Posess structures collectively known as apical complex found in sporozoite ormerozoite stages of the life cycle Polar rings at the anterior end, just beneath the plasma membrane In Toxoplasma gondii conoid lies within the polar rings The rhoptries located within the polar rings Except in Babesia subpellicular microrubules radiate from the polar rings These organelles probably serve as support elements and facillitate the limitedmotility Micronemes lie parallel to the rhoptries Rhoptries and micronemes probably secrete proteins that alter the host cell’splasma membrane Micropores are analogous to cytostomes All these organelles dissapear in trophozoite stage, except of micropores, theypersist through all stages
MALARIAHuman Malaria is caused by one of 4 protozoan parasites: Plasmodium falciparum Plasmodium vivax Plasmodium ovale Plasmodium malariae
Malaria is transmitted through the bite of aninfected female Anopheles mosquito May be acquired congenitally from mother to thechild across the placenta From platelet or blood transfusions From the use of shared needlesTransmission
Scope of the Malaria Problem:Scope of the Malaria Problem: Malaria is the most common life-threatening infectionMalaria is the most common life-threatening infection– 1.5 to 2.7 million deaths/yr1.5 to 2.7 million deaths/yr– 300-500 million infections/yr300-500 million infections/yr ~90% of these cases occur in sub-Saharan Africa~90% of these cases occur in sub-Saharan Africa Two-thirds of remaining cases are concentrated in sixTwo-thirds of remaining cases are concentrated in sixcountries: India, Brazil, Sri Lanka, Vietnam, Colombia,countries: India, Brazil, Sri Lanka, Vietnam, Colombia,Solomon IslandsSolomon Islands most victims are children <5 yrsmost victims are children <5 yrs Pregnant women are also especially vulnerablePregnant women are also especially vulnerable The majority of P.falciparum cases imported into NorthThe majority of P.falciparum cases imported into NorthAmerica and Europe are acquired in AfricaAmerica and Europe are acquired in Africa
P. Ovale is limited to tropical Africa and to discreteareas of the Western Pacific Most West Africans are negative for the Duffy blood-type, which is shown to be associated with receptor sites forP. vivax merozoites on the RBCs Therefore, many West Africans are not susceptible toinfection with P. vivax Falciparum Malaria is confined to sub-Saharian Africa,the Amazon region of South America, rural forested areas ofSoutheast Asia and urban and rural areas of the Indiansubcontinent Individuals with sickle-cell trait are more resistant tosevere falciparum malaria than normal homozygotesEpidemiology
Areas of Malaria Transmission and AntimalarialDrug Resistance
Life cycle The entire life span is spent in two hosts: the insectvector and a human host Only female Anopheles mosquitoes serve as vectors The alternation of sexual and asexual phases is asignificant feature The asexual phase, schizogony occurs in the human The sexual phase, gamogony occurs in the mosquito The subsequent another asexual reproductivephase, sporogony occurs in the mosquito
Infective form is the slender, elongated sporozoite Exoerythrocytic schizogonic phase (hepatocytes) Inside the hepatocyte sporozoite develops into a trophozoitewhich divides several times This multiple fission produces thousands of merozoites Erythrocytic schizogonic phase Inside the erythrocyte, the merozoite grows to an earlytrophozoite stage – the signet ring stage Early trophozoite develops into mature trophozoite andundergoes multiple fission into schizonts Merozoites may begin schizogony anew or may become a malemicrogametocyte or a female macrogametocyte Sexual phase occurs in the female mosquito Anopheles:microgametocytes – microgametes, macrogametocytes –macrogametes Syngamy produces a diploid zygote, ookynete, oocyst Oocysts rupture releasing the sporozoites into the hemocoel
Liver stageSporozoitesMosquito SalivaryGlandMalaria Life CycleGametocytesOocystRed Blood CellCycleZygote
P. vivax and P. ovale cause benign tertian malaria; duringschizogony 12 to 24 merozoites are produced; the rupture fromerythrocytes occurs synchronously at 48 hour interval P. malariae causes quartan malaria; the number ofmerozoites varies from 6 to 12; merozoites rupture from theinfected cell synchronously every 72 hours P. falciparum causes malignant quartan malaria; theschizonts produce 8 to 32 merozoites; rupture of merozoitesoccurs at 48 to 72 hour intervals Merozoites of P.falciparum can infect RBCs of all ages,whereas those of P.vivax and P.ovale infect reticulocytes andthose of P.malariae invade only older RBCs
Clinical manifestation Incubation period: 7 to 30 days Typical symptoms include: fever, chills, sweats,rigors, headache, nausea and vomiting, body aches andgeneral malaise, mild anemia and splenomegaly Uncomplicated malaria Complicated or severe malaria is associated withvital organ dysfunction: CNS (coma, seizures) RS (pulmonary edema, ARDS) GI complications Acute renal failure, severe anemia, metabolicacidosis
Clinically Mild malariaClinically Mild malaria An abrupt onset of an initial cold stageAn abrupt onset of an initial cold stageassociated with dramatic rigors in which theassociated with dramatic rigors in which thepatient visibly shakes; (10-15minutes)patient visibly shakes; (10-15minutes) An ensuing hot stage during which theAn ensuing hot stage during which thepatient may have a temperature of well overpatient may have a temperature of well over104°F (40°C), may be restless and excitable,104°F (40°C), may be restless and excitable,and may vomit or convulse; may have frontaland may vomit or convulse; may have frontalheadache and myalgia in limbs and back (2-6headache and myalgia in limbs and back (2-6housr) andhousr) and Finally, the sweating stage, during which theFinally, the sweating stage, during which thepatient feels better and may fall asleep.patient feels better and may fall asleep.
