Poxiviridae Flashcards
Family Poxiviridae
Subfamily: Chordopoxvirinae (poxvirus of vertebrates)
8 genera
Disease in humans, animals, birds
- genus: Orthopoxviurs
- genus: Parapoxvirus
- genus: Avipoxvirus
- genus: Capripoxvirus
- genus: Leporipoxvirus
- genus: suipoxvirus
Properties of poxviruses
Large, sometimes enveloped, DNA viruses with complex structure (symmetry)
Most are pleomorphic, typically brick-shaped
Possess irregular surface of projecting tubular or globular structures
Genus parapoxvirus= ovoid, covered with long thread-like surface tubules- criss cross fashion like ball of yarn
Two distinct infectious particles: intracellular mature; extracellular enveloped
Extracellular= 2 membranes: envelope, and inner membrane
Virions are released from cells by budding rather than by cellular disruption, acquire extra envelope that contains virus encoded-proteins from host membrane
IMV- only inner membrane. Out by disruption of host cell
Properties of poxviruses- cont
Do not conform to icosahedral or helical symmetry- have complex symmetry
Virion outer layer encloses a dumbbell-shaped core and two lateral bodies
Core contains viral DNA together with several proteins
Have more than 200 genes in genome. 100 encode proteins that are contained in virions
genome= single molecule of linear double-stranded DNA
Many proteins encoded by this genome are enzymes involved in nucleic acid synthesis and virion structural components
Also encode proteins that specifically counteract host adaptive and innate immune response
Properties of poxviruses- contt
Replication occurs predominantly in cytoplasm
Possible bc unlike other DNA viruses, poxviruses have evolved to encode the enzymes required for transcription and replication of viral genome
Following replication, virions are released by budding, exocytosis, or cell lysis
Most are not enveloped and released by lysis
enveloped are taken up by cells more readily and appear to be more important in the spread of virions through body of animal
Properties of poxviruses- stability
The virion of poxvirus is an enveloped particle that differs significantly from other enveloped viruses
Unlike other enveloped viruses, poxviruses show a high environmental stability and remain infectious over a period of several months in an ambient environment
Due to their low lipid content, they are less sensitive to organic solvents/disinfectant compared to other enveloped viruses
Poxvirus show an extraordinary high resistance to drying
Can survive for many years in dried scabs or other virus laden material
Properties of poxviruses- transmission
Several routes:
Skin: cannot infect intact skin. must be broken or lacerated. Common
respiratory: by aerosol route. Inhalation= infection
mechanically: by biting arthropods
Pathogenesis and Immunity
Poxviruses are highly epitheliotropic, causing cutaneous (skin) lesions
Occasionally, poxviruses causes systemic diseases in birds and wild animals
Many are host specific
However, orthopoxviruses infect a wide range of species
Spread of poxvirus
Following introduction into the body, the poxvirus usually gains access to the systemic circulation via the lymphatic system
A secondary viremia disseminated the virus back to the skin and to other target organs
Skin lesions in poxvirus infection
There are degenerative changes in the epithelium
Rupture of pustule can predispose to secondary bacterial infection
Ulceration may develop
Poxvirus can survive in dried scabs for many months or years
Order: macule, papule, vesicle, pustule, scab, scar (or ulcer complication)
Macule
Flat, red.
Local inflammation immune response infiltrating leukocytes
Papule
Raised, red
More marked inflammation
Invasion of neighboring tissues
Vesicle
Small blister
Microbe invades epithelium
Genus: Orthopoxvirus
Cowpox
Cowpox: distribution
Endemic only in europe and asia
Cowpox: Hosts
Cattle, wild and domestic cats, humans, zoo animals, etc
Cowpox: Reservoir hosts
Rodents
Cowpox: Transmission
From cow to cow in a herd is through infected milker’s hand or teat cups
Infected farm cats can also transmit the disease
Rodents serve as the reservoir and can transmit the disease
Cowpox: Economic importance
Losses to farmers due to inconvenience in milking because of soreness of teats and mastitis resulting from secondary bacterial infections
Cowpox: Clinical findings
During which cows may be mildly febrile, papules appear on the teats and udder. Sucking calves may develop lesions in mouth
Vesicles may not be evident or may rupture readily leaving raw, ulcerated areas that form scabs
Cowpox in cats: Transmission
Usual route of infection in cats in skin inoculation, probably through a bite or skin wound. Rodents are a common source of infection
Transmission by oro-nasal route is also possible
In exotic felids (cheetahs), viral pneumonia may be evident
Cowpox in cats: clinical signs- Primary lesions
Primary lesions:
Most affected cats have a history of a single primary skin lesion, usually on head, neck, or forelimb
Primary lesion can vary from a small, scabbed wound to a large abscess
Cowpox in cats: clinical signs- Secondary lesions
Secondary lesions:
After the primary lesion appears, widespread secondary ones begin to appear
Throughout 2-4 days, these develop into discrete, circular, ulcerated papules ~0.5-1 cm diameter
The ulcers soon become covered by scabs, and healing is usually complete by ~6wks
Many cats show no signs other than skin lesions, but ~20% may develop mild coryza or conjunctivitis
Complications can result from secondary bacterial infections
Cowpox in humans: transmission
Mainly caused by direct contact to cuddly cats
Rarely from rodents and zoo animals
Virus not commonly found in cattle so chances of getting it from cow is low
Cowpox in humans: clinical signs
Macropapular lesions first observed on hands and face. Later develop into vesicular and then ulcerative lesions
Enlarged painful local lymph nodes
Patients may report fever, vomiting, and sore throat
Monkeypox (other orthopoxvirus): in humans
Viral zoonosis with symptoms in humans similar to those seen in smallpox patients
Monkeypox (other orthopoxvirus): in humans: transmission- primary infection
Results from direct contact with the blood, bodily fluids, or rashes of infected animals.
