1. Themes:
Immune evasion by viruses
Zoonoses: transmission to humans
Viruses as prophylactics

2. Themes 1. Cell, tissue and host tropism of viruses
January 2008
Themes
1.     Cell, tissue and host tropism of viruses
2.     Arthropod transmitted viruses
3.     Cancer-causing (oncogenic) viruses
4.     Antigenic variation
5. Persistent infections
6.    Pathogenic variants generated in situ
7.    Zoonotic infections
8.    Emerging and re-emerging viral diseases
9. Immune evasion by viruses
10. Viruses as prophylactics/therapeutics
Steve Dunham Infection & Immunity GUVS

3. Poxviridae Key features
January 2008
Poxviridae
Key features
1. Poxviruses are the largest animal viruses and have a complex structure and mode of assembly. Unlike most other DNA viruses, poxviruses assemble in the cytoplasm.
2. Poxviruses affect many species of animals. Although generally species-specific, some poxviruses of domestic animals are zoonotic.
3. All poxviruses cause skin lesions and some additionally cause serious systemic disease.
4. Poxvirus infections are readily diagnosed by clinical signs and electron microscopy.
5. Poxviruses are very resistant to the environment and can persist for many months on dried lesion material.
6. Used as vectors for the delivery of new vaccines.
Steve Dunham Infection & Immunity GUVS

4. Poxviruses The poxviruses are very large, about 200-300 nm in length.
January 2008
Poxviruses
The poxviruses are very large, about nm in length.
The genome is double stranded DNA of kbp, depending on the genus, which encodes around 200 genes.
The parapoxviruses can be readily distinguished morphologically from the other genera since they are narrower and have a more oval shape.
The viral core contains an RNA polymerase which, immediately following infection, transcribes several viral genes necessary for viral DNA replication and protein synthesis.
Different viral proteins are translated before DNA replication (early proteins, mainly enzymes), or after DNA replication (late proteins, mainly structural).
Viral particles are constructed in the cytoplasm within viral factories. These factories can be visualised in stained cells as inclusion bodies.
Steve Dunham Infection & Immunity GUVS

5. Mechanisms of immune evasion
January 2008
Mechanisms of immune evasion
All poxviruses produce lesions on the skin
Viruses replicate in the face of a host immune response
Poxviruses produce many gene products that impair host immune responses
Genes may be direct homologues of host genes
Novel genes are also encoded
Theme : immune evasion by viruses
Steve Dunham Infection & Immunity GUVS

6. Mechanisms of immune evasion
January 2008
Mechanisms of immune evasion
Target many primary host immune mediators
complement proteins
cytokines e.g. Interferon-gamma binding protein
Enhance the viral environment
Epidermal growth factor homologue
Vascular endothelial growth factor homologue
Poxviruses have many genes that are homologous to cellular genes and encode proteins that are important factors in pathogenicity. For example, one important poxvirus gene codes for a protein that is homologous to cellular epidermal growth factor (EGF). In infected individuals, this protein is produced by infected cells, binds to the EGF receptor on uninfected epidermal cells which then proliferate. Presumably the advantage to the virus is the provision of more cells in which to grow. This stimulation of cell growth can be so strong in some poxvirus infections that the lesions may resemble tumours, for example in orf in sheep and in rabbits infected with myxoma virus or Shope fibroma virus. Other genes encode proteins that subvert the immune response to the virus. One of these proteins mimics the cellular interferon-γ receptor and binds to host interferon-γ, suppressing its effect on local immune and inflammatory responses that might lead to the inactivation of the virus.
Steve Dunham Infection & Immunity GUVS

7. Pathogenesis and immunity
January 2008
Pathogenesis and immunity
All poxviruses cause lesions on the skin.
In most cases initial replication at the site of infection (skin, respiratory tract) results in virus being taken to local lymph nodes and via the thoracic duct to the blood.
This viraemia spreads the virus throughout the body and particularly to the skin where lesions develop.
Immunity to many poxviruses is very strong and lifelong. The exception is the parapoxviruses.
Following recovery from natural infection with orf virus, immunity is short lived and sheep become susceptible to re-infection within a few months. Clearly this feature is advantageous to the virus, permitting its survival in flocks.
Steve Dunham Infection & Immunity GUVS

