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12 Cards in this Set
- Front
- Back
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What are the key points about poxviridae?
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-enveloped DNA viruses
-complex symmetry -replicate in cytoplasm -stable in the environment -skin lesions a prominent feature -individual pox viruses tend to infect a particular host species; some pox viruses are not species specific |
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Describe the viral properties, pathology & clinical signs, immune response, epidemiology, diagnosis, and control of poxviridae
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♦PROPERTIES
-brick shaped -parapoxviruses are cocoon shaped -complex with an outer layer of irregularly arranged tubular structures -resistant to inactivation in the environment, surviving on died scabs and other contaminated material for years ♦PATHOLOGY and CLINICAL SIGNS -typical lesion is a raised, reddened macule, which progresses to a papule, to a fluid-filled vesicle and then to a pustule, which ruptures to form a crater-like pock -healing may be accompanied by scarring -clinical signs are referable to the skin lesions in affected areas (ie. around mouth of lambs with parapox infection, on teats of cows with cowpox) or they may reflext the organ damage that occurs with those poxviruses that cause severe generalised infection (e.g. respiratory signs in sheep with sheep pox) -mortality is high in generalised infections (>80%) e.g. sheep pox, and recovery likely if localised ♦IMMUNE RESPONSE -humoral and CMI responses follow infection and there is resistance to reinfection -the duration of protection from reinfection within defined populations varies with the specific disease e.g. lambs need to be vaccinated for sheep parapox virus every year, humans are vaccinated every 10 years for smallpox ♦EPIDEMIOLOGY -animals which recover are not long-term carriers of virus -infectious virus survives for years on contaminated material -the duration of immunity is less than the lifespan of the animal -the virus persists within an infected population b/c it's in the environment and when immunity wanes, the animals become susceptible again -transmission of infection may be by entry of virus from a contaminated environment into abraded skin (eg. sheep parapoxvirus), by respiratory route by droplets from infected animals (eg. sheep pox) or by mechanical transmission by biting arthropods (e.g. rabbit myxomatosis) ♦DIAGNOSIS -usually possible based on clinical signs including the presence of pock lesions on skin or, in the case of generalized pox infections like sheeppox, by post-mortem examination for typical lesions -conformation if needed is done by electron microscopy of scab material or microscopy of biopsy specimens (eosinophilic, intracytoplasmic inclusion bodies are commonly seen in appropriate specimens) ♦CONTROL -vaccination is key -severe disease with sheep parapoxvirus infection occurs in lambs, which can be protected through the critical phase by prior vaccination with live virus vaccine -avoidance of skin trauma allowing entry of virus from the environment is important with some poxviral infections as is protection from biting arthropod vectors for those that are transmitted this way |
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Coxpox
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-doesn't occur in Australia
-the reservoir hosts are rodents from which the virus may spread to infect cattle, cats, humans and a wide range of zoo animals -in cattle pock lesions are on the teats and adjacent areas of the udder -diseases in cats is severe and may start as a single head or limb lesion but this becomes widespread -in zoo cats e.g. cheetahs, fatal pneumonia is common -human infection manifests as maculo-papular eruptions on the hands, face, often with systemic signs of nausea, fever, and lymphadenopathy |
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Monkeypox
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-human infection is acquired from wild animals, particularly monkeys
-it resembles smallpox and smallpox vaccination provides protection -human to human spread is rare -can come from rats |
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Sheeppox and goatpox
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-infection is systemic in sheep or goats and clinical signs include pox lesions overt the whole body surfact as well as respiratory distress and signs referable to infection of the liver and other organs
-mortality as high as 50% -spread between animals in close proximity is by arthropods and may also be important in mechanical transmission of infection -both attenuated and inactivated vaccines are used in endemic areas |
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Lumpy skin disease of cattle
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-closely related to sheeppox and capripox viruses, affects cattle throughout Africa
-most obvious lesions are in skin (reflecting the name of the disease) but generalized infection may also occur particularly affecting the lungs and alimentary tract -vaccines are available for control and are derived from either an attenuated strain of the virus or from sheep/goatpox virus that has been propagated in tissue culture -mechanical transmission by biting arthropods occurs |
