Infections of the Eye Flashcards
1
Q
What does Staphylococcus Aureus affect?
A
The eyelids
2
Q
What’s an example of an eyelid infection?
A
Staphylococci
3
Q
Where does Staphylococcus Aureus mulitply?
A
In the hair follicles of the eye lashes
4
Q
What are some features of Staphyloccus Aureus?
A
- Multiplies in hair follicles (eye lashes)
- Can produce infection and swelling of the eyelid known as a STYE
- If touched like a solid mass
- Can be opened with a scalpel – will release pus and a core (a white pea-like mass)
- Likely go away over time
- However, a persistent infection sees extended pathology – Blepharitis
- Edges of eyelids become red and swollen
Staph itself is found on the skin all of the time
5
Q
What are the symptoms of Staphylococci?
A
Can produce infection and swelling of the eyelid known as a STYE
6
Q
Can Staphylococci Aureus get worse?
A
Yes - a persistent infection leads to blepharitis (edges of eyelids become red & swollen)
7
Q
How do we view Staphylococci bacteria?
A
Pus from lesion on slide then Gram stained and visualised by microscopy
8
Q
What type of infection is Staphylococci?
A
Bacterial
9
Q
How does Staphylococci look on microscopy?
A
- Numerous polymorphonuclear (PMN) cells
Immune cells which kill and digest bacteria - Dead PMNs, tissue debris and bacteria produce pus
- Gram +ve cocci in clumps
Staphylococci
Looks like a “bunch of grapes”
10
Q
How does Staphylococci look on an agar plate?
A
- Start with confluent layer of bacteria
- Can produce single colonies
One bacteria starts, doubling every 20 minutes produces a colony
One colony ~1x109 bacteria - Staphylococci grow as pale, circular colonies on BcVod agar plates
Colonies with a yellow tinge – almost gold – Staphylococcus aureus
Staph growing with a yellow tinge is Staph Aureus (MRSA Staph; Aureus means “golden”) whereas when growing like the top plate it’s Staph Epidermadis which is the usual one found on the skin
11
Q
How do we differentiate staphylococcus aureus from less, or non-pathogenic species?
A
Staphylococcus aureus has properties which differentiate it from less or non-pathogenic species
12
Q
What does non-pathogenic staphylococci lack?
A
Non-pathogenic staphylococci lack invasive weaponry to cause disease
13
Q
What does pathogenic Staphylococcus Aureus produce?
A
Pathogenic Staphylococcus aureus produce toxins and enzymes (e.g. coagulase), which confer pathogenicity
14
Q
What is Coagulase an indictor of?
A
Coagulase is an indicator of the presence of other toxins and invasins in Staphylococci
15
Q
What does Staphylococcus Aureus, Epidermidis and Saprophyticus on tests of coagulase production, glucose fermentation or novobiocin sensitivity?
A
Staphylococci Aureus
- Coagulase production +ve
- Glucose fermentation +ve
- Novobiocin sensitivity +ve
Staphylococci Epidermidis
- Coagulase production -ve
- Glucose fermentation +ve
- Novobiocin sensitivity +ve
Staphylococci Saprophyticus
- Coagulase production -ve
- Glucose fermentation -ve
- Novobiocin sensitivity -ve
Staph aureus has 1 or more toxins or enzymes that allows it into the cells
16
Q
What is Coagulase?
A
Coagulase – enzyme which coagulates plasma
- Cleaves fibrinogen to fibrin
- If added to plasma it will clot
Coagulase test is best for determining the invasive versions of Staph = determines pathogenic species
17
Q
In Staphylococci what is the coagulant?
A
- Ball found in infected hair follicle is a coagulant
- If press on stye can express coagulant as one drop
- Once removed no need for further treatment – will heal
White core found in the stye is a coagulant – it produces coagulase around itself to protect itself which is why you get the pus around it
18
Q
How many people carry Staphylococci Aureus asymptomatically?
A
- 40% carry S. aureus asymptomatically
- Increases to 60% in hospital settings
19
Q
How is it easy to become a dispenser of Staphylococci even if previously asymptomatic?
A
Carriers can easily become dispensers
- Factors like having a cold etc. lead to spread
20
Q
Why is Whole Genome Sequencing useful?
