Poxviruses in Veterinary Science

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Questions and Answers

What is a significant characteristic of poxviruses?

Cylindrical virion shape

Large double stranded DNA genome (correct)

Single-stranded RNA genome

No lipid membrane structure

Which of the following poxviruses is associated with cattle?

Swinepox virus

Pseudocowpox virus (correct)

Cowpox virus

Myxoma virus

What differentiates poxviruses from other DNA viruses in terms of morphology?

Only able to infect vertebrates

Presence of a single envelope

Only pleomorphic shapes

Two lateral bodies for replication enzymes (correct)

Which poxvirus is known to affect rabbits?

Myxoma virus Signup and view all the answers

Which feature allows poxviruses to infect a broader range of hosts?

Double stranded DNA genome Signup and view all the answers

What is a significant risk when vaccinating against the Orf virus?

Potential transmission of the virus to unvaccinated animals Signup and view all the answers

Which rabbit breed is most prone to serious myxomatosis disease?

European rabbit Signup and view all the answers

How does myxoma virus typically spread among rabbits?

Via direct contact or biting insects Signup and view all the answers

What is the primary infection site for the myxoma virus?

Skin Signup and view all the answers

Which aspect of myxoma virus vaccination is important in endemic areas?

Vaccination of pet rabbits due to insect transmission risk Signup and view all the answers

What is the primary cause of cowpox infections in cats?

Rodents acting as a virus reservoir Signup and view all the answers

Which of the following is a characteristic of swinepox?

Heals without scarring Signup and view all the answers

What is a common outcome for cheetahs infected with cowpox?

High mortality rate due to pneumonia Signup and view all the answers

What is the most severe manifestation of cowpox infections in people?

Pneumonia leading to hospitalization Signup and view all the answers

Which disease form of fowlpox results from infection via inhalation?

Diphtheritic form Signup and view all the answers

How is swinepox primarily transmitted?

Via insect vectors and direct contact with lesions Signup and view all the answers

Which diagnostic method is NOT typically used for fowlpox?

Serological testing Signup and view all the answers

What type of lesions are characteristic of cowpox in dairy cows?

Papules or ulcerated areas that form scabs Signup and view all the answers

What is the primary causative agent of infectious laryngotracheitis (ILTV)?

GHV-1 Signup and view all the answers

What is a key characteristic that distinguishes bovine papular stomatitis from foot and mouth disease?

Absence of foot lesions Signup and view all the answers

What is the method of vaccination for chickens against infectious laryngotracheitis?

Wing web method or in ovo Signup and view all the answers

Which age group of cattle is primarily affected by small erosion lesions in bovine papular stomatitis?

Cattle less than 2 years Signup and view all the answers

What is a common source of infection for the Orf virus in young animals?

Direct contact and fomites Signup and view all the answers

What is a significant risk associated with Pseudocowpox infections in humans?

Skin lesions on hands Signup and view all the answers

What is one of the primary clinical signs of the Orf virus in young lambs?

Papules and pustules on the lips Signup and view all the answers

How long can the Orf virus remain resistant in the environment, particularly in dried crusts?

Several years Signup and view all the answers

What distinguishes poxviruses in their pathogenesis?

They cause only acute infections without any carrier state. Signup and view all the answers

Which factor contributed to the successful eradication of smallpox?

WHO implemented a coordinated vaccination program. Signup and view all the answers

Which statement about the replication of poxviruses is true?

Replication occurs in the cytoplasm. Signup and view all the answers

What characteristic of poxviruses poses a potential bioterrorism threat?

They can be easily synthesized in laboratories. Signup and view all the answers

Which poxvirus is recognized as being very species-specific?

Cowpox virus. Signup and view all the answers

Which of the following routes can poxviruses use for infection?

Through the skin, respiratory tract, and oral route. Signup and view all the answers

What is a common feature of all poxviruses?

They replicate in the cytoplasm and are large DNA viruses. Signup and view all the answers

Which condition makes poxviruses particularly effective at infecting hosts?

They possess complex immune evasion strategies. Signup and view all the answers

What are the clinical signs associated with a Myxoma virus infection in European rabbits?

Fever and anorexia Signup and view all the answers

Which of the following methods is appropriate for diagnosing Myxoma virus?

Histology showing myxoma cells Signup and view all the answers

What is the recommended control measure for Myxoma virus in the UK?

Vaccination with a live myxoma-vectored RHD vaccine Signup and view all the answers

What type of infection is caused by Ectromelia in mice?

A systemic infection leading to disseminated infection Signup and view all the answers

Which mouse strains are noted to be susceptible to Ectromelia?

BALB/c Signup and view all the answers

What is the primary mode of infection for Ectromelia in mice?

Direct contact with contaminated surfaces Signup and view all the answers

What is one significant clinical outcome observed in resistant strains of mice infected with Ectromelia?

Ability to spread the virus without showing symptoms Signup and view all the answers

What distinguishes intermediate susceptible strains of mice from resistant and highly susceptible strains in the context of Ectromelia?

