impair merozoite invasion?

RBC cytoskeleton abnormalitiy e.g. Ovalocytosis Rigid cytoskeleton → impaired merozoite invasion

Blackwater fever

Rare but potentially fatal-Occurs in non-immune adults Follows repeated attacks of falciparum malaria Autoimmune response. Rapid & massive intravascular haemolysis. Haemoglobinuria, haemoglobinaemia & jaundice, Renal failure

What is the Molecular mechanism of cytoadherence?

Receptor ligand interaction Ligands-Proteins expressed on surface of infected RBC & bind to receptors on endothelial cells. PfEMP-1 (Plasmodium falciparum erythrocyte membrane protein) parasite protein implicated as the cytoadherence ligand, expressed on electron dense protrusions (knobs) of infected RBC. Exhibits antigenic variation to evade immune system

What do merozoites infect?

Red blood cells

Relapse versus Recrudescence

Relapse: Seen only in P. vivax and P. ovale; Due to presence of dormant hypnozoites in the liver (hypnozoite-induced relapse) Recrudescence: (All species) Reappearance of blood forms of parasites after treatment. Due to drug resistance

Highest areas of transmission are

S. America, Central Africa, Indian Subcontinent, SE Asia and eastern and southern Arabia

Malaria Prodromal symptoms

Seen in all species Occurs few days before first febrile attack Non-specific 'flu-like' symptoms Anorexia, muscle pain, headaches etc

What is the cause of the severe anemia in P. falciparum?

Seen in young children-can be rapid onset and fatal Mechanisms: Direct hemolysis, Bone marrow suppression,Immune mediated destruction

What are the risks of malaria in pregnancy?

Susceptibility increases Placental sequestration of infected RBC Anaemia. Increased morbidity and mortality for both Premature labour, low birth weight, spontaneous abortions, 10,000 maternal deaths annually Might increase the risk of HIV transmission to child

Patients with HIV infections are more likely to develop:

Symptomatic illness when infected with malaria Anemia Adverse birth outcomes Failure of Tx due to supressed immune system Increased viral replication → HIV viral load → progression of HIV disease

What are the periodicities of tertian and quartian malaria?

Tertian malaria: P. falciparum, P. vivax; P. ovale-For these three the erythrocytic cycle is 48hrs Quartan malaria: P. malariae-Erythrocytic cycle is 72hrs

What is the Duffy antigen?

The Duffy antigen is located on the surface of red blood cells, and is named after the patient in which it was discovered. The protein encoded by this gene is a glycosylated membrane protein and a non-specific receptor for several chemokines. The protein is also the receptor for Plasmodium vivax. So a Duffy -ve result means you are protected from vivax

What is the second cycle?

The human blood stage - erythorocytic cycle. Parasites replicate by erythrocytic schizogony -asexual multiplication in the erythrocytes. Immature trophozoite (ring stage) to Mature trophozoite to Schizont which rupture and release merozoites. Some differentiate into sexual erythrocytic stages (gametocytes)

What is the first cycle?

The human liver stage called exo-erythrocytic stage - sporozoites infect the liver cells and replicate in the liver and mature into schizonts which rupture and release merozoites.

What is the sexual erythrocytic stage?

The male (microgametocytes) and female (macrogametocytes), are ingested by Anopheles mosquito during a blood meal and multiply in the mosquito (sporogonic cycle). In mosquito's stomach, the microgametes penetrate the macrogametes generating zygotes which become motile and elongated (ookinetes) and invade the midgut wallof the mosquito where they develop into oocysts . The oocysts grow, rupture, and release sporozoites , which make their way to the mosquito's salivary glands.

What occurs in the ring stage?

The ring stage trophozoites mature into schizonts, which rupture releasing merozoites .

What type of blood stain is examined?

Thick blood films for detection of presence of parasite Thin blood films for identification of species

What is Rosetting and what are its consequences?

adherence of infected RBC to non-infected RBC Consequences: More RBC destruction; Enhances sequesteration

What are common misdiagnoses for malaria?

influenza, viral hepatitis

What is unstable or epidemic malaria and what is the cause and how does this effect people?

marked increase in incidence - increase in malaria in areas of low endemicity outbreaks in areas previously without malaria. Population is non-immune morbidity and mortality can be high

What is Plasmodium knowlesi?

specie of Plasmodium that causes infections in primates now recognized as causing human infections especially prevalent in parts of South East Asia

What is Stable or endemic malaria and what are its levels?

sustained natural transmission; may be seasonal transmission. The various levels of endemicity are Holoendemic, Hyperendemic , Mesoendemic, Hypoendemic