7. Poxviridae Flashcards
SUBFAMILIES OF THE FAMILY POXVIRIDAE (2 subfamilies)
Chordopoxvirinae (poxviruses of vertebrates) and Entomopoxvirinae (poxviruses of insects).
MEMBERS OF THE SUBFAMILY CHORDOPOXVIRINAE (FAM. POXVIRIDAE, 8 genera)
[AviCaL MOPaSuYa]
Avipoxvirus, Capripoxvirus, Leporipoxvirus, Mollusipoxvirus, Orthopoxvirus, Parapoxvirus, Suipoxvirus, Yatapoxvirus
MEMBERS OF THE GENUS AVIPOXVIRUS (FAM. POXVIRIDAE, SUBFAMILY CHORDOPOXVIRINAE) (1 species)
FOWLPOX and other Avian poxvirus (e.g. canarypox, turkeypox, etc)
Are Fowlpox virus sensitive or resistant to desiccation?
Fowlpox virus is extremely resistant to desiccation: it
can survive for long periods under the most adverse environmental conditions in exfoliated scabs
Clinical forms of Fowlpox
- Cutaneous form—(most common) —is characterized by small papules on the comb, wattles, and around the beak; lesions occasionally develop on the legs and feet and around the cloaca. The nodules become yellowish and progress to a thick dark scab. Multiple lesions often coalesce. Involvement of the skin around the nares may cause nasal discharge, and lesions on the eyelids can cause excessive lacrimation and predispose poultry to secondary bacterial infections. In uncomplicated cases, healing occurs within 3 weeks.
- Diphtheritic or wet form. Involves infection of the mucous membranes of the mouth, pharynx, larynx, esophagus, and sometimes the trachea. The lesions, as they coalesce, result in a necrotic pseudomembrane, which can cause death by asphyxiation
Diseases that might confuse diagnosis of dihpteric Fowlpox (in the absence of skin lesions)
May be confused with:
- vitamin A, pantothenic acid, or biotin deficiencies,
- T-2 mycotoxicosis-induced contact necrosis,
- other respiratory diseases caused by viruses such as infectious laryngotracheitis virus (a herpesvirus)
Host species of Avipoxviruses
All species of poultry and many wild birds. e.g. Viruses recovered from various species of birds are given names pertaining to their respective host species, such as fowlpox (chickens), canarypox, turkeypox, pigeonpox, magpiepox, etc. each of which exhibits a substantial degree of host-range specificity
Mechanisms of transmission of Fowlpox
- Cutaneous form results from infection by biting arthropods (mosquitoes, lice and ticks), or mechanical transmission to injured or lacerated skin (figthing, pecking)
- The diphtheritic or wet form of fowlpox is caused by infection via droplets. (aerosol).
Primary cell target of chordopoxvirus
Whereas poxviruses (eg, sheeppox virus) that cause systemic infections can infect multiple cell types,
poxviruses that cause localized disease (eg, orf virus, molluscum contagiosum virus) appear to replicate exclusively in epidermal keratinocytes
Rank host sensitivity to Fowlpox virus:
canaries
chickens (large combs and small combs)
ducks
turkeys
pigeons
(highly infectious) chickens (large combs > small combs), turkeys > pigeons > ducks & canaries (resistant)
Turkeypox virus is virulent for which 2 animal species:
canaries
chickens
ducks
turkeys
pigeons
Turkeypox is virulent for turkeys and ducks
Vaccination protocol against Avipoxvirus:
- Vaccines are typically applied in chickens, turkeys, and pigeons by wing-web inoculation, but in turkeys, scarification of the skin of the thigh reduces complications of facial pocks that can occur from head rubbing of wing-web inoculation site. One vaccine can be administered in drinking water.
- In flocks with enzootic infection, birds are vaccinated during the first few weeks of life and again 8-12 weeks later.
Types of vaccines against Avipoxvirus:
Nonattenuated fowlpox virus and pigeonpox virus vaccines prepared in embryonated hens’ eggs, and live-attenuated virus vaccines prepared in avian cell cultures are widely used for vaccination.
