Intro to parasitology Flashcards
Parasitology
The study of parasites
Parasite
An organism living on or in, and at the expense, of another organism. This interaction is not always harmful, some are beneficial.
Parasitism
One organism is injured by activities of another.
Obligate parasite
A parasite that must always live in contact with a host. Malaria is a perfect example because it must be carrying out its life cycle either in the gut of a mosquito or in human cells
Facultative parasite
A parasite that can complete its life cycle in a free-living environment or, alternatively, that lives during part or all of its cycle within a host. Helminths are one example- they can mate in the intestinal tract
Endoparasite
Living within a host- tapeworms, chagas disease, malaria
Ectoparasite
Living outside the host (body surface)- fleas, lice, mites
Symbiosis
Member of different species of organisms living in close association with its host. You may not see any symptoms of infection. Usually, there is a nutritional benefit. An endosymbiont is a symbiont within the host. An ectosymbiont is a symbiont outside of the host
Commensalism
Beneficial to one partner and not problematic to the other (causes no harm). In a facultative association, both species live independently. In an obligatory association, one species must live in association of the partner
Mutualism
Beneficial relationship to both parasite and host organism. Some research suggests that having a parasite may reduce the inflammation caused by autoimmune diseases.
Protozoa
Single-celled eukaryote that are primarily unicellular, non photosynthetic and are further classified on their ability for movement (motility) – pseudopods, flagella, cilia
Sporozoa
A nonmotile protozoa
Trophozoites
The feeding, motile stage of protozoa
Cysts
Infectious stage of protozoa, highly condensed cytoplasm and thick cell wall
Karyosome
Concentrated clumps of chromatin material within the nucleus.
Peripheral chromatin
Non-active chromatin, providing the nucleus halo-like appearance.
Sporogony (microsporidia)
Productions of spores, asexual stage
Oocyst
A thick or thin-walled stage in the life cycle of coccidia, shed in feces in human infections
Proglottid
Tapeworm segments containing male and female reproductive systems; may be immature, mature or gravid. Proglottids can be around a half inch in length. Cestodes can have anywhere from one thousand to three thousand proglottids, and each proglottid is capable of producing eggs
Scolex
The head or attachment portion of a tapeworm; suckers or hooklets
Tachyzoite
Rapidly multiplying stage in development of tissue phase of Toxoplasma
Bradyzoite
Slowly multiplying trophozoite contained in the tissue cyst, chronic infection of Toxoplasma
Kinetoplast
Intensely staining rod or disk-shaped or spherical extranuclear DNA structure found in parasitic flagella near the base of the flagellum
Amastigote
Small round intracellular stage of Leishmania and Trypanosoma spp., base of flagella is anterior to the nucleus, no external flagellum
Promastigote
Development stage of Trypanosomes, the base of the flagellum is anterior to the nucleus, no undulating membrane
Trypanosome
A slender, flagellate protozoan found in the blood of humans; also called trypomastigote
How are protozoa classified?
Based on their ability to move
Sarcodina
Intestinal amebae
Mastigophora
Intestinal flagellates
Ciliophora
Intestinal ciliates
Plasmodium
Sporozoa from blood and tissue
Leishmania and Trypanosome
Flagellates from blood and tissue
Naegleria
Amebae from other body sites (outside the intestine)
Trichomonas
Flagellates from other body sites (outside the intestine and blood and tissue)
Toxoplasma
Coccidia from other body sites (outside the intestine)
Microsporidium
Microsporidia from other body sites (outside the intestine)
Classification of human parasites (3)
- Nematodes (roundworms)
- Cestodes (tapeworms)
- Trematodes (flukes)
Helminths
They are large, multicellular organisms (worms)- this term is broad and encompasses all worms. Includes nematode, cestode or trematode. Easily visible in adult stages (do not need microscope), although adults can’t multiply in humans due to their large size. Consuming a large ova burden can result in more worms being present in the body and more symptoms. Either free-living or parasitic in nature.
Nematodes (roundworms)
Unsegmented worms, bilateral symmetry, fully functioning digestive tract, long, cylindrical, mm to meter in length. They are very round and you may not see striations. Similar in morphology to an earthworm
Cestodes (tapeworms)
Ribbon-like body with a chain of segments/proglottids, contains both male and female reproductive systems, scolex allows for worm attachment to intestinal tissue. Proglottids are immature, mature or may be gravid (full of eggs). This category of worms is the largest. Cestodes can have anywhere from one thousand to three thousand proglottids and may even be able to produce one million eggs per day
Trematodes (flukes)
Flat, small worm with hooks (oral sucker), dorsoventrally flattened, all eggs are operculated (lid structure). Have a leaf-like morphology and are associated with biliary tract blockage. Adults worms have suckers that allow them to attach. Eggs are usually used for identification because they are found more easily in the stool- people generally do not purge the worms
Classification of Nematodes (3)
- Intestinal - Ascaris, Enterobius (pinworm), Trichuris (Whipworm)
- Tissue – Trichinella, Toxocara
- Blood & tissue – Wucheria, Loa- these worms are small
Classification of Cestodes (2)
- Intestinal – Diphyllobothrium, Taenia (associated with neurocysticercosis), Hymenolepis
- Tissue (larval form)– Taenia, Echinococcus
Classification of Trematodes (3)
- Intestinal - Fasciolopsis, Heterophyes heterophyes, Metagonimus yokogawai.
