Blood Protozoans

Promastigote

stage of Leishmania spp., found within the insect vector

Epimastigote

stage typical of Trypanosoma spp., in the insect vector

Trypomastigote

stage typical of the bloodstream form of Trypanosoma spp.

Amastigote

intracellular stage of T. cruzi and Leishmania spp.

Trypanosoma brucei - Epidemiology

• T. brucei (T.b.) gambiense (tropical West Africa and Central Africa)

  • human and animal reservoir (human most important)

• T. brucei (T.b.) rhodesiense (East Africa)

  • human and animal reservoir (animal most important)

Life Cycle of African Trypanosomiasis

• infection occurs through bite of the tsetse fly which injects the trypomastigote (infective stage)

• trypomastigote enters the lymphatics and passes to bloodstream where it is carried throughout body (diagnostic stage)

• fly takes a blood meal and becomes infected with trypomastigotes

• parasite multiples in fly midgut, leaves the midgut and transforms into epimastigote

• epimastigote reaches the salivary glands where it transforms into trypomastigotes

Infective stage of African Trypanosomiasis

trypomastigote

Diagnostic Stage of African Trypanosomiasis

trypomastigote enters the lymphatics and passes to bloodstream

Trypanosoma brucei - Clinical Syndrome

• African sleeping sickness (T.b. rhodesiense) - more acute

  • painful at bite site, can become a red sore, also called a chancre

  • haemolymphatic stage

  • meningoencephalitic stage

• African sleeping sickness (T.b. gambiense) - more chronic

  • occasionally, within 1 to 3 weeks, the infective bite develops into a chancre

  • similar symptoms as that seen by T.b. rhodesinse

Haemolymphatic stage

fever, severe headaches, irritability, extreme fatigue, swollen lymph nodes, and aching muscles and joints

Meningoencephalitic stage

progressive confusion, personality changes, and other neurologic problems occur after infection has invaded the central nervous system. if left untreated, infection becomes worse, and death will occur within months

Trypanosoma brucei - Diagnosis

• microscopic staining of body fluid (including blood or lymph node aspirate) for trypomastigote

  • small kinetoplast located at the posterior end, a centrally located nucleus

Trypanosoma brucei - Treatment and Prevention

• pentamidine/suramin

  • used to treat the first stage of disease

• nifurtimox-eflornithine

  • used to treat the second stage of the disease

• education and control the breeding of the tsetse fly

  • wear long pants/sleeves that are neutral colors (attracted to bright colors)

  • use insect repellent

Trypanosoma cruzi - Epidemiology

• distribution: central/south america (rarely in southern parts of US)

  • estimated 6-8 million people in Mexico, Central American and South America are infected

• Human and animal reservoirs (mostly wild animals; but dogs may be a significant reservoir)

Vector for Trypanosoma cruzi

• reduviid bug (triatomine; kissing bug)

  • associated with animal nesting areas; the bugs are found in houses made from materials such as mud, adobe, straw, and palm thatch; bugs emerge at night

  • bugs defecate after they ingest blood and parasite in feces enter body through mucous membranes or breaks in skin

Trypanosoma cruzi - Transmission

• congenital transmission

• blood transfusion

• organ transplantation

• consumption of uncooked food that is contaminated with triatomine bug feces

Life Cycle of T. Cruzi

• infection occurs when the vector takes a blood meal and releases trypomastigote in its feces near the site of the bite (infective)

• trypomastigotes invade cells near site of inoculation and differentiate into intracellular amastigotes which will multiply and become trypomastigotes which are release into the bloodstream (diagnostic stage)

• trypomastigotes infect cells from a variety of tissues and transform into intracellular amastigotes (alternative diagnostic stage)

• vector takes a blood meal and becomes infected with trypomastigotes which transform into epimastigotes

• epimastigotes multiply and differentiate in the midgut and become trypomastigotes in the hindgut

infective and diagnostic stage of T. cruzi

trypomastigotes

Alternative diagnostic stage of T. cruzi

intracellular amastigotes

Trypanosoma cruzi - Clinical Syndrome

• Chaga’s disease (American Trypanosomiasis)

