Phylum

Posess structures collectively known as apical complex found in sporozoite or merozoite 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 limited motility

Micronemes lie parallel to the rhoptries

Rhoptries and micronemes probably secrete proteins that alter the host cell’s plasma membrane

Micropores are analogous to cytostomes

All these organelles dissapear in trophozoite stage, except of micropores, they persist through all stages

MALARIA

Human Malaria is caused by one of 4 protozoan parasites:

Plasmodium falciparum

Plasmodium vivax

Plasmodium ovale

Plasmodium malariae

Kingdom Subkingdom Phylum Class Subclass Order Suborder Family Genus Species

ProtistaProtozoaApicomplexaSporozoasidaCoccidiasinaEucoccidioridaHaemosporinaPlasmodiidaePlasmodiumFalciparum, malariae, ovale, vivax

TAXONOMY

Malaria is transmitted through the bite of an infected female Anopheles mosquito

May be acquired congenitally from mother to the child across the placenta

From platelet or blood transfusions

From the use of shared needles

Transmission

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 six Two-thirds of remaining cases are concentrated in six

countries: India, Brazil, Sri Lanka, Vietnam, Colombia, countries: India, Brazil, Sri Lanka, Vietnam, Colombia, Solomon IslandsSolomon Islands

most victims are children <5 yrs most victims are children <5 yrs Pregnant women are also especially vulnerablePregnant women are also especially vulnerable The majority of P.falciparum cases imported into North The majority of P.falciparum cases imported into North

America and Europe are acquired in AfricaAmerica and Europe are acquired in Africa

P. Ovale is limited to tropical Africa and to discrete areas of the Western Pacific

Most West Africans are negative for the Duffy blood-type, which is shown to be associated with receptor sites for P. vivax merozoites on the RBCs

Therefore, many West Africans are not susceptible to infection with P. vivax

Falciparum Malaria is confined to sub-Saharian Africa, the Amazon region of South America, rural forested areas of Southeast Asia and urban and rural areas of the Indian subcontinent

Individuals with sickle-cell trait are more resistant to severe falciparum malaria than normal homozygotes

Epidemiology

Areas of Malaria Transmission and Antimalarial Drug Resistance

Life cycle

The entire life span is spent in two hosts: the insect vector and a human host Only female Anopheles mosquitoes serve as vectors The alternation of sexual and asexual phases is a significant feature The asexual phase, schizogony occurs in the human The sexual phase, gamogony occurs in the mosquito The subsequent another asexual reproductive phase, sporogony occurs in the mosquito

Infective form is the slender, elongated sporozoite Exoerythrocytic schizogonic phase (hepatocytes) Inside the hepatocyte sporozoite develops into a trophozoite which divides several times This multiple fission produces thousands of merozoites Erythrocytic schizogonic phase Inside the erythrocyte, the merozoite grows to an early trophozoite stage – the signet ring stage Early trophozoite develops into mature trophozoite and undergoes multiple fission into schizonts Merozoites may begin schizogony anew or may become a male microgametocyte 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

Life Cycle

Liver stage

Sporozoites

Mosquito Salivary Gland

Malaria Life Cycle

Gametocytes

Oocyst

Red Blood Cell Cycle

Zygote

P. vivax and P. ovale cause benign tertian malaria; during schizogony 12 to 24 merozoites are produced; the rupture from erythrocytes occurs synchronously at 48 hour interval

P. malariae causes quartan malaria; the number of merozoites varies from 6 to 12; merozoites rupture from the infected cell synchronously every 72 hours

P. falciparum causes malignant quartan malaria; the schizonts produce 8 to 32 merozoites; rupture of merozoites occurs 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 and those 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 and general malaise, mild anemia and splenomegaly Uncomplicated malaria Complicated or severe malaria is associated with vital organ dysfunction: CNS (coma, seizures) RS (pulmonary edema, ARDS) GI complications Acute renal failure, severe anemia, metabolic acidosis

Clinically Mild malariaClinically Mild malaria

An abrupt onset of an initial 'cold stage' associated with An abrupt onset of an initial 'cold stage' associated with dramatic rigors in which the patient visibly shakes; (10-dramatic rigors in which the patient visibly shakes; (10-15minutes)15minutes)

An ensuing 'hot stage' during which the patient may An ensuing 'hot stage' during which the patient may have a temperature of well over 104°F (40°C), may be have a temperature of well over 104°F (40°C), may be restless and excitable, and may vomit or convulse; may restless and excitable, and may vomit or convulse; may have frontal headache and myalgia in limbs and back (2-have frontal headache and myalgia in limbs and back (2-6 housr) and 6 housr) and

Finally, the sweating stage, during which the patient Finally, the sweating stage, during which the patient feels better and may fall asleep. feels better and may fall asleep.