Fever occurs on alternate days with P.vivax and P.ovaleand every 3 days with P.malariae With falciparum malaria, fever may be asynchronous,recurring every 36 to 48 hours P.falciparum is a deadly parasite, causing death asquickly as 36 hours from the onset of symptoms in non-immune individuals P.vivax is a relatively benign parasite that elicitsalternate day fever without causing mortality P.ovale also produces alternate day fever and isclinically similar to vivax malaria
Severe MalariaSevere Malaria Manifestations of severe malaria include:Manifestations of severe malaria include: Cerebral malaria, with abnormal behavior,Cerebral malaria, with abnormal behavior,impairment of consciousness, seizures, coma, orimpairment of consciousness, seizures, coma, orother neurologic abnormalitiesother neurologic abnormalities Severe anemia due to hemolysis (destruction ofSevere anemia due to hemolysis (destruction oferythrocytes) and dysertyhropoesiserythrocytes) and dysertyhropoesis HemoglobinuriaHemoglobinuria Pulmonary edemaPulmonary edema Abnormalities in blood coagulation andAbnormalities in blood coagulation andthrombocytopeniathrombocytopenia Cardiovascular collapse and shockCardiovascular collapse and shock
One pathological element unique toP.falciparum is vascular obstruction A condition known as “blackwater fever”often accompanies falciparum malariainfections Massive lysis of erythrocytes produces highlevels of hemoglobin in urine and blood Fever, vomiting with blood and jaundicealso occur 20-50 percent mortality rate due to renalfailure
In the case of P.vivax and P.ovale, the development of exo-erythrocytic forms allows the parasite to remain dormant within thehepatocyte These dormant parasites are called hypnozoites and can reinitiatethe infection causing relapsing disease P.falciparum and P.malariae do not develop hypnozoites and do notcause relapsing disease Recrudescence is the recurrence of symptoms of malaria after asubclinical or asymptomatic level of parasitemia for a certain period oftime This occurs when blood stages of malaria are maintained at very lowlevels after inadequate drug treatment All malaria species can cause recrudescenceRelapsing and recrudescence
DiagnosisThick blood films One or two drops of blood from a fingerprick areOne or two drops of blood from a fingerprick arestirred in a circle on a glass slide, allowed to air dry andstirred in a circle on a glass slide, allowed to air dry andthen stained with Giemsa or Fields .then stained with Giemsa or Fields . With this method, the red cells lyse whereas the whiteWith this method, the red cells lyse whereas the whitecells and parasites remain intact. Parasites arecells and parasites remain intact. Parasites areidentified by recognizing both the eosinophilic nucleusidentified by recognizing both the eosinophilic nucleusand the basophilic cytoplasm of the malarial parasite.and the basophilic cytoplasm of the malarial parasite.Parasite density can be related to the number of whiteParasite density can be related to the number of whitecells present. This method has far greater sensitivitycells present. This method has far greater sensitivitythan the thin blood film.than the thin blood film.
