Parasitology Exam 2 Review

Chapter 4

Tissue Nematodes

Tissue Nematodes

• Intermediate host- Some are vectors

• Long and thin- adapted to life in tissues

  Nonfilarial worms

• Dracunculus medinensis

  Filarial (filamentous) worms- Live in lymphatics or subcutaneous tissues

• Wucheria bancrofti

• Loa loa

• Onchocerca volvulus

Rule of Thumb

Blood and tissue parasites cause more pathology than lumen dwelling parasites

Drancunculus medinensis (Guinea Worm, Fiery Serpent)

Life Cycle

1. Human drinks unfiltered water containing copepods with L3 larva

2. Larva are released when copepods die. Larvae penetrate the host’s stomach and intestinal wall. They mature and reproduce

3. Fertilized female worm migrates to surface of skin causes blister, and discharges larvae

4. Female worm begins to emerge from skin one year after infection (through foot)

5. L1 larvae released into water from emerging female worm

6. Larva is consumed by a copepod

7. Larvae undergo two molts in the copepod and become an L3 larva

Copepods

is NOT a Vector!! (but is a intermediate host)

Because human infects itself by ingesting

Epidemiology

• Almost eradicated

• Related to the use of step wells from gathering water

Pathology and Clinical Manifestations

• Lesions on foot or ankle

• Worm grows up leg and sometimes damages knee joint (frozen joint due to scar tissue)

• Secondary bacterial infection

Diagnosis

Observation- anterior portion of worm, ulcer, release of larvae

Treatment

• Matchstick or rubber band

• Metronidiozole (Flagyl)- does not kill but aids in removal (interfers with DNA replication, but carcinogen)

Prevention

• Treat carriers

• Stop carriers from using wells

• Filter water to remove copepods

• Kill copepods

• Education

Wuchereria bancrifti- Bancroft’s filariasis or Elephatiasis

Life Cycle

1. A mosquito takes blood (L3 larva enters the skin)

2. Adults in lymphocytes

3. Adults produced sheathed microfilariae that migrate into lymph and blood channels

4. Mosquito takes a blood meal (ingests microfilariae)

5. Microfilariae shed sheaths, penetrate mosquitos midgut and migrate to thoracic muscles

6. L1 larva

7. L3 larva

8. Migrate to head and mosquitos proboscis

Epidemiology

• Mosquito vector- Culex, Anopheles, Aedes

• An estimated 120M people in tropical and subtropical areas of the world are infected with lymphatic filariasis

• Mosquitos are very successful vectors but even they have problems

Pathology can Clinical Manifestations

• Adult worms reside in lymphatic channels

  3 Clinical Presentations

• Asymptomatic- 70% of cases

• Acute Filariasis- 25% of cases

• Chronic Filariasis- 5% of cases

Lymphatic system return fluid from tissues to circulatory system

One of the main functions of the lymphatic system is to provide a return route to the circulatory system. The capillary flow rate is about 4L of fluid per day

Asymptomatic Filariasis (70% of cases)

Adult worms causing little to no blockage of lymph channels

• Mild lymphatic inflammation

• Some minor blockage on lymph channels

• Some minor swelling of tissues

Acute Filariasis (25% of cases)

Adult worms causing pathology

• Per-Endo (around or inside) lymphatic inflammation

• Inflammation results in scarring and narrowing of the lymphatic lumen- lymph stasis

Chronic Filariasis (5% of cases)

Results from:

• Repeated infections over 20yr period

• Increased worm burdens

• Blockage of collateral lymphatic circulation

• Hypersensitivity to worm metabolites/allergens

• Intense peri-endo lymphatic inflammation leading to lymphatic scarring'

• Narrow lymphatic channels

• Severe tissue swelling- lower limbs/genitalia

• Elephantic skin due to lack of nourishment

Diagnosis

Microfilaria in blood- thick or thin blood smear or concentration technique, also serology- presence of worm