In africa, human infections have been documented through the handling of infected monkeys, Gambian rats or squirrels
Monkeypox (other orthopoxvirus): in humans: transmission- Secondary transmission
Human-to-human
Resulting from close contact with infected respiratory tract excretions, with the skin lesions of an infected person or with recently contaminated objects
Genus: Parapoxviruses
Pseudocowpox (cattle, humans)
Contagious Ecthyma/Orf virus (sheep, goats, humans)
Bovine Papular Stomitis Virus (cattle, humans)
Pseudocowpox: definition
Viral skin disease that causes mild sores on the teats and udders of cattle
Can also infect humans and the condition is referred to as milker’s nodule
Pseudocowpox: etiology
Member of the genus parapoxvirus
Pseudocowpox: Epidemiology
Reported from most countries
Pseudocowpox: transmission
Source of infection is the infected cattle
Contaminated milkers hand, teat cups
biting insects may transmit virus
Calves get infected during sucking infected teats
semen of bulls
Pseudocowpox: pathogenesis
Lesions are characterized by hyperplasia of squamous epithelium
Pseudocowpox: clinical signs
Infections generally mild
Pseudocowpox: acute lesions
Erythema ->papules -> vesicle or pustule -> rupture -> thick scab
The thick scab is 0.5-25cm in diameter, becomes elevated due to accumulation of granulation tissue
After 7-10 d, the scab drops off, leaving a horseshow shaped ring of small scabs surrounding a small wart-like granuloma
Pseudocowpox: chronic lesions
Commences as erythema Yellow-gray, soft scurfy scabs which are rubbed off during milking Skin is corrugated No pain Lesions may persist for months
Pseudocowpox: Diagnosis
Horseshoe-shaped ring like lesion are pathognomonic for the disease
Isolation and detection of the virus by various diagnostic laboratory methods from vesicular fluid or from teat skin
Pseudocowpox: differential diagnosis
Cowpox virus Bovine herpesvirus ulcerative mammilitis Vesicular stomatitis Udder impetigo Teat chaps and frostbite Black spot
Pseudocowpox: treatment
Removal of scabs
Burn the scabs to prevent environmental contamination
Application of an emollient ointment before milking
Application of astringent preparation after milking
Pseudocowpox: prevention
Disinfection. Use iodophor teat dip
Isolation and tx of infected cows
Reduce teat trauma, as injuries to skin of teat predisposes to infection
Pseudocowpox in humans
Milkers nodule
Causes a milk skin lesion
On hands of dairy farmers milking teats or vet treating infected cows
May vary from multiple vesicles to a single, indurated nodule
Contagious ecthyma (ORF): etiology
Orf virus, Genus Parapoxvirus
Contagious ecthyma (ORF): Host
Sheep and goats. Primarily in lambs and kids
Contagious ecthyma (ORF): Distribution
Worldwide
Contagious ecthyma (ORF): Transmission
Scabs that fall off from the healing lesions contain virus
Virus are stable in the environment- remains highly infectious for long periods under dry conditions
Contaminated instruments, like docking instrument or ear tagging plier can transmit the virus
Spread in flocks v rapid
virus infects healthy animals primarily through damaged skin
Oral lesions in lambs or kids results from nursing dams with teat lesions and vice versa
Contagious ecthyma (ORF): Pathogenesis
Damage of skin is essential to establish infection
Skin reaction to viral infection consists of a cellular response with necrosis and sloughing of the affected epidermis and underlying stratum papillare of dermis
Cutaneous response to infection includes a delayed-type hypersensitivity reaction and an influx of inflammatory cells
Lesions evolve from macule -> papule -> vesicle -> pustule -> ulcers -> scab formation
Contagious ecthyma (ORF): Clinical signs
First lesions develop in the mucocutaneous junction and are accompanied by swelling of lips
From there, lesions spread to muzzle and nostrils, surrounding hairy skin and buccal mucosa
Animal may find it difficult to take food because of oral lesions: anorexia and weight loss
Affected lambs or kids sucking ewes or goats may result in lesions on teats
This may predisose to secondary bact infection, resulting in mastitis
