Parasitology Test 1

Phoresis

involves two organisms traveling together without any biological or physiological interdependence

Mutualism

both organisms benefit, often with a necessary physiological reliance; typically obligatory

Commensalism

one organism benefits while the other is unaffected

Parasitism

one organism either harms or lives at the expense of its host

Definitive Host

the host where the parasite achieves sexual maturity

Intermediate Host

necessary for the parasite’s developmental stages but without sexual maturation

Paratenic (transport) host

doesn’t support parasite development but can help bridge ecological gaps between hosts

Reservoir (amplifying) host

can carry a pathogen indefinitely without harm

Dead-end or Incidental hosts

don’t develop high parasite levels; unable to transmit the pathogen further

Hyperparasitism

a parasite hosting another parasite

Vector

an organism, often an arthropod, transmitting a pathogen from reservoir to host

Aberrant Host

an atypical host for the parasite it carries

Host Specificity

some parasites are specific to one host, while others can develop in multiple hosts

Ectoparasite

lives on the host’s surface

Endoparasite

resides inside the host

Facultative parasite

doesn’t rely on the host for survival; incidental

Obligate parasite

needs a host for survival and life cycle completion

Mechanical Damage

causes physical harm or obstruction in tissues

Physiologic damage

affects metabolism; consumes host’s nutrients

Direct Life Cycles

the parasite completes its life cycle within a single host species

Indirect life cycles

requires multiple host species for completion, typically involving 2-3 hosts: definitive, intermediate, and paratenic

Prevalence

proportion of a population infected at a specific time

• calculation: number of existing cases/ total population

Incidence

rate of new infections in a population

• calculations: number of new cases/ population at risk

Morbidity

refers to illness or disease state

Co-morbidities

presence of simultaneous illnesses

Mortality

incidence of death due to a disease

• calculation: number of specific disease deaths/ total population

Focus

ecological aspects of disease transmission and prevalence

Sexual reproduction

increases disease resistance\

• this process mixes genetic material from two parents to produce offspring

• it increases genetic diversity and can enhance the host population’s resistance to diseases, including parasitic infections

• can be resistant to anti parasitic by genetic recombination

Sexual selection

influence of parasites on mate choice

• parasites can affect this process by influencing the host’s choice of mates

• hosts often choose “healthy” mates over “unhealthy” ones based on indicators such as the quality of plumage in birds or body odors, which can signal good health and genetic fitness

Parasite reproduction types

asexual and sexual

Sexual dysfunction

• some parasites may interfere with the host’s reproductive capabilities to their advantage

• for example, a parasite may castrate the host, which diverts the host’s resources away from reproduction and towards sustaining the parasite

• additionally, some parasites might suppress visible signs of infection, allowing the host to reproduce and spread the parasite to the next generation through offspring or contact with mates

Polyembro

• development of many offspring from a single zygote

• occurs in larval stages

• ex: trematodes

Binary Fission

mitotic division of 1 cell into 2

• ex: some protozoa

Internal Budding

new individual grows from somatic tissue of parent

• ex: some larval cestodes

Schizogony ( multiple fission, merogony)

• produces many daughter cells

• nucleus divides (mitosis) many times before cytokinesis (cytoplasm division) occurs

• ex: protozoa

Monoecious

hermaphroditism

• single individual possesses gonads of both genders

• self-fertilization

• no need to find a mate

• can mate with another individual or can self-fertilize

  • ex: cestodes, most trematodes (except Schistosomes)

Dioecious

• each individual is a separate gender

• sexual dimorphism

  • ex: nematodes, schistosomes (trematode)