Treatment

• Diethylcarbamazine

• Polytherapy with diethylcarbamazine or albendazole with ivermectin

• Compressed bandages

• Surgery

• Lymphatic Bypass surgery

Prevention

• Mosquito control

• Mass chemotherapy

• Supportive treatment/psychotherapy

Loa loa- Eye Worm

Life Cycle

1. Fly (Genus: Chrysops) takes a blood meal (L3 larva enter skin)

2. Adults in subcutaneous tissue (under skin)

3. Adults produce sheathed microfilariae that are found in spinal fluid, urine, sputum, peripheral blood and in the lungs

4. Fly takes a blood meal (ingests microfilaria)

5. Microfilaria shed sheaths, penetrate fly’s midgut, and migrate to thoracic muscles

6. L1 larvae

7. L3 larvae

8. Migrate to head and fly’s proboscis

Epidemiology

• 40% of the 14.4M people who live in the area report that they have had eye worm in one time or another

• Mostly found in central Africa

Pathology and Clinical Manifestations

• Worms move freely through subcutaneous tissues

• Attracted to warmth

• Can wonder across eye

• Form subcutaneous nodules- groups of entwined worms

• Host forms a capsule due to hypersensitivity reaction- Calabar Swelling

Diagnosis

• Observation

• History of exposure

• Microfilaria in blood

Treatment

• surgical removal of Calabar swellings

• A single does of Ivermectin

Onchocerca volvulus- River Blindness

Life Cycle

1. Blackfly (genus Simulium) takes a blood meal (L3 larva enter)

2. Larva enter subcutaneous tissue

3. Adults in subcutaneous tissue (benign tumors)

4. Adults produced unsheathed microfilariae that typically are found in skin and in lymphatics of connective tissues, but also occasionally in peripheral blood, urine, and sputum

5. Blackfly takes a blood meal (ingests microfilariae)

6. Microfilariae penetrate blackfly’s midgut and migrate to thoracic muscles

7. L1 larva

8. L3 larva

9. Microfilariae migrate to head and blackfly’s proboscis

Epidemiology

The Global Burden of Disease Study estimated that in 2017 at least 20.9 million people infected worldwide

Pathology and Clinical Manifestations

-Damage caused by microfilaria

Benign tumors

associate with head- Adult releases microfilaria which migrate in skin causing hanging groin and across the eye causing corneal damage leading to blindness

• Collections of worms causing a hypersensitivity reaction

Skin

Migrating microfilaria causes skin to be detached and loose elasticity and malnourished resulting in parchment skin and hanging groin

Eyes

Corneal damage caused by migrating larva

• Though that Wolbachia, an endosymbiotic bacteria is responsible for the inflammatory reaction that caused river blindness

Mutualism

Essential metabolites (bacteria); food and shelter (nematode)

Diagnosis

Skin biopsy for microfilaria

Treatment

• Nodulectomy- remove benign tumor

• Ivermectin

• Promising treatment with doxycycline that kills adult worms by killing the Wolbachia bacteria which is intracellular and has a endosymbiotic relationship with the parasite

Prevention

Remove vector and treat carriers

Chapter 5

Cestodes: General Characteristics and Intestinal Tapeworms

Remember

Many intestinal tapeworms produce little or moderate pathology and draw nourishment from host food

Cestode General Characteristics and Morphology

• Flat and ribbon like— an old fashioned tape measurer

• Hermaphroditic- male and female reproductive track on same organism

General morphology

• Scolex

• Neck

• Proglottids (+ Neck = Strobila)

Scolex

Orientation of the worm, biological holdfast, not for support or physical anchor, not for feeding

• Rostellum, hooks (sometimes armed), suckers

Neck

Budding area for growth of worm, area where proglottids bud off ( where the worm grows)

• Undifferentiated stem cells that give rise to the proglottids

Proglottids

Worm segments that are sexually immature (growing), sexually mature (reproducing), or gravid (sacs of eggs, no uterus or ova) depending on age

