Parasitology Lab Exam 2

Trichuris trichiura Life Cycle

• Whipworm

• Phylum - Nematoda

• Eggs are barrel-shaped and have polar “plugs” at each end

1. Unembryonated eggs are passed in the stool

2. In the soil, eggs develop into a two-cell stage

3. An advanced cleavage stage takes place

4. Embryonated eggs are ingested (contaminated soil or food)

5. The eggs hatch in the small intestine and release larvae

6. The larvae mature and establish as adults in the colon

Trichuris trichiura Female Anatomy

• Sexual dimorphism, females are larger

Trichuris trichiura Male Anatomy

• Males are smaller than females

• Have a curved tail

• The curved tail has a copulatory spicule with a retractable sheath

Trichinella spiralis Life Cycle

• Contracted via undercooked pork containing encysted larvae

• Two host life cycle

1. Larvae are released from cysts after exposure to gastric acids

2. Larvae invade the small bowel mucosa and develop into adult worms

3. Females release larvae that migrate to striated muscles where they encyst

Trichinella spiralis Female Anatomy

• Sexual dimorphism, females are larger

Trichinella spiralis Male Anatomy

Trichinella spiralis Juvenile in Muscle

Ascaris lumbricoides Life Cycle

1. Unfertilized eggs are passed in stool

2. Eggs become fertilized in the environment (ideal conditions: moist, warm, shaded soil)

3. Infective eggs are swallowed

4. The larvae hatch and infect intestinal mucosa

5. Larvae are carried to the lungs (10 to 14 days)

6. Crawl up the throat and are swallowed

7. Reach the small intestine and mature into adults

• Eggs have a lipid coating and can persist in the environment

• Humans and swine are the major hosts, dogs may also be infected

Ascaris lumbricoides Female Anatomy

• Sexual dimorphism, females are larger

Ascaris lumbricoides Female Cross-section

• Gravid uterus (UT)

• Intestine (IN)

• Coiled ovary (OV)

Ascaris lumbricoides Male Anatomy

Ascaris lumbricoides Male Cross-section

Hookworm Life Cycle

1. Eggs are passed in stool

2. Larvae grow in feces and/or soil

3. Become a filariform larvae after two molts

4. Larvae penetrate the skin and are carried through the blood to the heart and the lungs

5. Crawl to the throat, are swallowed, and reach the small intestine and mature into adults

Necator americanus Adult Anatomy

• Copulatory bursa at posterior of male

• Two spicules

• Fleshy rays support lateral and dorsal lobes

Necator americanus Eggs

Dirofilaria immitis Life Cycle

1. A mosquito takes a blood meal and L3 larva enter the bite wound

2. In the definitive host L3 larvae undergo two more molts into L4 and adults

3. Adults reside in the pulmonary arteries

4. Female worms produce microfilariae which circulate in peripheral blood

5. A mosquito ingests the microfilariae, which migrate to the Malpighian tubes in the abdomen

Enterobius vermicularis Life Cycle

1. Gravid females deposit eggs on perianal folds

2. Self infection occurs from the transfer of eggs from the perianal region to the mouth

3. Larvae hatch in the small intestine

4. Adults establish themself in the colon

5. Gravid females migrate nocturnally outside the anus and deposit eggs

Enterobius vermicularis Egg

Class Insecta Characteristics

• Body segmentation (head, thorax, and abdomen)

• Parasitic adaptations include attachment organs, flattened bodies, and loss of wings

Flea (Siphonaptera) Life Cycle

1. After taking a blood meal, fleas mate and begin laying eggs

2. After hatching, fleas enter the larval stage

3. Larvae spin a cocoon and enter the pupa stage

4. Adult fleas emerge from the cocoon when there is the presence of a host

Phylum - Arthropoda

Class - Insecta

Order - Siphonaptera

Flea Morphology

Identify:

• Antenna

• Compound eyes - reduced eye structure due to parasitic lifestyle

• Genal ctenidia - anchoring mechanism, backward-facing spines lock onto fur, makes it difficult for hosts to remove the flea

• Pronotal ctenidia - anchor the flea in place, assist in locomotion through the host’s hair

