Ocular virology; an Introduction Lecture delivered by Dr. Iddi Ndyabawe (MMed Ophthalmology, 1st year at Makerere University, Uganda). Modulator: Dr. Lusobya Rebecca (Ophthalmologist)

1. OCULAR
VIROLOGY
Presenter: Dr. Iddi Ndyabawe
MMed Ophthalmology Year 1
.
Modulator: Dr. Lusobya Rebecca,
Ophthalmologist
Date: 22/08/2019

2. Outline
General virology:
-Definitions
-Classification of viruses
-Morphology
-Cellular affinity
-Viral replication and transmission
-Cellular and Host responses to viral infection
-Lab methods of detection of different viruses
affecting the eye

3. OCULAR VIROLOGY
• Herpes
• CMV
• VZV
• HIV ocular infections
• Pathological findings in the eyes for all the
common viral infections

4. What is a virus?
• A virus is an acellular infectious obligate
intracellular parasite comprising genetic
material (DNA or RNA) surrounded by a
protein coat (capsid) and/or an envelope
derived from a host cell membrane
-Viruses vary in size: 10 to 300 nm in diameter
-largest virus: Mimivirus
-

5. Structure of a virus

6. Morphology:
• Naked DNA viruses: Parvo, Adeno, Polyoma,
Papilloma
• Naked RNA viruses: Calci, Picorna, Retro, Hep.
E
Helical symmetry: Myxovirus, Rhabdo, Filo,
Bunya

7. Classification of viruses
• DNA viruses: Hepadna, Herpes, Adeno, Papo,
pox, papilloma, polyoma viruses. (All those
are dsDNA) Only ssDNA is Parvovirus B19
• RNA viruses: +ssRNA (Calcivirus, Picorna,
Flavivirus, Togavirus, Coronavirus, Retrovirus);
-ssRNA (Paramyxovirus, Rhabdoviridae,
Filovirus, Orthomyxovirus, Bunyavirus,
Arenavirus)

8. Cellular affinity
• Envelope helps virus attach to host cell
• Some viruses can infect only specific cells
based on presence of suitable receptors e.g
HIV virus attacks T-helper cells only because it
attaches to the CD-4 receptors

9. Viral replication
• All DNA viruses replicate in Nucleus except “Pox”. All RNA
viruses replicate in Cytoplasm except Retrovirus, and
Influenza.
• The stages of viral replication are as follows:
• ● Adsorption—attachment of the virus particle to a cell by
random collision, electrostatic attachment, or host cell
receptors.
• ● Penetration—fusion of the viral envelope and cell
membrane.
• ● Capsid removal—the capsid is removed by host cell
enzymes.
• ● Nucleic acid replication—most DNA viruses replicate in the
nucleus by host cell enzymes to make messenger RNA and to
replicate DNA. DNA virus will therefore produce intranuclear
inclusions. Replication of RNA viruses occurs in the cytoplasm.
They demonstrate cytoplasmic inclusions.

10. Viral transmission
• Viral transmission can be vertical, horizontal, or a
combination of the two.
• Vertical transmission occurs as a result of a
mother passing virus to her off spring. For
example, cytomegalovirus and rubella can be
transmitted vertically via a transplacental route.
• Horizontal transmission occurs when a virus is
passed from one individual to another by direct
contact, faecoorally (enteroviruses), airborne-
respiratory (paramyxoviruses), or parenteral
routes such as in hepatitis B or rabies.

11. Cellular response to viral infection
• The cellular effect of virus infection includes cell
shrinking, rounding, inclusion bodies, and the
formation of giant multinucleate cells. This can result in
cell death due to cytolysis or inhibition of cell
metabolism.
Chronic infection can result in:
● Latency—the viral genome is integrated into the host
DNA. It does not replicate until a trigger occurs, e.g.
stress. A classic example of this is the herpes simplex
virus.
● Persistence—the virus replicates at a very low rate.
● Transformation—the virus initiates new cell
properties, which lead to teratogenic change.

12. Host response to viral infection
• Innate immunity in the form of structural
barriers (cilia in the respiratory tract, acid in
the stomach) can prevent viruses invading the
epithelial surface. The presence of a fever
inhibits viral replication.
• The humoral response includes production of
antibody, complement, and interferon, and
the cellular production of T and B
lymphocytes, macrophages, and
polymorphonuclear leukocytes.