A
- Rapid and cost-effective
- Search for specific changes in seven key genes
- Specific changes allow grouping of S. aureus isolates
21
Q
What are some types of conjunctivitis?
A
- Neisseria gonorrhoeae
- Haemophilus influenzae
- Staphylococcus aureus
- Pseudomonas aeruginosa
- Streptococcus pneumoniae
22
Q
What is Neisseria Gonorrhoeae?
A
A type of conjunctivitis causing bacteria (also the cause of STI gonorrhoeae)
A causative organism of gonorrhoea
23
Q
Why is prevalence of neisseria gonorrhoeae increasing?
A
Prevalence rising again due to antibiotic resistance
24
Q
What are the male symptoms of Neisseria Gonorrhoeae?
A
Male – extreme pain during urination, purulent discharge
25
What are the female symptoms of Neisseria Gonorrhoeae?
Female – can be aymptomatic
- Considered carriers (clinical perspective)
- Infection can increase without knowledge causing core pelvic disease
- If infection moves to fallopian tubes can lead to sterility
26
How can infection of Neisseria Gonorrhoeae be contracted at birth?
Infection contracted at birth from mother’s genital tract: occurs from 1-5 days of age
Fast acting infection for a bacterial infection
27
What type of infection is Neisseria Gonorrhoeae?
Hyperpurulent Infection
28
What does Neisseria Gonorrhoeae look like under a microscope?
Pus from the eye placed on a slide and Gram stained shows:
- Numerous pus cells
- Gram –ve diplococci occurring inside the pus cells (Neisseria)
29
How is Neisseria gonorrhoeae differentiated from other Neisseria?
By Biochemical Tests
30
How many members of the Neisseria Gonorrhoeae are considered pathogenic? How do we differentiate between them?
Two members of genus considered pathogenic - Gonorrhoeae & Meningitidis
Neisseria gonorrhoeae differentiated from other Neisseria by biochemical tests (with different types of sugars) using an API strip
31
How does BA, CA, Glucose, Maltose or Lactose look like in Neisseria Meningitidis, Gonorrhoeae and Lactamica (species of neisseria)?
N. meningitidis
BA +ve
CA +ve
Glucose +ve
Maltose +ve
Lactose -ve
N. gonorrhoeae
BA +ve
CA +ve
Glucose +ve
Maltose -ve
Lactose -ve
N. lactamica
BA (some haemolytic) +ve
CA +ve
Glucose +ve
Maltose +ve
Lactose +ve
32
What does Neisseria Gonorrhoeae look like on chocolate agar?
Neisseria grown on chocolate agar (boiled blood) shows small, white circular colonies
33
What treatment do we use in Neisseria Gonorrhoeae?
Used to treat with penicillin or chloramphenicol ointment or eye drops but quickly developed resistance so now recommend to give injection of ceftriaxone
34
If left untreated, what can Neisseria Gonorrhoeae lead to?
Rapidly required to stop irreversible vision impairment through corneal ulceration
35
What do we have to report Neisseria Gonorrhoeae to and how is it tested for antibiotic resistance?
- N. gonorrhoeae infections are reportable to PHE
- Isolate is tested for antibiotic resistance using E-test
36
What is Haemophilus a type of infection of?
Conjunctivitis
37
What age does Haemophilus Infleunzae occur?
Infection by Haemophilus influenzae can occur at any age, either sporadically or as an outbreak involving a number of persons
38
What is the causative agent from Haemophilus Influenza?
Originally thought to be isolated from influenza patients in the 20th century but actually a cause of secondary pneumonia leading from influenza
39
How does Haemophilus Influenza look under a microscope?
Pus from the infected eye placed on a slide and Gram stained:
- Pus cells
- Gram –ve rods, which are PLEOMORPHIC (some very short-like cocci and some long rod shaped)
Cocci means the circles
Rods are seen also
40
How does Haemophilus Influenza grow?
For growth Haemophilus requires Haematin (found in blood) and/or NAD+ produced by staphylococci (obtained from a supplied source)
Bacteria can’t break open the blood cells so on a gar need to do on chocolate agar plates or have other bacteria to open it (like staphylococci) and so haemophilus often grows around staphylococci
41
How does Haemophilus Influenza grow on blood agar?