• Pygidium - detect air movements and vibrations, allow the flea to sense potential hosts and threats

• Spiracle - regulate respiration, minimize water loss, allow for air exchange

• Spermatheca (females) - stores, nourishes, and protects sperm for an extended period of time

• Copulatory apparatus (males) - locks securely onto the female and ensures sperm transfer

Flea Leg Morphology

• Coxa - the base of the jumping mechanism, enables movement through the host’s hair

• Trochanter - acts as a lever to release jumping power, transfers stored energy from the resilin protein

• Femur - activates the internal spring system (resilin), compress the elastic protein before releasing it

• Tibia - allows for long distance leaps, is pressed against the the ground with the trochanter to build energy, backward facing spines help to grip the substrate

• Tarsus - anchor point for jumping, equipped with claws that grip the host’s hair and allow the friction to push off the ground

Ctenocephalides Larvae/Adult

• The cat flea, primarily impacts mammal animal hosts

• Four-stage, 30-75 day life-cycle (egg, larvae, pupa, adult)

Pulex irritans Larvae/Adult

• Human flea or house flea

• Wide host spectrum

Lice (Phthiraptera) Life Cycle

1. Nits, or eggs, are laid by the adult female and are cemented at the base of the hair shaft near the scalp

2. The egg hatches and releases a nymph, nymphs mature after 3 molts

3. Nymphs become adults after 7 days after hatching

4. Adult lice are the size of a sesame seed and have six legs

Body lice - body lice reside and lay their eggs on clothing and migrate to the human body to feed

Phylum - Arthropoda

Class - Insecta

Order - Phthiraptera

Lice Anatomy

• Antennae

• Compound eye

• Coxa - helps to anchor the large muscles

• Trochanter - provides flexibility and allows the rotational movement of the leg

• Femur

• Tibia - used to anchor the louse, a tibial thumb works in opposition to the tarsal claw

• Tarsus - grasps human hair and clothing fibers, allows a secure hold on the hair during movement

Pediculus humanus humanus (body louse)

Pediculus humanus capitalis (head louse)

Phthirus pubis

Tick Life Cycle

Four life stages: egg, larva, nymph, adult

• A tick needs a blood meal at each stage to survive

• Spring - eggs are laid

• Summer - hungry 6-legged larva hatch

• Next spring - 8-legged nymphs look for their next blood meal, can now transmit pathogens

• Fall or winter - nymphs transition into adults, females seek out another blood meal to reproduce

Phylum - Arthropoda

Class - Arachnida

Subclass - Acari

Tick Anatomy

Anterior - gnathosoma

Posterior - idiosoma

Hypostome - embeds in skin

Scutum - provides structural support and protection

Spiracular plate - allow oxygen to enter and carbon dioxide to exit, manages water loss

Festoon - allow for expansion of the body with blood

Entamoeba histolytica Life Cycle

1. Cysts and trophozoites are passed in feces

2. Mature cysts are ingested

3. Excystation occurs in the small intestine

4. Trophozoites can invade the intestinal mucosa and other sites like the blood, liver, and brain

Phylum - Amoebozoa

Class - Lobosea

Order - Amoebida

Entamoeba histolytica Anatomy

Giardia lamblia Life Cycle

• Phylum: Metamonada

• Class: Trepomonadea

• Order: Distomatida

• Genus: Giardia

1. Cysts or trophozoites are found in feces

2. Ingestion of cysts

3. Trophozoites multiply in the small bowel

4. Encystation occurs and the parasites travel towards the colon

Trypanosome brucei

• Phylum: Euglenozoa

• Class: Kinetoplastea

• Order: Trypanosomatida

• Genus: Trypanosoma

1. A tsetse fly takes a blood meal

2. Parasites enter the blood stream

3. Transform into trypomastigotes, are carried to other sites in the body

4. A fly takes a blood meal and becomes infected

Plasmodium spp.

1. A mosquito ingests gametocytes that mate within the gut of the mosquito

2. Sporozoites are injected into a human during the next blood meal

3. Sporozoites travel to the liver, infect hepatocytes, and begin asexually replicating

4. Merozoites infect the red blood cells, the cell then ruptures

5. The cycle repeats