- Liver & lung – Clonorchis (Opisthorchis), Paragonimus
- Blood - Schistosoma
Common parasitic infections in the US (5)
Based on stool samples:
1. 3.8% Giardia (water contamination)
2. 2.7% Trichuris ova
3. 2.3% Ascaris ova
4. 1.6% Enterobius ova (probably higher as stool not best sample)
5. 0.6% Entamoeba
How many people in the US have parasitic infections?
Definitive numbers not available – estimates ~64 million in the US are infected based on NPI data. Multiple parasites are commonly found in those infected.
Problematic parasitic organisms outside of the US (4)
- Leishmaniasis
- Schistosomiasis (contaminated water)
- Helminths- ascaris is the most common- soil transmission
- Malaria- children most affected
Total estimated infected individuals - ~2 billion infected, which is about 30% of the world population
Notifiable parasitic disease in the US (6)
- Babesiosis (tick borne)
- Cryptosporidiosis (water associated)
- Cyclosporiasis (water and food associated)
- Giardiasis (water associated)
- Malaria (mosquito borne)
- Trichinellosis (Trichinosis- undercooked food)
NPI
Neglected Parasitic Infections. The CDC is most concerned with chagas disease, neurocysticercosis (cause of seizures), toxocariasis (cats and dogs), toxoplasmosis (cats, venison, improperly treated meat), and trichomoniasis
Risk factors for parasitic infections (4)
- Travel to or immigration from endemic areas
- Consumption of contaminated food or water- undercooked food or ice or water that was not appropriately heated
- Exposure to arthropod-mediated infection- protection by repellent products – DEET, mosquito netting, appropriate clothing.
- Swimming in fresh water, pools if inappropriate levels of chlorine.
Symptoms of parasitic infections
The most common symptoms are diarrheal disease (bloody or watery diarrhea, abdominal pain, bowel obstructions, belching or flatulence, and steatorrhea). Other symptoms include eosinophilia, skin rash or itching, hepatosplenomegaly or lymphadenopathy, jaundice,
urinary tract associated symptoms (increased frequency, dysuria, hematuria), inflammation of the lungs (cough, pain, eosinophilia), and fever, chills, night sweats, malaise, muscle pain
4 super-groups of human parasites
- Sar
- Excavata
- Amoebozoa
- Opisthokonta- contains all fungi, animals, and protists
Cryptosporidium parvum
One of the intestinal protozoa that is associated with contaminated drinking water. Part of the Sar super-group
Giardia duodenalis
Associated with contaminated freshwater. It is part of the normal flora of beavers and another animals. Part of the Excavata super-group
Amoebozoa super-group
Includes Entamoeba coli, mana, histolyticum, and others. Very few of these species are pathogenic. They are all found in the same environment and can therefore be difficult to identify. Contains genera with amoeboid locomotion and ciliated microorganisms
Transmission of disease (3 methods)
- No intermediate host- these infections are more problematic and are considered contagious as they spread from person to person
- One intermediate host- environmental exposures, like contaminated food
- Many intermediate hosts- these infections are more difficult to acquire
DALY
Disability adjusted life years, associated with people who are sick due to a parasitic infection.