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Swinepox
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-mild disease with typical pox lesions confined to the skin
-pig louse Haematopinus suis acts as a mechanical vector -infection can be controlled by eliminating lice and by improving hygiene |
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Myxomatosis
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-causes only a benign localized fibroma in wild rabbits in the Americas but a generalized disease in European rabbits, with high mortality (99% within 12 days)
-mosquitoes act as mechanical vector although ticks, black flies etc. can as well -clinical signs of head swelling, blepharitis, and gelatinous, subcutaneous swellings enable presumptive diagnosis -in Australia attenuated strans have appeared an the rabbit populations have become more resistant |
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Fowlpox
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-serologically related to poxviruses and has been isolated from poultry and a wide range of other birds
-severe disease in domestic poultry includes extensive pock lesions on the unfeathered areas and diptheric inflammation in the trachea -virus is spread by aerosol droplets & biting insects -can use vaccination with live attenuated or heteologous virus (applied by skin scarification but one vaccine can be put in water) |
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Orf (contagious pustular dermatitis, "scabby mouth")
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-parapoxviral disease of sheep
-may cause significant losses of lambs that are unable to suck because of the lesions around the mouth -they starve to death -harsh feed (thistles & stubble) is important in creating lesions that allow entry of the virus -diagnosis can be made on clinical signs -control is by vaccination applied by scarification in the inner thigh or axilla -immunity < 1 year -humans may be infected by handling infected sheep or goats or by inadvertent self inoculation with the vaccine virus |
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Pseudocowpox and papular stomatitis
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-caused by parapoxviruses
-manifested by lesions of the teat of cows arranged in a characteristic horseshoe pattern -similar lesions occur in thr mouths of calves -mechanical transmission between cows by milking machine teat clusters is usual in outbreaks and flies may act as mechanical vectors |
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Describe the properties, pathology & clinical signs, immune response, epidemiology, diagnosis and control of African swine fever virus.
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♦PROPERTIES
-large, enveloped, icosahedral capsid -ds DNA -the virus is inactivated at moderately raised temperatures and in the presence of lipid solvents -resistant in a wide pH range and survives for months or longer in refrigerated meat -member of the family Asfarviridae, genus Asfivirus -ONLY DNA VIRUSES THAT IS A TRUE ARBOVIRUS (spread & replicates in arthropods); transmitted by soft ticks of the genus Ornithodoros ♦PATHOLOGY & CLINICAL SIGNS -only pigs can be infected -in Africa, warthogs and bush pigs become infected but severe clinical disease with high mortality is only seen in domestic pigs -infected pigs develop a high fever, diarrhea, become uncoordinated and prostrate, and may die at this stage without other signs -some pigs have dyspnea, vomiting, cyanosis of the ears and snout and haemorrhages from the anus and nose -pregnant sows abort -mortality may be 100% in 1-3 days of onset of fever -at necroscopy there are extensive hemorrhages, & lymph nodes may resemble blood clots -spleen is enlarged -petechial hemorrhages on kidney -virus replicates in many cell types of the reticuloendothelial system causing severe leukopenia -in infected macrophages the virus inhibits synthesis and secretion of a range of antivirul immune modulators including interferons -persistent infection in warthogs -pugs that survive may appear normal or chronically sick, they remain persistently infected ♦IMMUNE RESPONSE -virus specific antibodies detected in infected pigs but they do not neutralize the virus -no vaccine ♦EPIDEMIOLOGY -ticks become infected from viraemic warthogs (juveniles) and infection within tick populations is maintained by sexual, trans-ovarial and trans-stadial transmission -when infected ticks attach to susceptible pigs, they transmit infection to them -infection may also be transmitted pig to pig in the absence of ticks and infection may become endemic in pig populations with persistently infected recovered pigs -disease spreads by contact and, within buildings by aerosol ♦DIAGNOSIS & CONTROL -clinical sign suggestive but confirmation is needed by virus isolation in swine macrophage cultures and detection of specific antibody in serum of recovered pigs -control & eradication is difficult -eradication involves slaughter of infected and in contact swine, safe disposal of carcases, and prohibition of movement of swine between premises and feeding of wast food -where soft ticks are known to occur, spray with acaricides |
