Foundations in Microbiology cervicitis

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					 The Parasites of
Medical Importance
  Protozoa, Helminths, and
     Arthropod Vectors


           Chapter 23
                             1
Parasitology

• the study of eucaryotic parasites, protozoa
  and helminths
• cause 20% of all infectious diseases
• less prevalent in industrialized countries




                                               2
Protozoans



             3
Protozoa

• single-celled, animal-like microbes, usually
  having some form of motility
• life cycles vary
  – most reproduce by simple asexual cell division
    of the active feeding cell (trophozoite)
  – many undergo formation of a cyst
  – others have a complex life cycle that includes
    asexual & sexual phases

                                                 4
         amoebas


          ciliates

         flagellates




Apicomplexans/sporozoans



                           5
Entamoeba histolytica
• alternates between a large trophozoite,
  motile by means of pseudopods & a
  smaller nonmotile cyst
• trophozoite has a large nucleus and lacks
  most other organelles
• humans are the primary hosts
• Ingested (fecal-oral transmission)
• carried by 10% of world population
                                              6
Entamoeba histolytica




                        7
Entamoeba histolytica
                                                   cyst

• cysts are swallowed & arrive at the small
    intestine; alkaline pH & digestive juices
    stimulate cyst to release 4 trophozoites
•   trophozoites attach, multiply, actively move
    about & feed
•   asymptomatic in 90% of patients
•   ameba may secrete enzymes that dissolve
    tissues & penetrate deeper layers of the
    mucosa
•   causing dysentery, abdominal pain, fever,
    diarrhea & weight loss                         8
Entamoeba histolytica




                        9
Entamoeba histolytica
• life-threatening manifestations are
  hemorrhage, perforation, appendicitis, &
  tumorlike growths (amebomas)
• may invade liver & lung
• severe forms of disease result in 10%
  fatality rate
• effective drugs are iodoquinol,
  metronidazole, & chloroquine

                                             10
Amebic brain infections

• caused by Naegleria fowleri &
 Acanthamoeba
• ordinarily inhabit standing water
• primary acute meningoencephalitis is
  acquired though nasal contact with water
  or traumatic eye damage.
• infiltration of brain is usually fatal

                                             11
Naegleria fowleri

                      Phase-contrast of
                    Naegleria feeding on
                    bacteria. Organism is
                     free-living in fresh
                            water




                                  12
Balantidium coli
• an occupant of the intestines of domestic
    animals such as pigs & cattle
•   acquired by ingesting cyst-containing food or
    water
•   trophozoite erodes intestine & elicits intestinal
    symptoms
•   healthy humans are resistant
•   rarely penetrates intestine or enters blood
•   treatment – tetracycline, iodoquinol,
    nitrimidazine or metronidazole
                                                        13
Balantidium coli




                   14
15
Trichomonas
• Small, pear-shaped
• 4 anterior flagella & an undulating
  membrane
• Exist only in trophozoite form
• 3 species infect humans
   – T. vaginalis
   – T. tenax
   – T. hominis
                                        16
                            Trichomonas




T. vaginalis (urogenital)     T. tenax (gingival)   T. hominis (intestinal)   17
Trichomonas vaginalis
•   causes an STD called trichomoniasis
•   reservoir is human urogenital tract
•   50% of infected are asymptomatic
•   strict parasite, cannot survive long outside of
    host
•   3 Million new cases a year in U.S., a top STD
•   female symptoms – foul-smelling, green-to-
    yellow discharge; vulvitis; cervicitis; urinary
    frequency & pain
•   male symptoms – urethritis, thin, milky
    discharge, occasionally prostate infection
•   metronidazole                                     18
Trichomonas tenax
• small
• resides in oral cavity of 5-10%
• only flagellate in oral cavity
• not a true pathogen, but an opportunist in
 lesions of gingivitis & peridontal pockets




                                              19
Trichomonas hominis
• a resident of the cecum of a small
  percentage of humans & great apes
• not associated with disease




                                       20
           Giardia lamblia
• pathogenic flagellate
• unique symmetrical heart shape
• cysts can survive for 2 months in
    environment
•   cysts enter duodenum, germinate, & travel to
    jejunum to feed & multiply
•   causes giardiasis – diarrhea, abdominal pain
•   diagnosis is difficult because organism is
    shed in feces intermittently
•   Treatment: quinacrine or metronidazole
•   agent is killed by boiling, ozone, & iodine