Early Infection Phase of Trypanosoma brucei

trypanosomes in lymph and blood systems

Advantage Stage of Trypanosoma brucei

presence in brain parenchyma and cerebrospinal fluid

Heteroxenous Life Cycle

alternates between vertebrate blood/tissues and invertebrate gut

Hemoflagellates

require blood in laboratory culture media

one bite

several thousand metacyclic trypomastigotes transferred in ___________________

remain extracellular

trypomastigotes never enter the host cell

Trypanosoma brucei

infects animals only

• affects various animals with distinct symptoms——

  • anemia, edema, watery eyes and nose, fever

  • emaciation, paralysis, death

horses, donkeys, ruminants (Nagana); acute: 2-4 months

cattle (infection lasts for months

dogs (blindness)

pigs (usually recover)

T.b. gambiense

• characterized by chronic sleeping sickness symptoms such as disinterest, cognitive decline, unsteady movements, progressing to paralysis, seizures, escalating drowsiness, coma, and potentially death

• is found in central and western Africa; it causes a chronic condition that can extend in a passive phase for months or years before symptoms emerge

T.b. rhodesiense

• associated with an acute version of the disease marked by swift weight reduction and death within a few months

• is found in southern and eastern Africa; its infection emerges in a few weeks and is more virulent and faster developing

T.b. gambiense (chronic form)

typical sleeping sickness

• apathy, mental dullness, lack of coordination

• paralysis, convulsions

• increasing sleepiness

• coma, death

T.b. rhodesiense (acute form)

• rapid weight loss

• death in a few months

Diagnosis of Trypanosoma brucei

• identification is made by the detection of trypomastigotes in bodily fluids like blood, lymph, and CSF

• serological testing can identify antibodies, particularly in T.b. gambiense infections, though it may result in false negatives

Tsetse fly

• large, brown, and stealthy

• while taking blood from a mammalian host, an infected one injects metacyclic trypomastigotes into skin tissue

• the parasites enter the lymphatic system and pass into the bloodstream

Amastigote

kinetoplast and kinetosome above the nucleus, flagellum short and confine in pocket

• cell is globular

Promastigote

kinetoplast and kinetosome at anterior end of cell, flagellum free and lone

• cell is elongated

Epimastigote

kinetoplast and kinetosome close and anterior to the nucleus

• there is a short undulating membrane before the flagellum emerges at the anterior of the cell

• cell is elongated

Leishmaniasis Vector

female sand flies

• Phlebotomus spp (Old World)

• Lutzomyia spp (New World)

Leishmaniasis Distribution

• 1 million cases worldwide

• distribution depends on species complex

• poverty-related disease

  • malnutrition

  • displacement

  • poor housing

  • illiteracy

  • comprised immune systems

• environmental changes

  • deforestation

  • dam construction, irrigation schemes

  • urbanization

  • migration of native people to endemic areas

• serious impediment to socioeconomic development

Cutaneous Leishmaniasis ulcers

• oriental sore, Jericho boil

• on exposed parts of the body (face, arms, legs)

L. tropica

• distributed throughout asia, africa, mediterranean, russia, densly populated areas

• definitive host is human

• vector is phlebotomus sand fly

• dogs and foxes are reservoir hosts

L. major

• distributed throughout the middle east, russia, brazil and rural areas

• humans are the definitive host

• the phlebotomus sand fly is the vector

• rodents are the reservoir host

• causes ulcers

L. mexicana

• distributed throughout central and south america, bolivia, brazil, colombia, peru and north america

• causes chiclero ulcers, bay sores, cartilage ulcers, ulcers can last for up to 40+ years

