Protozoa II

Question 1

Toxoplasma gondii infectious cycle

Answer 1

• definitive host: domestic cats and relatives
• unsporulated oocysts are shed in cat’s feces
• Ooocysts take 1-5 days to sporulate in the environment and become infective
• Intermediate hosts (birds, rodents) become infected after ingesting soil, water, plant material
• Oocysts transform into tachyzoites shortly after ingestion
• Tachyzoites localize in neural and muscle tissue and develop into cyst bradzoites
• Cats infected after consuming intermediate hosts harboring tissue cysts
• Cats may also become infected directly by ingestion of sporulated oocysts
• Humans become infected by:
  1. eating undercooked meat of animals w/ cysts
  2. consuming food or water contaminated with cat feces or by contaminated environmental samples (fecal in soil or changing cat’s litter box)
  3. blood tranfusion, organ tranplant
  4. transplacentally from mom to fetus
• in human, parasites form tissue cysts (skel muscle, myocardium, brain, eyes)
• Cysts may remain in human for life

Ingestion of a single cyst can cause infection

Question 2

T. gondii diagnosis

Answer 2

• (apicomplexan parasite)
• most common protozoa infection in humans
• dx acute infection in immunocompetent with IgM and IgG antibodies against the organism are present in serum; also IgA
• can also see tachyzoites in lymph nodes (acute infec)

Prior infection established by bradyzoites in tissue

PCR

Question 3

When is risk of SEVERE disease from T. gondii greatest for a fetus?

Answer 3

If primary infection of mother occurs during the first trimester

Intrauterine infections can result in:
chorioretinitis
malformations
neurological sequelae

Mother and newborn can be asymptomatic

Question 4

What disease is often seen in immunocompromised infected with T. gondii?

Answer 4

In pts with AIDS or Hodgkin’s disease, often see toxoplasma encephalitis

Question 5

What cell does T. gondii infect?

Answer 5

Macrophages, then replicates in endosomes.

If immunocompetent, macrophages can eventually kill the parasites

Question 6

How to reduce risk of infection with T. gondii

Answer 6

• thoroughly cook meat
• avoid exposure to cat feces
• prophylactic therapy in immunocompromised with evidence of prior infection (Ab)

Question 7

General overview of T. gondii

Answer 7

• widespread infection causing flu-like sx and then typically becomes dormant
• reactivates in immunocompromised
• transplacental transmission
• INTRACELLULAR parasite that can infect ANY cell
• higher prevalence in countries that eat raw meat or have many stray cats
• Transmission: oocysts (cats), improperly cooked meat, congenital

Question 8

Clinical syndromes of T. gondii

Answer 8

-acute acquired toxoplasmosis
-ocular toxoplasmosis
-cerebral toxoplasmosis (AIDS)
-congenital toxoplasmosis (If woman infected before pregnancy, child likely unaffected; if maternal infection occurs less than 6 mo b/f conception, the risk of fetal infection increases; if infected during first tri: fetal incidence at 15% but can cause:
miscarriage
stillbirth
chorioretinitis, hydrocephalus, intracranial calcifications, hepatosplenomegaly, jaundice, fever, anemia, pneumonia

-if maternal infection in 3rd trimester, 65% of fetuses are infected. Neonate usually asx @ birth, but have long term learning disabilities and neurological sequelae

Question 9

Incidence of T. gondii in US

Answer 9

More than 60 mill chronically infected

over 1 mill new infections/yr

Question 10

Trypanosomai cruzi (Chagas’ disease) infectious cycle

Answer 10

• an infected triatomine insect vector (“kissing bug”) takes blood meal and releases trypomastigotes in its feces near site
• Trypomastigotes enter the host through the wound or through intact mucosal membranes
• Trypomastigotes invade cells near site of inoculation and differentiate into intracellular amastigotes
• Amastigotes multiply by binary fission, differentiate into trypomastigotes which infect cells and transform to amastigotes
• Bloodstream trypomastigotes do not replicate (resumes when enter cell or ingested by vector)
• When consumed by a new vector (like kissing bug), transform into epimastigotes in vector’s midgut and then into trypomastigotes in hindgut

Transmission can occur in organ transplants, blood transfusions, lab accidents

Question 11

What causes Chagas’ disease? Sx?

