Emerging Viral Diseases

what is the definition of emerging disease?

infectious illness whose incidence has recently increased in a specific population, geographic range, or host species, or one that threatens to increase in the near future

why do viral diseases emerge?

they emerge due to infectious agent and reservoir hosts, environmental and human

how does the reservoir host increase risk of an emerging disease?

• can increase in number

• genetic change

• disease dynamics in reservoir

how does the environment increase risk of an emerging disease?

• climate change

• irrigation/damming

• deforestation

• change in land use

how do humans increase the risk of an emerging disease?

• globalisation

• increased trade/travel

• resource poor settings

• host factors such as immunodeficient

• change in land use

• wildlife as food

what are the things to consider for disease control?

• vaccinations available?

• who is most at risk

• are agents or viruses changing

• where are the vectors

• education

what are two examples of emerging viral diseases?

• Paramyxoviruses

• West Nile Virus

what are the examples of contemporary re-emerging veterinary viruses?

• bluetongue

• influenza

• coronavirus

what are three examples of paramyxoviruses?

• menangle

• nipah

• hendra

what is menangle virus?

reproductive disease in pigs and causes still born and mummified foetuses

can menangle virus spread to humans?

yes

how to identify menangle disease?

• virus can be isolated in BHK21 cells from tissues collected from affected piglets - brain or heart

• serology to determine source of virus outbreak

• PCR and antibody based tests to rule out known pathogens

what can be the source of a menangle virus outbreak?

• large breeding colony of grey headed and little red fruit bats

• blood samples from bats showed evidence of antibody to the virus

where is nipah virus found and who can it affect?

• in Malaysia, Singapore, Sungai Nipah and Ipoh in the 1990s

• human cases of encephalitis

• respiratory disease in pigs

• can be in dogs, cats and horses

what are the signs of nipah virus in humans?

clinical presentations from asymptomatic infections to acute respiratory infection and fatal encephalitis

how is nipah virus transmitted?

from animals such as pigs and bats to humans or through contaminated food and human to human

what does hendra virus cause in humans and horses?

pneumonia and encephalitis

how is hendra spread?

• horses infected via fruit bat urine, saliva and other secretions

• humans infected 5-12 days after close contact with infected horses

what are the signs of hendra virus in humans?

fever, tiredness, headache and then can progress to meningitis or encephalitis

what is West Nile Virus?

• a vector borne disease

• Flavirus +ve sense ssRNA virus

• arbovirus

what is an arbovirus?

arthropod borne virus

where is the west nile virus maintained?

wild birds

are human cases of west nile virus seasonally?

yes due to mosquitos only breeding and moving during warmer months and not during winter

what happens in second year of west nile virus in horses?

there is a second year phenomenon due to birds staying active during winter containing the virus which then spreads to more mosquitos in the following spring and causing a greater spread in disease

what happens in the third year of west nile virus in horses?

there is a drop in disease because horses become more resistant

how are human cases of WNV predicted?

• dead WMV infected birds

• equine illness

• seroconverting sentinel chicken

• infected mosquito pool

what is the control of WNV?

• avoid exposure

• insect control via insecticides and environmental

• environment control such as drainage

• vaccination of horses

what type of disease is blutongue virus?

Orbivirus infection transmitted by midges

what animals does bluetongue affect?

wild and domestic ruminants

what’s the genome of bluetongue?

dsRNA genome with 10 segments

why is bluetongue hard to control?

over 25 serotypes and vaccination is limited to one serotype

what are the sheep symptoms with the emerging BTV-3?

lethargy, hpersalivation, ulcerations and erosions of the oral and nasal mucosal membranes, facial oedema, lameness and mortality

what are the cattle symptoms of BTV-3?

similar to sheep but also teat lesions

how do you test for BTV-3?

• testing blood samples by RT-PCR and antibody ELISA

• positive PCR samples sequenced using oxford Nanopore providing whole genome sequencing

• VP2 encoding sequence confirms virus as BTV-3

why is control of BTV-3 challenging?

due to vector transmission

how it BTV-3 controlled in the UK?

• notifiable disease

• livestock movements are banned in restriction zones

how does BTV-3 vaccine work?

does not prevent the spread of disease but reduces clinical signs and mortality

how do RNA viruses spread and last more easily?

they are more prone to spontaneous mutations

what avian influenza can infect humans directly from infected poultry?

H5N1 but can’t spread human to human very easily

what mutation of avian influenza would confer airborne transmission between mammals?

as few as five amino acid substitutions (four in HA and one in PB2) may be sufficient

can H5N1 spread from poultry to cows?

yes and was first reported in March 2024

what are the symptoms of H5N1 in cattle?

• low appetite

• reduced milk production

• abnormal milk - thickened and discoloured

which cows are most highly affected and why?

lactating cows as affects mammary gland in cattle

what is the structure of coronoavirus?

large RNA virus, positive sense and single stranded, and enveloped surface spike

what type of pathogens are coronavirus?

enteric and respiratory pathogens

what environments do coronaviruses survive and not survive in?

survive relatively well in some environments and tolerate low pH but are destroyed by common disinfectants

what does it mean if the virus is enveloped?

surrounded by lipids

what are the novel coronaviruses?

• SARS

• MERS

• SARS-CoV2

what are the symptoms of SARS?

severe acute respiratory syndrome

how to manage emerging diseases?

• surveillance

• banning of live markets

• control of interactions with wildlife

• capacity in healthcare systems and availability for all