Leishmania braciliensis

known as Espundia or Uta

• humans are definitive host

• Lutzomyia sand flies are the vectors

• sloths and anteaters are the reservoir hosts

• found in central and south america

Northern range of Leishmania baziliensis

ulcer

• self limiting

• itchy

• flat

• open

• oozing

• similar to cutaneous Leishmaniasis

• appears in 1-4 weeks

• heals within 6-15 months

Leishmania braziliensis Southern Range

• begins as cutaneous leishmaniasis

• ulcer metastasizes to mucocutaneous zones

  • occurs before primary ulcer heals or up to 30 years later

  • nose, mouth, lips, trachea, pharynx

  • destroys cartilage and soft tissues

  • necrosis

  • secondary bacterial infection

• ulcers may last for years

• death— secondary infections, respiratory problems

Leishmania donovani

• known as dum dum fever and kala-azar

• humans are the definitive host

• Phlebotomus spp and Lutzomyia spp are the vectors

• found throughout asia, africa, south and central america

Giardia intestinalis

• most common flagellate of human GI tract

  • discovered by Anton van Leeuwenhoek

• 40+ species descriptions

• now only 5 valid species

• mammals

  • G. duodenalis

  • G. muris

• birds

  • G. ardeae

  • G. psittacii

• amphibians

  • G. agilis

Giardia oral infection

• ingestion of cysts; contaminated water

• feal-oral

• hands

Giardia zoonosis

• risk of humans acquiring this infection from dogs or cats is small

• exact type of this that infects humans is usually not the same type that infects dogs and cats

Giardia triggers

• resorption of locomotor organelles

• adverse environmental conditions

  • low food

  • desiccation, low O2, pH

  • temperature change

  • osmotic change

Giardia mechanisms

• secretion of cyst wall

• storage of food, e.g. glycogen, starch

Giardia intestinalis— cysts

• found in feces (diagnostic stage)

• stage found most commonly in non-diarrheal feces

  • responsible for transmission of giardiasis

• infectious when passed in stool or shortly afterward

• resistant forms

  • hardy; can survive several months in cold water

• excystation

  • in small intestine

  • each cyst produces two trophozoites

Giardia intestinalis— Trophozoites

• found in feces (diagnostic stage)

• active feeding stage

• multiply by longitudinal binary fission

• remain in lumen of proximal small bowel

  • free or attached to the mucosa by a ventral sucking disk

• encystation occurs as parasites transit toward the colon

Giardia Life cycle

• direct life cycle

• mammals are definitive hosts

• beavers, dogs, cats, horses, humans, cattle, and birds are the reservoir hosts

• molecular characterization

Morphology— trophozoites

• pyriform— pear shaped

  • 2 nuclei with karyosomes

• 8 flagella— 4 pairs

  • 2 median bodies

    • function unknown

    • possible metabolic rule

• adhesive disc on ventral surface

Morphology— cysts

• 8-12 μm long

• 4 nuclei

• 4 median bodies

• 6 flagella (in mature cysts)

Giardia distribution

• very common worldwide

  • warm climates

• children most affected

  • fecal-oral transmission

• prevalence rates

  • 2-7% in developed countries

  • 20-30% in most developing countries

Giardia distribution in the United States

• 2011, a total of 16,868 giardiasis cases were reported

• 2019, total cases = 14,887

• CDC estimates upwards of 2.5 million cases annually

Giardia Pathology

• enteritis

• mechanical damage to intestinal villi

  • damage caused by adhesive disc and large number of parasites

  • shortening and blunting of villi and epithelial cells

  • malabsorption

    • fat, fat soluble vitamins, Folic acid

• incubation period: 8 days

• prepatent period: 10-36 days

• self limiting

• range of symptoms

• all age class, but especially children

Giardia Diagnosis

• presence of trophozoites or cysts

  • feces

    • cysts shed intermittently— must take several samples over a period of days

  • duodenal aspiration or biopsy

• immunodiagnostics

  • ELISA

  • immunofluoresence

• PCR

Giardia Treatment

• Atabrine

  • may cause unwanted symptoms in children

• Metronidazole (Flagyl)

  • less toxic to children

• all members of household must be treated

Control the spread of Giardia

• reduce fecal contamination of water

  • can be resistant to filtration and chlorination

  • portable water filtration systems— iodine (for campers)

• travelers to endemic areas are advised to avoid uncooked foods that might have been grown, washed, or prepared with water that was potentially contaminated

• sanitation!