• Acute phase: mild to asymptomatic

  • fever and local swelling where the parasite entered the body

• Chronic phase: no organisms in the bloodstream; organism enters the heart, liver, spleen, brain and lymph nodes

  • asymptomatic for life OR symptomatic (20%)

Trypanosoma cruzi - Diagnosis

• microscopic staining of blood or CSF for trypomastigote (only acute stage)

  • large, subterminal or terminal kinetoplast, a centrally located located nucleus

• antibody detection (chronic stage)

• microscopic staining of biopsied tissue for amastigotes

• molecular analysis (only acute stage)

Trypanosoma cruzi - Treatment and Prevention

• benzidazole and nifurtimox

• education and vector control (improve housing to eliminate bugs)

• screen blood and tissue donors

Leishmania - Epidemiology

• distribution: found in parts of the tropics, subtropics, and southern Europe (varies with the species)

  • number of new cases of cutaneous leishmaniasis each year in the world is about 1 million; numbers of new cases of visceral leishmaniasis is abt 300,000

• human and animal reservoir: dogs and rodents

Leishmania - Vector

sand flies

Leishmania - Infections

• cutaneous leishmaniasis (skin sores)

• visceral leishmaniasis (kala-azar) (affect internal organs of the body; spleen, liver and bone marrow)

• mucocutaneous leishmanisasis (partial or total destruction of facial muscous membranes)

Life Cycle of Leishmaniasis

• infection occurs when the vector takes a blood meal and injects the promastigotes (infective stage)

• promastigotes get phagocyted by macrophages and transform into amastigotes

• amastigotes multiply in cells of various tissues (diagnostic stage) and proceed to infect other phagocytic cells

• vector takes a blood meal and becomes infected with amastigotes in macrophages which transform into epimastigotes in the gut

• epimastigotes multiply and migrate to proboscis

Leishmania - Cutaneous

within ~2 weeks, a red papule at bite site; lesion becomes irritated with intense itching and begins to enlarged and ulcerate - lesion may heal without treatment within months but usually leaves a disfiguring scare

Leishmania - Visceral (Kala-azar)

within a few weeks (or even years), a gradual onset of fever, diarrhea and anemia - chills that resemble malaria are common; organisms invade liver, spleen, kidney

• if untreated can become a lethal disease in a few weeks or may persist as a chronic disease and lead to death in 1 or 2 years

Leishmania - Diagnosis

• cutaneous:

  • microscopic staining of tissue for amastigotes

  • molecular analysis

• visceral:

  • microscopic staining of tissue or bones marrow for amastigotes

  • antibody detection

  • molecular analysis

Leishmania - Treatment and Prevention

• cutaneous: skin lesions may heal on their own (take months/years and leave an ugly scar)

  • miltefosine

• visceral:

  • amphotericin B by IV infusion

• education and protection from vector

  • wear long-sleeves/pants

  • insect repellent

  • use of mosquito net (need smaller hole sizes)

Plasmodium (Malaria) - Epidemiology

• distribution: worldwide in tropics/subtropics

  • in 2022 an estimated 249 million cases occurred worldwide with an estimated 608,000 death

  • Africa accounts for 95% of malaria cases and 96% of malaria deaths (children under 5 years of age accounted for ~80% of the deaths)

  • ~2000 cases and 5 deaths each year in the US

• human reservoir

Plasmodium - Vector and Species

• vector: anopheles mosquito

• major species: Plasmodium vivax, P. falciparum, P. malariae, P. ovale

  • P. falciparum is most severe and life-threatening; most prevalent in Africa

  • P vivax is dominant in most countries outside of Africa

Plasmodium - Transmission

• blood transfusions (only 1 case every 2 years in US)

• congenital transmission (rare)

• “airport” malaria

  • infected mosquitos that are transported rapidly by aircraft from a malaria-endemic country to a non-endemic country