Absorption of Nutrients

• Tapeworms are highly specialized and lack a digestive tract

• Food is digested by the host and tapeworms absorb nutrients directly across their tegument using- pinocytosis, diffusion, facilitated diffusion, and active transport

• Nutrients: amino acid, monosaccharides, absorbance assisted by microvilli and microtriches

Intestinal Tapeworms

Adult worms found in the small intestine of the definitive host (because this is where nutrients is absorbed)

• Hymenolepsis nana- Dwarf Tapeworm

• Taenia saginata- Beef Tapeworm

• Taenia solium- Pork Tapeworm

• Diphyllobothrium latum- Fish Tapeworm

Hymenolepsis nana- Dwarf Tapeworm

• 1-3 inches long

• Scolex- 4 sockers and hooks on rostellum

• Eggs free in host gut as proglottids usually disintegrate in the gut as eggs pass in feces

Life Cycle

• Direct- Ingestion of eggs or mouse pills

• Indirect- Ingest larvae via ingestion of insects (Tenebrio beetle)

• Internal Autoinfection- Eggs laid and hatch in intestine

Life Cycle Steps

1. Embryonated eggs in feces

2. Egg ingested by insect and cysticercoid develops in insect

3. Humans and rodents are infected when they ingest cysticercoid infected arthropods

4. Instead of 2/3, Embryonated eggs ingested by humans from contaminated food, water, hands

5. Onchosphere hatches cysticercoid develops in intestinal villus

6. Scolex

7. Adult in ileal portion of the small intestine

8. Eggs can be released through the genital atrium of the gravid proglottids. Gravid proglottids can also disintegrate released eggs passed in stools

Autoinfection

can occur if eggs remain in the intestine. The eggs then release the hexacanth embryo, which penetrates the intestinal villus continuing the cycle

Epidemiology

• This parasite does not need an intermediate host

• Person to person contact like pinworm

• common in children

• Mouse pills

• Tenebrio Beetle can serve as intermediate host

Mouse Life Cycle

1. Growth and maturation in small intestine

2. Ova released in gravid proglottids into feces, ingested by beetle

3. Infective cysticercoid develops in beetle, ingested by rat

Pathology and Clinical Manifestations

• Adult Worms in small intestine

• Asymptomatic to mild symptoms- irritation to gut wall

• Allergic reactions to worm metabolites (nervousness, headache, dizzy, diarrhea

• Oncosphere penetrates villus and develops into cysticercoid

Diagnosis

Eggs in stool

Treatment

Praziquantel and Niclosamide

Prevention

• Personal hygiene

• Mass chemotherapy

Taenia Tapeworms- Morphological Differences

• Taenia saginata- Beef tapeworm- little pathology

• Taenia solium- Pork tapeworm- high degree of potential pathology (due to human physiology being similar to a pig)

Taenia saginata- Beef Tapeworm

• Very long proglottids: 5-10 meters, but up to 25m

• Scolex: 4 suckers, no hooks

• Proglottids- IMPORTANT: longer than wide, more than 15 uterine branches, found whole in stool, mobile in stool, can migrate out of anus

Life Cycle

1. Eggs or gravid proglottids in feces and passed into environment

2. Cattle become infected by ingesting vegetation contaminated by eggs or gravid proglottids

3. Oncospheres hatch, penetrate intestinal wall, and circulate the musculature

4. Oncospheres develop into cysticerci in muscle

5. Humans infected by ingesting raw or undercooked infected meat

6. Scolex attaches to intestine

7. Adults in small intestine

Epidemiology

• Cattle infection due to grazing areas polluted with sewage, cattle in feed lots infected by feed lot workers

