Parasites:
Invertebrates
Invertebrates
 35 phyla of invertebrates
 Half are entirely marine
Classification by Developmental Pattern
 Multicellular invertebrates are divided into two groups based upon the number of germ
layers formed during embryogenesis.
 Germ layers are groups of cells that behave as a unit during early embryonic
development and give rise to distinctly different tissue systems in the adult.
Germ Layers
 Diploblastic animals have two germ layers.

Ectoderm (outermost layer)

Endoderm (innermost layer)

Triploblastic animals have three germ layers

Ectoderm

Mesoderm

Endoderm
Triploblastic Animals
 Triploblastic animals are further classified by their internal body cavity
 Acoelomate: No internal body cavity
 Pseudocoelomate: fluid-filled cavity between endoderm and mesoderm
 Coelomate: internal, fluid-filled cavity between endoderm and mesoderm, lined with
mesoderm
Kingdom Animalia
Sub-kingdom Invertebrata
•
I. Phylum Platyhelminthes (flatworms)
–
•
II. Phylum Nematoda
–
•
Tapeworms, flukes, and non-parasitic flatworms
Roundworms, hookworms, threadworms
III. Phylum Annelida
–
•
segmented worms
IV. Phylum Arthropoda
–
Ticks, mites, lice
Phylum Platyhelminthes (Flatworms)
A. Class Cestoda -tapeworms
1. Taenia pisiformis – dog or cat tapeworm
B. Class Trematoda - Flukes
2. Clonorchis sinensis - liver fluke
3. Fasciolopsis buski - giant intestinal fluke
4. Schistosoma mansoni- blood fluke
C. Class Turbellaria - free-living flatworms, not parasitic
5. Planaria spp.
 TapewormsTapeworms are missing their entire digestive system. Therefore, the best
place for them to live are in the intestines. Thus, they need a structure to latch onto the
intestine.
 Scolex (head): has suckers and hooks to grab onto the mucosa of the intestine.
 Segmented into sections
•
The sections are called proglottids. Each proglottid has all of the organs within it.
The segments are narrow like ribbons. They are muscular, so each segment can
wiggle.
 Gravid proglottids (filled with eggs).
Class Cestoda –tapeworms
Taenia pisiformis -dog or cat tapeworm
Head (scolex)
Suckers
Hooks
Segments (proglottids)
Testes
Ovaries
Tapeworm Diseases
 1. TAENIASIS (Pork and Beef)
 2. CYSTICERCOSIS (Pork only)
 3. Dog and cat tapeworms:
diarrhea and gas
 TAENIASIS
 This form of disease can be from either pork or beef intestinal infections. It is usually
asymptomatic, mild GI pain, but you may see the proglottids wiggling in the stool.
 CYSTICERCOSIS
 This is caused by pork tapeworms only. It is much more serious, even life-threatening.
The Tania egg is ingested by the fecal-oral route. Larvae embed in any tissue (esp.
muscle, brain, eye). Once ingested, the eggs hatch and invade.
 Dog and cat tapeworms: mild symptoms of diarrhea and gas
Fluke Diseases
 Flukes differ from tapeworms in that they are non-segmented.
 They live in tiny veins in humans called venuoles.
 The large number of eggs is what causes the damage in the human.
 They cause granulomas (inflammatory lesions).
 These granulomas can occur in the brain, spinal cord, liver, and many other organs.
Class Trematoda - FlukesClonorchis sinensis - liver fluke
Oral sucker
Pharynx
Intestines (cecum)
Uterus
Testes
Class Trematoda – Flukes
Fasciolopsis buski - giant intestinal fluke
Mouth (for feeding)
Ventral sucker (for attachment)
Intestines (cecum)
Testes
Schistosoma mansoni
Female blood fluke:
Ventral sucker (for attachment)
Ovary
Mouth (for feeding)
Schistosomiasis
 The blood fluke is called Schistostoma. “Schisto” means “split” and “soma” means
opening.
 The male’s body is split into a gynecohoric canal; this is where the females live. The
female is smaller and lives within the male her whole life.
 She lays thousands of eggs a day.
Blood Fluke Diseases
 Schistosomiasis
 Swimmer’s Itch
 Schistosomiasis kills 1-2 million people per year; it’s almost as bad as malaria. It is a
tropical disease. It is also known as “Male menstruation” because there is a bladder fluke
which causes hematuria (blood in the urine). When Napoleon invaded Egypt, his men got
this disease and called it the Curse of the Pharaoh.