Struggles to grow on blood agar, grows as satellite colonies around staphylococci (termed Satellitism)
- Haematin and NAD found within cells
- Heat blood agar to lyse cells, Haemophilus can grow
Where it doesn’t grow (in “zone in inhibition”) know the antibiotic works at XYZ level
42
What is Satellitism?
On blood agar, Haemophilus influenzae grow as satellite colonies around staphylococci
43
How many Haemophilus pathogenic species are there?
Three -
Influenzae
Parainfluenzae
Ducreyi
44
How do we identify the forms of Haemophilus that are pathogenic?
By Haematin and/or NAD+ requirement
45
Does Haemophilus Influenzae, Parainfluenzae and Ducreyi present in terms of X (haematin) or V (NAD+)?
Haemophilus Influenzae
X = +ve
V = +ve
Haemophilus Parainfluenzae
X = -ve
V = +ve
Haemophilus Ducreyi
X = +ve
V = -ve
46
What is X & V referring to when determining haemophilus pathogenic species?
X = Haematin
V = NAD+
47
What is 'sticky-eye'?
‘Sticky-eye’ infection in neonates due to Staphylococcus is a conjunctivitis that occurs 5 - 10 days after birth
Introduction of bacteria from patient’s nose or skin by fingers
48
What is Staphylococci a form of?
Conjunctivitis
49
How do we treat staphylococci?
Treat with appropriate antibiotics as infecting agent is commonly resistant to some antibiotics
50
What is a critical issue in Staphylococci?
Resistance is now a critical issue
- Emergence of MRSA and now VRSA
- Rapidly running out of effective antibiotics
51
What is Pseudomonas Aeruginosa a form of?
Conjunctivitis but it is not an invasive pathogen
52
Where is Pseudomonas Aeruginosa commonly found?
Commonly found in soil and water (baths/sinks/toilets/eye drops/soap dishes)
53
How does one get infected with Pseudomonas Aeruginosa?
Can infect the eye after trauma
- Eye surgery, presence of a foreign body or suppressed immune status within the patient
- Contact lens
54
What does Pseudomonas Aeruginosa look like under a microscope?
Accumulation of infected pus containing Gram –ve, rod-shaped bacteria
55
What does Pseudomonas Aeruginosa look like when grown on a simple nutrient agar?
When grown on simple nutrient agar, produce a blue green fluorescent pigment – only bacteria with this property
56
What bacteria is the only one to have the property of producing a blue-green fluorescent pigment when grown on a simple nutrient?
Pseudomonas Aeruginosa
57
How do we treat Pseudomonas Aeruginosa?
Difficult to treat as it has innate resistance to a wide range of antibiotics – environmental bacteria
Best treatment is prevention
Elimination or control of potential sources on wards, theatres and outpatient departments
58
What is Streptococcus Pneumoniae an type of?
Conjunctivitis
59
What can Streptococcus Pneumoniae cause?
Streptococcus pneumoniae can cause pneumonia or meningitis as well as keratitis (inflammation of the cornea) either following injury or by invasion
- Asymptomatic carriage in the throat
- Traversal to lungs causes pneumonia
- Keratitis is introduced from the throat (coughs or fingers)
60
How do we get pneumonia from Streptococcus Pneumoniae?
Traversal to lungs causes pneumonia
61
What is a symptom of Streptococcus Pneumoniae?
Accumulation of pus
62
What does Streptococcus Pneumoniae look like under a microscope?
Pus on slide, Gram stained and viewed by microscopy:
- Pus cells
- Gram +ve
63
What is Diplococci?
A bacterium that occurs as pairs of cocci
64
What does Diplococci look like in Streptococcus Pneumoniae?
- Surrounded by clear, unstained space which mark the presence of capsule
- Capsule allows bacteria to invade tissues and resist phagocytosis
Capsule allows bacteria to invade tissues and resist phagocytosis and to attach directly to your cells
65
How does Streptococcus Pneumoniae grow on agar plate?
- Loss of capsule --> loss of virulence
- Colonisation of body leads to a re-established capsule
Grown on blood agar and in the presence of optochin
66
What do colonies on Streptococcus Pneumoniae show on agar plates?