Fever occurs on alternate days with P.vivax and P.ovale and 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 as quickly as 36 hours from the onset of symptoms in non-immune individuals

P.vivax is a relatively benign parasite that elicits alternate day fever without causing mortality

P.ovale also produces alternate day fever and is clinically 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, or impairment of consciousness, seizures, coma, or other neurologic abnormalities other neurologic abnormalities

Severe anemia due to hemolysis (destruction of Severe anemia due to hemolysis (destruction of erythrocytes) and dysertyhropoesiserythrocytes) and dysertyhropoesis

HemoglobinuriaHemoglobinuria Pulmonary edema Pulmonary edema Abnormalities in blood coagulation and Abnormalities in blood coagulation and

thrombocytopeniathrombocytopenia Cardiovascular collapse and shockCardiovascular collapse and shock

One pathological element unique to P.falciparum is vascular obstruction A condition known as “blackwater fever” often accompanies falciparum malaria infections Massive lysis of erythrocytes produces high levels of hemoglobin in urine and blood Fever, vomiting with blood and jaundice also occur 20-50 percent mortality rate due to renal failure

In the case of P.vivax and P.ovale, the development of exo-erythrocytic forms allows the parasite to remain dormant within the hepatocyte

These dormant parasites are called hypnozoites and can reinitiate the infection causing relapsing disease

P.falciparum and P.malariae do not develop hypnozoites and do not cause relapsing disease

Recrudescence is the recurrence of symptoms of malaria after a subclinical or asymptomatic level of parasitemia for a certain period of time

This occurs when blood stages of malaria are maintained at very low levels after inadequate drug treatment

All malaria species can cause recrudescence

Relapsing and recrudescence

Diagnosis

Thick blood films

One or two drops of blood from a fingerprick are One or two drops of blood from a fingerprick are stirred in a circle on a glass slide, allowed to air dry and stirred in a circle on a glass slide, allowed to air dry and then stained with Giemsa or Field's .then stained with Giemsa or Field's .

With this method, the red cells lyse whereas the white With this method, the red cells lyse whereas the white cells and parasites remain intact. Parasites are cells and parasites remain intact. Parasites are identified by recognizing both the eosinophilic nucleus identified by recognizing both the eosinophilic nucleus and the basophilic cytoplasm of the malarial parasite. and the basophilic cytoplasm of the malarial parasite. Parasite density can be related to the number of white Parasite density can be related to the number of white cells present. This method has far greater sensitivity cells present. This method has far greater sensitivity than the thin blood film. than the thin blood film.

Thin blood filmsThin blood films

A thin film is produced by spreading a A thin film is produced by spreading a small drop of blood across a slide using small drop of blood across a slide using the edge of a second slide, thereby the edge of a second slide, thereby producing a monolayer of red cells. producing a monolayer of red cells.

The thin blood film allows accurate The thin blood film allows accurate speciation of the parasite and speciation of the parasite and quantitation, in which the number of quantitation, in which the number of parasites is related to the number of red parasites is related to the number of red cells present. cells present.

The ring stage derives its name from signet ring-like appearance

With a blue-stained nucleus and a pink-stained ring of cytoplasm

The trophozoite is a feeding stage and contains single nucleus with pigment granules, called hemozoin (a product of hemoglobin digestion), located within the cytoplasm

The schizont stage is initiated by the division of the trophozoite nucleus

Each individual nucleus then becomes surrounded by parasite cytoplasm to form a merozoite

Recent Diagnostic TestsRecent Diagnostic Tests Malaria PF antigen capture tests use a monoclonal antibody Malaria PF antigen capture tests use a monoclonal antibody

to the to the P. falciparumP. falciparum and are very useful tests in those who and are very useful tests in those who have not had malaria before .can only detect the presence of have not had malaria before .can only detect the presence of P. falciparumP. falciparum..

The optimal test detects parasite lactate dehydrogenase The optimal test detects parasite lactate dehydrogenase (pLDH) which can be distinguished from human LDH. This (pLDH) which can be distinguished from human LDH. This test can also distinguish test can also distinguish falciparumfalciparum from from vivaxvivax infections. infections.

The polymerase chain reaction is useful for making an The polymerase chain reaction is useful for making an accurate species diagnosis and detecting low level accurate species diagnosis and detecting low level parasitemiasparasitemias

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 gainst exoerythrocytoic 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 – against chloroquin-resistant malaria, chemoprophylaxis

Lapdap – chlorproguanil and dapsone – effective against drug-resistant mlria

Treatment

Exchange transfusionExchange transfusion

CDC recommends that exchange transfusion be strongly CDC recommends that exchange transfusion be strongly considered for persons with a parasite density of more considered for persons with a parasite density of more than 10% or if complications such as cerebral malaria, than 10% or if complications such as cerebral malaria, non-volume overload pulmonary edema, or renal non-volume overload pulmonary edema, or renal complications 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, and improving the rheological properties of blood, and reducing 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 control

A. Be Aware of the risk, the symptoms and understand that malaria is a serious infection

B. Avoid mosquito Bites

C. Take Chemoprophylaxis when appropriate

D. Seek immediate Diagnosis and treatment if they develop fever during or after travel

Susceptibility to Malaria

Susceptibility conferred by the presence of Duffy antigen Genetic deficiency in glucose-6-phosphate dehydrogenase in erythrocytes (favism) creates an inhospitable environment for the parasites Humans heterozygous for sickle-cell anemia posesses a selective advantage over individuals with normal hemoglobin Sickle erythrocyte membrane leaks potassium from the infected cell The parasite dies

Vector

Sporogony

Sporozoites Liver schizonts

Merozoite

Red blood cell invasion

Diagnosis

Like most of the Apicomplexa, Toxoplasma is an obligate intracellular parasite.  Its life cycle includes two phases called the intestinal - enteric (or enteroepithelial) and extraintestinal phases.