8. Diseases caused by poxviruses
January 2008
Diseases caused by poxviruses
Orthopoxviruses
Cowpox (cats), ectromelia (mice), camel pox,
(variola, vaccinia)
Parapoxviruses
Orf (sheep), bovine papular stomatitis,
paravaccinia (pseudocowpox) (cattle)
Capripoxviruses
Sheep pox, goat pox, lumpyskin disease (cattle)
Camelpoxviruses
Camel pox
Leporipoxviruses
Myxomatosis, Shope fibroma
Avipoxviruses
Fowl pox, pigeon pox, canarypox, wild birds
Steve Dunham Infection & Immunity GUVS

9. The beginnings of vaccination
January 2008
Orthopoxviruses
Smallpox:
The beginnings of vaccination
Steve Dunham Infection & Immunity GUVS

10. Smallpox (variola): 1000 BC - 1977 AD
January 2008
Smallpox (variola): 1000 BC AD
"The smallpox was always present, filling the churchyards with corpses, tormenting with constant fears all whom it had stricken, leaving on those whose lives it spared the hideous traces of its power, turning the babe into a changeling at which the mother shuddered, and making the eyes and cheeks of the betrothed maiden objects of horror to the lover.”
Steve Dunham Infection & Immunity GUVS

11. Smallpox and vaccination
January 2008
Smallpox and vaccination
In the 18th century Edward Jenner, an English country doctor, combined two observations to produce a theory that changed the world.
Dairy workers had a very much reduced incidence of smallpox compared to other people who were exposed
Often dairy workers were afflicted with the lesions of cowpox, the common disease of dairy cattle
Therefore, infection with cowpox prevents smallpox
Then Jenner carried out the appropriate experiment
Steve Dunham Infection & Immunity GUVS

12. January 2008
Smallpox vaccination
Sarah
Jenner
Edward Jenner used cowpox from a lesion on the hand of the milkmaid Sarah Nemes to inoculate 8 year old James Phipps.
Jenner later challenged James with live smallpox virus and showed that he was protected.
Steve Dunham Infection & Immunity GUVS

13. Smallpox: nomenclature
January 2008
Smallpox: nomenclature
The classical name for smallpox is variola
The old name for cowpox was vaccinia
Therefore the process of immunisation against smallpox was called vaccination
The agent that was continually passaged in people (then cattle) for the purposes of vaccination continued to be called vaccinia
Steve Dunham Infection & Immunity GUVS

14. January 2008
Smallpox vaccination
Smallpox was eradicated in 1977 due to surveillance and vaccination: last case occurred in eastern Africa
Now stocks only held in two secure laboratories in Russia and the USA (Centers for Disease Control, Atlanta)
Potential for bioterrorism!!
Steve Dunham Infection & Immunity GUVS

15. January 2008
Where is cowpox today?
Cowpox is zoonotic and the lesions that it produces in man resemble those of smallpox, but are localised and transient
The virus produces lesions on the teats and the contiguous parts of the udder of cows and is spread through herds by the process of milking. However, Cowpox has almost disappeared from domestic cattle.
Steve Dunham Infection & Immunity GUVS

16. Here it is! Rodents are reservoirs. Also infects zoo animals
January 2008
Here it is!
Rodents are reservoirs. Also infects zoo animals
Infects felids, anteaters, okapi, elephants
Particularly severe in cheetahs
Steve Dunham Infection & Immunity GUVS

17. Cowpox infection in cats
January 2008
Cowpox infection in cats
Highest risk of infection
Free range cats in rural or suburban areas
Cat-to-cat transmission
Occurs, but disease is uncommon
Cat-to-human transmission must be prevented
Immunodeficient people are at high risk
N.B. Lesions in humans usually appear as single maculopapular eruptions on the hands or the face; infection is accompanied by systemic signs such as nausea, fever, and lymphadenopathy
Theme : zoonotic disease
Steve Dunham Infection & Immunity GUVS

18. Cowpox infection in cats
January 2008
Cowpox infection in cats
How is the virus maintained?
Likely to be transmitted from small wild mammals. Bank vole, field voles and wood mice
But 40% of bank voles have anti-cowpox antibodies
May be maintained in burrows by insect transmission
Steve Dunham Infection & Immunity GUVS

