38 - Protozoa II

Which Plasmodium species causes the most infections and deaths worldwide?

Plasmodium falciparum

What are the other Plasmodium species that infect humans?

• P. vivax

• P. ovale

• P. malariae

• P. knowlesi (zoonotic from macaques, only in Southeast Asia)

What is the vector for malaria?

Anopheles spp. mosquitoes

What are general symptoms of malaria?

• Fever

• Rigors (shaking chills)

• Headache

• Nausea/vomiting

• Malaise

• Back pain (from splenomegaly or kidney damage)

What is the hallmark clinical pattern of malaria?

Recurrent fever cycles with:

1. Cold stage (chills)

2. Hot stage (fever, headache, nausea/vomiting)

3. Sweating stage (sweats, malaise, fever resolves)

What severe complications are specific to P. falciparum infection?

• Cerebral malaria

• Blackwater fever

What causes cerebral malaria in P. falciparum infection?

A Plasmodial protein expressed on infected RBCs causes them to adhere to vessel walls → capillary plugging

What are symptoms of cerebral malaria?

• Altered behavior

• Impaired consciousness

• Seizures

• Coma

What is blackwater fever?

A hemolytic crisis with kidney involvement due to massive RBC lysis and hemoglobin release

What species cause malaria relapse?

Plasmodium vivax and Plasmodium ovale

What stage allows P. vivax and P. ovale to cause relapse?

Hypnozoite stage – a dormant stage in hepatocytes lasting ≥28 days

Describe the relapse mechanism of malaria?

• Hypnozoites “awaken” and replicate

• Infected hepatocytes rupture → release of merozoites

• Merozoites infect RBCs → fever/chills cycles return

What is the gold standard for malaria diagnosis?

Thick and thin blood smears (look for trophozoite "signet rings")

What types of drugs are used to treat malaria?

Quinine-containing compounds, including:

• Quinine

• Chloroquine

• Mefloquine

What must be considered when selecting malaria treatment?

Drug resistance (important consideration in treatment planning)

What is the most common Babesia species infecting humans?

Babesia microti

What is the vector for Babesia microti?

Ixodes scapularis tick (also known as deer tick or blacklegged tick)

Where in the U.S. is Babesia microti most commonly found?

• Northeast U.S. (e.g., New England, NY, NJ)

• Upper Midwest (e.g., Minnesota)

How is Babesia microti transmitted?

• Bite of infected Ixodes tick (usually young nymph stage, size of a poppy seed)

• Blood transfusion (contaminated blood)

• Vertical transmission (in utero or during delivery from mother to baby)

What is the cellular tropism of Babesia microti?

Red blood cells (RBCs) → leads to hemolytic anemia

How is Babesia infection diagnosed?

Thick and thin blood smears to visualize parasites in RBCs

What forms of Babesia are seen on microscopy?

• Trophozoite form = gamete, appears as signet ring

• Merozoite form = appears as Maltese cross

What animals are reservoirs for Toxoplasma gondii?

• Wild birds and rodents (infect cats)

• Cats are definitive hosts (infected by eating infected prey)

How can livestock and produce become contaminated with T. gondii?

Through contact with oocyst-contaminated soil

What tissues can T. gondii oocysts form in?

• Skeletal muscle

• Myocardium

• Brain

• Eyes

What are the routes of transmission for T. gondii?

• Inhaling/ingesting oocysts (e.g., when changing litter box)

Who is at high risk for severe toxoplasmosis?

• Pregnant women

• Immunocompromised individuals, especially:

  • AIDS patients

  • Those immunosuppressed for cancer or transplant

How is Leishmania transmitted?

Via the sandfly in a human–sandfly–human cycle

What disease does Leishmania tropica cause?

Cutaneous leishmaniasis (skin ulcers)

What disease does Leishmania donovani cause?

Visceral leishmaniasis (kala-azar)

What cells does Leishmania infect, and how does it affect them?

• Infects reticuloendothelial system cells (e.g., macrophages)

• Alters signaling processes in macrophages

What organs are affected by visceral leishmaniasis?

• Liver

• Spleen

• Bone marrow

What are symptoms of visceral leishmaniasis?

• Hepatosplenomegaly

• Spiking fevers

• Weight loss

• Pancytopenia (↓ RBCs, WBCs, platelets)

How is leishmaniasis diagnosed?

• Bone marrow macrophages with intracellular amastigotes

• Occasionally seen in peripheral macrophages

• Serum antibodies may be present in visceral disease

How does cutaneous leishmaniasis usually begin?

A papule develops at the sandfly bite site

What does the papule develop into?

An ulcer with raised edges = VOLCANO SIGN

What are other characteristics of cutaneous lesions?

• May be painless or painful

• May have enlarged regional lymph nodes (LN)

• Heals with crater/pit in skin

What is the key virulence mechanism of Trypanosoma cruzi?

Immune evasion by changing coat proteins

What is the vector for T. cruzi (Chagas Disease)?

Triatomine bug, also known as:

• Reduviid bug

• “Kissing bug”

How is T. cruzi transmitted?

• The bug defecates while feeding

• Trypomastigotes in feces enter through bite wound or mucous membranes when the person rubs or scratches

What are the symptoms of acute Chagas Disease?

• Often mild

• Chagoma – localized swelling at bite site

• Romaña sign – unilateral periorbital swelling (classic finding)

How is acute Chagas diagnosed?

• Detection of trypomastigotes in blood

  • Blood smears

  • Fluorescent staining

• Along with clinical presentation