Thin blood filmsThin blood films A thin film is produced by spreading aA thin film is produced by spreading asmall drop of blood across a slide usingsmall drop of blood across a slide usingthe edge of a second slide, therebythe edge of a second slide, therebyproducing a monolayer of red cells.producing a monolayer of red cells. The thin blood film allows accurateThe thin blood film allows accuratespeciation of the parasite andspeciation of the parasite andquantitation, in which the number ofquantitation, in which the number ofparasites is related to the number of redparasites is related to the number of redcells present.cells present.
The ring stage derives its name from signet ring-likeappearance With a blue-stained nucleus and a pink-stained ring ofcytoplasm The trophozoite is a feeding stage and contains singlenucleus with pigment granules, called hemozoin (a productof hemoglobin digestion), located within the cytoplasm The schizont stage is initiated by the division of thetrophozoite nucleus Each individual nucleus then becomes surrounded byparasite cytoplasm to form a merozoite
Recent Diagnostic TestsRecent Diagnostic Tests Malaria PF antigen capture tests use a monoclonalMalaria PF antigen capture tests use a monoclonalantibody to theantibody to the P. falciparumP. falciparum and are very usefuland are very usefultests in those who have not had malaria before .cantests in those who have not had malaria before .canonly detect the presence ofonly detect the presence of P. falciparumP. falciparum.. The optimal test detects parasite lactateThe optimal test detects parasite lactatedehydrogenase (pLDH) which can be distinguisheddehydrogenase (pLDH) which can be distinguishedfrom human LDH. This test can also distinguishfrom human LDH. This test can also distinguishfalciparumfalciparum fromfrom vivaxvivax infections.infections. The polymerase chain reaction is useful for makingThe polymerase chain reaction is useful for makingan accurate species diagnosis and detecting lowan accurate species diagnosis and detecting lowlevel parasitemiaslevel parasitemias
The first known antimalarial drug was quinine – destroys the schizogonic stages,but has little or no effect on exoerythrocytic stages or gametocytes A synthetic drug Atabrine dihydrochloride, which, like quinine is ineffective gainstexoerythrocytoic stages Chloroquine, amodiaquine, primaquine should be administered in combination Chloroquine, amodiauine – effective against erythrocytic stages, primaquine –against exoerythrocytic stages 3 days of chloroquine, followed by a single dose of primaquine Fansidar, combnation of pyrimethamine andsulfadoxine – inhibits folic acid cycle Mefloquine - is being added to pyrimethmine-sulfadoxin combination – againstchloroquin-resistant malaria, chemoprophylaxis Lapdap – chlorproguanil and dapsone – effective against drug-resistant mlriaTreatment
Exchange transfusionExchange transfusion CDC recommends that exchange transfusion be stronglyCDC recommends that exchange transfusion be stronglyconsidered for persons with a parasite density of moreconsidered for persons with a parasite density of morethan 10% or if complications such as cerebral malaria,than 10% or if complications such as cerebral malaria,non-volume overload pulmonary edema, or renalnon-volume overload pulmonary edema, or renalcomplications exist.complications exist. Its beneficial effect by removing infected red cells,Its beneficial effect by removing infected red cells,improving the rheological properties of blood, andimproving the rheological properties of blood, andreducing toxic factors such as parasite derived toxins,reducing toxic factors such as parasite derived toxins,harmful metabolites, and cytokines.harmful metabolites, and cytokines.
Prevention and controlA. Be Aware of the risk, the symptoms andunderstand that malaria is a serious infectionB. Avoid mosquito BitesC. Take Chemoprophylaxis when appropriateD. Seek immediate Diagnosis and treatment ifthey develop fever during or after travel
Susceptibility to Malaria Susceptibility conferred by the presence of Duffyantigen Genetic deficiency in glucose-6-phosphatedehydrogenase in erythrocytes (favism) creates aninhospitable environment for the parasites Humans heterozygous for sickle-cell anemiaposesses a selective advantage over individuals withnormal hemoglobin Sickle erythrocyte membrane leaks potassiumfrom the infected cell The parasite dies
Like most of the Apicomplexa, Toxoplasma is an obligateintracellular parasite. Its life cycle includes two phases called theintestinal - enteric (or enteroepithelial) and extraintestinal phases.The intestinal phase occurs in cats only (wild as well asdomesticated cats) and produces "oocysts."The extraintestinal phase occurs in all infected animals (includingcats) and produces "tachyzoites" and, eventually, "bradyzoites"or "zoitocysts."The disease toxoplasmosis can be transmitted by ingestion ofoocysts (in cat feces) or bradyzoites (in raw or undercooked meat).
