Intestinal Parasites

What is a parasite?

• An organism that lives inside of a host and benefits from it at the host’s expense

Define these stages of a parasite’s life:

• Infective

• Adult

• Immature

• Infective: A form of the parasite that can start an infection when contacting a host(Larva, cyst, egg)

• Adult: The fully grown form where sexual reproduction occurs

• Immature: Includes eggs and larva, often require a different environment than the host

Define these forms of hosts

• Definitive

• Intermediate

• Reservoir

• Accidental

• Paratenic

• The final destination, where they can reach sexual maturity and do sexual reproduction

• A secondary host where the parasite can reproduce asexually or develop, but won’t reach sexual maturity

• Reservoir hosts allows normal growth and reproduction of the parasite, just like the definitive host, it’s just not the host being studied as the definitive one, and parasites can definitely go from reservoir to definitive

• Accidental hosts can hold the parasite and it can cause disease for the host, but the parasite can’t reach full maturity and is often stuck, making accidental hosts “dead-end” hosts

• A waiting room, parasite won’t grow or reproduce, but can still be transmitted

What is the diff btwn a direct and indirect life cycle of a parasite?

• Direct has one host, indirect has more

How are parasites usually divided?

Helminths, protozoa, arthropods

Protozoa

• Cell amount

• __karyote

• Reproduction

• Life stages

• Single celled

• Eukaryote

• Asexual reproduction

• Trophozoite(active, feeding, motile) and cyst(dormant stage that can survive outside the host)

Helminths

• Cell amount

• __karyote

• Reproduction

• Classification

• Multicellular

• Eukaryote

• Usually not great at multiplying inside humans, so they have to repeatedly expose the host to new eggs/larvae

• Nematodes(round worm), cestodes, trematodes

Arthropods

• Thai name

• Usually…

• สัตว์ขาปล้อง

• Carry other parasites

What are some common modes of transmission of parasites?

1. Ingestion of the infective stage

2. Skin penetration

3. Sexual transmission

4. Insect bite

Compare an adult to and egg to a larva(and the 2 forms)

• Egg: The egg is a shell for the parasite used as an exit vehicle from the host, but it can also be infective

• Larva: The hatched egg. Two important forms are rhabditiform(more non-infective and growth focused) and filariform(thinner and designed to infect)

• Adult: Obvious sexual dimorphism, living in the host, focusing on reproduction

Cysticercus

• A larval stage in an intermediate host, like Taenia solium being ingested by a pig and entering it’s tissues, waiting for human ingestion

Cercaria and metacercaria

Cercaria: A form for trematodes that’s tad-pole like. Found after it leaves a snail and hunts for secondary host

Metacercaria: An immobile, protective stage hiding in the tissues of a secondary host, waiting for ingestion by the definitive host

Trophozoite vs cyst

• What are they

• Found in?

• Motile, feeding, multiplying, disease-causing form vs dormant, protected form

• Protozoa

Nematode

• Thai name

• Large group

• Key characteristics

• พยาธิตัวกลม

• Type of helminth, specifically called Roundworms

• 3 layered body with an outer cuticle that can form teeth, narrowings at the ant/post. ends, non-segmented body, alae, and a “tube within a tube” digestive system

Capillaria philippinensis

• Classification

• Key characteristics

• Disease

• Nematode(A kind of helminth)

• Females larger than males, slender tip and end, stichosomal esophagus that extends for half the body

• Intestinal capillariasis

Eggs are often found within the female body, how do we diff. between a embryonated or unembryonated egg?

• Embryonic eggs have thin shells while unembryonic ones have thick shells

• Embryonic capillaria eggs will hatch IN the intestine, causing autoinfection while unembryonic eggs will be shed in the feces to allow for the cycle to continue

What does a Capillaria philippinensis egg look like?

• Oval-ish with flattened plugs on both ends, a pitted shell, and an oval cell inside

Capillaria philippinensis life cycle

1. Humans(the definitive host) have them in their intestines and shit out the eggs

2. The eggs enter water, taken up by fish(the intermediate host)

3. Humans eat the fish

• Remember the autoinfection nuance, where embryonated eggs are hatched w/in the human intestine, boosting numbers of C. philippinensis in humans

Capillaria philippinensis pathology

1. They bury into crypts of Lieberkuhn, using enzymes to destroy microvilli

2. Na+ K+ ATPase broken, so K+ leaks into the lumen → Hypokalemia → Muscle weakness/arrhythmias in severe cases

3. Albumin also leaks out → Less oncotic pressure in blood vessels → pitting edema

Why does Capillaria philippinensis cause these symptoms?