 Many people are asymptomatic, but the acute form (Katayama’s Fever) can occur weeks
later, manifesting with fever, coughing, nausea, vomiting, diarrhea, hepatosplenomegaly,
and eosinophilia (excess eosinophils, a type of white blood cell that responds to parasitic
infections).
 The schistosomulae migrate to the veins:
 The females are smaller and live inside the male.
 They deposit eggs in the small venules.
 The eggs are moved progressively toward the lumen of the intestine and are
eliminated with feces or urine.
 Human contact with water is necessary for infection by schistosomes. Skin penetration is
required.
 Symptoms include: Katayama fever, granulomas (occasionally in brain or spinal cord).
SWIMMER’S ITCH
 This is the only schistosome disease in the USA.
 It is caused by a schistosome that should have a bird as a host, but humans can become an
accidental host. An infected duck passes the eggs in the water. Humans who are
swimming in late July and August are more likely to get this.
 Since the organism cannot live in humans, it dies under the skin after it penetrates. This
causes an itchy reaction. The treatment is oral trimeprazine and topical cortisone (antiinflammatory) creams. The prevention is to rub your skin hard with a towel as soon as
you get out of the water to prevent the worms from penetrating.
Class Turbellaria - free-living flatworms (not parasitic)
 Planaria spp.
 Pharynx
 Eyespots (light sensitive)
 Gastrovascular cavity
Kingdom Animalia
Sub-kingdom Invertebrata
•
I. Phylum Platyhelminthes (flatworms)
– Tapeworms, flukes, and non-parasitic flatworms
•
II. Phylum Nematoda
– Roundworms, hookworms, threadworms
•
III. Phylum Annelida
–
•
segmented worms
IV. Phylum Arthropoda
– Ticks, mites, lice
Phylum Nematoda roundworms
Enterobius vermicularis – pinworm
Female
Mouth
Pharynx
Pinworm Disease:
Enterobiasis
 This is the most common roundworm in the USA, but the best one to have because it
produces the least symptoms. It has a simple life cycle; humans are the only host.
 The males are smaller than the female. Male tails have specialized ornamentation that are
shaped into a curl which allows the male to clasp the female during copulation. The male
tail also has spicules to allow attachment to the female.
 The female then migrates to the rectum, crawls out onto the skin, and deposits eggs on
the perianal folds. This causes itching, called anal pruritis. Self-infection occurs by
transferring infective eggs to the mouth with hands that have scratched the perianal
area. This occurs more often in children since they don’t wash their hands as well. The
eggs are sticky. Person-to-person transmission can also occur through handling of
contaminated clothes or bed linens or contact with contaminated curtains, carpeting, etc.
Phylum Nematoda roundworms
Ascaris lumbricoides - intestinal round worm- (plastimount)
Ascariasis
 A female may produce approximately 200,000 eggs per day, which are passed with the
feces and are ingested from soil contamination. The larvae are very migratory. They can
end up in the lungs and may crawl out the nose. They develop into adults in the intestine.
A heavy worm load can lead to intestinal blockage, with a bolus of worms inside; may
need surgical removal.
 This is the largest worm pathogen, so there are no slides. We do have the entire specimen
in a plastic container.
 This worm should be considered for the Hall of Fame for two reasons:
•
It is the biggest worm.
•
It causes the most infections of all the parasitic worms world-wide.
Dog and Cat Roundworms
 Toxocara canis and Toxocara cati are roundworms that infect dogs and cats, but humans
can become an accidental host. Preschool children are most often affected, since it is
spread by ingestion of contaminated dirt.
 They cause a disease in humans called Visceral larva migrans (VLM).
Visceral Larva Migrans (VLM)
 The larvae migrate from the intestines to other tissues, especially the liver.
 Most people become only mildly ill.
Others can have severe symptoms, such as brain damage, respiratory failure, cardiac
arrhythmias, or eye lesions that resemble cancer or retinal detachment
“My worm collection”
Phylum Nematoda roundworms
Necator americanus- American hookworm
Teeth
Muscular pharynx
Male
Posterior bursa
Rays
Hookworm Diseases
 The larvae travel to the heart, then to the lungs, where they penetrate the alveoli, make