  • wash hands, food, water, fomites contaminated with infective cysts

Giardia presentation in animals

• dogs/cats

  • diarrhea

• cattle (calves)

  • chronic diarrhea

    • death uncommon

• lambs

  • neonatal infections

    • low weight gain

    • periparturient rise (PPR)

    • PPR of excretion of cysts in ewes— major source of giardiasis in lambs

• wild animals

  • especially beavers

The periparturient egg rise

is a well-documented phenomenon in small ruminants: a temporary loss of naturally-acquired immunity to gastro-internal parasites that begins approximately two weeks before parturition and continues for up to eight weeks after

Parturition

the action of giving birth to young

Trichomonads

• 3 flagella= tritrichomonas

• 4 flagella= trichomonas

• 5 flagella= pentatrichomonas

• undulating membrane

• axostyle

  • median tube-like organelle

Distribution of Trichomonas vaginalis

• worldwide

• definitive hosts

• humans

  • reproductive tracts of males and females

    • most are asymptomatic

  • females— vagina, urethra

  • males— prostate, seminal vesicles, urethra

• morphology

  • 4 anterior flagella

  • undulating membrane

  • 7-32 μm long, 5-12 μm wide

Trichomonas vaginalis life cycle

• direct life cycle

  • sexual transmission

• extracellular

  • no cyst stage

• parasites attach to epithelial cells with cytoplasmic extensions

• transmission

  • primarily sexual

  • possible by artificial insemination

  • congenital— documented in newborns

  • young children— contaminated clothing

Trichomonas vaginalis— diagnosis

• presence of parasite

  • in secretions or urine— wet mount

  • in culture of vaginal secretions

    • good for detecting low numbers of parasites

    • time-consuming

• molecular diagnosis

  • DNA hybridization

  • PCR

Trichomonas vaginalis female pathology

• inflammation, itching, leukorrhea (white, green with trichomonads)

• frequent and painful urination

• during pregnancy

  • premature births

  • low birthrate

Trichomonas vaginalis male pathology

• usually asymptomatic

• inflammation of urethra, prostate

• painful urination, thin discharge

• may enhance HIV transmission

Trichomonas vaginalis treatment

• metronidazole (flagyl)

  • cures in ~5 days

  • some strains are resistant

• sexual partners should be treated as well

Tritrichomonas foetus distribution

• United States

• Europe

Tritrichomonas foetus definitive hosts

• cattle, horse, other large mammals

• cats

Tritrichomonas foetus life cycle

• sexual transmission, no cyst stage

• asymptomatic male (penis sheath) infects female (asymptomatic in vagina)

• pregnancy triggers systemic infection

• trophozoites invade uterus

Tritrichomonas foetus morphology

• 3 anterior flagella

• undulating membrane

• nucleus

• axostyle

Tritrichomonas foetus diagnosis

• presence of parasites

• smears— amniotic fluid, vaginal/uterine secretions, placenta, fetal tissues, preputial secretions

• PCR

• IFA

Tritrichomonas foetus bull pathology

• occur in preputial cavity, also in testes, epididymus, seminal vesicles

• asymptomatic carriers

• cannot be used for breeding

Tritrichomonas foetus cow pathology

• occurs in vagina, uterus

• abortion

Control Tritrichomonas foetus

• proper herd management

  • use artificial insemination only for breeding infected cows

  • check bulls before purchase

  • cull infected bulls

• vaccine

  • given to cows

  • does not prevent infections

  • may increase number of viable offspring

Tritrichomonas foetus in cats

• diarrhea

• giemsa-stained fecal smear

• characteristic appearance of Tritrichomonas foetus

• 3 anterior flagella and long, undulating membrane

Entamoeba

• vesicular nucleus

• small endosome near center

• amoebic dysentery

• ameobiasis

• infects 10% of world population

  • 100,000 deaths per year

    • caused by crowding, poor santitation

People at Risk for Entamoeba

• immigrants/travelers

• people in institutions, daycares

• refugees

• people engaging in anal-oral sexual practices

• soldiers

• night soil users (human feces used as fertilizer)