• Borborygmi(gurgling from stomach)

• Abdominal pain and distention

• Watery diarrhea

• Pitting edema

• Weight loss

• Weakness

• Anorexia

• Cachexia

• Borborygmi(gurgling from stomach) → Broken microvilli means we can’t absorb normally, so as the excess fluid and gas is pushed forward by peristalsis, it makes these sounds

• Abdominal pain and distention → Inflammation thanks to the worms burrowing, and distention due to food being fermented + fluid build up

• Watery diarrhea → The leaked K+ and Na+ cause osmosis to follow them

• Pitting edema → Albumin leak → No oncotic pressure

• Weight loss → Loss of amino acids being absorbed, so we do proteolysis

• Weakness → Hypokalemia → Worse muscle contraction

• Anorexia → Inflammatory cytokines suppress hunger

• Cachexia → Final stage of muscle wasting

Red flags for Capillaria philippinensis

• Chronic diarrhea

• Weight loss

• Abdominal distention

• Edema

• Borborygmi

• History of raw freshwater fish consumption

Capillaria philippinensis treatments

• Mebendazole, Albendazole(Anti-parasites)

• Electrolyte replacement(To treat symptoms)

What stage is the infective stage of C. philippinensis?

• Infective larvae in freshwater fish

Strongyloides stercoralis

• Thai name

• Classification

• Key characteristics

• Diseases

• Diagnostic stage

• พยาธิเส้นด้าย

• Nematode(A kind of helminth)

• Short buccal cavity(aka cavity before esophagus starts, large genital primordium(future repro. system)

• Strongyloidiasis

• Rhabditiform larvae(Larvae because eggs hatch super fast)

Strongyloides stercoralis life cycle

• Direct life cycle: Larvae penetrate human skin(like thru feet) where they enter the bloodstream to the lungs where they’re coughed up, then swallowed to intestines and grow into females who burrow in the mucosa and produce w/o needing a male. Then, those eggs hatch immediately, becoming Rhabditiform larva who get passed out in feces

• Indirect life cycle: Rhabditiform forms develop into free living males and females who mate in the soil, producing more rhabditiform larvae and will become filariform to enter hosts

• HOWEVER, these rhabditiform forms can become filariform while in the colon, and enter the skin again, go to the lungs, and get coughed and swallowed to continue the cycle(and can get out of hand in immunocompromised people)

Uncomplicated strongyloidiasis symptoms:

ACUTE SYMPTOMS

• Rash at entry site

• Coughing and wheezing due to entry of larva to lungs

• Nausea/diarrhea: Burrowing of larva causes inflammation

• Vomitting/abdominal pain: Due to the irritation/inflammation

CHRONIC SYMPTOMS

• Larva currens: An itchy, rapid moving skin rash

• Vomitting/abdominal pain: Due to the irritation/inflammation

Severe strongyloidiasis caused in who and causes what symptoms?

• In IMMUNOCOMPROMISED

• Hyperinfection syndrome: Pneumonia due to massive amount of worms in gut-lung cycle, causing cough, shortness of breath, asthma-like presentations.

• Disseminated strongyloidiasis: The parasites themselves can cause meningitis and other inflammation, but they also carry bacteria like E. coli who can then cause the meningitis or sepsis

Strongyloides stercoralis treatment

• Ivermectin, wearing shoes, disposing waste properly

Taenia solium and saginata

• Casual and Thai name

• Classification

• Transmission

• Key characteristics

• Diseases

• Tapeworm/ตืดหมู/ตืดวัว

• Tapeworm aka Cestode, a type of flat worm, which is a type of Helminth

• Food-borne

• Flat, long and segmented

• Intestinal Taeniasis, Cysticercosis

Differentiate T. solium and saginata via head

• Solium will have a beak-like rostellum and hooks while saginata doesn’t. Both have suckers though.