Domestic cat and other Felidae are theDomestic cat and other Felidae are the definitive hostdefinitive hostVertebrates areVertebrates are intermediate hostintermediate host1. amphibians1. amphibians2. fish2. fish3. reptiles3. reptiles4. all warm-blooded animals including man4. all warm-blooded animals including manTransmission1. Accidental ingestion of oocysts passed in cat feces throughcontaminated soil or handling of cat litter2. Ingestion of tissue cysts with raw or undercooked meat (lamb,pork, beef), drinking unpasterized milk, contaminated water, orunwashed fruits or vegetables3. Transplacental transmission. Tachyzoites multiply within theplacenta and spread to the fetus.
In most humans infected with Toxoplasma, the diseaseis asymptomatic.However, under some conditions, toxoplasmosis cancause serious pathology, including hepatitis, pneumonia,blindness, and severe neurological disorders.This is especially true in individuals whose immunesystems are compromised (e.g., AIDS patients).Toxoplasmosis can also be transmitted transplacentallyresulting in a spontaneous abortion, a still birth, or achild that is severely handicapped mentally and/orphysically.
MorphologyOocyst – infective stage transmitted viacat fecesTachyzoites – infect macrophages, arecarried throughout the human body viamacrophages, causing pathologyTissue cysts (pseudocysts) – large cyst-like formsBradyzoites – slowly developing formswithin tissue cyst
MORPHOLOGYThe intracellularparasites (tachyzoite)are 3x6µ, crescentshaped organisms thatare enclosed in aparasite membrane toform a cyst measuring10-100 µ in size. Cystsin cat feces (oocysts)are 10-13 µ in diameter
A sporulated oocyst ofToxoplasma gondii. Theoocyst contains twosporocysts, each of whichcontain four sporozoites.Thus, they resemble theoocysts of Isospora sp.Only cats will produce andpass Toxoplasma oocysts;approximate diameter = 10µm.
SYMPTOMSAlthough Toxoplasma infection is common, it rarely producessymptoms in normal individuals. Its serious consequences are limitedto pregnant women and immunodeficient hosts. Congenital infectionsoccur in about 1-5 per 1000 pregnancies of which 5-10% result inmiscarriage, 8-10% result in serious brain and eye damage to thefetus, 10-13% of the babies will have visual handicaps. Although 58-70% of infected women will give a normal birth, a small proportionof babies will develop active retino-chorditis or mental retardation inchildhood or young adulthood.In immunocompetent adults, toxoplasmosis, may produce flu-likesymptoms, sometimes associated with lymphadenopathy. Inimmunocompromised individuals, infection results in generalizedparasitemia involvement of brain, liver, lung and other organs, andoften death.
TOXOPLASMOSIS IN HUMANS1. Majority of cases are asymptomatic2. Mild fever, myalgia, swollen glands and lymph nodes (cervical oroccipital lymphadenopathy), headache, rash, sore throat3.Immunocompromized individuals are at greater risk: HIV patients,Organ transplant patients, people on chemotherapy4.Brain lesions associated with fever, headache, confusion, seizures,abnormal neurological findings, myocarditis, pneumonitis, chorioretinitis4. Pregnant women’s fetus are at risk if the mother acquires theinfection during gestation.5. CDC estimates 400-4000 cases of congenital toxoplasmosis per year.6.Blindness, hydrocephalus, microcephaly, seizures and mentalretardation are common among infants7.Hepatosplenomegaly, rash, fever, jaundice, anemia may also be present8.Most common pathology is chorioretinitis which may result instrabismus and blindness
DIAGNOSIS Indirect serological test or direct detection of the organism ELISA, IFA, complement fixation PCR Presence of high IgM in the absence of a significant IgGtiters indicates early stages of primary infection A negative IgM titer is helpful for ruling out recentinfection Measurement of maternal and infant IgG antobodies iscritical An infant: maternal Ig G ratio of four or higher isindicative of new infection The presence of high titers of specific IgM antibodies in theinfant’s serum is diagnostic
TREATMENTAcute infections benefit from pyrimethamine or sulphadiazine.Spiramycin is a successful alternative. Pregnant women are advisedto avoid cat litter, handle uncooked meat carefully and undercookedmeat.Additional drugsSulfonamide drugsFolinic acidClindamycinTrimethoprim-sulfamethoxazole
BabesiosisCausitive agent: Babesia microtiVector: tick Ixodes damminiSymptoms mimic mild malariaHemolytic anemiaClindamycin plus quinine has been used successfullyto treat the disease