Emerging Virus Infections

• emerging viruses are ones that until recently have not been cause for serious public or animal health concern 
• most emerging human viruses are initially zoonoses transmitted from an animal host and undergone adaptation to be maintained in the human host 
• emerging animal viruses often originate from an animal reservoir and undergo cross-species adaptation 
• viruses that have shifted their geographical location are also seen as emerging viruses 

• West Nile Fever - Old virus new location 
• Bluetongue/African Horse sickness - vector changes, climate change and re-emergence
• Henipaviruses - cross-species transmission, encroachment 
• Schmallenberg - out of the blue, importance of disease surveillance 
• Foot and Mouth disease - old enemy, need for constant vigilance 

• first isolated in West Nile district, Uganda, 1937 
• 25% of human infections show mild symptoms - fever, aches, occasional rash and lymph node swelling
• small percentage of these develop encephalitis, ~10% die 
• severe disease in horses 
• transmitted by Culex pipiens mosquitoes 
• short duration, sylvatic life cycle in passerines 
• humans and horses are incidental, dead-end hosts

• member of Japanese Encephalitis virus complex 
• geographically restricted and originally absent from USA 
• introduced to NY state from Middle East in 1999 - unknown source 
• spread rapidly N>S along bird migration routes and E>W
• naive bird popualtion highly susceptible 
• very high attack rate in the primary wave when virus first entered a region/state 
• subsequent years herd immunity causes incidence to fall 
• 2002 - incidence soared - climate reasons? - adaptation of virus?
• massive incidence in horses especially in colorado 
• virus is now endemic - incidence of disease has fallen 
• serological evidence that WNFV circulates in UK but no evidence of disease or isolation of live virus from screening 

Closely related paramoxyviruses 50% fatality in humans 

Hendra  

• fatalaties due to pneumonia and/or encephalitis 
• outbreak in 1994 killed 13/24 racehorses and 2/3 humans 
• one farmer infected after PM on horse, one was a year after apparent recovery 
• may also infect cats and dogs 

Nipah 

• fatalaties due mainly to encephalitis 
• 1999 large outbreak caused by Nipah virus occured in Malaysia 
• 265 human cases - 105 deaths 
• most human cases could be traced to contacts with pigs (amplifier species)
• Nipah was found in 6% of pig farms in Malaysia 1-5% mortality pigs 40% in piglets 
• end of outbreak pig stocks reduced by 50% - culling
• 2004 recent outbreak in Bangladesh - no pigs involved 
• direct transmission to humans - human-to-human transmission 
• virus circulation in African fruit bats 

• originated from fruit bats
• nasal/oral transmission requiring direct contact 
• virus excreted in urine and saliva 

Hendra                                                                 

• Horse to human transmission (rare)
• Horse to horse transmission inefficient
• Cats susceptible - transmit to horses
• No human-human, cat-cat, horse-cat transmission

Nipah

• Pig to human transmission inefficient, relatively rare
• V efficient pig-pig transmission (100% morbidity)
• also infects dogs, cats, horses and goats

• Bunyaviridae - close relative of Shamonda virus 
• first recognised - summer 2011 on continent
• causes diarrhoea and milk-drop in cattle 
• also transplacental infection and abnormalities in sheep 
• deformed lambs - arthrogryposis hydranencephaly syndrome - is what alerted APHA
• very rapidly identified using 'next gen sequencing' and diagnostic PCR developed 
• identical to virus in NL/Belgium and Germany
• re-emerged Jan 2012, spread in south, 2013 all UK and Europe

• bunyavirus
• arbovirus spread by Culicoides pulicaris, dewulfi and obseletus
• hosts - cattle, sheep and goats (and dogs) 
• serological evidence for infection in all species of deer (and alpacas) found in UK
• rapidly declined in subsequent years - high herd immunity 
• in 2016 currently absent from UK - still considered a potential threat 

• little known about specific pathogenesis 
• very high intra-herd prevalence of mild symptoms of acute infection 
• increased temp - not necessarily fever
• diarrhoea - not necessarily 
• very short, pronounced viraemia 
• sites of viral replication largely undetermined but replicates extensively in neurones 
• vaccines now available - SBVax and Bovillis 