13. Diagnostic tests and serology
The diagnosis of viral infection can be via:
● direct viral isolation—use of electron microscopy
to demonstrate virus in body fluids/tissue
● serological techniques for detection of antigen
or antibody—complement fixation measures the
reaction between viral antigen and a specific
antibody, and gives a direct measure of the
consumption of complement added.
● ELISA
● radioimmunoassay (RIA)

14. Con’t
● reverse passive haemagglutination, such as
in detection of hep B surface antigen
● organism-specific humoral responses can be
detected in ocular fluids—Goldmann and
Witmer reported a method to calculate whether
antimicrobial antibodies are being produced
within tissues and hence demonstrating local
infection
● PCR—this can be used to detect genetic
material via analysis of intraocular fluid or
tissue, for example a vitreous biopsy in possible
acute retinal necrosis or chronic
endophthalmitis

15. Goldmann and Witmer coefficient (C)
• C = (antibody titre in ocular fluid/antibody
titre in serum) × (total IgG in ocular fluid/total
IgG in serum)
• C ≥ 3, local antibody production present.

16. IMPORTANT OCULAR VIRAL
PATHOGENS
• DNA VIRUSES: Herpes, Adeno, Papo, pox
• Herpes viruses
These are double-stranded DNA viruses with an icosahedral
capsid. An important feature of some of the herpes family,
namely herpes simplex and varicella zoster, is that they possess
the ability to lie dormant in neuronal sites and reactivate
under certain conditions, e.g. stress or other illness. This is
known as latency. Members of the herpes virus family are the
causative agents of acute retinal necrosis.
• The herpes virus family includes:
● herpes simplex
● varicella zoster
● cytomegalovirus
● Epstein–Barr virus (EBV).

17. Herpes simplex virus
• Herpes simplex type 1(HSV-1) is most
commonly associated with oral infection (cold
sores). Normally the primary infection is in
childhood and is subclinical, with the cold sore
occurring as a consequence of viral
reactivation.
• HSV-1 is relevant in ocular disease. It can give
rise to conjunctivitis, keratitis, uveitis, and
uveoretinitis.
• A culture or smear of the affected tissue
shows intraepithelial vesicles and contains
syncytial giant cells and eosinophilic
intranuclear inclusions.

18. There are four stages in the life cycle of HSV-1
1. Entry into the host and replication at this
peripheral site (e.g. eyes, skin, or mucosae).
2. Spread to the axonal terminals of sensory
neurons followed by retrograde intra-axonal
transport to neuronal cell bodies in sensory and
autonomic ganglia.
3. Latency in ganglia, e.g. trigeminal ganglion.
4. Reactivation with the production in the
ganglia of infectious virus transported
anterogradedly to the periphery, with further
replication at the site of primary infection.

19. .• The pathogenicity of herpes simplex is
increased in immunosuppression, malignancy,
and with the use of topical steroid.
Reactivation itself can be triggered by these
or hormonal changes, ultraviolet light, stress,
and trauma.
• The viral envelope is highly immunogenic and
stromal disease, e.g. disciform keratitis, is due
to a hypersensitivity reaction to viral antigen
rather than the virus itself.

22. Disciform keratitis in HSV

24. Rx
• Cure not yet developed. Rx minimises cornea
damage and vision loss…
• Topical antivirals Gaciclovir Ophthalmic gel or
Triluridine
• AVOID STEROIDS!!!!

25. Varicella zoster virus (VZV)
• Varicella zoster virus (VZV) is the cause of
chickenpox (collections of intraepidermal vesicles
on the trunk, face, and mouth). Chickenpox is
spread by the respiratory route. The virus can
become latent in certain ganglia, most commonly
the trigeminal, thoracic, lumbar, and cervical
nerve ganglia.
• Reactivation leads to shingles.
If reactivated in the trigeminal ganglion VZV can
lead to ophthalmic shingles or herpes zoster
ophthalmicus. Cell-mediated immunity maintains
the virus in its latent state.
Reactivation can be due to concurrent illness,
immunosuppression, or radiotherapy.