Colonies show α-haemolysis
- Hydrogen peroxide produced by bacteria, oxidises haemoglobin, blood cells turn green beneath bacteria
- Blood cell is fragile and may lyse thinning blood around the bacterial colony
Able to break open red blood cells through the production of hydrogen peroxide and affects the iron in your haemoglobin = fragile and turn green
67
What does sensitivity to optochin allow for in streptococcus pneumoniae?
Sensitivity to optochin allows for specific identification
- Other Streptococci resistant
68
What is Streptococcus Pneumoniae sensitive to?
Penicillins
69
What is Leptospira?
An inner eye infection
70
What is Leptospira common in?
Common infection of rats
- Systemic infection of the rat, excreted in faeces and urine and, due to the proximity of rats to water this often means water sources are colonised
71
How does one get infected with Leptospira?
- Swimming in contaminated water can lead to infection
- Swallowing of water, contamination of mucous membranes or through breaks in the skin
72
What is the incubation period of Leptospira?
2 - 4 week incubation period, clinical multi-organ infection occurs, known as Weil’s disease
Liver infection leads to cell destruction and jaundice
73
What are the symptoms of Leptospira?
Clinical multi-organ infection occurs, known as Weil’s disease
Liver infection leads to cell destruction and jaundice
Evidence of infection is seen in the eyes where bleeding, yellowing and vision impairment manifest
74
What is the histology of Leptospira?
Histology shows infiltration of the eye by numerous corkscrew-shaped (Spirochete) bacteria together with cellular invasion
Spirochete’s move fast in fluids as they have a corkscrew-shape but they wont grow on agar plates as a result of this
75
What can Leptospira lead to?
Severe immune response that can severely impair vision & lead to blindness
76
How is Leptospira treated?
With Doxycycline or Penicillin
77
How is Syphilis related to the eye?
Causes an inner eye infection
78
What is Syphilis? How many infection states are there?
Syphilis is a sexually transmitted infection, increasing in prevalence
3 different infection states:
- Primary
- Secondary
- Tertiary
Appears to spontaneously resolve over time (if not treated) and so you get secondary syphilis in a few months time. If then not getting it treated it resolves and then comes back as Tertiary Syphilis and the damage at this point is irreversible (whereas before it would have been easily treatable)
79
What is Primary Syphilis?
Primary syphilis - Flat ulcer appears on genitalia
- Corkscrew organisms called Treponema pallidum
- 50% of cases heal spontaneously
80
What is Secondary Syphilis?
Dissemination of organism from primary ulcer throughout the body causing a widespread rash – may present with a wide range of symptoms like a cold or osteoporosis
81
What is Tertiary Syphilis?
Continuation of secondary stage alongside infection of neurons and a severe immune reaction – neurological symptoms such as Tabes Dorsalis (lose sensation and feels like you’re walking on air) and general paralysis of the insane
82
What can chronic persistent infection of Syphilis cause in women?
- Can lead to stillborn births
- Can result in birth of child with irreversibly damaged eyes
Retinitis
Interstitial keratitis --> can lead to blindness and potentially death
83
What is Chlamydia Trachomatis a form of?
Bacteria
84
What are some features of the bacteria of chlamydia trachomatis?
Different to other bacterias as it cannot produce its own energy so have to parasitise cells (so cannot grow outside of the body)
- Inability to produce energy
- Parasitise cells
Grow and multiply inside host cells
- Use host cells to produce energy allowing function of enzymes
85
Can Chlamydia Trachomatis be asymptomatic? Who can this be dangerous to?
Yes - 10% of women subclinical infection which can be dangerous to child being born
Develops after infection from mother at birth (similar to N. gonorrhoeae)
86
What are 3 forms of infection in Chlamydia Trachomatis?
- Genitourinary (associated with the STI)
- Pulmonary
- Ocular (Trachoma)
87
What occurs at 4 - 7 days of age in Chlamydia Trachomatis?
A kerato conjunctivitis occurring at 4-7 days of age
88
What is the most common, but treatable, cause of blindness in the world?
Chlamydia Trachomatis
89
What does Chlamydia Trachomatis cause to the eyes?
Caused by Trachoma:
- Thickening of eyelids, inner eyelid becomes abrasive
- Untreated or repeated infection leads to scarring of the inner eyelid, leading to distortion (your eyelid will invert)
- Eyelid everts, forcing eyelashes to irritate and damage the eye
- Scratching of eye leads to secondary infections and blindness
90
How does Chlamydia Trachomatis grow on agar?