Answer 11

• T. cruzi (S. and Central America)
• transmitted to humans by triatomine insects (reduviid bugs)

-indurated inflammatory lesion @ bite site
-acute sx in about 2 weeks
-fever, enlargement of lymph glands, liver and spleen, and damage to the heart.
- Painless edema
of the eyelids and periorbital tissues (Romana’s sign) may occur when the conjunctiva is the portal of
entry.
-Children are especially susceptible, and mortality rates may reach 10%.
- In the chronic disease, the heart and the intestinal tract are the most common target organs. Symptoms are often caused by dilated
cardiomyopathy, thromboembolism and abnormalities of cardiac conduction

Question 12

Prevention of Chagas’ disease

Answer 12

bug control, construction and treatment of homes to prevent nesting of bugs, and routine screening of blood for transfusions

Question 13

Phases of infection

Answer 13

Blood form: extracellular, acute (mild sx @ site of inoculation)

tissue form (intracellular, chronic)

Both stages can be asymptomatic, but 20-30% develop heart abnormalities and dilated esophagus or colon in chronic phase

Can reactivate in immunocompromised hosts

Question 14

Dx of Trypanosoma infection

Answer 14

-Clinical signs and travel history
- Trypomastigotes in circulating blood or CSF in acute phase
- During the chronic stage, trypomastigotes are usually not found circulating in blood and serologic testing is recommended (biopsy can ID tissue forms)
-Molecular diagnosis (PCR) of Chagas disease is performed when cases of transfusion or transplant
transmission are suspected and for congenital Chagas

Question 15

Leishmania spp. infectious cycle

Answer 15

• Sandfly takes a blood meal and injects promastigote stage into skin
• Promastigotes are phagocytized by macrophages
• Promastigotes transform into amastigotes inside macrophages
• Amastigotes multiply in cells (including mac) of various tissues
• Sandfly takes a blood meal and ingests macrophages infected with amastigotes
• Amastigotes transform into promastigote stage in midgut
• Divide in midgut and migrate to proboscis

About 20 different species cause infection in humans

Question 16

Causes of visceral leishmaniasis (kala-azar)

Answer 16

-members of L. donavani complex (L. donovani, L. infantum)

Other forms:
Cutaneous leishmaniasis
Mucosal leishmaniasis

Question 17

Diagnosis of Leishmaniasis

Answer 17

Lymph node aspirates
and scrapings or biopsies from the edge of lesions are used to diagnose cutaneous forms

specimens of blood, bone marrow, nodes, liver and spleen are used to diagnose visceral leishmaniasis.

The parasites are detected by microscopic examination or by culture of the specimens.

Individual species distinguished using isoenzyme analysis of cultured promastigotes

Serologic methods to test for Ab

Question 18

Amastigote vs promastigote (leishmaniasis)

Answer 18

Amastigote is only form found in humans

Promastigote only in insect vector

Question 19

Clinical feature of leishmaniasis

Answer 19

-localized skin ulcers (cutaneous or dermal leishmaniasis)– L. tropica, L. mexicana

• Primary infections in skin that metastasize to mucosal tissues in nose, pharynx where they produce more destructive lesions (mucosal leishmaniasis)–L. braziliensis
• hard palate, nasal septum, larynx erosion may render victim speechless

-Members of L. donavani complex cause disseminated visceral lesions (visceral leishmaniasis or “kala-azar”, ie black disease); can be highly lethal
-Macrophages of the liver, spleen, bone
marrow, lymph nodes and intestine are infected.
-Symptoms take from 3-12 months to appear, and
include fever, diarrhea and malabsorption, hepatosplenomegaly, ascites and lymphadenopathy.
-White victims may have darkened skin, giving the disease its alternate name.
-In patients who are co-infected with HIV, Leishmania species that usually cause cutaneous leishmaniasis may produce disseminated
disease or other atypical presentations.

Question 20

Prevention of Leishmaniasis

Answer 20

-controlling the vector, preventing insect bites, promptly treating human cases, and eliminating animal reservoirs.

use of insecticide-treated bednets reduces risk.

