Parasitology Lecture 3: Helminths-Nematodes infective in the larval stage

Hookworms include which two species

Necator americanus, Ancylostoma duodenale

Necator americanus is also known as what?

New World Hookworm, also known as the “American Killer”

Necator americanus possesses ________ in it’s oral cavity

Lunar cutting plates

Anclyostoma duodenale is also known as what?

Old World Hookworm, also known as the “crooked mouth” worm

Ancylostoma duodenale possesses ________ in its oral cavity

Fangs or teeth

The hookworm life cycle involves which organ systems

Skin, Circulation, Lungs, Small intestine

How do hookworms begin on the skin

Infective filariform larvae in the soil penetrate the skin, typically when a person walks barefoot

How do hookworms enter the lungs

Larvae enter the bloodstream and them travel through the circulation to the lungs, where they break out of capillaries into the alveolar spaces

How do hookworms enter the small intestine

Larvae are coughed up from the lungs and swallowed, migrating to the small intestine. Here they mature into adult worms, attach to the intestinal wall and begin feeding

How are hookworms usually distributed

In the tropics, subtropics, and temperate zones, with mixing due to population. Temperature and rainfall are important environmental factors and all ages are susceptible

Ancylostoma species first spread through where?

Via the Silk Road trade routes from Europe to Asia

Necator Species first spread through where?

From Africa to the Americas and Europe, and then to Asia, largelt as a result of the slave trade

The ___________ funded hookworm treatment in the U.S., which included providing drugs and encouraging the use of shoes, helping to combat the perception of Southerners as “lazy” due to hookworm infections

Rockefeller Foundation

Larval penetrations of Hookworms in the skin can cause what?

Papule, vesicle, and itchy lesions. Symptoms include pruritis (itching), edema (swelling) and erythema (redness)

Repeated infections of larval hookworms on the skin can cause what?

Can lead to allergic reactions (hypersensitivity), known as “Ground itch”

Larval migration of hookworms to the lungs can cause what?

Petechial hemorrhages (small, pinpoint bleeds in the lungs)

Hookworms feed by doing what

By ingesting mucosal tissue and disrupting blood vessels to consume blood

Consequences of blood loss due to parasites

Anemia, Iron deficiency, Stunted growth

Iron deficiency

Can lead to “pica", the urge to eat non-food substances like dirt

How to diagnose Hookworms

Eggs found in stool samples

Prevention of Hookworm

Sanitation, proper disposal of feces. Proper treatment of night soil (human waste used as fertilizer), Personal hygiene, WEARING SHOES

Cutaneous Larval Migrans (CLM) consists of which species of animal hookworms

Ancylostoma caninum, Ancylostoma Brasiliensis

CLM is caused by the larval stages of what kinds of hookworms?

Animal Hookworms

Ancylostoma caninum is also known as what

Dog hookworm

Ancylostoma brasiliensis is also known as what

Cat hookworm

What is the source of Cutaneous Larva Migrans eggs

Pets are the source of eggs

Infection of Cutaneous Larva Migrans

Filariform larvae penetrate the skin of humans but cannot complete their life cycle because humans are the wrong host, they usually infect animals

Migration of Cutaneous Larva Migrans

Larvae migrate subcutaneously, creating characteristic serpiginous (snake-like) tracks

What is the life cycle of Cutaneous Larva Migrans

The life cycle in dogs and cats is similar to human hookworm infections, but in humans the larvae are only confined to the skin. Larvae remain in the epidermis and typically cannot penetrate the dermis to enter the bloodstream

How to diagnose Ancylostoma Caninum and Ancylostoma brasiliensis (CLM)

Observation of the characteristic skin tracks

How to prevent Ancylostoma Caninum and Ancylostoma brasiliensis (CLM)

Avoid allowing pets in sandboxes or on beaches, exercise caution when working or playing around animal quarters and use plastic drop cloths in crawl spaces under houses to prevent larval exposure

Trichinella spiralis causes what?

Trichinellosis

How is trichinellosis acquired

By consuming undercooked meat containing encysted larvae

Rhabditiform larvae develop into what to then break into the skin and pass into the tissues?

Filariform larvae

Trichinella spiralis (pork worm) is one of the first parasites where ______ occurs within the host

Multiplication

When migrating within a host, larvae of Trichinella spiralis favor what?

Well oxygenated muscles, which include eye muscles, diaphragm, larynx, tongue, intercostal muscles, and biceps/triceps/pectorals

Due to its varied symptoms, Trichinella spiralis is also known as what

The Great Imitator, as it causes symptoms such as nausea, vomiting, diarrhea, fever

After encysted larvae of Trichinella spiralis is consumed through undercooked meat, the larvae release where?