It can't! It can't grow on agar so have to grow it on tissue cultures
91
How does Chlamydia grow on tissue cultures?
Infected cells contain Chlamydia inclusion bodies
Stained with antibody linked to fluorescent dyes
92
What treatments do we have to Chlamydia Trachomatis?
Very preventable
- Infection treated with azithromycin
- Antibiotic eye drops also recommended
Chlamydia growing inside the cells = inclusion bodies
93
What is Rubella caused from?
Mild infection caused by Rubella virus – German measles
Previously very common, now covered by vaccines
94
How is Rubella contracted?
Contracted as a droplet infection
95
What is the incubation period of Rubella?
14 - 21 days (2 - 3 weeks)
96
What are the symptoms of Rubella?
- Onset – low grade fever and catarrh for 2 days
Prodromal symptoms (cold-like symptoms) – non-specific symptoms followed by classical symptoms
- Rash – maculopapular, begins on face and neck
- General lymphadenopathy - swelling of lymph nodes in neck
- Some cases mild with no rash
Many cases sub-clinical – produce lifetime immunity with no symptoms
97
Are Rubella symptoms usually worse in children or adults?
Very mild or asymptomatic infection in children
Symptoms usually worse in adults
98
Who is greatly affected by Rubella?
Extremely serious if infected whilst pregnant
Miscarriage or congenital rubella syndrome (CRS)
99
Is Rubella a bacteria or virus?
Virus
100
How does Rubella affect a baby in utero?
Virus can pass across the placenta and infect the foetus
In womb, every pore, gland and fluid exudes virus – completely takes over
Foetus surrounded by a cloud of virus
Exist in a cocoon of perpetual infection
- First trimester – 90% will suffer Rubella syndrome
- Second trimester – 20%
- Third trimester – quite rare
101
What are the symptoms of contracting rubella in utero?
Whole host of symptoms
- Mental incompetence
- Microcephaly
- Cerebral palsy
- Deafness
- Congenital heart disease
- High proportion of miscarriage
- Stillborn child
- Cataract Retinopathy (Microphthalmos, Glaucoma, Corneal Cataract)
102
How does Rubella syndrome ocularly affect a baby born with Rubella?
- Rubella syndrome includes cataracts and glaucoma
- Irreversible
- Very common in CRS
103
How is Rubella treated?
Preventable through the MMR vaccine
Once you have it you're also protected for life after
104
What are Adenoviruses?
A large group of 42 viruses sharing a common structure
If you get 1 of them, you're still susceptible to the 41 other viruses
105
How do Adenovrisues look on electron microscopy?
- 12 triangular plates in geometric pattern
- Stalks from each corner
- Proteins in white are same across all 42 strains
Hexons – Six proteins touching each white ball
Pentons – Corners can only house 5 proteins
- Proteins in black differ – 42 different forms
Penton base with fiber
Infection from one will not give immunity to others
106
How many groups of pathogenesis are there in Adenoviruses?
Three different groups in pathogenesis
First group – More severe form of a cold
107
What are the symptoms of first group Adenoviruses? How does it differ from a common cold?
Common cold
- Trivial infection - 2/3 days
- No temperature/fever
- Infection of nasal passages – mucus produced – irritates throat
- Symptoms from immune response
Adenovirus colds
- Respiratory and influenza like symptoms
- 7-8 days
- Glands swell
- Infection of throat and nasal passages
No treatments for these
108
What are examples of second group Adenoviruses?
- Adenoid Pharyngeal Conjunctivitis (APC)
- Swimming Pool Conjunctivitis
109
What is Adenoid Pharyngeal Conjunctivitis (APC) a form of? What are the symptoms?
Second Group Adenovirus
- Swelling of adenoids
- Throat infection - very red throat
- Conjunctivitis
110
What is Swimming Pool Conjunctivitis a form of? What are the symptoms?
Second Group Adenovirus
- By law public swimming baths must use chlorine
- Irritates and damages eyes
- Vulnerable through contact with an infected individual
- Eye acts as point of entry – virus an traverse and cause other symptoms
- Mild infections – US troops often vaccinated against but not in the UK.
No treatment once you have the infection and need to just let them run their course.
111
What is an example of a third group Adenoviruses?