their way up the trachea, up to the epiglottis, and then they are swallowed. They live in
the small intestine lumen. They attach to the mucosa by either teeth or cutting flakes,
which causes bleeding and persistent anemia. The patient may also have cardiac
symptoms.
 In the southern US, there is a condition known as “pica”, which is a desire to eat soil.
This is caused from an iron deficiency in the diet, sometimes because of a hookworm
infection.
 The male has a feathered copulatory bursae,on the tail and the female’s tail is just pointy.
Dog and Cat Hookworms
Ancylostoma braziliense
 Humans are accidental hosts.
 The lavae create serpentine tunnels.
 Lesions are very red (erythemic) and itchy (pruitic).
 If they migrate to the lungs, it is called Loeffler’s syndrome.
Dog and Cat Hookworms:
Cutaneous Larva Migrans
This is when a dog or cat hookworm gets into a human by accident. Since we are not the right
kind of host, the worm dies under the skin and causes an allergic reaction.
Phylum Nematoda roundworms
Trichinella spiralis- threadworm encysted in muscle
Cyst
Muscle
Larva
 Trichinellosis - Humans are infected when eating improperly processed meat. The larvae
migrate to the skeletal muscles where they encyst.
 There are very few cases of this disease in the USA because by law, pigs are not allowed
to free-graze. If they eat an infected rodent, they can get the disease and pass it on to
humans. Pigs are fed only grains to deter them from a desire to eat meat. However,
sometimes they eat each other’s tails!
 Within the US, this disease is most common in Alaska, where wild bear meat might be
undercooked. The bears can be infected.
Elephantitis
 Wuchereria bancrofti
 Mosquito: anopheles or Culex (Asia)
 Blocks lymph drainage
 During a blood meal, an infected mosquito introduces filarial larvae onto the skin of the
human host, where they penetrate into the bite wound.
 They develop in adults that commonly reside in the lymphatics.
 The microfilariae migrate into lymph and blood channels moving actively through lymph
and blood.
 Another mosquito ingests the microfilariae during a blood meal and work their way to the
mosquito's midgut and develop into infective larvae.
 The infective larvae migrate through to the mosquito's prosbocis and can infect another
human when the mosquito takes a blood meal.
Loa loa: The “eye worm”
 The vector for Loa loa filariasis are flies from two species of the genus Chrysops, C.
silacea and C. dimidiata.
 During a blood meal, an infected fly (genus Chrysops, day-biting flies) introduces filarial
larvae onto the skin of the human host, where they penetrate into the bite wound.
 The larvae develop into adults that commonly reside in subcutaneous tissue but can
migrate into spinal fluids, urine, and sputum. During the day they are found in peripheral
blood, but during the noncirculation phase, they are found in the lungs.
 The fly ingests microfilariae during a blood meal, which migrate to the thoracic muscles
and develop into infective larvae. They migrate to the fly's proboscis and can infect
another human when the fly takes a blood meal.
Kingdom Animalia
Sub-kingdom Invertebrata
•
I. Phylum Platyhelminthes (flatworms)
– Tapeworms, flukes, and non-parasitic flatworms
•
II. Phylum Nematoda
– Roundworms, hookworms, threadworms
•
III. Phylum Annelida
–
•
segmented worms
IV. Phylum Arthropoda
– Ticks, mites, lice
Phylum Annelida
segmented worms
Class Hirudinea
Leech (Hirudo medicinalis)
Anterior sucker (for cutting skin)
Mouth (for feeding)
Intestine
Posterior sucker (for attachment)
Leech
 Leeches have been used as a medicinal agent for centuries.
 They were first used in ancient Egypt to bleed people of “bad blood” that they thought
was causing illness.
 In medieval times, they were used in conjunction with blood letting by incisions.
They are used today for patients with finger amputations, to keep the veins open until the finger
can be reattached because their saliva has anesthesia and prevents clotting
 The leech has two suckers:
 The posterior sucker attaches to the host
 The anterior sucker makes a slit in the host’s skin so it can suck the blood.
 The leech can take in up to 5 times its weight in blood.
 Leeches are only used for one person for medicinal purposes, then they are destroyed to