                                                   21
hemoflagellates
•   live in blood & tissues of human host
•   obligate parasites
•   cause life-threatening and debilitating zoonoses
•   spread by blood-sucking insects that serve as
    intermediate hosts
•   acquired in specific tropical regions
•   have complicated life cycles & undergo
    morphological changes
• Trypanosoma
• Leishmania
                                                       22
Too much information. You don’t really need to know this part

                                                                23
Trypanosoma
• distinguished by their infective stage,
  trypomastigote is an elongate, spindle-
  shaped cell with tapered ends, eel-like
  motility
• 2 types of trypanosomiasis
   – T. brucei – African sleeping sickness
   – T. cruzi – Chagas disease – endemic to
     Central and South America

                                              24
Trypanosoma brucei
•   causes African Sleeping Sickness
•   spread by tsetse flies
•   harbored by reservoir mammals
•   biting of fly inoculates skin with trypanosome,
    which multiplies in blood & damages spleen,
    lymph nodes & brain
•   chronic disease symptoms are sleep
    disturbances, tremors, paralysis & coma
•   treatment before neurological involvement
    melarsoprol, difluormethylornithine
                                                      25
Trypanosoma
brucei




              26
Trypanosoma cruzi
• causes Chagas disease
• reduviid bug (kissing) bug is the vector
• infection occurs when bug feces are inoculated
    into a cutaneous portal
•   local lesion, fever, & swelling of lymph nodes,
    spleen, & liver
•   heart muscle & large intestine harbor masses of
    amastigotes
•   chronic inflammation occurs in the organs
    (especially heart & brain)
•   treatment nifurtimox & benzonidazole
                                                   27
Trypanosoma cruzi   Heart pathology in Chagas
                             disease




                                        28
Leishmania
• Leishmaniasis is a zoonosis transmitted among
    mammalian hosts by female sand flies that
    require a blood meal to produce eggs
•   infected macrophages carry the pathogen into
    the skin (cutaneous leishmaniasis) &
    bloodstream (systemic or visceral leishmaniasis),
    giving rise to fever, enlarged organs & anemia
    (Kala azar is the most severe & fatal form)




                                                    29
            Life cycle of
                Leishmania




Disseminated
leishmaniasis                30
Apicomplexan parasites
• sporozoans
• lack locomotor organelles in the mature state
• alternate between sexual & asexual phases &
    between different animal hosts
•   most form specialized infective bodies that are
    transmitted by arthropod vectors, food, water,
    or other means
     – Plasmodium
     – Toxoplasma
     – Cryptosporidium
                                                      31
Plasmodium
• causes malaria
• female Anopheles mosquito is the vector
• obligate intracellular sporozoan
• 4 species: P. malariae, P. vivax, P.
 falciparum & P. ovale
• 300-500 Million new cases each year
• 2 Million deaths each year
                                            32
Plasmodium
• infective forms for humans (sporozoites)
  enter blood with mosquito saliva,
  penetrate liver cells, multiply, and form
  hundreds of merozoites, which multiply in
  & lyse RBCs.
• symptoms include episodes of chills-fever-
  sweating, anemia, and organ
  enlargement.
• therapy is chloroquine, quinine, or
  primaquine                                33
                                                         Sexual phase
 Asexual                                                with sporozoite
 phase in                                                formation in
humans as                                               the mosquito)
sporozoite
  enters




                                                        Gametocytes
                                                        produced and
                                                         ingested by
                                                           mosquito

Liver phase
(sporozoites
  invade &
 merozoites
 produced)




               RBCs infected by merozoites from the liver        34
Plasmodium falciparum infection of RBCs showing ring form




                                                            35
Toxoplasma gondii
• obligate apicomplexan parasite with extensive
    distribution
•   lives naturally in cats that harbor oocysts in the
    GI tract
•   acquired by ingesting raw meats or substances
    contaminated by cat feces
•   most cases of toxoplasmosis go unnoticed
    except in fetus & AIDS patients which can suffer
    brain & heart damage
•   treatment: pyrimethamine & sulfadiazine
                                                     36
Life cycle of
Toxoplasma
   gondii




                37
                                              Biopsy showing clusters of
CAT scan of brain showing lesion
                                                 intracelluar T. gondii

                    Toxoplasmosis in an AIDS patient                       38
Cryptosporidium                                      Oocysts
                                                     shed in
                                                      feces