Gravid proglottid

• What is it

• Purpose

• How we can use it

• Segments of the Taenia’s body. Mature ones are male and female and mate with themselves or other segments, but Gravid proglottids are the oldest ones at the end of the tail

• Gravid means pregnant, with the male organs gone, and can break off and get passed via stool

• One gravid proglottid of a Taenia solium will have 15-20 pairs of lateral branches while saginata will have 7-13

Egg form of Taenia solium/saginata

• Pretty circular with a thick, darker radiate(has radial striations) shell, and hooklets can be seen within the oncosphere

• Unable to tell solium and saginata in egg phase

Taenia solium life cycle

• Normal: The tapeworm eggs are passed from the definitive host(humans), and into water or soil that pigs eat. The oncosphere hatches in the pig and travels to the muscles, becoming a cysticercus until a human eats the pig, where the cysticercus dissolves and the Taenia attaches to the gut and grows

• Cysticercosis: If humans somehow ingest the eggs directly like contaminated vegetables or poor hand hygiene, the eggs hatch in the stomach and enter the bloodstream, traveling to the brain, eyes, and muscles(seizures, intracranial pressure, blindness, lumps)

Taenia saginata life cycle

• The same as the normal life cycle of Taeniae solium, but with the cow as the intermediate host

Taeniasis symptoms

• Asymptomatic

• Chronic abdominal pain

• Abdominal distention

Taenia solium/saginata medicine

Praziquantel

Opisthorchis viverrini

• Casual and Thai name

• Classification

• Key characteristics

• Diseases

• Intestinal fluke/ใบไม้ตับ

• Fluke, aka a Trematode, which is a type of flat worm, which is a helminth

• The adult is lancet shaped, with the internal organs visible, glands on the sides of the body with 2 lobular testes as the end of the body

• Opisthorchiasis(w link to cancer)

Opisthorchis viverrini egg form

• Lightbulb shaped with a knob at the bottom, an operculum/lid-like top, with 2 “shoulders”

Opisthorchis viverrini life cycle

• The egg is released via feces of the definitive host(humans) or reservoir hosts(dogs and cats), but the eggs won’t hatch until eaten by a freshwater snail(หอยไซ) where it grows into larva called cercariae, where they swim and find fresh water fish(the 2nd intermediate host) and encase themselves in a cyst, becoming metacercaria, which is the infective stage for humans. Now, if humans eat these fish raw, the fluke swims up the Ampulla of Vater and into the bile ducts of the liver where it lays eggs.

Opisthorchiasis

• Asymptomatic

• RUQ pain due to the presence of the worms causing cholangitis

  • This constant cholangitis can lead to cholangiocarcinoma due to constant division and oxidative stress damaging DNA

• The scarring(or if worm count is super high) can block bile flow and cause jaundice

Opisthorchis viverrini is treated by

Praziquantel

How are intestinal protozoa classified?

• Via the organelle they use to move: Amoeba, flagellate, ciliate, sporozoa

Giardia lamblia

• Classification

• Found in

• Stages

• Characteristics

• A flagellate protozoa

• Found in contaminated soil, food, water

• Cyst and trophozoite

• In trophozoite form; shaped with 4 flagella and 2 nuclei, look like spongebob jellyfish

• In cyst form; oval shaped with 2-4 nuclei and 2 median bodies

Giardia lamblia life cycle

• Starts via ingestion of the cyst form and is the infective stage. The stomach acid allows it to open up at the small intestine and it breaks open into 2 trophozoites which are the active form(This process is called excystation). Then they attach to the wall, seal themselves in and start reproducing via binary fission. However, some of the trophozoites are carried to the LI and become cyst form(Encystation)before getting shed. That’s why we only see cyst form in stool

Giardiasis

• Water diarrhea: Microvilli blunting which prevents us from absorbing sugars → Osmosis follows them out into the lumen

• Steatorrhea → Giardia consumes bile salts, decreasing our ability to break down fats → Greasy and floating shit

• Gas, abdominal cramps → Sugar and fats not absorbed so it reaches the large intestine where the bacteria ferment them → Massive amounts of gas

• Nausea/vomiting → Irritation

• Malabsorption of Vitamin A, B12, and lactose: Vitamin A is fat soluble, Vitamin B12 is absorbed at the ileum, lactase enzymes get destroyed at the brush border

Giardia lamblia treatment

Systemic: ***Metronidazole, tinidazole

Luminal: Paromomycin, nitrazoxanide

What type of parasite(and what type of that type) are Cryptosporidium spp, Cyclospora cayetanensis, Cystoisospora belli?

Protozoa, Sporozoa

What is Microsporidia?

A fungus

Where do these 4 live, and what can they cause in patients?

In the small intestine, causing chronic watery diarrhea in immunocompromised patients

Cryptosporidium spp.