• Eat undercooked beef

• Endemic in all beef eating areas

• In US about 0.37% of cattle infected

Pathology and Clinical Manifestations

• Adult worm in small intestine

• No real problem

• No weight loss

• Can potentially cause intestinal blockage

• Diarrhea can be present due to reactions to worm metabolites

• Since little pathology was sold as weight loss treatment before there was FDA

Diagnosis

Proglottids in stool

Treatment

• Single oral dose of praziquantel

• Single dose of niclosamide

Prevention

• Inspect beef

• Cook beef at 56C- denatures protein

• No sewage in grazing areas

• Importation of canned not fresh beef (also a good treatment for cancer, bacterial, and viral infections)

Taenia solium- Pork Tapeworm

• Long worm: 8-10m

• Scolex: suckers and hooks

• Proglottids: less than 13 uterine branches

Life Cycle

1. Eggs or gravid proglottids in feces and passed into environment

2. Embryonated eggs and/or gravid proglottids ingested by pigs or humans

3. Oncospheres hatch, penetrate intestinal wall and circulate to musculature in pigs or humans

4. Oncosphere develop into cysticerci in muscles of pigs or humans (can cause cysticercosis)

5. Humans acquire the infection by ingesting raw or undercooked meat from infected animal host

6. Scolex attaches to intestine

7. Adults in small intestine

Cysticercosis

Cysticerci may develop in any organ, being more common in subcutaneous tissue, brain, and eyes

Epidemiology

Endemic in areas of high pork consumption and lax meat inspection

Pathology and Clinical Manifestations

• Adult worm in small intestine- asymptomatic to mild symptoms like Taenia saginata

• DANGER- ingestion of eggs can result in autoinfection or self-contamination or infection of people in close proximity resulting in…

• Cystercercus cellulosae: ingestion of embryonated eggs- oncosphere hatches in gut- enters circulation- travels to any organ in body. Pathology and danger are determined by the organ system affected

Organ/tissue Affected

• Intramuscular: encystment in muscle, calcification, dead end for parasite, usually found in X-ray

• Brain: no encystment: can grow into grapelike clusters. Causes Jacksonian epilepsy. Surgery needed with death common

• Eye: appears to be a floater in vitreous humor, no encystment, can get into sub-retinal space. Death of organisms results in massive inflammation causing loss of eye

• Lungs, Liver, etc

Diagnosis

• Proglottids in feces for adult worm

• X-Ray, CT scan, MRI for cysticercus cellulosae

Treatment

• Praziquantel

• If cysts are present, caution, since antibiotic is cysticidal and can cause inflammation around dying cysts in those with cystercosis, which may lead to seizures and other serious symptoms

• Surgery may be required to clear cyst

Prevention

• Proper disposal of feces

• Cook or freeze pork

• Inspect pork

Diphyllobothrium latum- Fish Tapeworm

• Long worm: 5-10 meters

• As with all of these large tapeworms there is one worm per person

• As with all these large tapeworms this worm is very long lived

• Scolex-Bothrium- leaf-like suckers or sucking groove

Life Cycle

1. Unembryonated eggs passed in feces

2. Eggs embryonate in water

3. Coracidia hatch from eggs and are ingested by crustaceans

4. Procercoid larvae in body cavity or crustations

5. Infected crustacean ingested by small freshwater fish. Procercoid larva released from crustacean, develops into plerocercoid larvae

6. Predator fish eats infected small fish

7. Human ingests raw or undercooked infected fish

8. Adults in small intestine

9. Proglottids release immature eggs

Epidemiology

• Found in temperature regions in areas with high freshwater fish consumption

= Great Lakes and Pacific Northwest, Finland, Baltic region, Russia

• Scandinavians brought the parasite to the USA

Pathology and Clinical Manifestations

• Mild attachment damage

• Some allergic reaction to metabolites

• Worm has great affinity for Vitamin B12- Pernicious anemia is common in those infected