Can shed the virus after developing skin lesions Signup and view all the answers

Study Notes

Poxviruses

Poxviruses are large, double-stranded DNA viruses (130-375 Kbp).
They are enveloped by a core membrane and two lateral bodies containing replication enzymes.
They can infect both vertebrate and invertebrate animals, but many are species-specific.
Some are zoonotic.
They have oval, brick-shaped, or pleomorphic shapes.
They replicate exclusively in the cytoplasm.
They cause acute infections with no persistent or chronic stages.
Infection routes are diverse: skin, respiratory tract, and oral.
The resulting infection forms can be local or systemic, which can be fatal.
Poxviruses have two subfamilies, Chordopoxvirinae and Entomopoxvirinae.

Poxvirus Structure

Virion properties include having large double-stranded DNA (genome) that is 130-375 Kbp, and are enclosed by a core membrane and 2 lateral bodies (replication enzymes).
Presence of one or two (envelope) lipid membranes.
Shapes vary, including oval, brick-shaped, or pleomorphic.
Host range is extensive, including vertebrate and invertebrate animals.
Many are species-specific, but some are zoonotic.
Virion size ranges between 220-450 nm in length & 140–260 nm in width, containing numerous virion enzymes.

Poxvirus Replication

Replication occurs in the cytoplasm (exception for DNA virus). This process leads to the formation of cytoplasmic inclusion bodies.
The replication cycle is complex and involves several stages (early, intermediate, and late).
Replication progression is described as cytoplasmic.
Viral particles mature, wrapped, and transported out of the cell via exocytosis.

Poxvirus Pathogenesis

Poxviruses have a variety of routes of infection, including through the skin or the respiratory tract or oral route.
Acute infections produce either local (skin lesions) or systemic (often fatal) consequences depending on the entry route.

Poxvirus Properties

Poxviruses have a long evolutionary history with smallpox infecting pharaoh Ramses V ~1000 BC.
Large genomes, are commonly used as vectors for gene therapy or recombinant vaccines (rabies, wildlife, canarypox).
Diverse immune evasion strategies, and smallpox is eradicated (vaccine).
Public health concern about MPOX (monkeypox).

Poxvirus Successful Eradication Causes

Presence of no animal reservoir aside from humans in the case of smallpox.
Variola virus creates only acute infections (no long term carrier state).
Coordinated vaccination programs (cheap) with a needle.
Simple surveillance due to observable rash localizations of various pox virus infections.

Poxvirus Subfamilies

Poxviruses include a variety of genera within two subfamilies: Chordopoxvirinae and Entomopoxvirinae.

Cowpox

General features: Orthopoxvirus genus, similar to smallpox, now rare in Western Europe.
Observed in cows, affecting the udder and teats (papules or ulcerated areas, scabs).
Zoonosis capable of affecting humans and causing localized lesions, especially in Western Europe.
Can cause mild lesions in humans, and is a zoonosis that is prevalent primarily in Western Europe.
It inspires the first smallpox vaccine in humans.

Cowpox in Cats

Cats in Eurasia get Cowpox from rodents.
A single lesion can progress to a more widespread skin rash (erythematous macules, vesicles → ulcers→ scabs).
Recovery takes 6-8 weeks, but concurrent infections can cause death, especially pneumonia.
Cheetahs are particularly vulnerable.

Cowpox in Humans

Eurasia is the most common source of cowpox in humans.
Cats are the most common vector for human infection.
Localized skin lesions are the primary symptoms.
Fever, general malaise, and lymphadenopathy are also possible.
Children are often more severely affected.

Swinepox

General features: Suipoxvirus genus, worldwide presence but low incidence in the Midwest, USA.
Mostly affects piglets with papules and pustules on the face, ears, legs, and abdomen, which become scabs and heal without scarring.
Control strategies include eradicating pig lice, an important vector.

Fowlpox

General features: Avipoxvirus genus, widespread in poultry, especially backyard chickens.
Two forms:
- Cutaneous: skin lesions, thick scab formation.
- Diphtheritic: diphtheritic membranes; affect upper respiratory (and/or gastrointestinal) tract.
Pathogenesis - characterized by Infection routes include biting insects (mosquitoes) and wound contamination.
Clinical signs include Skin lesions on the comb, beak. Recovery within a few weeks.
Diphtheritic form is usually more severe, characterized by inhalation and sloughed necrotic membrane formation in the pharynx and trachea → often fatal.
Histology includes Bollinger bodies in cytoplasm , can be confused with GHV-1 infections.
Control strategy includes management of mosquito populations, vaccination (often with pigeon pox), and recombinant fowlpox vaccine.

Pseudocowpox

General features: Parapoxvirus genus. It's an important diagnostic differentiator from Foot and Mouth Disease.
Cause of bovine papular stomatitis.
Most cases go unnoticed.
Small erosions occur mainly on margins of the lips, muzzle, and buccal mucosa; heal within weeks in cattle younger than 2 years.
Adult cattle show teat lesions.
Frequent reinfections due to short immunity.
Zoonotic (farmyard pox, especially milkers → hand lesions).
Clinical signs include lesions on the hard palate and gums.