19. Cowpox infection in cats
January 2008
Cowpox infection in cats
Original single skin lesion
on head, neck or forelimb
Skin inoculation
Secondary
skin lesions
Local growth
of virus
Lymph nodes
Viraemia
Dermal nodules
Ulcerated papules
Vesicles (tongue)
Scabbing
Recovery (6-8 weeks)
Rarely
fatal in cats
Accurate diagnosis is important
Virus isolation - sensitive
Electron microscopy – rapid
PCR
Steve Dunham Infection & Immunity GUVS

20. Camel pox
Camelpox virus is responsible for a very important systemic disease of camels in Africa and Asia, with extensive skin lesions.
Up to 25% of affected animals may die.

21. Parapoxviruses Orf, bovine papular stomatitis, pseudocowpox
January 2008
Parapoxviruses
Orf, bovine papular stomatitis, pseudocowpox
Viruses very closely related
All are potential zoonoses
Steve Dunham Infection & Immunity GUVS

22. Orf
Orf, or contagious pustular dermatitis, is a very common infection of sheep and goats.
The name is derived from an old word for ‘rough’, referring to the lesions.
The virus is generally spread to lambs from their mothers and causes large proliferative lesions on the lips & nose, particularly at muco-cutaneous junctions.
Although often extensive, the lesions usually resolve within a few weeks and the animal recovers completely. However, immunity is short lived and sheep can become re-infected.

23. Orf in sheep and goats Contagious pustular dermatitis
January 2008
Orf in sheep and goats
Contagious pustular dermatitis
Typically affects mouth and nasal planum, eyelids, feet, teats.
Crusty lesions which can bleed
* May prevent lambs from suckling *
Live, virulent vaccine virus. Only use in affected flocks
Use in ewes pre-lambing. Short-lived immunity
Steve Dunham Infection & Immunity GUVS

24. Orf as a zoonosis Papule Oedema Crust
January 2008
Orf as a zoonosis
Papule
Oedema
Crust
Spontaneous recovery from orf in 3 to 6 weeks
Orf appears as a solitary or a few lesions on the fingers, hands, or forearms.
The lesion starts as a small, firm, red-to-blue papule that grows to form a hemorrhagic, flat-topped pustule or bulla. The bulla may have a crust in its umbilicated center. The fully developed lesion normally is 2-3 cm in diameter, but may reach 5 cm, often is tender, and may bleed easily. Regional adenitis and/or mild lymphangitis may occur.
Large and fungating lesions have been reported in immunosuppressed patients and in patients with atopic dermatitis.
The infection goes through six clinical stages, each lasting about one week.
Stage 1: Maculopapular - A red elevated lesion.
Stage 2: Target - A bulla with an irislike configuration (nodule with a red center, a white middle ring, and a red periphery).
Stage 3: Acute - A weeping nodule.
Stage 4: Regenerative - A firm nodule covered by a thin crust through which black dots are seen.
Stage 5: Papillomatous - Small papillomas appear over the surface.
Stage 6: Regressive - A thick crust covers the resolving elevation.
Steve Dunham Infection & Immunity GUVS

25. Bovine papular stomatitis
January 2008
Bovine papular stomatitis
BPS is endemic in cattle causing vesicular lesions in the mouth and lips. The condition is not usually serious but on occasion, when the lesions are more severe, has to be distinguished from other vesicular diseases such as foot-and-mouth disease or mucosal disease.
Little clinical significance
Worldwide distribution
Steve Dunham Infection & Immunity GUVS

26. Pseudocowpox Common in cattle Pseudocowpox (paravaccinia) in cattle
January 2008
Pseudocowpox
Common in cattle
Pseudocowpox (paravaccinia) in cattle
Characteristic “horseshoe” scabs
Milker’s nodules in humans
Steve Dunham Infection & Immunity GUVS

27. January 2008
Capripoxviruses
Economically the most impt. pox disease of domestic spp.
Endemic in Africa, Middle East, India
Notifiable Disease
Morbidity rate: Endemic areas 70-90%
Mortality rate: Endemic areas 5-10%
Early lesions
of sheep pox
Steve Dunham Infection & Immunity GUVS