prevent disease transmission.
Kingdom Animalia
Sub-kingdom Invertebrata
•
I. Phylum Platyhelminthes (flatworms)
– Tapeworms, flukes, and non-parasitic flatworms
•
II. Phylum Nematoda
– Roundworms, hookworms, threadworms
•
III. Phylum Annelida
–
•
segmented worms
IV. Phylum Arthropoda
– Ticks, mites, lice
Phylum Arthropoda
(Jointed feet)
•
Class Arachnia (ticks and mites)
•
Class Insecta (fleas and lice)
Class Arachnia
Dermacentor spp.- tick
Head
Thorax
Abdomen
Legs
•
•
Hard Ticks
•
Have a hard body
•
Mouth parts are visible from the top surface
•
Feed for days
Soft Ticks
•
Have a soft, leathery body
•
Mouth parts are on the bottom surface
•
Feed from minutes to hours
Diseases Transmitted by Hard Ticks
•
Diseases Transmitted by Hard Ticks
•
•
•
Dermacenter
•
Ehrlichiosis (Ehrlichia spp)
•
Rocky Mountain Spotted Fever (Rickettsia rickettsii)
Ixodes
•
Lyme Disease (Borrelia burgdorferi)
•
Babbesiosis (Babesia microti; USA protozoa)
Amblyomma
•
•
Ehrlichiosis
•
•
Ehrlickiosis
Fever, headache, fatigue, and muscle aches
Rocky Mountain Spotted Fever
•
•
Lyme Disease
•
•
Fever, headache, abdominal pain, vomiting, and muscle pain. A rash may also
develop, but is often absent in the first few days, and in some patients, never
develops. Rocky Mountain spotted fever can be a severe or even fatal illness if
not treated in the first few days of symptoms.
Fever, headache, fatigue, and a characteristic skin rash called erythema migrans.
If left untreated, infection can spread to joints, the heart, and the nervous system.
Babesiosis
•
Fever, chills, sweating, myalgias (muscle aches), fatigue, hepatosplenomegaly
(enlargement of the liver and spleen) and hemolytic anemia (anemia due to breakup of red cells). Symptoms typically occur after an incubation period of 1 to 4
weeks and can last several weeks. The disease is more severe in patients who are
immunosuppressed, splenectomized (lack their spleen), or elderly. It can cause
death.
Diseases Transmitted by Soft Ticks
•
Diseases Transmitted by Soft Ticks
•
Ornithidoros
•
Endemic relapsing fever (Borrelia hermsii)
•
High fever, rigors, severe headache, muscle pains, weakness,
anorexia, weight loss, and cough. Systemic complications can
include nausea, vomiting, upper abdominal pain due to liver and
spleen involvement, and a dry cough. Other manifestations include
splenomegaly, hepatomegaly, jaundice, rash, respiratory
symptoms, and central nervous system involvement.
Tick Diseases
•
Tick paralysis
•
More common in children than adults.
•
It is an ascending flaccid paralysis, accompanied by fever and toxemia (toxins in their
saliva) that can lead to respiratory compromise and death.
Class Arachnia
Sarcoptes scabiei - itch mite
Mouth
Legs
Bristles on rear legs
Bristles on abdomen
Scabies
•
Scabies is an itchy, highly contagious skin disease.
•
Mites are small eight-legged parasites (in contrast to insects, which have six legs).
•
They are tiny, just 1/3 millimeter long. The mite is harmless, but causes an allergic
reaction when it burrows into the skin to produce intense itching (pruitis), which
tends to be worse at night.
•
They prefer thin skin like the areas between the fingers, and the bends of the
elbows, wrists, and knees. They can move one inch a minute.
•
They are sometimes transmitted by contact with contaminated gym equipment.
Itch Mite - Class Arachnia
Dermatophagoides spp.- dust mite
Thorax
Legs
Abdomen
•
Dust mites feed on organic detritus such as flakes of shed human skin.
•
They are a common cause of asthma and allergic symptoms. The mite's gut contains
potent digestive enzymes that persists in their feces and are major inducers of
allergic reactions such as wheezing. The mite's exoskeleton can also contribute to
allergic reactions.
•
A dust mite allergy can range from mild to severe. A mild case of dust mite allergy
may cause an occasional runny nose, watery eyes and sneezing. In severe cases, the
condition may be ongoing, or chronic, resulting in persistent sneezing, cough,
congestion, facial pressure or severe asthma attack.
Dust Mite
Phylum Arthropoda
•
Class Arachnia (ticks and mites)
•
Class Insecta (fleas and lice)
Class Insecta
Flea
Head
Thorax
Abdomen
Legs
Fleas are vectors for diseases
 Fleas do not live on their hosts. They take their blood meal and return to their nest
(carpet, etc).
 Bubonic plague (Yersinia pestis)