Question 21

African Sleeping Sickness (African Trypanosomiasis) infectious cycle

Answer 21

• Tsetse fly takes a blood meal an injects metacyclic trypomastigotes
• metacyclic trypomastigotes transform into bloodstream trypomastigotes, carried to other sites
• multiply by binary fission in body fluids (blood, lymph, spinal fluid)
• trypomastigotes in blood
• Tsetse fly takes blood meal
• Bloodstream trypomastigotes transform into procyclic trypomastigotes in tsetse fly’s midgut
• Multiply by binary fission
• Procyclic trypomastigotes exit midgut, transform into epimastigotes
• Multiply in salivary gland and transorm into metacyclic trypomastigotes

Question 22

Species that infect humans and cause African sleeping sickness

Answer 22

T. brucei rhodesiense (E. africa)

T. brucei gambiense (w. africa)

Question 23

Diagnosis of African trypanosomiasis

Answer 23

parasite in body fluid or tissue by microscopy (blood, lymph node aspirates or spinal
fluid)
-IgM in spinal fluid is diagnostic for encephalitic phase of illness
-cannot culture
-mouse inoculation

Question 24

Clinical features of African trypanosome infection

Answer 24

-trypanosomal chancre at site of bite after 2-3 d
-spreads to bloodstream via lymphatic channels after 2-3 w
-low-grade parasitemia
accompanied by recurrent fever, prominent lymphadenopathy, rash, headache and confusion (Stage I disease)
-Predominatly IgM production reduces parasitemia
-But it can evade immune response by antigenic variation
-Destruction of parasites leads to the formation of circulating immune complexes that are the
probable cause of the anemia and vasculitis seen in the disease
-East African/Rhodesian form: has a primary reservoir in antelope and cattle, the early symptoms and signs are followed by CNS
involvement (Stage II disease) with convulsions, coma and death in 5–9 months.
-West African/Gambian
sleeping sickness, for which humans are the primary reservoir, progresses more slowly.
Lymphadenopathy is more prominent, and bouts of fever may persist for years before the CNS
involvement (Stage II disease) leads to coma and death

Question 25

Sx of Infection with African trypanosomiasis

Answer 25

Multiply in blood stream and can eventually enter CNS
• Leads to wasting with fever, severe headaches, irritability, extreme fatigue, swollen lymph
nodes, and aching muscles and joints; CNS involvement later (progressive confusion, personality changes, and other neurologic problems)
-Presence of parasites leads to meningo-encephalitis with progressive neurological
involvement, which ultimately ends in coma (sleeping sickness)
• Lethal if not treated

Question 26

Plasmodium spp infectious cycle (Malaria)

Answer 26

• Apicomplexan species that cause malaria
• 2 hosts
• Malaria infected Anopheles mosquito inoculates sporozoites into the human host
• Sporozoites infect liver cells and mature into schizonts, which rupture and release merozoites
• [P.vivax and ovale have dormant stage called hypnozoites that can persist in liver and causes relapses weeks or years later]
• -Merozoites infect RBCs
• Asexual replication in erythrocytes
• Ring stage trophozoites mature into schizonts, which rupture releasing merozoites
• Blood stage parasites are responsible for clinical manifestations
• Gametocytes, formed in some erythrocytes (male: microgametocytes and female: macrogametocytes) are ingested by Anopheles mosquito during blood meal
• Multiplication in mosquito= sporogonic cycle
• Zygotes generated in mosquite become motile, elongated (ookinetes) which invade midgut wall of mosquito where they develop into oocysts
• Oocysts rupture and release sporozoites

Question 27

Four species that cause malaria in man

Answer 27

P. vivax, P. ovale, P. malariae, and P. falciparum

Malaria affects over 1 billion people and causes 0.5-1 million deaths/year.
P. falciparum causes most of the deaths.

P falciparum can invade RBCs of all ages
P. vivax and ovale invade younger RBCs
P. malariae invades old RBCs

Question 28

Diagnosis of malaria

Answer 28

traditionally via parasites in blood (microscopy)

Question 29

Sx of malaria infection

Answer 29

• 9-14 d incubation
• symptoms of malaria are primarily associated with the rupture of infected erythrocytes and release of merozoites
• The classical (but rarely observed) malaria attack lasts 6-10 hours. It consists of a cold stage (sensation of cold, shivering) a hot stage (fever, headaches, vomiting; seizures in young children) and finally a sweating stage (sweats, return to normal temperature, tiredness).
• See: fever and flu-like illness, including shaking chills, headache, muscle aches, and tiredness

Regular periodicity of fever paroxysms if pt untreated:
48 hrs for benign tertian malaria caused by P. vivax or P. ovale;

72 hr. for quartan malaria caused by P. malariae;

and 36-48 hr. for malignant tertian malaria caused by P.
falciparum.