Recombinant vaccines for poultry have been developed using either fowlpox or canarypox viruses as vectors. In poultry, fowlpox-vectored vaccines have been licensed with gene inserts for:
- Newcastle disease virus,
- H5 and H7 avian influenza viruses,
- infectious laryngotracheitis virus,
- infectious bursal disease virus, and
- Mycoplasma spp.
[These viruses have also been utilized as vaccine vectors in mammals, for example for expression of rabies glycoprotein C for immunization of cats, the HA and F glycoproteins of distemper virus for immunization of dogs, and the H3 hemaggluinin of influenza A virus and premembrane and E glycoproteins of West Nile virus for use in horses]
Which viral Family has the following characteristics:
Virions in most genera are brick-shaped (220-450x140-260 nm), with an irregular arrangement of surface tubules. Virions of members of the genus (1) are ovoid (250-300x160-190 nm), with a regular crisscross arrangement of surface tubules (ball of yarn).
Virions have a complex structure with a core, lateral bodies, outer membrane, and sometimes an envelope. Genome is composed of a single molecule of linear dsDNA, 130-150 kbp (genus1), 170-250 kbp (genus 2), or 300 kbp (genus3 ) in size. Genomes have the capacity to encode about 200 proteins. Unlike other DNA viruses, these encode all the enzymes required for transcription and replication.
Cytoplasmic replication, mature (nonenveloped) virions released by cell lysis or budding; enveloped virions released by exocytosis.
Family Poxvirus.
Genus 1: Parapoxvirus
Genus 2: Orthopoxvirus
Genus 3: Avianpoxvirus
MEMBERS OF THE GENUS CAPRIPOXVIRUS (FAM. POXVIRIDAE, SUBFAMILY CHORDOPOXVIRINAE) (3 species)
SHEEPPOX VIRUS,
GOATPOX VIRUS, and
LUMPY SKIN DISEASE VIRUS
Morbidity and mortality of lumpy skin disease and significance of disease.
Morbidity in susceptible herds can be as high as 100%, but mortality is rarely more than 1-2%. Breeds of cattle such as the Jersey and Guernsey may have enhanced susceptibility.
The economic importance of the disease relates to the prolonged convalescence and, in this respect, lumpy skin disease is similar to foot-and-mouth disease.
Age, morbidity and mortality of sheeppox and goatpox?
Sheep and goats of all ages may be affected although disease is typically more severe in young and/or immunologically naı¨ve animals.
An epizootic in a susceptible flock: morbidity over 75% of the animals, with mortality as high as 50%; case-fatality rates in young and/or naı¨ve sheep may approach 100%.
Animal species susceptible to the genus Capripoxvirus
- lumpy skin disease virus infects only cattle,
- some strains of sheeppox and goatpox viruses may infect both sheep and goats. Most isolates of sheeppox and goatpox viruses, however, cause more severe disease in either sheep or goats and only mild or asymptomatic infection in the other species
Clinical signs of Lumpy Skin virus?
- Fever, followed shortly thereafter by the development of nodules in the skin that can cover the entire body. Generalized lymphadenitis and edema of the limbs are common. During the early stages of the disease, affected cattle show lacrimation, nasal discharge, and loss of appetite.
- The skin nodules involve both the dermis and epidermis; they are raised and later ulcerate, and may become infected secondarily. Ulcerated lesions may be present in the mouth and nares.
- Healing is slow and affected cattle often remain debilitated for several months. Signs are similar to foot-and-mouth disease.
Clinical signs of sheeppox/goatpox virus?
Incubation period of 4-12 days.
- There is an increase in temperature and respiratory rate, edema of the eyelids, lacrimation, and a mucous discharge from the nose. Affected sheep may lose their appetite and stand with an arched back.
- One to 2 days later, papules (skin nodules) up to 1 cm in diameter develop apparently randomly on the skin and in the subcutis. In enzootic regions, the more common presentation is a few papules beneath the tail; in naı¨ve animals, however, the papules may extend widely over the body, with the most obvious lesions in areas of skin where the wool is shortest, such as the head, neck, ears, axillae, and under the tail.