• Classification

• Microscope morphology

• Pathogenesis

• Disease

• Lab test to find

• Sporozoa type of protozoa

• Oocyst form: Small circles with 4 sporozoites inside(should be crescent shaped but irl it’s hard to see)

• Invades epithelial cells intracellularly but extracytoplasmically

• Cryptosporidiosis causes acute watery diarrhea in imm.competent, but can cause fever, resp/biliary tract infections along w chronic watery diarrhea in imm.compromsied patients

• Mod. acid fast stain

Cryptosporidium spp life cycle

• Humans ingest a thick-walled oocyst often found in places like swimming pools, these oocysts contain 4 sporozoites who get released at the small intestine and become their trophozoite form that becomes a type I meront that can divide into 6-8 merozoites which will mature and continue the cycle. Meanwhile, some merozoites will stop dividing and will become male and female, reproducing to make oocysts, with thin-walled ones hatching in the small intestine(auto-infection) and others being released in feces

Cyclospora cayetanensis

• Classification

• Microscope morphology

• Pathogenesis

• Disease

• Lab test to find

• Sporozoa type of protozoa

• Unsporulated oocyst: Circular with “bubbles inside”

• Also uses sporozoites like Cryptosporidium, but no auto-infection

• Cyclosporosis: Acute/chronic watery diarrhea in competent hosts, chronic watery diarrhea along w fever and vomitting and nausea in compromised hosts

• Mod. AF test

Cyclospora cayetanensis life cycle

• Humans poop out the oocyst in unsporulated form, and it grows into the sporulated(infective stage) form in vegetables and we ingest them, allowing them to get to the small intestine where they use the sporozoites to drill in to start reproducing(sexually and asexually)

Cyclospora caytanensis treatment

• TMP SMX

Cystoisospora belli

• Classification

• Microscope morphology

• Pathogenesis

• Disease

• Lab test to find

• Sporozoa type of protozoa

• Oval shape with 2 sporoblasts inside

• Also causes villous atrophy like the previous 2, invading the epithelial cells of the small intestine

• Cystoisosporiasis: Acute/chronic watery diarrhea in competent hosts, chronic watery diarrhea along w fever and vomitting and nausea in compromised hosts

• Mod. AF stain

Cystoisospora belli life cycle

• Humans poop out the oocyst in unsporulated form(oval with 1 sporoblast) and it grows into the sporulated(infective stage with 2 sporoblasts) form in soil or water, and we ingest them, allowing them to get to the small intestine where they break open and use the sporozoites to drill in to start reproducing(sexually and asexually)

Cystoisopsora treatment

TMP-SMX

Microsporidia

• Classification

• Microscope morphology

• Life cycle and pathology

• Disease

• Obligate intracellular fungi

• Oval-like with a band inside

• Exists in spores outside, and when consumed, will drill into our cells at the small intestine and lives inside

• Microsporidiosis causes watery diarrhea but it can also cause keratoconjunctivitis

Microsporidia treatment

Albendazole

Bloody stool often indicates…

• An invasive agent

What would fresh blood indicate vs old?

• Bacteria vs protozoa

Entamoeba histolytica

• Classification

• Forms & their morphology

• Disease

• An amoeba type of protozoa

• Trophozoite form is ireggularly shaped with a vesicular nucleus with a central karyosome and ingested RBCs in the cytoplasm while the cyst form is circular shaped with 1-4 nuclei and a chromatoidal body shaped like a cigar

• Amebiasis: Can be intestinal, causing bloody and mucousy diarrhea with tenesmus, but can also get to extraintestinal locations but rare

Entamoeba histolytica life cycle

• The cyst form is passed in the stool, contaminating water, food, or soil. A human swallows the mature form(that has 4 nuclei) and in the small inestine, excystation happens which releases the trophozoites. These go to the large intestine and multiply by binary fission, eating the cells and forming flask shaped ulcers(and if it eats enough it can reach the bloodstream and get to the liver, creating abscesses and creating “anchovy paste” The ones who don’t get it will encyst and get released with the feces.