Anemia:
lysis of RBCs, but also from their phagocytosis by the stimulated reticuloendothelial system, their sequestration in the enlarged spleen,
and depressed bone marrow function

Physical examination reveals jaundice, hypotension and tachycardia in addition to
fever and hepatosplenomegaly

P. falciparum-infected red blood cells bind to
the microvascular endothelium, which is especially significant in cerebral malaria (up to 50% mortality).
Multi-organ failure is the major cause of death in adults.
With P. malariae infections, immune complex deposition leading to glomerulonephritis is common.

Question 30

Distribution of parasites causing malaria

Answer 30

P. vivax is widely distributed from tropical to temperate
zones, but P. falciparum occurs primarily in the tropics and subtropics.

P. falciparum prevalence has selected for traits like sickle cell, thalassemia, G6PD deficiency

Question 31

What allows P. falciparum to infect RBCs, causing them to become “sticky”, and adhering to endothelial cells?

Answer 31

PfEMP1 (P. falciparum erythrocyte membrane protein)
Infected RBCs will adhere to the endothelium as well as to each other and cause clogging and hemmorhaging
• Response of host to adhering parasites is to make high cytokine levels which induce
expression of endothelial adhesins leading to inflammation which makes the endothelia
‘stickier’
• Adherence and inflammation reinforce each other in an unholy circle causing pathology

Question 32

Malaria in the US

Answer 32

-eliminated from US in early 1950s
-1,500–2,000 cases of malaria are reported every year in the United States, almost all
in recent travelers
• First- and second-generation immigrants returning to their home
countries to visit friends and relatives tend not to use appropriate malaria prevention measures and
thus are more likely to become infected with malaria

Immunity to malaria relatively weak (variants and antigenic variation), but some exists

Question 33

Control and prevention of malaria

Answer 33

Mosquito Control
o Reduction of mosquito numbers (DDT issue)
• Reduce mosquito bites
o Insecticide impregnated bed nets
• Prophylactic Treatment
o Leads to drug resistance
• Treatment:
o New drugs needed as drug resistance readily develops
o Why? Attribute of parasite and massive replication

Behavioral factors:
housing, use of bed nets, financial situation, standing water, agricultural work, domestic
animals (reservoir hosts), war, and migration

Question 34

Duffy blood group

Answer 34

Negative for the Duffy blood group have rbc resistant to infection by P. vivax

Question 35

Babesia microti infectious cycle

Answer 35

• 2 hosts (rodent and Ixodes tick)
• tick takes a blood meal and sporozoites introduced into mouse host
• Sporozoites enter erythrocytes and asexual replication occurs
• In blood, parasites differentiate into male and female gametes
• These are ingested by tick, gametes unite and eventually results in sporozoites
• Tick introduces sporozoites into human host
• Sporozoites enter erythrocytes, asexual replication occurs
• Multiplication of the blood-stage parasites is responsible for the clinical manifestations of the disease. Humans usually are dead-end hosts but human to human transmission occurs via blood transfusions

Question 36

Location of Babesia infections

Answer 36

US mainly occurs in parts of the Northeast and upper Midwest and usually peaks during the
warm months (1,800 cases in 2013)
• Transmission may also occur from blood transfusion and to fetus

Question 37

Clinical features of Babesia infection

Answer 37

-ranges in severity from asymptomatic to life threatening
• Can be a severe, life-threatening disease, particularly in people who do not have a spleen,
immunocompromised, elderly, or weak liver or spleen
• Some people develop flu-like symptoms, such as fever, chills, sweats, headache, body aches,
loss of appetite, nausea, or fatigue.
• Because Babesia parasites infect red blood cells, babesiosis can cause hemolytic anemia

Question 38

Dx of Babesiosis

Answer 38

examining blood specimens under a microscope and seeing Babesia parasites inside
red blood cells