Toxoplasmosis
The leading cause of foodborne illness and death. It can be associated with cats (cleaning the litter box) as well as venison or improperly treating meat. It can be very serious if a pregnant person is infected- associated with spontaneous abortion, neurological and birth defects in the fetus
Trichomoniasis
One of the most common STIs in the US. It is actually more problematic than gonorrhea and chlamydia
Most common laboratory method to detect parasites
A stool sample to do an ova (eggs of adult worms) and parasite examination. The sample are examined under the microscope using a wet mount. Preservatives are used to increase recovery of the parasites, since some organisms (like adult amoebas) may die or degrade quickly
Preservatives used for an O&P (4)
- Formalin
- PVA – polyvinyl alcohol
- SAF – sodium acetate-acetic acid formalin
- Schaudinn’s Fluid – PVA & mercuric chloride
Macroscopic analysis of stool
Visual determination of eggs, intact worms, proglottids (off white color), color determination
Microscopic analysis of stool
Wet mount is done to view under the microscope– either done directly or after concentration of sample. You are looking for motile (swimming) trophozoites, cysts, or helminth eggs. Can use a trichrome stain or modified acid-fast stains
Trichrome stains
Permanent stains, best for identification of protozoan trophozoites or cysts. Used for samples preserved with formalin or PVA
Acid-fast stains
Used to view the acid-fast oocysts produced by Cryptosporidium, Microsporidia and others
Specimens collected to diagnose parasites (6)
- Duodenal Aspirates & Sigmoidoscopy
- Cellophane Tape prep
- Urine, Vaginal, Urethral- especially done for trichomonas
- Blood
- CSF
- Others – tissues (look for worms), sputum, corneal scrapings, corneal biopsy, muscle
Duodenal Aspirates & Sigmoidoscopy samples
A wash of fluid is collected and immediately brought to the lab. Some parasites have a characteristic motility and can be diagnosed using this test. An enterotest can be done to check for motile trophozoites, trichrome for others. Uses a gel capsule attached to a string which the patient then swallows. When the string is removed, it is put in a tube with a vortex of fluid. The fluid is then examined under the microscope to view parasites. This is mainly done for Giardia
Cellophane tape prep
Done for Pinworm (Enterobius vermicularis) to collect the
1st morning collection of ova deposited in perianal area. Pinworm is the most common parasite found in children. At night, the adult female migrates out of the anus and deposits eggs in the perianal area. In the morning, the eggs hatch and the small worms migrate back into the anus and to the intestinal tract. This causes itching. Cellophane tape prep is a paddle with tape that is touched to the outside of the anus, ideally before the patient wakes up in the morning. The ova can be observed on the scotch tape in the lab
When are blood samples collected?
Thick and thin smears are done to diagnose malaria, babesia, or trypanosomes
When are CSF samples collected?
Samples are observed for amebic mobility in encephalitis patients. However, if an amoeba is present in the CSF, the patient will have almost no chance of survival
When are muscle biopsies done?
Biopsies can be done, typically of the large muscles of the calves or leg, to view encysted parasites. However, this is typically a last resort as serology or another method can be used first
Laboratory methods (4)
- Serology
- ELISA
- Molecular testing
- Direct fluorescent antibody (DFA) Techniques
Serology testing
IgM (acute phase) and IgG (recovery). Not helpful in populations with endemic exposures since everyone has been exposed and will test positive. This type of testing is
helpful for travelers
ELISA
FDA has given approval of malaria ELISA kit (whole blood), and ELISA is becoming a more popular method of diagnosis. Used for detection of parasitic antigens, which confirms current infection. It is the preferred method for commonly isolated parasites in the US, like Giardia, Cryptosporidium, and Entamoeba histolytica. Also utilized for Toxoplasmosis, Chaga’s Disease, Leishmaniasis, Schitosomiasis, Echinococcosis, Trichinellosis, Filariasis
Molecular testing
This method has become more common over time in order to diagnose the common parasitic organisms. NAAT - Cryptosporidium, Giardia, Trichimonas, E. histolytica – FDA approved. BioFire parasite detection identifies Cryptosporidium, Cyclospora, Entamoeba histolytica, Giardia
Direct fluorescent antibody (DFA) Techniques
Becoming outdated but still used for Cryptosporidium or Giardia sometimes. However, there are better and faster ways to diagnose these parasites
Antihelminthic treatment
2/3 of world population live in conditions where parasite exposure and infection avoidance is impossible, so drugs are necessary. Most common target of these drugs is the helminth neuromuscular system. 3 groups of drugs cover all human infections – albendazole, praziquantel, ivermectin. There are few treatment options available
due to poor efficacy and safety, and some infections are untreatable. Giardia may also be able to be treated with an antibacterial agent
Benzimidazoles
Includes Albendazole, mebendazole. Only administered orally. These drugs are well tolerated but may cause nausea or vomiting. Main mechanisms are stopping cell division and reducing ATP stores of the organism
Benzimidazoles mode of action
Binds to nematode ß-tubulin, inhibiting polymerization of the tubulin and preventing the formation of microtubules. This causes the inhibition of cell division. These drugs also cause impaired uptake of glucose, leading to depletion of glycogen and reduced stores of ATP. Can stimulate Ascaris worms to emerge from mouth and nostrils, patients should be forewarned.
Pyrazinoisoquinolones
Includes Praziquantel, delivered orally only. This drug is well tolerated
Pyrazinoisoquinolones mode of action
Disrupts calcium ion homeostasis in the worm, antagonizing voltage-gated calcium channels. This results in uncontrolled calcium ion influx, leading to uncontrolled muscle contraction and paralysis- can cause the worm to detach from the tissue. Exposes schistosome antigens at the parasite surface. The binding site for the drug remains to be identified
Macrocyclic lactones
Includes Ivermectin and doramectin. Delivery can be topical, oral (most common), or even IV. These drugs are generally well tolerated but may cause neurotoxicity (confusion, ataxia, coma)
Macrocyclic lactones mode of action
Binds to glutamate-activated chloride channels existing in nerve or muscle cells of nematode causing hyperpolarization of nerve or muscle cells by increasing permeability of chloride ion through the cell membrane, parasites are paralyzed to death.