Ascaris lumbricoides

• Classification

• Thai name

• Morphology

• Diseases

• Helminth, specifically a roundworm

• พยาธิไส้เดือน

• In the mature form, females are larger than males with a straight, conical tail while the male has a hook-like posterior end, and both sexes have a 3 lipped mouth

• In the egg form, it can be fertilized, where it’s 3 layered, ตะปุ่มตะป่ํา, with a clear inner embryo. The unfertilized form is uninfective but indicates the presence of a female, and inside appears disorganized and the shell is much more oval like. Finally, a decorticated egg is a fertilized egg without the outer shell but it’s the same thing

• Ascariasis

Ascaris lumbricoides life cycle and pathology

• Fertilized Ascaris eggs are passed in feces, where they mature to second stage larva(L2) in soil, and these get ingested via dirty hands to mouth or soil-contaminated vegetables, and the eggs hatch in the small intestine where they penetrate the wall and can get to the portal vein and go to the liver, then even get to the heart and then the lungs. Once they do, they break through the alveolar walls, growing to L3, and causing coughs. When the infected human coughs and swallows, the Ascaris is swalloed and get’s back in to the small intestine, growing into the large worms

Ascariasis phases

1. Respiratory(Loeffler’s Syndrome): Cough, wheezing, and dyspnea to go with fever + eosinophilia due to the larvae in the lung tissue

2. Intestinal: If there are many worms, they can physically cause pain, distention, trigger vomiting, and even steal vitamin A and stunt growth in children, or at worst, literally block the intestine

3. In conditions like fever or taking drugs, the worms move to a “better” spot, which could be the CBD(Causing jaundice) or the pancreas(Pancreatitis) or intestinal perforation and peritonitis

Ascaris lumbricoides treatment

• Albenadzole

• Mebendazole

Hookworms

• Classification

• Thai name

• Which one is more common in Thailand, which one isn’t?

• Helminths, specifically Nematodes(Roundworms)

• พย่าธิปากคอ

• Necator americanus while Ancylostoma duodenale isn’t that prevalent

Hookworm morphology

• Adult: Their front ends are curved, looking like a hook; A. duodenale has 2 pairs of ventral teeth while N. americanus has cutting plates

• Egg and larva: The egg is oval, colorless, with a gap between cell membrane and the oval clump of egg inside. Meanwhile the rhabditiform larva is thicker with a long buccal cavity(unlike strongyloides) and the filariform one is thinner with a pointed tail

Hookworm life cycle and pathology

• Their eggs are passed in stool, where they grow into Rhabditiform larva in soil, then becoming the filariform(L3) larvae, the infective stage. It penetrates the skin of people walking barefoot, and do the same as Ascaris: travel via blood to lungs, get coughed up and swallowed, ending at the small intestine where they drink our blood

Hookworm infections cause…

• Redness, maculopapular rash and itching called a ground itch due to them entering the skin

• Pulmonary phase can cause bronchitis, pneumonitis

• When they get to the intestines, they can cause anemia, hypoproteinemia, etc.

Hookworm infection

• Albendazole

• Mebendazole

Trichuris trichiura

• Classification

• Thai name

• Morphology

• Nematode/Roundworm, part of the helminth family

• พยาธิแส้ม้า

• The adult has a thick, whip-like tail while the head is coiled and thin, while the egg is barrel-shaped with bipolar mucoid plugs

Trichuris trichiura lifecycle + disease pathology

• Excreted in the feces in unembryonated egg form and grow in the soil, gets ingested via contaminated food/water or finger-mouth contact, and hatch in the small intestine and move to the large intestine, sticking their thin anterior end into the mucosal lining, causing Trichuriasis

• Trichuriasis can be asymptomatic but also cause pain, diarrhea with mucus, and can be bloody or even cause rectal prolapse

Trichuris trichiura treatment

• Albendazole

• Mebendazole

Enterobius vermicularis

• Classification

• Common and Thai name

• Morphology

• Nematode, a type of Helminth

• Pinworm or พยาธิเข็มหมุด

• The adult form is spindle-shaped with a rhabditiform esophagus(sometimes called bulbous due to the large posterior end) with a cephalic alae. The egg form is D-shaped w the embryo inside

Enterobius vermicularis life cycle

• Adult females will move from the large intestine and go to the perianal area, depositing the eggs, using a gelatinous substance which can cause pruritus ani(nighttime itching). The egg becomes infective within a matter of hours, and when the host(like a child) itches the area, they get under the fingernails, then gets in the body whenever the host touches their mouth(but the eggs can also fall onto stuff in the house and even get inhaled). Then they hatch in the small intestine and then move to the large intestine, and doesn’t go into blood or anything. However, some eggs hatch at the perianal area and just crawl back in, called retroinfection

Enterobiasis symptoms

• Pruritus ani

• Vulvovaginitis

• Insomnia, irritability

• Abdominal pain and anorexia

Enterobius vermicularis tests and treatments

• Scotch tape/paddle test

• Albendazole, Mebendazole, Pyrantel pamoate done for all household members