Parasitology and pathogenesis of parasite infections Flashcards
What is a parasite?
A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host.
e.g may live in skin or blood
What are the three main classes of parasites?
Protozoa
Helminths
ectoparasites
What are protozoa?
How can they be transmitted?
Protozoa are microscopic, single-celled organisms that can be free-living or parasitic in nature
Able to multiply in humans allowing serious infections to develop from a single organism
Transmission:
- Protozoa living in human intestine can be transmitted by fecal-oral route
- Protozoa living in tissue
Protozoa are classified by mode of movement
What are the types of protozoa?
Amoeba e.g Entamoeba
Flagellates e.g Giardia, Leishmania
Ciliates e.g Balantidium
Sporoza – organisms whose adult stage is not motile e.g Plasmodium, Cryptosporidium
What are helminths?
What are the three main groups of helminths?
Helminths are large, multicellular organisms (Worms) generally visible to naked eye in adult stages.
In their adult form, helminths cannot multiply in humans
There are three main groups of helminths that are human parasites:
- Nermatodes
- Trematodes
- Cestodes
What are the medically important helminths - nermatodes?
Soil-transmitted helminths
- Ascaris lumbricoides
- Trichuris trichiura
- Hookwork Spp
- Enterobius vermicularis – itchy anal margin in young children
Filarial parasites
- Wuchereria bancrofti
- Loa loa
- Onchocerca volvulus
- Dracunculus medinensis
Others
- Toxocara canis/cati
- Trichinella spiralis
What are some examples of termatodes?
Schistosoma mansoni/haematobium/japonicum
Clonorchis sinensis
Fasciola hepatica
Paragonimus spp. - lung worm, transmitted through eating poorly cooked shrimps and crabs
What are some examples of cestodes?
Taenia saginata – cow tapeworm
Taenia solium – pig tape worm, not as long
Echinococcus granulosus - production of lesions in viscera composed of multiple cysts
What are ectoparasites?
Blood sucking arthropods suck as ticks, fleas, lice and mites that attach or burrow into skin and remain there for long periods of times e.g weeks to months
What are some medically important ectoparasites?
Mites
- Scabies
- Trombiculid
Ticks
- Hard
- Soft
Lice
- Pediculus humanus capitis
- Pediculus humanus humanus
- Pthirus pubis – pubic lice
Flies
- botflies
What are the two types of hosts of parasites?
Intermediate – host in which larval or asexual stages develop
Definitive – host in which adult of sexual stage occurs
What are the determinants of parasitic infections?
Depends on mode of transmission and opportunities for transmission
Faceo-oral route
Prevented by
- Household sanitation
- Access to clean water
- Personal hygiene behaviours
Food
Prevented by
- Animal husbandry
- Surveillance
- Regulations and government controls e.g of slaughter houses
Complex life cycles
- Distributions of vectors and intermediate/definitive hosts
Other factors determining opportunity for parasitic infections
- Education
- Government resources and level of human development
- Country-level and regional control programmes
- Availability of cheap and efficacious treatments
- Construction and building regulations e.g chagas
- Urban vs rural residence
- Environmental sanitation e.g proper sewage disposal
What is the acute phase od chagase disease?
Incubation period 1-2 weeks after bite
Up to months after transfusion
Can see trypanosomes in blood
What is the chronic phase of chagas disease?
Lifelong injection
Generally trypanosomes not detectable but often positive for parasite DNA
Seropositive
60-70% develop indeterminate chagas disease
Normal ECG and x rays
What is determinate chronic chagas disease?
Seropositive
30-40% of infected , occurs 10-30 years after infection
5-10% develop chronic chagas immediately after acute disease – sevre or end organ damage
What organs are affected by chornic chagas?
Heart, intestintal tract
- infect purkinje fibres causing fibrosis
- can cause arrthymias and damage to heart muscle, becomes thinner - heart doesn’t contract efficiently
digestive
- esophagus, rectum and sigmoid colon most affected
- persitalsis affected, causes enlagred colon due to impact faeces and constipation
Megacolon
- Presentation with constipation
Complications include
- Faecaloma
- Obstruction
- Sigmoid volvulus
- Ulceration
- perforation
What are the clinical forms of cutaneous leishmaniasis?
Ulcers on face
Plaque that expands before it breaks down then forms ulcer
In ulcer if you take sample you can see parasite under microscope
Scars, can give immunity
Or may get re-activation, new lesions forming around old scars
Diffuse cutaneous leishmaniasis, nodules are packed with amastigotes
Mucocutaneous leishmaniasis, occurs in people that have already been infected, 10-15 years they get nasal stuffiness and damage to tissue, may cause loss of nasal septum. Difficult to treat
What is the pathogenesis of cutaneous leishmaniasis?
Tissue damage caused by inflammatory response to presence of parasites in macrophages
Parasite killing by Th1 pro-inflammatory responses and macrophage killing
When does relapse of cutaneous leishmaniasis occur?
Occurs when there is alternation in immune response e.g change in Th1 vs immune regulation secondary to HIV, malnutrition may trigger relapse
- Mucocutaneous disease associated with strong but inadequate inflamatory response to parasites that have metastasised to mucosa
- Diffuse cutaneous leishmaniasis associated with uncontrolled parasite replication
- Recividans – recurrence of lesions at old ulcer site