'Shipyard Eye'
112
What is a 'Shipyard Eye' a form of?
Third Group Adenoviruses
113
What are some symptoms of 'Shipyard Eye'?
Third Group Adenovirus
- Complaint in shipyard workers and metal workers
- Eye infection with no pharyngitis (an inflammation of the pharynx, resulting in a sore throat)
- Intense inflammation in one or both eyes
Doesn't infect rest of family
- Atmosphere full of microscopic metal particles
Cause = trauma in the eye
- Contact with adenovirus infected patient causes spread
114
What are some clinical problems with 'Shipyard Eye'?
- Examination involves slight damage to eye
- Patient with Shipyard Eye can easily transmit to other patients and so have to keep them separated!
Eye --> throat
- Infections must run course
115
What is Molluscum Contagiosum a form of?
Poxvirus
116
Who is Molluscum Contagiosum common in?
Young children
117
What are some symptoms of Molluscum Contagiosum?
- Causes small bladder-like lesions on the neck, arms or legs
If opened – no pus
- Usually painless
- Can last up to 2 years
- Eventually recognised and removed by the body
- Occasionally occurs on the eyelids and looks like a stye and unlike in staphylococci it's not solid but "balloon like"
118
How do you manage Molluscum Contagiosum on the eyelid?
Best to leave it alone as it's reversible (but sometimes freeze them off, but not ideal)
119
How does Molluscum Contagiosum lesions differ from Staphylococci?
- Occasionally occurs on the eyelids and looks like a stye and unlike in staphylococci it's not solid but "balloon like"
- Material from lesion does not contain pus unlike in staphylococci
120
Is Molluscum Contagiosum a virus or bacteria?
Virus
120
How does Molluscum Contagiosum look under an electron microscope?
Large brick-shaped virus particles
121
What is the treatment for Molluscum Contagiosum?
No treatment, should resolve spontaneously
122
What does SARS-CoV-2 cause?
Evidence that it causes conjunctivitis
123
How is SARS-CoV-2 caught?
Mucous membranes of the eye considered a pathway to infection
People with glasses 2-3 times less likely to contract (Saxena, 2021)
124
Is Herpes Simplex a bacteria or virus?
Virus
125
How many Herpesviridae are infectious to humans? Which is the most common?
Herpesviridae – 8 known to infect humans
Herpes simplex (HSV-1) is the most common
126
When is the most common period of time of primary infection of Herpes Simplex (HSV-1)?
Usually children 6 months - 5 years old
127
How is Herpes Simplex acquired?
- Acquired by contact from patients or carriers
- Often passed to children – when adults secreting virus (cold sore and kissing newborn)
- Can be transferred by rubbing/scratching to other skin surfaces e.g. near the eye leading to secondary lesions that can also be transferred directly to the eye
128
What are some symptoms of Herpes Simplex (HSV-1)?
- Produces a blister/ulcer on the mouth (cold sore), face etc.
- Virus retreats to ganglia – can periodically reactivate
- Lesion normally forms on the lips and is very itchy
- Conjunctivitis
- Dendritic Ulcers
- Keratitis
- Blindness
129
What is the most common infective cause of blindness in high income countries?
Herpes Simplex
130
What treatment might be needed in Herpes Simplex?
- Corneal Graft due to dendritic uclers affecting the eye
- Aciclovir (analogue to nucleotides, inactivates viral DNA replication)
131
What are some benefits of Aciclovir in treating Herpes Simplex?
Stops DNA replication
- Very potent
- Non-toxic
- No resistance
- Affects majority of herpesviridae
Available over the counter at pharmacists
Initial ‘tingle’ 48 hours prior
Treatment will abort infection
132
What is Chicken Pox also known as?
Varicella Zoster
133
What is Varicella Zoster?
Chicken Pox
134
What is Varicella Zoster/Chicken Pox a form of?
Herpesviridae
135
How is Varicella Zoster spread?
Spread by inhaling virus (dried from lesions or as droplets)
136
What is the incubation period of Varicella Zoster/Chicken Pox?
14 - 21 days
137
What are the symptoms of Varicella Zoster/Chicken Pox?
Manifests in outbreak of respiratory symptoms and rash
Face and in hair, central body more than hands and feet
Lesions are like blisters and very itchy
138
When is a vaccine for Varicella Zoster/Chicken Pox used in the UK?