The intestinal phase occurs in cats only (wild as well as domesticated cats) and produces "oocysts." 

The extraintestinal phase occurs in all infected animals (including cats) and produces "tachyzoites" and, eventually, "bradyzoites" or "zoitocysts." 

The disease toxoplasmosis can be transmitted by ingestion of oocysts (in cat feces) or bradyzoites (in raw or undercooked meat).

Domestic cat and other Felidae are the Domestic cat and other Felidae are the definitive hostdefinitive host

Vertebrates are Vertebrates are intermediate hostintermediate host

1. amphibians1. amphibians

2. fish2. fish

3. reptiles3. reptiles

4. all warm-blooded animals including man4. all warm-blooded animals including man

Transmission

1. Accidental ingestion of oocysts passed in cat feces through contaminated soil or handling of cat litter2. Ingestion of tissue cysts with raw or undercooked meat (lamb, pork, beef), drinking unpasterized milk, contaminated water, or unwashed fruits or vegetables3. Transplacental transmission. Tachyzoites multiply within the placenta and spread to the fetus.

In most humans infected with Toxoplasma, the disease is asymptomatic.

  However, under some conditions, toxoplasmosis can cause serious pathology, including hepatitis, pneumonia, blindness, and severe neurological disorders. 

This is especially true in individuals whose immune systems are compromised (e.g., AIDS patients).  Toxoplasmosis can also be transmitted transplacentally resulting in a spontaneous abortion, a still birth, or a child that is severely handicapped mentally and/or physically.

Morphology

Oocyst – infective stage transmitted via cat fecesTachyzoites – infect macrophages, are carried throughout the human body via macrophages, causing pathologyTissue cysts (pseudocysts) – large cyst-like forms Bradyzoites – slowly developing forms within tissue cyst

MORPHOLOGY

The intracellular parasites (tachyzoite) are 3x6µ, crescent shaped organisms that are enclosed in a parasite membrane to form a cyst measuring 10-100 µ in size. Cysts in cat feces (oocysts) are 10-13 µ in diameter

A sporulated oocyst of Toxoplasma gondii.  The oocyst contains two sporocysts, each of which contain four sporozoites.  Thus, they resemble the oocysts of Isospora sp.  Only cats will produce and pass Toxoplasma oocysts; approximate diameter = 10 µm.

SYMPTOMS

Although Toxoplasma infection is common, it rarely produces symptoms in normal individuals. Its serious consequences are limited to pregnant women and immunodeficient hosts. Congenital infections occur in about 1-5 per 1000 pregnancies of which 5-10% result in miscarriage, 8-10% result in serious brain and eye damage to the fetus, 10-13% of the babies will have visual handicaps. Although 58-70% of infected women will give a normal birth, a small proportion of babies will develop active retino-chorditis or mental retardation in childhood or young adulthood.

In immunocompetent adults, toxoplasmosis, may produce flu-like symptoms, sometimes associated with lymphadenopathy. In immunocompromised individuals, infection results in generalized parasitemia involvement of brain, liver, lung and other organs, and often death.

TOXOPLASMOSIS IN HUMANS

1. Majority of cases are asymptomatic2. Mild fever, myalgia, swollen glands and lymph nodes (cervical or occipital 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 the infection during gestation.5. CDC estimates 400-4000 cases of congenital toxoplasmosis per year.6.Blindness, hydrocephalus, microcephaly, seizures and mental retardation are common among infants7.Hepatosplenomegaly, rash, fever, jaundice, anemia may also be present8.Most common pathology is chorioretinitis which may result in strabismus 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 IgG titers indicates early stages of primary infection A negative IgM titer is helpful for ruling out recent infection Measurement of maternal and infant IgG antobodies is critical An infant: maternal Ig G ratio of four or higher is indicative of new infection The presence of high titers of specific IgM antibodies in the infant’s serum is diagnostic

TREATMENT

Acute infections benefit from pyrimethamine or sulphadiazine. Spiramycin is a successful alternative. Pregnant women are advised to avoid cat litter, handle uncooked meat carefully and undercooked meat.

Additional drugs

Sulfonamide drugs

Folinic acid

Clindamycin

Trimethoprim-sulfamethoxazole

Babesiosis

Causitive agent: Babesia microtiVector: tick Ixodes dammini

Symptoms mimic mild malariaHemolytic anemiaClindamycin plus quinine has been used successfully to treat the disease