Wiped out almost 1/3 of Europe

Still have outbreaks from rodent population on West Coast (Squirrels in San
Bernardino)
 Endemic typhus (Rickettsia typhi)
 Rodents in Texas
 The fleas that are vectors for the above diseases prefer to use a rodent for a host.
 Tapeworms in pets

When the dog or cat ingests the flea, it ingests the eggs and larvae inside the
flea.
Class Insecta
Pediculus humanis corporus - human body louse
Abdomen
Thorax
Head
Antennae (for feeling)
Eyes
Plates (protection)
Legs
Human Body Louse
 Nests in the seams of clothing, and lays eggs there.
 It comes out for a blood meal.
 They are associated with crowded, unsanitary conditions, such as during war,
famines, and natural disasters.
 Diseases Transmitted by Body Lice

Epidemic Typhus (Rickettsia prowasekii)

Relapsing Fever (Borrelia recurrentis and B. hermsii)
 Treatment
 Clothing must be treated with insecticide or dry cleaning.
 In the old days, they would boil the clothes.
 The host also is also treated with Lindane solution and washed off 4-24 hours later.
Class Insecta
Pthirus pubis- crab louse
Thorax
Abdominal segments
Eyes
Legs
Antennae
Crab Louse
 Crab lice tend to infest human pubic hair. The species may also live on other areas
with hair, including the eyelashes.
 They feed exclusively on blood.
 Humans are the only known hosts.
 The main symptom is itching, usually in the pubic-hair area, resulting from
hypersensitivity to louse saliva, which can become stronger over two or more weeks
following initial infestation.
 Pubic lice usually infect a new host only by close contact between individuals,
usually through sexual intercourse because they primarily spread through sweat,
body fluids. Parent-to-child infestations are more likely to occur through routes of
shared towels, clothing, beds or closets. Adults are more frequently infested than
children.