Vaccine available, not used in UK
- Immunocompromised may be offered (can cause haemorrhagic chicken pox where they bleed profusely)
139
Following recovery, does the Varicella Zoster/Chicken Pox remain in the body?
Yes - after recovery the virus remains in the dorsal root ganglia for life but can also retreat to other ganglia and doesn't usually reoccur
140
How does Varicella Zoster/Chicken Pox virus reactivate in later life?
Reactivates to produce shingles
141
What happens in Shingles?
- Multiplies within the nerves
- Intensely painful rash which follows the nerve
- Manifests on skin associated with tight clothing
- No treatment for it
- Aciclovir can reduce symptoms
142
When might Varicella Zoster/Chicken Pox reactivate?
Occasionally can reactivate from facial ganglion (trigeminal nerve)
143
What are the symptoms of reactivation of the Varicella Zoster/Chicken Pox across the trigeminal nerve?
- Large rash across face – demarcation due to infection of specific nerve
- From here can spread to eye
- Very damaging but quite rare
- Virus can travel along the optic nerve (if it gets into the eye) to the brain to cause encephalitis
144
What is an Amoebae?
Some free-living amoebae can cause keratitis – quite rare
145
What is an example of an amoebae?
Acanthamoeba
146
What are some features of Acanthamoeba?
- Usually associated with contact lenses which have not been cleaned with sterile saline solutions – enter after trauma to eye
- Amoebae found in plain tap water
- Must not use for cleaning contact lens or equipment for examining eyes
- Very difficult to treat so best cause of action is prevention
147
What is Onchocerca Volvulus also known as?
"River Blindness" caused by a parasitic worm
148
What causes Onchocerca Volvulus?
Microscopic African worm living in freshwater rivers
99% of infected people live in 30 countries across sub-Saharan Africa
37 million people in East and Central Africa are carriers (800,000 blind)
149
How might you contract Onchocerca Volvulus?
- Eaten by simulian flies and transferred to humans through insect bites
- Parasite multiplies at site of bite to cause swelling, nodules protect parasite from immune response
- Parasite produce embryonic larvae which migrate to all organs of the body
- Migrating larvae die and initiate an intense immune response
150
What are some symptoms of Onchocerca Volvulus?
- In skin, intense itching, swelling and inflammation
- Can penetrate all areas of the eye
- Often migrates to surface of the cornea causing keratitis
- Eventually leads to blindness
River blindness
151
Where is Onchocerca Volvulus most common?
Can occur in >90% of adults in some African tribes
- Younger generations required to lead infected generation
- Proximity means high likelihood of passing on the parasite
Also found in Yemen, Brazil and Venezuela
152
What is the treatment for Onchocerca Volvulus?
- No vaccine or medication to prevent infection
- Best option is prevention
- Ivermectin can kill larvae but not adult worms (6 - 12 months)
153
What is Toxocara?
Parasitic roundworm of cats and dogs, eggs excreted in faeces
154
How is Toxocara spread to humans?
Spread to humans through ingestion of eggs
Children in parks - like sandboxes or soil
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What are the symptoms of Toxocara?
- Larvae can migrate throughout body causing a severe allergic reaction
- Parasitic larvae can encyst within the eye
- Can form a granuloma in the eye (when unable to get rid of an organism the body just capsulates it = granuloma), and cause a peripheral eosinopimulia
- Mass (granuloma) often confused with malignant retinoblastoma
- Loss of vision over days or weeks
- Damage is permanent, can result in blindness
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What is Toxoplasma Gondii?
- Protozoa - apicomplexan
- Parasite commonly infects cats, who excrete it in faeces
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How can Toxoplasma Gondii be contracted?
Children playing in sandpits can accidentally acquire this infection
Hands to face or mouth
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What are the symptoms of Toxoplasma Gondii?
Parasite grows in intestine and migrates to the eye to cause chronic choroidoretinitis
Possible to infect foetus in womb (Congenital ocular toxoplasmosis)
- Inflames a small patch of retina which resolves but causes scarring
- Potentially an area for reactivation of infection
- Serious infection with vision impaired
- Must be diagnosed rapidly and treated (anti-parasitic pyrimethamine)
