Medical Parasitology test 1

Phylum Nematoda (Roundworms)

one of most abundant types of worms. 12,000 species

live in almost every type of habitat

can detect touch, light, and certain chemicals,

breath across their whole body

parasitize almost every type of plant and animal

5 cm in length

Largest known is 28 ft.

first multicellular organism to have its genome sequenced

nematode C. elegans

Nematodes can live via

free-living or parasitic and live within a host

parasitic nematodes

feed on digestive contents or blood/tissue of their hosts

GI Tract Nematodes

Ascaridida: Ascaris and Pinworms

Strongylida: Hookworms

Trichurida: Trichinella/Trichuris

Filarial Nematodes

Spirurida: Filarial worms

Nematode Basic Anatomy

bilaterally symmetrical

3 cell layers (triploblastic)

known as psuedocoelomates bc they have internal cavity that is not lined w/ mesoderm

3 cell layers of nematode

Ectoderm: outer tissue layer (epidermis)

Mesoderm: middle tissue layer (muscle)

Endoderm: innermost tissue layer (body cavity)

basic anatomy continued

vermiform structure w/ tapering formed both posteriorly and anteriorly

round body w/ mouth and anus

hypodermis: cellular subcuticular layer that secretes the cuticle

mostly a moving eating tube w/ attached reproductive organs

how is nitrogenous waste excreted vs other material

released through skin while others via the excretory pore

nematode muscles like?

longitudinal and line ventral/dorsal portion

cannot crawl like other wormsd

do nematodes have blood or gas exchange systems

NO

nematodes are most closely related to

anthropods; grow via molting

nematode development

L1: larval nematode develops inside an egg

H: hatched

M1: grows quickly and molts

L2: another rapid growth spurt

M2: transition into a second melting

M3 grows and molts

L4: final larvae stage inside the host

M4: nematodes final molt

Adult: when they become sexually mature

at what stage can nematode become infected

L3

earthworm movement

peristaltic wave; setae anchor

sets own length and girth, anchor, then push

nematode movement

body wall is covered by a thick cuticle which is secreted by the syncytial (multinucleated) epidermis

only longitudinal muscles no circular or diagonal

longitudinal muscles work antagonistically against the outer cuticle like a spring

when muscles contract the restoring force is provided by elastic components of cuticle and hydrostatic force of the pseudocoel

MOVES MORE LIKE A SNAKE

what is cuticle made of

collagen, making it both tough and flexible

this is what is shed as worm grows

nematode mobility is thus generated by

interplay of muscles, pressurized pseudocoel and cuticle

why doesn’t nematode shorten

blocked by geometry

nematode don’t swim they

burrow

they need something to push against to move

nematode eating

have complete (but simple) digestive system w/ mouth at very tip of the animal

nematode eating cont.

food has to be pumped agianst the pseudocoel pressure by muscular esophagus

Contraction of pharyngeal muscle draws fluid containing suspended food particles (dots) into pharyngeal lumen

Relaxation ejects fluids while trapping particles

(D) Isthmus peristaisis carries food from anterior isthmus to terminal bulb and intestine

food passed rapidly (minutes)

nematode neuroanatomy

brain consists of a single ring of cells around the pharynx

a dorsal and ventral nerve extend back through the length of the worm

these nerves control muscle contraction

why are the brains of a female different form male worm

different behavior wiring and anatomical differences

scientist have labled individual types of neurons of C. elegans with

fluorescent reporters and can track real time neuron activation when exposed to different compoounds

neuroanatomy continued

labial and amphid nerves extend forward to enervate sensory organs

amphids are anterior depressions that contain chemoreceptors

phasmids are posterior chemoreceptors

configurations of neural wiring get established by

natural selection;

behaviors we see are the behaviors which are favorable for survival

Nematode Reproduction

most nematodes are DIOECIOUS (male and female are sep sexes)

exhibit sexual dimorphism - males are smaller

fertilization is internal, and eggs are stored in the uterus

eggs are deposited by the female, embryo develops, juvenile hatches from an egg

male anatomy

during mating, female is held by the male within the bursa

male inserts 2 sclerotized copulatory spicules

sperm duct is muscular and sperm is transferred to female against the pseudocoel pressure

shape and size of spicules and bursa are important features to tell different nematode species apart

males can cement closed the vulva after mating in some species

Female anatomy

most females have 2 ovaries

oogonia are produced at the distal end and mature into oocytes while they move into the growth zone

as oocytes enter the oviduct, they are fertilized by sperm stored in the seminal receptacles

diagram of nematode reproduction

male sperms

not flagellated but have amoeboid movement that isn’t acting based

motility is powered by a dynamic filament system composed of polymers of the 14-kDa major sperm protein (MSP)

after fertilization

eggs are laid

what part of the male anatomy is designed for sensing and attaching to females?