Severe cases may show lesions in genitals, coronets, and ears
Lesions on feet= lameness
Lesions on scrotum= infertility
Contagious ecthyma (ORF): CS (pt 2)
scabs can drop off and underlying tissues heal without scarring
Complications can result from secondary bact infections or from invasion of lesions by fly larvae
Malignant form of disease has also been observed in sheep
Contagious ecthyma (ORF): Vaccination
Prepared from suspension of scabs in glycerol saline and painted onto a small area of scarified skin inside thigh, where a localized lesion develops
In no circumstances should the vaccine be used on farms that do not have a problem with orf
You should inspect lamb 1 wk after vx for local rxn which indicated viability of vaccine
Vx do not offer long-lasting immunity ~1-2 yrs
In problem flocks lambs/kids need to be vx at 6-8 wks
Vaccinate preg ewes before lambing
Contagious ecthyma (ORF): in humans
Macro-papular lesions and large nodular lesions in finger, hand, arm, face, and even penis
secondary bact infections of lesions may cause complications
Genus: Capripoxvirus
Sheep pox
Goat pox
Lumpy skin disease (of cattle)
Sheeppox and Goatpox: etiology
Members of genus Capripoxvirus
Sheeppox and Goatpox: distribution
Endemic in Africa, Asia, and parts of europe
Sheeppox and Goatpox
SPV and GPV once believed to be strains of same virus, but genetic sequencing shows they are separate
Most strains are host specific and cause severe clinical disease in either sheep or goats, while some strains have equal virulence in both spp
SPV and GPV cannot be distinguished from each other with serological tests
Closely related to lumpy skin disease virus in cattle but no evidence LSDV can cause disease in sheep and goats
Sheeppox and Goatpox: transmission
Highly contagious
Virus enters respiratory tract and transmission is commonly aerosol route
Spread can also occur through mucous membrane or abraded skin, esp by direct contact with contaminated iatrogenic materials
Virus is present in nasal and oral secretions for several weeks after infection
Can survive in dry scabs for months
Evidence for mechanical transmission by biting arthropods
Transmission by aerosol (resp route is considered important/common route of transmission)
Sheeppox: pathogenesis
A systemic disease
incubation period is followed by a leukocyte-associated viremia
The virus localized in the skin and other internal organs
Deposition of immune-complexes results in severe necrotizing vasculitis develop in arterioles and postcapillary venules of the skin (type III hypersensitivity)
Results in ischemic necrosis of dermis and overlying epidermis `
Sheeppox: Clinical signs
There are two forms of disease:
Malignant and Benign
Sheeppox: Malignant form
Seen in lambs and susceptible nonnative breeds
Pox lesions develop on skin and on buccal, respiratory, digestive and urinary tract mucosae
Pox lesions extend to pharynx, larynx, lungs, vagina, abomasum and spleen
Secondary pneumonia common
Abortion rare
Cutaneous nodules are distributed widely over body
Nodules, occasionally become vesicular, pustular and finally scab
Lesions heal leaving star shaped scar, free of hair or wool
High mortality and case fatality rate
Sheeppox: Benign form
More common in adults and resistant breeds
Only skin lesions occur
No, or a very mild systemic reaction
Sheeppox: Prevention and control
Notifiable disease in most countries
Sheeppox: Vaccination
A large variety of commercial vxs available, including subunit vaccine
Killed vaccines elicit, at best, temporary protection
Live attenuated vaccines offer excellent protects >1 yr
Goatpox
Occurs in Africa, Asia, and parts of Europe Reportable Clinically similar to sheeppox Young kids suffer systemic disease Milder form of disease seen in adults
Lumpy skin disease: etiology
Member of genus Capripoxvirus
Lumpy skin disease: Distrivution
Enzootic in sub-saharan africa and middle east with recent incursion in iraq
Lumpy skin disease: Transmission
Arthropod vector (most common) also direct contact
Lumpy skin disease: Host
Cattle, all ages and types
Lumpy skin disease: clinical findings
Fever, multiple nodular lesions on skin and mucous membrane, lumphadenopathy
Genus: Suipoxvirus