  • bite a local resident

Life Cycle of Plasmodium

• infection occurs when the vector takes a blood meals and injects the sporozoite (infective stage)

• sporozoites infect liver cells and mature into schizonts which rupture and release merozoites

• merozoites infect red blood cells and continue to mature, resulting in a variety of developmental stages of the parasite (diagnostic stage)

• the late-stage gametocytes are ingested by the vectors multiply (sporogonic cycle) with later stages of the parasite developing into oocysts which grow, rupture and release sporozoites

• sporozoites go salivary glands of the vector

Plasmodium - Infection

• incubation: 7 to 30 days

• erythrocytes (RBCs) infected:

  • P. vivax and P. ovale infect younger reticulocytes (density of infected cells rarely exceeds 3%)

    • individuals who lack the duffy antigen on the surface of their RBCs are protective against P. vivax

  • P. malariae infects older RBCs

  • P. falciparum infects ALL erythrocytes (can produce a high density of infected RBCs)

    • individuals with sickle cell trait are predominately protective from infection

Malaria - Clinical Syndromes

• fever, chills, sweats, headaches, nausea and vomiting, body aches, and general malaise

  • benign tertian fever (every 48 hrs): P. vivax and P. ovale

  • benign quartan fever (every 72 hrs): P. malariae

  • malignant tertian fever: P. falciparum (fever is usually continuous or briefly remittent)

3 stages of malaria paroxysm

• “cold": shaking chills

• “hot”: temperature to 40 C or high, systemic symptoms

• “sweating”: diaphoresis (sweating), fever resolves, fatigue

Severe malaria manifestations

• cerebral malaria

• severe anemia

• hemoglobinuria

• pulmonary edema

• abnormalities in blood coagulation and thrombocytopenia

• cardiovascular

Plasmodium - Diagnosis

• microscopic staining of blood

  • thick (detect parasite) and thin (species-level identification) smear preparations

  • must determine parasitemia

• antibody detection

• antigen detection (rapid diagnostic tests)

• molecular assays

Plasmodium - Treatment

• all patients should be treated

• resistance to commonly used chloroquine is occurring

• utilize alternative treatment for resistant strains

  • atovaquone-proguanil or artemether-lumefantrine

Plasmodium - Prevention

• education

• malaria prophylaxis

  • can delay the appearance of malaria symptoms by weeks or months

    • P. vivax and P. ovale, dormant liver stage parasites, the liver stages may reactivate and cause disease months after the infective mosquito bite; relapse for as long as 3 to 4 years

• control mosquito population

  • use mosquito nets, insect repellent, wear long sleeves/pants

• vaccine

  • for children living in regions with moderate to high P. falciparum transmission

Babesia spp. - Epidemiology

• distribution:

  • mostly found in North America followed by China

  • highest prevalence in the US is along the northeastern seaboard

• human and animal reservoir (mostly mouse)

  • tick vector (Ixodid)

• most common species in US: B. microti

Life Cycle of Babesia

• infection occurs the vector takes a blood meal and injects the sporozoite (infective stage)

• sporozoites enter erythrocytes and reproduce (diagnostic stage)

• humans are considered “dead-end hosts”

• ticks acquire sporozoite by taking a bite of the mouse and the parasite multiplies in the tick (sporogonic cycle)

Infective and diagnostic stage of Babesia

sporozoite

Babesia spp. - Clinical Syndromes

• most infections are probably asymptomatic

• incubation: 1 to 4 weeks

• general malaise, fever, headache, chills, sweating, fatigue, and weakness

• as infection progresses get destruction of erythrocytes, thus anemia develops (can see renal failure)

• more severe disease in immunocompromised, individuals with no spleen and the elderly

Babesia spp. - Diagnosis

• microscopic staining of blood smear

  • must distinguish from Plasmodium

• antibody detection

Babesia spp. - Treatment and Prevention

• asymptomatic persons typically do not receive treatment

• high risk individuals and patients that received parasite by blood transfusion should be treated

• education

  • wear long sleeves/pants and use insect repellent

  • remove ticks within a few hours