•   an intestinal pathogen
•   infects a variety of animals
•   exists in tissue & oocyst (passed in feces) phases
•   1990s – 370,000 cases in Milwaukee, WI due to
    contaminated water
•   causes enteric symptoms
•   AIDS patients may suffer chronic persistent
    diarrhea
•   no real effective drugs

                                                      39
Babesia
• causes babesiosis
• first protozoan found to cause a disease
• first protozoan found to be associated with
  a tick
• infection resembles malaria



                                           40
Helminths
• adults are large, multicellular animals with specialized
  tissues & organs
• adult worms mate & produce fertilized eggs that
  hatch into larvae that mature in several stages to
  adults (the sexes may separate or hermaphroditic)
• Hosts
   – adults live in the definitive host
   – eggs & larvae may develop in the same host, external
     environment, or intermediate host
   – a transport host experiences no parasitic development
• pathology arises from worms feeding on & migrating
  through tissues and accumulation of worms & worm
  products
                                                             41
Nematodes - roundworms

• Filamentous with protective cuticles, a
    complete digestive tract, & separate sexes
•   Ascaris lumbricoides
•   Trichuris trichiura (whipworm)
•   Enterobius vermicularis (pinworm)
•   Hookworms
•   Strongyloides stercoralis
•   Trichinella spiralis
•   Filarial worms
                                                 42
Ascaris lumbricoides
•   a large (up to a foot long) intestinal roundworm
•   1 Billion cases worldwide
•   Most cases in the US occur in the southeastern states
•   indigenous to humans
•   Ascaris spends its larval & adult stages in humans &
    releases embryonic eggs in feces, which are spread to
    other humans
•   ingested eggs hatch into larvae & burrow through the
    intestine into circulation & travel to the lungs & pharynx &
    are swallowed. Adult worms complete cycle in intestines.


                                                             43
Ascaris lumbricoides
Ascaris lumbricoides
• worms retain motility, do not attach
• severe inflammatory reactions mark the
  migratory route,
• allergic reactions can occur
• heavy worm loads can retard physical &
  mental development


                                           45
Roundworm Zoonoses-1
• Don’t play with the animal feces !
• Don’t eat dirt !
• Dog and Cat Roundworms (toxocariasis)
  – estimated 10,000 new cases of roundworm infection
    occur in children every year, most often as a result of
    eating dirt contaminated with animal feces.
  – Most human infections are mild enough to go
    unnoticed and apparently produce no permanent
    damage……But….
  – Visceral Larval Migrans (VLM)
  – Ocular Larval Migrans (OLM).

                                                          46
Roundworm Zoonoses-2
• Raccoon roundworm (Baylisascaris
 procyonis)
  – Raccoons are very common in the
    urban/suburban environment, and perhaps
    80%+ carry the roundworm.
  – Worm eggs are very hardy, surviving years
    outdoors.
  – When ingested by humans the larvae migrate
    throughout the body. Some enter the brain
    and death my ensue.

                                             47
Trichuris trichiura
• whipworm
• humans sole host
• trichuriasis has its highest incidence in
  tropics
• remains in intestine


               Egg in fecal
                 sample
                                              48
Enterobius vermicularis
 • pinworm
 • enterobiasis most common worm disease of
     children in temperate zones
 •   eggs are picked up from surroundings &
     swallowed.
 •   after hatching in the small intestine, they
     develop into adults
 •   anal itching occurs when mature females
     emerge from intestine to release eggs
 •   self-inoculation is common
 •   tape test
                                                   49
Tape test for pinworms




 Flashlight Test: At night, the female adult
   worms deposit their eggs outside the
            rectum or anal area.
 Enterobius
vermicularis
 pinworm
Hookworms
•   characteristic curved ends & hooked mouths
•   Endemic to tropics and subtropics
•   Necator americanus & Ancylostoma duodenale
•   humans shed eggs in feces, which hatch into
    filariform (threadlike) larvae & burrow into the skin of
    lower legs (may cause a local irritation…”ground itch”)
•   larvae travel from blood to lungs, proceed up bronchi
    & throat & are swallowed.
•   worms mature & reproduce in small intestine &
    complete cycle
•   may cause pneumonia, nausea, vomiting, cramps &
    bloody diarrhea…blood loss can be significant -
    anemia

                                                               52
Hookworms
Strongyloides stercoralis

•   threadworm
•   tiny roundworm
•   completes life cycle in humans or moist soil
•   larvae penetrate skin & migrate to lungs, are
    swallowed & complete development in intestine
•   can reinfect the same host without leaving the
    body
•   heavy worm loads can cause pneumonitis &
    eosinophilia, bloody diarrhea, liver enlargement,
    bowel obstruction & malabsorption
                                                    54
   Strongyloides stercoralis