Swinepox
Swinepox: Etiology
Member of genus Suipoxvirus
Swinepox: Distribution
Worldwide
Widespread sporadic disease
Swinepox: Host
Pigs
Generally benign with low mortality and low morbidity in older pigs
High case fatality in congenitally infected and v young suckling piglets
Swinepox: Transmission
Direct contact with skin injury. Virus can survive in scab for years
Mechanical transmission by pig louse, Haematopinus suis
These lice can carry the virus for weeks or months
Also mechanical transmission by flies and insects
There is evidence of transplacental infection of neonatal pigs
Swinepox: Clinical signs
Typical pox lesions
Skin lesions may occur anywhere but most obvious on skin of abdomen and inner aspects of thighs
Exudative epidermitis (greasy pig disease) and secondary bact dermatitis occasionally occur as a sequel to swine pox
In sever infections, esp in congenitally-aquired pox infections (piglets born w/ or develop lesions all over after birth) lesions may occur in upper resp and gi tracts
Swinepox: Control
Eradication of lice from piggery
No commercially available vx
Genus: Avipoxvirus
Fowlpox and other avian poxviruses
Fowlpox: etiology
Member of genus Avipoxvirus
First virus to be grown in embryonated eggs
Fowlpox: Host
Highly infectious disease of poultry and turkeys
Fowlpox: Distribution
Worldwide
Fowlpox: Transmission
Virus is: extremely resistant to desiccation; can survive in exfoliated scabs for a long time.
Routes:
Within flock through minor wounds and abrasions in mouth, comb, wattles, or skin as result of fighting, pecking or other injuries
Mechanically by mosquitoes, lice, ticks
Possibly aerosol route
Fowlpox: clinical signs
3 forms:
Cutaneous (dry)
Diphtheritic (wet)
Ocular
Fowlpox: Cutaneous form
Most common
Low mortality
Probably results from injecting by biting arthropods or mechanical transmission to injured or lacerated skin
Small papules on comb, wattles, and around beak
Lesions occasionally develop on legs, feet and around cloaca
Nodules become yellowish and progress to a thick scab
Sharp fall in egg production
In uncomplicated cases, affected birds recover in about 4 weeks
Fowlpox: Diphtheritic form
Probs causes by droplet infection
Involved infection of mucous membranes of mouth, pharynx, larynx, and sometimes trachea
Lesions, as they coaslesce, result in necrotic pseudomembrane, which may cause death by asphyxiation
Prognosis poor
Fowlpox: Ocular form
Conjunctivitis
Cheesy exudate accumulates under eyelids
Avipoxvirus: Bollinger bodies
Eosinophilic granular intracytoplasmic inclusion bodies
Avipoxvirus: Borrel bodies
Occur inside bollinger bodies.
Minute spherical bodies obtained by tryptic digestion of bollinger bodies
Fowlpox: Control- Vaccination
Modified live fowlpox or pigeon pox virus vxs of chicken embryo or avian cell culture origin are available commercially
Recombinant fowlpox vectored vxns have been develeoped
Control mosquito pop and other biting insects
Unclassified poxviruses
Ulcerative dermatosis of sheep
Ulcerative dermatosis of sheep: transmission
Virus infection through damages skin or by coitus
Ulcerative dermatosis of sheep: Clinical forms
Lesions usually ulcers with a raw crater that bleeds easily
2 forms:
Lip and leg ulceration
Venereal form
Ulcerative dermatosis of sheep: venereal form
Venereally transmitted ulceration of the prepuce and penis or vulva
Ram can become unfit for natural breeding
Dx of poxviruses
CS
Sampling material: scrapings from skin lesions, vesicular fluid, crusts, scabs
Electron microscopy: characteristic morphology and size of poxviruses
Orthopoxviruses are brick shaped
Parapoxviruses are ovoid
Inoculation of embryonated egg (parapoxviruses do not multiply in chicken embryo)- CAM
Serological assay (ELISA)
Detection of poxvirus nucleic acid by PCR
Dx of poxviruses: histopathology
Presence of characteristic intracytoplasmic inclusion bodies
- type B or Guarnieri inclusion bodies: most poxviruses induce the presence of these. Slightly basophilic and composed of viral particles and protein aggregates
- type A or ATI inclusion bodies: cowpox and ectromelia virus. Strongly eosinophilic
- Bollinger and Borrel bodies in avipoxvirus infection
