Lecture 4: Approach to Understanding Parasites Flashcards
What are parasitic organisms
- Organisms that live on or in another organism (host) and derives a benefit and/or nutrients at the expense of the host
- Acquired as a result of a bite (tick, mosquitoes); contaminated water, contaminated environment (bed bugs etc…) or contaminated food
2 types of parasites
- Exoparasite: lives on the host and causes an infestation
- Lives in the host and causes an infection
Examples of exo(ecto) parasites
- Scabies
- Body Louse
- Head Lice
- Pubic Lice (head lice)
2 Parasitic life cycles
- Direct Life Cycle
- Complex/indirect life cycle
What is the Direct Life Cycle
The entire lifecycle is completed in one host.
Control is easier.
Eggs often only viable for a short time in the environment.
What is the complex/indirect life cycle
The life cycle is completed in more than one host.
Control of the parasite is often much more difficult.
Examples include: Malaria, Lyme Disease
Classifying single celled parasites
Parasites -> Single celled -> Protozoa -> Intestinal or Blood and Tissue
Classifying multicellular parasites
Parasites -> Multicellular -> Helminths -> Cestodes (flatworms) or Trematodes (flukes) or Nematodes (roundworms)
Name all 5 Types of Protozoa: Intestinal Protozoa
- Entamoeba histolytica
- Giardia lamblia
- Cyclospora cayetanensis
- Dientamoeba fragilis
- Cryptosporidium parvum
Intestinal Protozoa: Entamoeba histolytica
Major pathogen associated with poor sanitation
Intestinal Protozoa: Giardia lamblia
“Beaver Fever” associated with contaminated H20
Intestinal Protozoa: Cyclospora cayetanensis
Contaminated water and produce exposed to contaminated water including raspberries, lettuce, fresh fruit, and vegetables.
Intestinal Protozoa: Dientamoeba fragilis
Ubiquitous and found in children worldwide. Transmitted person to person.
Intestinal Protozoa: Cryptosporidium parvum
Major outbreaks. Carried in cattle and other zoonosis. Can transmit human to human or from cattle.
Characteristics of Intestinal Protozoa
- 500 million cases/yr worldwide
- All of them have a direct lifecycle
- Route of transmission is typically via contaminated H20, food, or soil (indirect contact) and zoonosis (direct contact)
- Virulence factors include either production of toxins (watery diarrhea) or the ability to invade the GI epithelia (bloody diarrhea)
3 types of Protozoa: Blood/Tissue Protozoa
- Trichomonas vaginalis
- Plasmodium spp.
- Toxoplasma gondii
Blood/Tissue Protozoa: Trichomonas vaginalis
2-3 million infections/yr. Common sexually transmitted infection. Diagnosis is via a wet-prep and antigen detection.
Blood/Tissue Protozoa: Plasmodium spp.
Malaria ~ 3 million infections/yr. Transmission via anopheles mosquitoes.
Blood/Tissue Protozoa: Toxoplasma gondii
~ 60% of cats are infected and can infect other invertebrates. Human infection as a result of exposure to cat feces or uncooked meat.
What is Trichomonas vaginalis
- One of the most common sexually transmitted infection
- Most common complaint is vaginal discharge
- May be associated with urinary frequency and dysuria - cystitis observed in a small proportion of women
Malaria (Plasmodium spp.)
- Has 5 species; P. faliciparum, P. malariae, P. knowlesi, P vivax, P. ovale
- Over 3 million infections each yr, with almost a million deaths
- Transmitted by mosquitos (indirect life cycle) - sexually mature in the mosquito and asexual states in human red blood cells
- The mosquitos that transmit Malaria bite dusk to dawn so mosquito nets are other control measures work quite well
Look on lecture slides for image about the lifecycle
Lab diagnosis of Malaria Mechanisms
- Microscopy
- Molecular Detection
- Protein Detection
What is Protozoa: Toxoplasma gondii
- Complex life cycle with multiple hosts and environmental maturation
- Humans and other mammals are dead end hosts (doesn’t get transmitted onwards)
- Asymptomatic infections in immunocompetent hosts
- Serious clinical manifestations if acute infection during pregnancy - infects the baby in utero and lead to significant morbidity to the baby including deafness, microcephaly, meningitis, encephalitis, hydrocephalus, retinitis and even death
3 Types of Helminths: Cestodes (Tapeworms)
- Diphyllobothrium latum (fish)
- Tinea solium (pork)
- Tinea saginata (beef)
Cestodes: Taenea solium (Pork tapeworm)
- Multiple hosts
- Human gets teniasis is contaminated meat is ingested
- In the case of tinea solium - if the eggs in feces are ingested by humans they can migrate to different tissues including the eye, brain (neurocysticercosis), muscle and bone
(reason why some cultures won’t eat pork)
Cestodes: Taenea saginata (Beef tapeworm)
- Multiple hosts***** BIG DIFF.
- Human get Tenaisis if they ingest contaminated meat or are exposed to cattle faecal matter
- Does not develop tissue phase disease
Cestodes: Diphyllobothrium latum (Fish tapeworm)
- This is why you don’t fish out of Lake Ontario
- Complex life cycles with multiple hosts
- Crustaceans, fish, and humans
- Humans can transmit
- Can live outside a host in water
- But always looking for a host
3 types Helminths: Nematodes (Round worms)
- Ascaris lumbricoides
- Enterobius vermacularis
- Strongyloides stercoralaris
Helminths Nematodes (Round worms): Ascaris lumbricoides
- Contaminated food/water ingestion of eggs
- Largest worm, very rare
- Almost 1 billion people infected worldwide
- Eggs have to mature in the environment or several days
- Life of the worm is between 10 months and 2 years
- Sometimes they get lost
- You can have multiple worms
- It cannot reinfect you or transmit
- You swallow them, reach gut, they hatch, they migrate into the lungs, keeps coming up because it wants to be reswallowed
Helminths Nematodes (Round worms): Enterobius vermacularis
- Females come out at night lay their eggs outside the anus - very itchy
- Very common
- Transmission is from person to person via contaminated surfaces
- Often in day care centres
- Most common worm infection in North America
- Leads to intense anal itching and often is passed on person via faecal matter (after they itch their bum)
Helminths Nematodes (Roundworms): Strongyloides stercoralaris
- Very serious/most severe
- Contact with the environment
- Free larval forms found in contaminated soil
- Single cycle with only ONE host
- Can be free living
- Found in warm climates with beaches
- Symptoms of infections include dermatitis, swelling, itching, larva currens
- Immunocompromised individuals - can develop a hyper-infective syndrome - associated with 90% mortality
- The worm can cause autoinfection so can continue a cycle of infection for over 30 yrs
Name 2 types of Helminths: Trematodes
- Shistosoma species (blood flukes)
- Clonorchis sinensis (chinese liver fluke)
Trematodes: Shistosoma spp.
- Complex life cycle with > 1 host
- Includes an environmental stage with an intermediate host
- Found in tropical to semi tropical waters
- Burrow into the skin of humans when in contact with contaminated water
- Can be ingested
- One to bladder
- Other goes to gut
Trematodes: Clonorchis spp.
- Complex life cycle > 1 host
- Includes an environmental stage with an intermediate host
- Found in tropical to semi tropical waters
- Result of ingestion of contaminated or infected fish
- Easily treated