Worm migration
 tracks under
    the skin




                               55
Trichinella spiralis
 •   causes trichinosis
 •   life cycle entirely within mammalian host
 •   acquired from eating undercooked pork (also bear)
 •   larvae migrate from intestine to blood vessels,
     muscle, heart, & brain, where it forms cysts
 •   first symptoms –flulike, diarrhea
 •   second symptoms – muscle & joint pain,
     shortness of breath, pronounced eosinophilia
 •   no cure after larva have encysted
                                                     56
57
Filarial worms
• long threadlike
    worms with tiny
    larvae that circulate
    in blood & reside in
    various organs
•   spread by biting
    insects
• Wuchereia bancrofti –
    elephantitis
• Onchocerca volvulus
    – river blindness
•   Loa loa – eye worm
                            Edema from
                            blockage of
                             lymphatics   58
Trematodes (flukes)
• flatworms with ovoid leaflike bodies
• have digestive, excretory,
    neuromuscular, & reproductive
    systems
•   lack circulatory & respiratory systems
•   animals such as snails or fish are
    usually the intermediate hosts &
    humans are the definitive hosts


                                             59
Blood flukes: Schistosomes
• schistomiasis is the 2nd most prominent parasitic
    disease (after malaria)
•   adult flukes live in humans & release eggs into
    water. The early larva develops in freshwater
    snail into a 2nd larva
•   this larva penetrates human skin & moves into
    the liver to mature; adults migrate to intestine
    or bladder & shed eggs, giving rise to chronic
    organ enlargement

                                                       60
Tapeworms
• flatworms
• long, very thin, ribbonlike bodies composed of
    sacs (proglottids) & a scolex that grips the
    intestine
•   each proglottid is an independent unit adapted
    to absorbing food & making & releasing eggs
• Taenia saginata
• Taenia solium

                                                     61
Taenia saginata
•   beef tapeworm
•   very large, up to 2,000 proglottids
•   humans are the definitive host
•   animals are infected by grazing on land
    contaminated with human feces
•   infection occurs from eating raw beef in which
    the larval form has encysted
•   larva attaches to the small intestine & becomes
    an adult
•   causes few symptoms
                                                      62
Beef Tapeworm
Tanenia saginata




                   63
Taenia solium
• pork tapeworm
• infects humans through ingesting cysts or
  eggs
• eggs hatch in intestine, releasing
  tapeworm larva that migrate to all tissues
  & encyst
• most damaging if they lodge in heart
  muscle, eye, or brain
• may cause seizures, psychiatric
  disturbances
                                               64
Arthropod Vectors

• Vectors are animals that carry microbial
  pathogens
• Arthropods are a common vector
• Some arthropods also serve as hosts for
  the pathogens they transmit
• Disease vectors belong to two classes of
  arthropods
  – Arachnida
  – Insecta
Tick   Mite              Flea             Lice




              Mosquito


                            Kissing Bug

 Fly
                                                 66
Arachnids
• Adult arachnids have four pairs of legs
• Ticks and mites resemble each other
  morphologically
• Ticks are the most important arachnid
  vectors
  – Serve as vectors for bacterial, viral, and protozoan diseases
  – Second only to mosquitoes in the number of diseases they
    transmit
  – Hard ticks are the most prominent disease vector
  – Transmit Lyme disease, Rocky Mountain spotted fever,
    tularemia, relapsing fever, and tick-borne encephalitis
Arachnids

• Parasitic mites are found wherever
 humans and animals coexist
  – Transmit rickettsial diseases among animals
    and humans
Insects
• Adults have three pairs of legs as well as a
  head, thorax, and abdomen
• Fleas
  – Most fleas are not associated with humans but
    a few do feed on humans
  – Plague is the most significant disease
    transmitted by fleas
• Body lice
  – Parasites that can also transmit disease
  – Most common among poor or overcrowded
    communities
Insects
• Flies
     – Among the most common insects
     – Those that transmit disease are generally
       bloodsuckers
•   Mosquitoes
     – Most important arthropod vector of disease
     – Carry some of the world’s most devastating diseases
•   Kissing bugs
     – Often take blood meals near the mouth of their
       human hosts
     – Feed on blood nocturnally while the host sleeps

				
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