spicules

majority of infections disccused are from

soil transmitted helminths (STHs)

___% of all people in the world are currently infected with GI nematodes

50

Infection generally associated w/ low mortality but can cause considerable morbidity

Ascaris lumbricoides

largest intestinal nematodes parasitizing humans

most common found in humans

most prevalent throughout the tropics, sub-tropics and infects 1.2 billion ppl

can live 1-2 years inside host

single female can lay ~240k eggs per day

eggs are very environmentally resistant (survive up to 15 years in an environment)

Ascaris lumbricoides life cycle

fertilized ascaris egg, still at unicellular stage

passed in stool

Ascaris lumbricoides complete life cycle

beings with ingestion of infectious eggs

eggs become infectious after embryogenesis and molting 2x within the egg

Larvae hatch from egg in small intestine

worms penetrate intestine and go to bloodstream

worms get caught in lung tissue capillaries and enter the alveolar spaces

cough the worm up and swallow it where it goes back into your stomach

one in small intestine again, matures via 1 additional molt and starts laying eggs and feeding on intestinal contents

high worm burdens can lead to bowel obstructions of perforations

time from egg ingestion to egg shedding by mature worms is 60-75 days

Ascaris lumbricoides pathology larval worm phase

larval worm phase:

• pneumonitis due to larvae in pulmonary alveoli

• migration of larvae through lungs = blood vessels of lungs to hemorrhage

• resulting inflammatory response and edema in lungs = ascaris pneumonia which can be fatal

Ascaris lumbricoides pathology adult worm phase

malnutrition and impaired physical growth

mild abdominal discomfort →→small bowel obstruction

wandering ascaris: bile duct obstruction, perforation of small intestine, pancreatitis and liver abscess

Ascaris lumbricoides treatment and prevention

anthelmintic medications such as albendazole and mebendazole

• can inhibit microtubule assembly in worm and block glucose uptake by worm cells

infections generally treated for 1-3 days

reducing reinfection based on sanitary disposal of feces

hygienic habits such as cleaning of hands before meals and health education

highlights that poverty itself is a major driver of infection and that access to clean water and sanitation could eliminate vast majority of infection

GI nematode parasites: Pinworms (Enterobius vermicularis)

aka threadworms: cause very few symptoms but are most common worm parasite in US

estimate 30% of children and 16% adults have it

infection occurs via self-innoculation or through exposure to eggs in envi

Pinworms life cycle

GI Nematode Parasites: Hookworms

burrow their hook mouths into the intestines of humans and such blook

can cause anemia in people, delay mental and physical growth in children, and cause physical fatigue

576-740 million of people in world are infected

two main species: Necator americanus and Ancylostoma duodenale

Hookworms life cycle

eggs passed in feces after hatching are free living in the soil

after 5-10 days and 2 molts they become filariform (3rd stage) larvae that are infective

infectious larvae hang out on blades of grass waiting to penetrate the skin of a passing human

Nematode L3 stage potential to become a ____ larva. which is..

Dauer

• ‘the enduring’

• arrested in prepubescent state

• can move around but doesn’t eat and is able to survive long-term in the environment

• will do this until “conditions improve” and in the case of parasites, this means until they get into their next host

• ability to pause is not possible for any of other stages

Hookworm life cycle

eggs passed in feces and after hatching are free living in soil

after 5-10 days and 2 molts they become filariform (3rd stage) larvae that are infective

infectious larvae hang out on blades of grass waiting to penetrate the skin of passing humans

what makes hookworms different

small and life cycle creates potential advantages and disadvantages

ascaris egg identification and function

often released as unicellular embryos although they are fertilized

have a thick chitin shell that protects them from the environment

have a heavy, albuminous coating that is characterized as ‘mammilated’

has small protrusions on its surface

hookworm egg identification

Often at some stage of development when released

have a thin shell that is not there to protect them from environmental insults as these larvae hatch and initially grow in the soil

main difference between hookworm and ascaris

ascaris eggs are ingested while hookworms quest on blades of grass and enter bloodstream

what has been suggested about ascarid worms evolution

evolved from previously dixenous (2 host) parasites transmitted by biting insects

others suggested they were originally 2 host parasites w/ one being an intermediate stage in prey animals and a definitive stage in predators

different strategies evolve to maximize dissemination

can get big and blanket the earth in hardy eggs and hope for accidental ingestion

or can get mobile and seek out host directly

hookworm life cycle facts and world trend

1 year life span (A. duodenale)