The cyst dissolves and the larva is released in the small intestine where they mature into adult worms.

Adult worms of Trichinella spiralis deposit larvae where?

In the intestinal mucosa to which larvae are released into circulation and migrate to striated muscles.

Stage 1 (intestinal phase) of infection of Trichinella spiralis (1-10 days post infection)

Larvae mature into adults in the small intestine. Necrosis and pan-mucosal inflammation of the small intestine begins around 72 hours. Worms burrow deep into intestinal mucosa which causes inflammation and stimulated an immune response. This process typically results in the expulsion of worms by day 14

Stage 2 (migration phase) of Trichinella spiralis (7-14 days post infection)

Adults are expelled from the intestines and larvae migrate via circulation to muscles through inflammation or “self-cure”

Symptoms of the Stage 2 (migration phase) of Trichinella spiralis

Small capillary hemorrhages as larvae rupture capillaries. Hemorrhages may be visible under fingernails.

Bilateral ocular edema

Hyper-eosinophilia (as high as 25% eosinophils in blood0

Bilateral ocular edema

Swelling around the eyes as the eyes muscles are invaded. This is a primary sign of Trichinella spiralis infection

Stage 3 (muscular phase) of Trichinella spiralis (approx. 3 weeks post infection)

Larval encystment in muscles, Myostitis (muscle inflammation), Myalgia (muscle pain) and degeneration of muscle fibers occur.

Stage 4 (calcification) of Trichinella spiralis

Larvae eventually calcify in the muscles, becoming symptomless

Trichinella spiralis diagnosis

History of eating undercooked pork, bear or boar.

Ocular edema (appears 10-14 day post ingestion)

Why is treatment for adult Trichinella spiralis infections not usually necessary

The immune system expels the adults from the body in a sort of “self-healing” process

How to prevent Trichinella spiralis

Thoroughly cook and freeze pork, Remove rodents from pig farms and cook garbage if used to feed pigs

Strongyloides stercoralis is also known as what?

Threadworm

Direct life cycle of Strongyloides stercoralis

Filariform larvae penetrate intact skin, enter circulation, migrate to lungs, are coughed up, swallowed, and mature into adult female worms in the small intestine. Eggs are deposited in the INTESTINAL MUCOSA, hatch, and larvae migrate to the LUMEN where they are expelled through stool

Indirect life cycle of Strongyloides stercoralis

Larvae expelled through stool can develop into free-living worms in the environment. These free living adults reproduce and offspring can become infective filariform larvae.

Internal autoinfection of Strongyloides stercoralis

Rhabditiform larvae in the large intestine can develop into filariform larvae, penetrate the intestinal mucosa and lungs and re-initiate the infective cycle within the same host. This is a critical aspect of pathogenesis

External autoinfection of Strongyloides stercoralis

Occurs when non-infective larvae turn into infective larvae inside the host's digestive tract and then re-enter the body by penetrating the skin around the anus or perineal area

Rhabditiform larvae

Non-infective, diagnostic stage. Characterized by a relatively short, stout esophagus.

Filariform larvae

Infective stage. Characterized by a long, slender esophagus and a notched tail.

What are the characteristics of Strongyloides stercoralis being a NEW parasite

Has a free living cycle

Has multiple hosts

Causes a high degree of pathology

Larval penetration of Strongyloides stercoralis causes papules, vesicles, and lesions, similar to hookworm but with ________

Less mechanical damage due to slimmer larvae

Similar to hookworm, Strongyloides stercoralis in the lungs can cause _______

Petechial hemorrhages

Adult females of Strongyloides stercoralis in the intestine

Adult females burrow deep into the intestinal mucosa and lay eggs that hatch.

This causes SIGNIFICANT MECHANICAL DAMAGE as cavitation, mucosal sloughing, fluid and blood loss, dysentery, and secondary bacterial infections occur

The internal autoinfection cycle of Strongyloides stercoralis is particularly dangerous in what kind of individuals?

Immunosuppressed individuals (those on immunosuppressive drugs, with HIV, or organ transplants) The immune response that normally leads to the expulsion of worms is suppressed and worm population increases which leads to hyperinfection

Diagnosis of Strongyloides stercoralis

Continuous mucoid diarrhea that may change due to dysentery

Rhabditiform larvae found in fresh stool

Filariform larvae in older stool

Larvae in sputum and lung aspirates

Who are the people that invented Ivermectin

William C. Campbell and Satoshi Omura