• 7 serotypes - large number of antigenically distinct subtypes 
• wide geographic distribution  - esp Africa, Middle East, Southern and Eastern Asia and India 
• Pan-Asiatic type O most widely distributed and has caused most recent outbreaks in countries free from FMDV 
• susceptible species (and others)
  • cattle
  • goats
  • sheep
  • pigs
  • buffalo
  • zebu 

• clinically indistinguishable from other vesicular virus diseases 
• signs in cattle include salivation, depression, anorexia, lameness, caused by painful vesicles in skin of lips, tongue, gums, nostrils, coronary bands, inter-digital spaces and teats 
• fever and decreased milk production usually precede appearance of vesicles 
• vesicle rupture, leaving large denuded areas prone to secondary infection 
• in pigs, sheep and goats clinical signs are similar but milder
• lameness is predominant sign 

• respiratory infection results in initial asymptomatic replication in the pharynx
• virus detected in the soft palette and tonsils 
• virus spreads systemically to many tissues and organs before the onset of clinical disease
• replication in stratum spinosum at multiple eplithelial sites leads to vesicle formation 

• one of the most infectious viruses known 
• lots of virus in breath, saliva, faeces, urine, and milk - up to 4 days before clinical signs 
• pigs shed a particularly large amount of virus 
• cattle infection usually respiratory 
• pigs via ingestion of infected foods - need higher dose
• other routes - insemination with infected sem en; contact with contaminated clothing, instruments, vehicles and people 
• inadequately activated vaccine caused 1981 outbreak (France) - major factor or ceasing use of vaccine in Europe 

• most likely route into UK is illegal importation of meat and unprocessed swill feeding 
• bio-terrorism possibility for the future 
• long distance - airbone plumes, esp. in temperate climates, transport vehicles eg UK 2007 
• local spread - within 3km of another case - ~80% of cases, multiple possible routes - mainly aerosol; cross boundary contacts, farm labour, vehicle and animal movements, vets and wildlife 

• mortality generally low - except in young animals 
• economic impact is more significant than animal welfare 
• decreased productivity - 50% reduction in milk yield, retarded growth
• OIE listed pathogen
• epidemics are very expensive 
• UK 2001 
  • 6.5million animals slaughtered - 2.5 million on welfare grounds 
  • £3 billion to control plus £3 billion lost in tourist revenue - 0.2% GDP lost 

• majority of developed countries no longer used, or never used vaccination 
• traditional approach 
• prevention - strict quarantine laws and standstill policies
• control by movement band and slaughter policies 
• 3Km exclusion zones - 10Km surveillance zones 
• rapid slaughter of animals of infected premises (IP) and dangerous contacts (DC)
• adaptive approach 
• computer prediction is used to identify secondary risk areas 
• culling of contiguous premises - apparently unaffected 
• firebreak culling 

• Universal - not cost effective - emergeny vaccination? 

Pros

• reduced excretion of virus
• logistical benefits - animal movement 
• conserve resources
• more palatable to public 

Cons 

• delay before protective - slaughter?
• confounds serological surveillance 
• conceals carriers 
• prolongs reacquisition of disease free status  

• difficult to detect as vaccine suppresses replication may reduce response to NSP proteins - false negative 
• anecdotal evidence suggests transmission from persistently infected animals exists - no experimental evidence for transmission 
• may be a trigger required to facilitate transmission from persistently infected animals 

• recognise the threat early 
• trying to anticipate is unlikely to be cost effective 
• global national monitoring for new disease outbreaks (GOARN) necessary to identify new patterns of disease 
• respond effectively and rapidly 
• vaccination and movement control policies are best tools for containment 
• next gen sequencing is an extremely rapid way to identify and characterise a new virus - valuable tool 

• factors promoting cross-species transmission
  • encroachment into new habitats - inevitable 
  • changing distribution of vectors - reduce vector numbers? - impractical
  • mixed species farming/markets etc - can be achieved 
• factors that promote epidemic transmission 
  • high population densities - intensive production, urban populations 
  • international travel and animal importation 
  • global warming