26. SHINGLES

31. Cytomegalovirus (CMV)
• Cytomegalovirus (CMV) infection is very common, but
it is subclinical in 80% of cases. The virus is shed from
the genital or urinary tracts and becomes latent in
lymphocytes. Reactivation can occur during pregnancy,
leading to asymptomatic infection of the foetus. If the
primary infection occurs in pregnancy, congenital
anomalies can occur (this is more likely if primary
infection is in the first trimester).
• Congenital infection with CMV can cause cytomegalic
inclusion disease, leading to:
● strabismus
● chorioretinitis
● microphthalmia
● childhood hepatitis

32. .
• Interestingly the virus is shed at birth by 1% of
infants, with 10% of these having minor
abnormalities, including hearing deficits.
• CMV infection in the immunosuppressed can
lead to:
● CMV retinitis: (Hx: flashes, floaters, blurred
vision, blind spots, specks in vision)
● transplant rejection
● CMV pneumonia.

34. Owl’s eye

35. CMV retinitis

36. Adenovirus
• Adenovirus is a diverse group of double-stranded
DNA viruses consisting of over 30 antigenic types or
serotypes.
• The infective particle has an icosahedral capsid
without an envelope. Transmission of the ocular
infection is by direct contact with virus in ocular
secretions. Contaminated instruments, eye drops,
or the hands of health professionals can be the
fomite. Adenovirus is highly prolific:
• a single infected cell can produce 10,000 virions per
cycle of 30–36 hours.

43. Papovarirus
• Human papillomavirus
• Human papillomavirus (HPV) is a double-
stranded DNA virus of which there are over
60 types.
• HPV 6 and HPV 11 are associated with benign
conjunctival papillomata.
• Malignant change is caused by insertion of a
particular type of HPV DNA into the host
genome.

44. Benign conjuctival papillomata

45. Pox virus
• Pox viruses are DNA viruses that replicate in
the cytoplasm with very limited nuclear
involvement.
• This is because they possess a DNA-
dependent RNA polymerase, a transcript
poly-A polymerase, a capping enzyme, and
methylating enzymes, hence allowing them to
replicate independently of the host cell.

46. Molluscum contagiosum
• Molluscum contagiosum is the most common
pox virus to cause ocular infection. It causes
conjunctivitis and the appearance of pearly
white or flesh-coloured lesions on the face,
extremities, and trunk. It is commonly seen in
children and is spread by direct contact or
through contaminated fomites or water. Adult
cases tend to be sexually transmitted.
• Epidermal hyperplasia is due to the
production of a protein related to the
conserved domain of epidermal growth factor.

47. Molluscum contagiosum

48. RNA Viruses; Retroviruses, Toga,
Paramyxo
• Human immunodeficiency virus (HIV)
• HIV-1 and HIV-2 are retroviruses possessing
the ability to infect CD4 + lymphocytes. They
contain a single strand of RNA and reverse
transcriptase. They differ in the structure of
their glycoprotein envelopes.

49. Diagnostics for HIV

50. Specific tests for HIV
• HIV antibody: ELISA, Western blot, HIV
differentiation assay
• HIV antigen detection: p24
• HIV nucleic acids: PCR can be used to amplify
the HIV genome RNA.
• HIV culture: virus isolated by co-culture with
IL-2.

52. Ocular infections associated with AIDS
● CMV retinitis—treatment with ganciclovir or foscarnet
is successful in up to 80% of cases; maintenance therapy
is required; rate of relapse depends on the presence of
positive leukocyte CMV cultures
● Cotton wool spots
● Toxoplasma chorioretinitis—treatment is with
pyrimethamine and sulfadiazine or clindamycin;
maintenance is usually required to prevent relapse
● Herpetic keratitis (simplex and zoster)
● Herpetic acute retinal necrosis and retinitis
● Candidal (in intravenous drug users) and cryptococcal
endophthalmitis
● Tuberculous chorioretinitis
● Histoplasma retinitis
● Pneumocystis carinii choroidopathy

53. KS on eyelid

56. HIV Rx - HAART

57. Paramyxovirus
• Measles
• Measles infection is characterized by pyrexia,
cough, coryza, and conjunctivitis.
Complications include secondary bacterial
respiratory infection, encephalitis, and rarely
subacute sclerosing panencephalitis (SSPE),
which can be associated with chorioretinitis
and maculopathy.

59. THYGESON’S SPK

60. Togavirus
• Rubella
Rubella is subclinical in 80% of small children and 10% of
adults. If a mother is infected in the first trimester of
pregnancy congenital anomalies occur due to spread to
the placenta and hence foetus. Miscarriage or stillbirth
may occur.
Congenital defects include cataract, microphthalmia, ‘salt
and pepper’ retinitis, glaucoma, conductive deafness, and
heart defects. For this reason a live attenuated vaccine is
given to children under the age of 12 years