2-5 years lifespan (N. americanus)

worm burdens do not decline in adult years

Hookworm Pathology of Infection

skin penetration

secondary bacterial infection = ground itch

ground itch = dry cough, wheezing (1-2 weeks later) in primary infection

pulmonary phase is however usually asymptomatic

Intestinal phase: worms attach to mucosa and feed on blood. worms continuously move to new places exacerbating bleeding

Hookworm treatment and prevention

hookworms were wide spread in south US

Control programs were big part of public health campaigns in South during and right after WWII

1972 12% of school children from rural coastal Georgia tested positive for hookworm infection

Anthelmintic medications (drugs that rid the body of parasitic worms) such as albendazole and mebendazole, drugs of choice for treatment

infections treated for 1-3 days

GI Nematode Trichinella (T. spiralis)

responsible for a potentially fatal disease called trichinosis

worldwide, and an estimated 10k cases occur every year

Females produce live young

Juveniles penetrate skeletal muscles, where they burrow and develop into cysts in muscle tissue called nurse cells

Transmission occurs when undercooked meat from an infected animal is ingested, juvenile worms are liberated into the intestine where they mature

Trichinella life cycle

Encysted larvae are ingested in raw or undercooked meats, released in the stomach

larvae (L1) enter small intestine where they mature and live

mature worms produce live offspring that migrate into the bloodstream

newborn worms (L1) entering into different tissues are the major source of the pathology

juvenile larvae enter skeletal muscle cells where they encyst, waiting to be transmitted to the next host via carnivorism

person infected both a definitive host (where the sexual cycle occurs) and an intermediate host (transmission) at the same time

Trichinella pathology of infection Initial Phase

within 1-2 days after consumption, the person experiences general gastroenteritis

Symptoms include fever, diarrhea, nausea, and vomiting

males have a copulatory pseudobursa at the tail end

Trichinella pathology of infection Late Phase (part 1)

Live (L1) young released in small intestine migrate into the surrounding tissues 2-8 weeks after infection

this is followed by rashes, joint-pain, headache, face swelling, and splinter hemorrhages

symptoms can become more severe but generally subside in 1-2 weeks after beginning

Trichinella pathology of infection Late Phase (Part 2)

Larvae (L1) invade multinucleated muscle cell fibers where they encyst

they use the vasculature of muscle tissue itself to provide nutrients for long term viability

larvae reside in a vascularized collagen capsule waiting to be eaten by a carnivore

fatal infections of trichinosis effects heart, lungs, and central nervous system, giving rise to serious complications including myocarditis, pneumonia, and encephalopathy

Trichinella Treatment and Prevention

prompt treatment w/ antiparasitic drugs can help prevent to progression of trichinosis by killing the adult worms and so preventing further release of larvae

once larvae established in skeletal muscle cells, usually 3-4 weeks post infection, treatment may not completely eliminate the infection and associated symptoms

mebendazole or albendazole

if no initiated within first several days of infection, alternate treatment needed

best way to avoid infection = thoroughly cook meat

Trichuris (whipworm)

infects up to 800 mil ppl globally

comes from ingesting worm eggs passed in feces of infected individuals

live in the colon

adults live in cecum where female produces 20k eggs per day

embryonation occurs in eggs within 3 weeks in soil

children w/ heavy infection = severely anemic and growth-re.

mouth (or front) is at the tin end

Trichuris Life cycle

begins with ingestion of infectious eggs from contaminated dirt or non washed food

larvae hatch in small intestine

worms migrate to colon where they mature, mate and being laying bipolar-plugged eggs

unembryonated eggs pass out into the environment via feces

Trichuris egg

Trichuris pathology of infection

adult worms remain embedded with their thin front end in intestinal mucosa

infections with less than 10 worms are often asymptomatic

moderate to heavy infection = abdominal pain, diarrhea, and weight loss

heavy infected children = profuse bloody diarrhea, cramps, and rectal prolapse

heavy infections = developmental delays

adult worms can live for years

Trichuris Treatment and Prevention

mebendazole or albendazole

reducing reinfection is based on sanitary disposal of feces

hygienic habits such as cleaning of hands before meals and health education help reduce reinfection

availability of clean water, sewage removal and treatment = best chances of reducing overall worm burdens in children

Parasite Biology: obligate relationship

essential for life of one or both (eg tapeworms)

Parasite Biology: facultative relationship

not essential for life or reproduction of one or both associates (free living amoebae)

infection vs disease

infection does not imply malfunctioning process

parasites do not always induce frank disease

dangerous symbionts may cause no disease in some hosts (carriers) (eg polio virus)

types of parasitism

ectoparasite

endoparasite (intracellular (malaria) ; extracellular (tapeworm))

facultative

obligate

accidental parasite

temporary/intermittent

types of hosts

definitive: sexual reproduction, usually vertebrate host

intermediate: asexual, invertebrate (vector)