28. Sheep pox Skin lesions Extensive lung lesions
January 2008
Sheep pox
These are by far the most severe poxvirus conditions of domestic animals. In outbreaks in fully susceptible animals the mortality rate may reach 50%. The disease is particularly severe in young lambs or kids.
Sheeppox is a systemic disease in which widespread nodules develop in the skin, particularly in areas with little hair. Lesions may extend to lungs
Skin lesions
Extensive lung lesions
Steve Dunham Infection & Immunity GUVS

29. January 2008
Lumpy skin disease
Lumpyskin disease is a condition similar to sheepox but affects cattle and buffalo in some parts of Africa. The mortality rate is very much less than in sheeppox infection. A vaccine against sheeppox also protects against lumpyskin disease
Steve Dunham Infection & Immunity GUVS

30. Lumpy skin disease High morbidity, low mortality
January 2008
Lumpy skin disease
High morbidity, low mortality
Prolonged recovery affects productivity
Transmitted by insect vectors
Steve Dunham Infection & Immunity GUVS

31. Leporipoxviruses Two closely related viruses
January 2008
Leporipoxviruses
Two closely related viruses
Myxoma virus - myxomatosis
Shope fibroma virus - vaccine
Steve Dunham Infection & Immunity GUVS

32. Myxomatosis Only mild disease in cottontail rabbits
January 2008
Myxomatosis
Only mild disease in cottontail rabbits
Spread by fleas/mosquitos
Skin ‘tumours’ result from an initial proliferation of undifferentiated mesenchymal cells in the dermis which become large stellate cells termed ‘myxoma cells’
Steve Dunham Infection & Immunity GUVS

33. Myxomatosis The characteristic signs of myxomatosis are:
January 2008
Myxomatosis
The characteristic signs of myxomatosis are:
Swollen head, eyelids, genitalia
Purulent conjunctivitis
Transmitted by the rabbit flea
Mechanical vector
Live, attenuated myxoma virus vaccine
Steve Dunham Infection & Immunity GUVS

34. Shope fibroma Shope fibroma virus causes benign, self-limiting tumours
January 2008
Shope fibroma
Shope fibroma virus causes benign, self-limiting tumours
The virus is antigenically related to myxoma virus and can be used as a vaccine against myxomatosis
Steve Dunham Infection & Immunity GUVS

35. Myxomatosis was the first agent used for the biological control
January 2008
Myxomatosis was the first agent used for the biological control
Australia in the 1950s
Myxomatosis vaccines are not available in Australia
Steve Dunham Infection & Immunity GUVS

36. January 2008
Avipoxvirus :Fowlpox
Lesions on non-feathered areas of the skin (nodules develop on the head, comb and wattles).
Transmission by biting arthropods.
Also diphtheritic form
Birds with the other more serious form, which spreads by aerosol, have proliferative lesions in the epithelium of the upper respiratory tract, which frequently leads to asphyxia and death
Fowlpox is now uncommon in commercial poultry flocks
Virus elimination is difficult
Steve Dunham Infection & Immunity GUVS

37. Poxviruses are used as vectors for genetically modified vaccines
January 2008
Poxviruses are used as vectors
for genetically modified vaccines
Foreign gene inserted into poxvirus genome
Recombinant
Poxvirus
Protein expressed when infecting cells
i.e. following vaccination
Theme: viruses
As prophylactics
Steve Dunham Infection & Immunity GUVS

38. Canarypox as a vaccine vector
January 2008
Canarypox as a vaccine vector
Because of their large content of DNA, poxviruses are good candidates as vectors for the delivery of genes of interest into cells.
Several poxvirus genes have been identified which are not essential for viral growth and can be deleted without affecting the growth of the virus. Therefore any gene of interest can be swapped for one of these non-essential genes.
The resulting recombinant poxvirus will then deliver that gene into cells by infection and will promote the expression of the gene and the production of the encoded protein, as well as poxvirus proteins.
Avipoxviruses, which complete their full replication cycle only in avian cells, go through an abortive replication cycle in mammalian cells, expressing only their early genes.
Steve Dunham Infection & Immunity GUVS