In what 5 situations would you suspect parasites in the eye/appendages? Explain each if applicable (6).
Infection in contact lens users
- not responding to antibiotics
- poor/doubtful CL hygiene
Immunocompromised patients
-malignancy, HIV, steroids etc
Returning traveller/migrant from a developing country
- insect bites
- swam in a river/lake
- consumed exotic raw/undercooked food
zoonosis: contact with animals/faeces
- poor/doubtful hygiene
Sexual partner has similar lesions (including around the genitals)
Define parasitism.
A living organism living in/on another living organism, gaining benefit at the expense of the host.
Define commensalism.
Living in/on a host with no harm to the host.
Define symbiosis.
Two mutual orgnaisms gaining benefit from one another, where both are dependent on one another.
Are parasites necessarily micro-organisms?
No, they can be in the animal kingdom as well.
Briefly describe the classification of parasites, including uni/multicellular forms (3).
Unicellular - protozoa
Multicellular - metazoa
-helminths (worms)
-arthropods (insects)
Define definitive host.
Carrier of adult or sexual stage of the parasite
Define intermediate host.
Carrier of all or part of the larval or asexual stage of the parasite
Can there be multiple intermediate hosts or is the limit just one?
Sometimes there are two
Define incidental/accidental host.
Host is not necessarily for the parasite’s survival
Define reservoir/natural host.
Animals which normally harbour the parasite and are part of its life-cycle
Define the two types of vectors.
Biological - in which part of the life cycle is passed
Mechanical - life cycle is not passed
What are the usual vectors for parasites?
Arthropods
What is the taxonomy of acanthamoeba?
Unicellular protozoa - a soil amoeba.
What structure of the eye does acanthamoeba infect?
The cornea
How is acanthamoeba transmitted?
Poor contact lens hygiene
Name 5 symptoms of an acanthamoeba infection.
Irritation Pain Photophobia Blurry vision (leading to blindness) Conjunctivitis
Name two secondary complications of an acanthamoeba infection.
Ulceration
Bacterial infection
What are two ways to diagnose an acanthamoeba infection (laboratory)?
Demo of amoeba in corneal scrapings
Culture on non-nutrient agar
In what two ways can an acanthamoeba infection be treated (3)?
Surgical debridement ± keratoplasty
Complex medical topical therapy
Do all amoeba cause keratitis?
No
Do all amoeba infection require extensive surgical care?
No, some just require changing lens and paying more attention to CL hygiene.
What is the taxonomy of toxoplasma gondii?
A small intracellular protozoa
How is toxoplasma gondii transmitted (2)?
Contact with cats, especially kittens
Eating undercooked meat
What is the definitive host (and possible other intermediate hosts) of toxoplasma gondii?
Cats/kittens the definitive host
Many species of animals that humans eat are intermediates
What are two clinical presentations of congenitcal toxoplasma gondii?
Severe foetal disease
Chorioretinitis (late in life)
What is a clinical presentation of acquired toxoplasma gondii in an immunocompetent patient? What does it depend on?
Usually asymptomatic and depends on the position.
Do toxoplasma gondii cysts persist for life?
They might
Describe 5 ways to diagnose toxoplasma gondii and describe it if possible, whether it is in use or not, and name the main way it is done.
Serology - rise in titr of IgG and IgM Histopathology of tissue Culture - tedious and not done PCR - tissue/vitreous - mainstay Foetal infection - PCR on amniotic fluid/foetal blood
How is congenital toxoplasma gondii infection treated (2)?
Termination (especially if 1st or 2nd trimester)
Spiramycin to the mother (difficult to get)
How is a reactivated toxoplasma gondii infection treated (3)?
Pyrimethamine + sulphadiazine + prednisolone
If you suspect an infection to be toxoplasma gondii, and the patient presents with nystagmus, what does this suggest?
It may be congenital
What is the scientific name for pig tape worm?
Taenia solium
How is taenia solium transmitted?
Ingestion of eggs shed by a human tapeworm carrier
How do individuals infected with taenia solium present? Comment on the state of their eyes, and name two conditions they might have.
Usually present in skeletal muscles with no symptoms
Eyes are rarely involed
May present with a scotoma, space occupying lesion, or cyst
In what two ways can taenia solium be diagnosed?
Radiology and serology
How is a taenia solium infection treated and what does it depend on?
Treatment is either surgical and/or with praziquantel or albendazole + steroids
It depends on the location of the lesion
List 5 regions of the eye that ocular cysticercosis can occur.
Orbital tissue Subconjunctiva Anterior chamber Subretinal space Vitreous
What is the scientific name for dog round worm?
Toxocara canis
How is toxocara canis transmitted?
Accidental infection by larvae entering through the skin
What does the severity of a toxocara canis infection depend on?
The site where it deposits
What are two clinical presentations of a toxocara canis infection?
Retino-choroiditis
Granuloma resembling a tumour
How can a toxocara canis infection be diagnosed?
Serology
Is there a high incidence of filarial worm infection in australia? Explain.
No, due to the heart worm control program
What is phthirus pubis and what 4 regions of the body can they infest?
An arthropod that can infect pubic, axillary, truncal hair, and eyelashes.
How is phthirus pubis transmitted.
Person to person by direct contact
Is a phthirus pubis an STI?
Yesd
List two symptoms of phthirus pubis.
Pruritis
Macules/papules with excoriation
How can phthirus pubis be diagnosed?
Demonstration of lice or eggs (stuck to hair)
Name three treatment options for phthirus pubis.
1% permethrin to all hair-bearing areas except the eyes
Eyelashes - remove with forceps
Clothes and bed linen - hot wash
Give thetwo examples of eyelash mites.
Demodex folliculorum
Demodex brevis
How are eyelash mites transmitted.
Person to person contact
What four conditions might someone with eyelash mites present with?
Folliculitis
Blepharitis
Blepharo-conjunctivitis
Corneal lesions
How can eyelash mites be diagnosed.
Demonstration of mites in skin scrapings or a biopsy
List three treatment options for eyelash mites.
Topical tea tree oil/ointment for skin only
Ivemrectin - single dose
Oral doxycycline for secondary bacteria (symbionts)
What is the scientific name of an itch mite?
Sarcoptes scabei
How are itch mites transmitted (2).
Person to person - bad hygiene
Sexual contact
List three symptoms of an itch mite infestation.
Severe pruritis
Erythematous papules
Crusted nodules/plaques
How can itch mites be diagnosed?
Demonstration of mites, eggs, or faecal pellets
Name four treatment options for itch mites.
Topical 5% permethrin from head to toe except the face
Ivermectin orally
Treat close contacts
Hot wash, including clothes and bed linen