Diagnosis

Eggs in stool

Treatment

• Praziquantel

• Niclosamide

Prevention

• Cook fish

• Prevent sewage from contaminating water

Chapter 6

Cestodes: Tissue Tapeworms

Tissue Cestodes

• Echinococcus granuloses- Unilocular (1 chamber) Hyatid Disease

• Enchinococcus multilocularis- Multilocular Hyatid Disease (more pathogenic, less common)

Enchinococcus granulosus -Hyatid Cyst Disease

Small worm, only ¼ inches long, composed of Scolex-Neck-Three Proglottids (immature, mature, gravid)

Life Cycle

• Normal life cycle has two players: Dog (definitive host) and Sheep (intermediate host)

• Humans play the role of sheep when they ingest the eggs

Life Cycle Steps

1. Adults in small intestine of dogs

2. Embryonated eggs passed in feces (ingested by humans causes pathology)

3. Oncosphere hatches; penetrates intestinal wall after sheep ingests

4. Hyatid cyst in liver, lungs, etc

5. Protoscolex from cyst ingested by dogs

6. Scolex attaches from intestine

7. Adults in small intestine

Hyatid Cyst

• Contains Brood Capsule

• Brood Capsule hold Protoscolex

• Protoscolex: Become adults in host

Epidemiology

• Enchinococcus spp. are zoonotic tapeworm currently infecting 2-3 million persons worldwide causing US $200-800 million in annual economic losses related to human infections

• 1990-2017 US had 41 deaths

Pathology and Clinical Manifestations

• Cyst expands/grows as a sphere (perfect sphere due to its strong membrane) in soft tissue- increasing in diameter

• Pea to golf ball to baseball to softball to volleyball etc

• Parasite fibrous capsule is very strong and resilient with no weak spots so it expands uniformly

Organs Effeted

• Liver: mechanical damage as cyst grows causing pressure atrophy

• Brain: very serious

• Heart valves: very serious

• Lungs

• Allergic reaction to hyatid fluid can cause anaphylaxis if cyst ruptures

Diagnosis

• Observation

• X-ray, CT scan, MRI

Treatment

• Based on size, location, manifestations, and overall health of patient

• Surgery most common

• Risk of surgery from leakage of fluid include anaphylaxis and dissemination of infectious solices, cholangitis (inflammation of bile duct), hyperatremia (electrolyte imbalance, increase in sodium concentration)

Prevention

• Treat dogs

• Cook sheep organs before feeding them to dogs

Enchinococcus multilocularis- Alveolar hyatid disease

• Normal life cycle involves dog/fox (definitive host)— Moles/voles/rodents (intermediate host)

• Humans play role of the moles/voles/rodents when they ingest eggs

Life Cycle

1. Egg (Humans ingest eggs and are infected)

2. Rodents ingest egg

3. Mestacestode in rodent liver

4. Fox/dog ingest eggs through rodents

5. Adult in the intestine

Epidemiology

• Northern USA possible

• Easting wild blackberries/blueberries/mushrooms contaminated with eggs

• Almost all cases confined to Northern Hemisphere in Europe, Russia, China, Japan, and North America

Pathology and Clinical Manifestations

• Alveolar hyatid cyst forms: Multi-locular cyst that spreads because the cyst wall is weak and germinal layer is neoplastic-like

• Cavitation of infected organ results- organ replaced by cyst. Slow in developing may take 5 to 15 years

Diagnosis

• Indirect: X-Ray, CT scan, MRI

• Liver Function

• Observation

Treatment

• Surgery: same as E. granulosus, except if any germinal layer is left it will regrow the cyst, similar to neoplasia- matastaiss cell travel to other tissues/organs

Prevention

• Treat/control infected dogs

• Wash fruits

• Non-surgical options induce cyst drainage, scolicidal solution and continuous treatment with albendazole- parasitostatic not parasitocidal

Chapter 7

Trematodes: General Characteristics and Trematodes Infective in the Metacercarial Stage

Trematodes

Flukes- Looks like flukes of an anchor

• Trematodes (trematos) literally mean pierced with holes- refers to sucker on the worms