Platyhelminthes (flat worms) as human parasites

planaria: free-living flatworms that live in quiet bodies of water; bilateral symmetry

soft bodies, no body cavity w/ no specialized circulatory and respiratory organs.

flat shape = oxygen and nutrients to pass through bodies via diffusion

Digenea

body plan variations according to attachment organ position

all important trematodes of humans are distomes

among most common and abundant parasitic worms

development occurs in at least 2 hosts

Trematodes or flukes anatomy

digenea: alternate b/w sexual and asexual

possess 2 suckers to attach within the host

oral sucker contains the mouth

muscular pharynx permits worm to pump food into the blind ending gut

most are hermaphrodites

what other organ do trematodes use for food uptake besides the gut

Tegument (skin)

epidermis of trematode is essentially

a singe cell (syncytium) formed by fusion of multiple cells

teguments cell bodies and nuclei unerlie 2 muscle layers under a basal lamina

what are found in many trematode species to help anchor

actin spines

distal cytoplasm is lined by a plasma membrane associated with

layer of glycocalyx

proximal cytoplasm is the cellular region and contains

nuclei, ER, Golgi, mitochondria, and vesicles

trematodes Excretory system

simple protonephridial excretion (kidney) system

protonephridium consists of flame cell and tubule cell

both cells interdigitate forming a micro filter and cilia beating within this cage act as mechanical pump

metabolic wastes are collected from protonephridia through small ducts which merge to central duct, opens to excretion pores

cells can also regulate osmotic pressure of worm and maintain ionic balance

Trematodes reproduction system

produce massive number of offspring

adults most often hermaphrodites

female system complex

• oocytes associates with vitelline or yolk cells in ootype which is surrounded by mehlis gland

• egg shell forms from secretions of vitelline cells

• elongated uterus opens to exterior in genital pore, close to male opening.

  • sperm travel through uterus to ootype where fertilization occurs

trematode eggs

size and shape distinctive and used for diagnosis

Trematodes Life Cycle

digenic produce enormous number of offspring by combining sexual and asexual

all have at least 2 hosts of which one is a snail

not all stages are found in all species

asexual reproduction (green) occurs in germinal balls. home to omnipotent progenitor cells that can initiate w/o fertilization

what stages are infective

Miracidia and cercariae

Trematode Life Cycle The Egg

contains embryo rather than an oocyte

must leave body of final host to continue development

mature miracidium in egg uses light, osmolarity, and temperature as clues to when hatching is appropriate

hatching proceeds in most species through preformed ‘dorr’ the operculum

the miracidium

highly motile due to the cilia on surface

may have simple eyes (avoid light) and several chemical and mechanical receptors which use to find intermediate host

penetration glands secrete proteases and other lytic enzymes on contact w/ appropriate host

miracidia of flukes w/ land snails as intermediate host will hatch upon ingestion by snail and penetrate the gut epithelium

the sporocyst

after penetration, miracidum undergoes metamorphosis into sporocyst

this stage = most organ systems reduced to bare minimum and acts as germinal sac

takes up nutrients only over its tegument and germinal mass expands and develops into daughter sporocysts, redia, or cercaria

the redia

sporocyst can produce more sporocysts, cercariae, or redia

have features of adult fluke like oral and ventral sucker, a gut, and ‘birth pore’ to release cercaria

mobile in intermediate host and can prey on sporocysts and redia of same or other species (competition)

the cercaria

stages that leave the intermediate host and infect final host

can be many consecutive waves of ‘shedding’ from snail

already show many anatomical features of adult fluke

metacercaria

cercaria have developed an array of adaptations to acheive successful infection

direct penetration of host skin upon water contact

encystation within muscle of intermediate hosts

encystation on plants

fish an turtle blood flukes life cycle

Dicrocoelium dendriticum

normally found in biliary tract of sheep

bizarre method of transmission

trematodes enhanced transmission

Dicrocoelium dendriticum the lancet fluke

one metacercaria becomes the ‘brain worm’ and lodges into central ganglia of the end

brain worm manipulates behavior of ant, in evening when temp drops, experience spasms of mandibles

Leucochloridium sp.

tiny digenic trematode living in gut of small birds

worm eggs passed with feces and are taken up by amber snails

miracidia hatch, penetrate epithelium and develop into sporocysts within hepatopancreas

cercaria develop which infect birds that eat infected snails

eyes bulge of snail

trematodes of medical importance

Schistosoma, blood flukes

clonorchis & opistorchis, liver flukes with metacercaria in fish

paragonimus, lung flukes with metacercaria in crabs

fasciolopsis, fasciola, dicrocoelium, instestinal and liver flukes w/ metacercaria on plants

Fascioliases

flukes in situ (sheep liver at autopsy)

what is a virulence factor

cathepsin