Orf Virus

General features: Parapoxvirus genus, also known as ecthyma contagiosum.
Primarily affects lips of young animals, but usually more severe in goats.
Highly resistant to the environment, especially in dry crusts (lasting for years).
Differential diagnosis can be challenging from other pox viruses.
Zoonotic.
Pathogenesis is direct contact and fomites, scratches from thistles.
Clinical signs include papules and pustules → scabs on the lips and muzzle of young lambs that heal without scarring.

Orf Virus (Diagnosis, Treatment, and Control)

Diagnosis is achieved through observation of clinical signs and confirmation using methods like EM or PCR on scab materials.
Prevention of secondary bacterial infections.
Vaccination is a strategy. Live vaccines, small amount are used in light scarifications of the skin (thigh or elbow) of unvaccinated animals; wait until scabs heal before vaccination.

Myxoma Virus

General features: Leporipox genus, spreads via direct contact to biting insects (fleas, mosquitoes).
Clinical outcomes vary by rabbit breed: -Mild cutaneous fibroma in wild hosts (Argentinians, Mexicans, Californians). -Serious, life-threatening systemic disease (myxomatosis) in European rabbits.
Reportable disease; a serious disease that has been introduced to help curb rabbit populations.

Myxoma Virus (Pathogenesis)

Primary infection in the skin replicates in dermal tissue causing mild primary skin lesions, followed by infection.
Langerhans cells migrate to draining lymph nodes via 'viremia', infecting T-cells—spreading through blood and lymph to the liver, spleen, and other lymph nodes—and causing secondary viremia, with secondary replication in the dermis resulting in high levels of virus.
This causes high viral titers in the secondary skin lesions.

Myxoma Virus (Clinical Signs)

Californian rabbits (Sylvilagus bachmani) show localized fibromas.
European rabbits (Oryctolagus cuniculus), are more severely affected, developing lumps, skin lesions, facial edema, conjunctivitis, weeping eyes, fever, anorexia, secondary bacterial infections, and eventually death in 2-14 days.

Myxoma Virus (Diagnosis)

Clinical signs are observable. Histology involves observing large stellate connective tissue cells with a large nucleus and abundant cytoplasm. (myxoma cells).
The identification of cytoplasmic inclusion bodies within the epithelium of cells through microscopy confirms diagnosis.

Myxoma Virus (Treatment and Control)

No treatment for the disease, Euthanasia of the affected pet rabbits.
Vaccination was used in the UK (with a live myxoma-vectored RHD vaccine), but now banned in areas like Australia.
Flea and mosquito control is used to help control spread in the US.

Ectromelia

General features: Orthopoxvirus genus, a natural pathogen for mice. Observed primarily in mouse colonies.
Infection through skin abrasions, via direct contact, to contaminated fomites.
Diverse effects ranging from localized skin lesions (feet, snout, belly) to highly fatal outcomes (extensive necrosis).
The outcome of infection is variable, determined by the strain of the mice. Mice have varying outcomes.

Ectromelia (Pathogenesis)

Primary viremia occurs when the virus infects the liver and spleen, causing high titers and necrosis.
First a primary skin lesion develops via infection.
Virus then replicates in the skin, spreading to lymph nodes and causing secondary viremia that moves to the skin, resulting in a generalized rash.

Ectromelia (Clinical Signs)

Susceptible mouse strains (BALB/c) show rapid death before virus shedding.
Intermediate-susceptible strains result in skin lesions but they survive long enough to spread the infection (important for outbreaks).
Resistant strains (C57/BL6) may spread the virus without exhibiting clinical signs.

Ectromelia (Diagnosis and Control)

Rapid diagnosis of necrosis of tissues and cytoplasmic inclusion bodies is crucial.
Prevention involves isolation, importation restrictions, and serological testing (ELISA).
Vaccination with vaccinia virus is possible, but interferes with ELISA testing.

Take Home #2

Cowpox: Rare in cattle, zoonotic, causes localized skin lesions (mostly in cats from rodents).
Fowlpox: Two forms (skin vs. respiratory membranes), Bollinger bodies, zoonotic.
Pseudocowpox: Important for differentiating from FMD, zoonotic, causes skin lesions, margins of lips, muzzle, buccal mucosa etc..
Orf virus: Ecthyma contagiosum, mainly on lips, zoonotic, can occur in young animals.
Myxoma virus: Fatal disease in European rabbits, zoonotic, but causes mild effects in other rabbits.
Ectromelia: Mouse pathogen causing fatal disease in mouse colonies (effects range by strain).

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Description

This quiz explores significant characteristics of various poxviruses, their impact on different animal species, and vaccination considerations. Participants will answer questions about the transmission, morphology, and specific diseases related to cattle, rabbits, and other animals affected by these viruses.