- These lesions usually scab and persist for 3-4 weeks, healing to leave a permanent depressed scar. Lesions within the mouth affect the tongue and gums, and ulcerate. Such lesions constitute an important source of virus for infection of other animals. In animals that survive the infection, infectious virus can be detected in some secretions for up to a month following resolution of acute disease.
Geographic distribution of sheeppox, goatpox, and lumpy skin disease
- Sheeppox and goatpox extends from Africa north of the Equator into the Middle East and Asia, including regions in India and China. More recently, the diseases have expanded their range into Vietnam, Kazakhstan, and Mongolia, with incursions in Greece, Bulgaria, Israel, Russia, and Taiwan.
- Lumpy skin disease. Largely a sub-Saharan endemic disease in the past century, has extended its range into Egypt and Israel, with recent incursions into various regions of the Middle East.
- Capripoxviruses are not present in the Americas, south East Asia (excluding Vietnam) or Australasia.
Importance of the genus Capripoxvirus
Sheeppox, goatpox, and lumpy skin disease of cattle are considered, collectively, to be the most important poxviral diseases of livestock as they cause significant economic losses due to reduced milk production, increased abortion rates, decreased weight gain, increased susceptibility to secondary bacterial infections, and high mortality.
Negative impact on international trade of livestock and livestock products, and are on the World Organization for Animal Health list of important animal diseases that need to be notified
Methods of transmission of genus Capripoxvirus? (Sheeppox, goatpox and lumpy skin virus)
Common with most poxviruses:
Sheep or goat poxviruses:
- environmental contamination can lead to the introduction of virus into small skin wounds. Scabs shed by infected sheep remain infective for several months. The common practice of herding sheep and goats at night in countries where the disease occurs can provide sufficient exposure to maintain enzootic infection.
- During an outbreak, the virus is probably transmitted between sheep by respiratory droplets;
- Mechanical transmission by biting insects, such as stable flies, may be important.
Lumpy skin disease virus:
- Mechanically between cattle by biting insects
Pathology of Sheeppox, goatpox, and lumpy skin disease
- systemic diseases, with cell-associated viremia preceding the appearance of lesions and marked lymphadenopathy.
- blood monocytes spread virus to secondary sites of infection. Distinct tropism for keratinocytes.
- Skin lesions: hyperplasia and ballooning degeneration of keratinocytes of the stratum spinosum, formation of epidermal microvesicles, and infiltration of inflammatory cells into the dermis.
- In lumpy skin disease: epidermal microvesicles coalesce into large vesicles that quickly ulcerate.
- Severe sheeppox and goatpox: Nodular proliferative lesions can occur internally: lungs and forestomachs, (less frequently in liver, tongue, and kidneys). Lung lesions are markedly proliferative, involving hyperplasia of type II pneumocytes and the bronchiolar epithelium. The presence of mature viral particles (= productive viral replication).
Wildlife reservoir host of Lumpy skin virus?
Affrican Cape buffalo
Diagnosis of Capripoxvirus species (i.e. sheeppox, goatpox, lumpy skin virus)
- sheeppox and goatpox:
- clinical diagnosis (DD with orf)
- laboratory diagnosis:
- Several serological and PCR-based tests
- negative-contrast electron microscopy
- viral isolation in cell cultures (derived from sheep, cattle, or goats; cytopathology and cytoplasmic inclusion bodies)
- Lumpy skin disease:
- clinical diagnosis (early skin lesions can be confused with pseudo lumpy skin disease, caused by bovine herpesvirus 2)
- Several serological and PCR-based tests
MEMBERS OF THE GENUS PARAPOXVIRUS (FAM. POXVIRIDAE, SUBFAMILY CHORDOPOXVIRINAE) (3 species)
ORF VIRUS (CONTAGIOUS ECTHYMA/CONTAGIOUS PUSTULAR DERMATITIS VIRUS),
PSEUDOCOWPOX VIRUS,
BOVINE PAPULAR STOMATITIS VIRUS
