Transcript How we control viral diseases of man and animals

How we control viral diseases of
man and animals.
by Peter Russell
[email protected]
http://www.rvc.ac.uk/Staff/prussell.cfm
Background
I contributed some 23 lectures on
veterinary virology to the
Supercourse several years ago.
The aim of this new lecture is to talk
about the control of human and
animal viruses.
Viral diseases.
How viruses are transferred.
How viruses are controlled (this lecture).
Viral diseases.
Viral diseases cause distress to man and animals and
the most worrying ones are those that are difficult to
control.
Human immunodeficiency virus (HIV) continues to
spread in an uncontrolled manner.
How viruses are transferred.
Viruses are carried by infected people or animals and
excreted in discharges such as those from the nose, gut
and reproductive fluids. The control of viruses blocks
this transfer.
How viruses are controlled (this lecture).
Control measures for viruses.
Obstacles to the control of viruses.
Ways to improve the control of viruses.
Control measures for viruses.
1) Quarantine
2) Import controls
3) Notification
4) Slaughter
5) Decontamination
6) Isolation
7) Treatment
8) Vaccination
9) Insect controls
1) Quarantine.
Separate the infected persons or animals with signs
suspicious of an acute viral disease such as rash, vesicles,
vomiting with diarrhoea.
2) Import controls
Blocking animal imports from a country such as one
infected with foot and mouth disease virus (FMDV) or
avian influenza.
3) Notification.
Notifiable diseases of man include HIV, measles, mumps
and rubella and those of animals include FMDV, swine
fever and rabies.
Anyone who suspects a notifiable disease must contact
the national authorities. See UK links for those of man
and animal below.
The authorities inform the World Health organisation
(WHO) or World organisation for animal health (formerly
the OIE).
These organisations publicise the global spread of
diseases.
Control measures for viruses.
1) Quarantine
2) Import controls
3) Notification
4) Slaughter
5) Decontamination
6) Isolation
7) Treatment
8) Vaccination
9) Insect controls
4) Slaughter.
Culling the infected animal or herd.
Viruses require living cells to multiply and this is halted by
the death or slaughter of an animal.
5) Decontamination.
Washing and disinfecting hands, clothing and equipment.
Disposing of dead bodies in a safe manner like incineration or
burial in lime.
Treatment of waste water and chlorination of mains water.
Personal hygiene e.g. not coughing over people and washing
hands after toilet and before food preparation.
6) Isolation.
Avoiding multiple close contacts such as in crowded housing.
A secure farm will also exclude other animals and visitors
that might transfer the virus.
Control measures for viruses.
1) Quarantine
2) Import controls
3) Notification
4) Slaughter
5) Decontamination
6) Isolation
7) Treatment
8) Vaccination, part 1
9) Insect controls
7) Treatment.
Antiviral drugs are used for only a few viruses because
they are expensive, often have side effects and they select
for resistant viruses.
They exist for HIV, hepatitis B, hepatitis C, herpes simplex,
respiratory syncytial virus and influenza of man.
Antiserum to rabies soon after a bite from a suspect.
8) Vaccination.
Vaccine protect against infection and disease.
They exist for certain viruses such as mumps, measles,
rubella and yellow fever.
They are made of a living harmless strain of the virus or of
dead virus.
They induce antibodies, cytotoxic T cells and clones of
memory cells but only to the vaccine virus.
Control measures for viruses.
1) Quarantine
2) Import controls
3) Notification
4) Slaughter
5) Decontamination
6) Isolation
7) Treatment
8) Vaccination, part 2
9) Insect controls
After several years the clones of memory cells start to
die and revaccination is needed.
Newborns receive antibodies from their mothers and
these not only protect from challenge but also
prevent the vaccine working for a few months.
Childhood vaccination requires careful timing e.g. a
first dose at 12-15 months and a second at 4-6 years of
age. It is 10-12 weeks then every 2 years for pets.
To prevent the spread of a virus in a population it is
important to vaccinate and protect at least 80-90% of
the individuals. The amount of virus circulating
becomes low and even the few unvaccinated avoid
infection.
Control measures for viruses.
1) Quarantine
2) Import controls
3) Notification
4) Slaughter
5) Decontamination
6) Isolation
7) Treatment
8) Vaccination, part 3
9) Insect controls
Although vaccines only protect against a particular
virus, like FMDV, they can also be specific to a
particular serotype, FMDV O, or even a particular
subdivision of a serotype termed subtype, FMDV O1.
One function of viral diagnostic laboratories is to
determine exactly which serotypes and subtypes of
viruses are circulating so the vaccine industry then
makes vaccines that work against the virus causing an
outbreak.
9) Insect controls.
Individuals use insecticidal creams, protective clothing
and mosquito nets.
Governments can interrupt the lifecycle of insects by
chemicals that kill their larvae or by removing their
habitats e.g. by draining stagnant water.
Obstacles to the control of viruses.
1) Poor infrastructure
2) Global transport
3) Mutation
4) Vaccine design
5) Reservoir hosts and insect hosts
6) Rumours about vaccines
7) Unsatisfactory vaccines
1) Poor infrastructure.
If there is a shortage of infrastructure to enforce the controls
of human and animal viruses.
For instance viruses spread during conflicts when hygiene
and borders are disrupted and people are displaced into
camps.
Urban poverty is where antisocial behaviour such as drug
use and prostitution become more likely.
2) Global transport.
HIV originated in Africa and has spread worldwide.
FMDV has re-entered Europe as waste meat in untreated pig
swill and has then spread rapidly via animal movements and
markets when animals with vesicles escaped notice.
3) Mutation.
Viruses might mutate to infect new species for instance the
worry that avian influenza virus might mutate to become a
pandemic not only of birds but of man.
Obstacles to the control of viruses.
1) Poor infrastructure
2) Global transport
3) Mutation
4) Vaccine design
5) Reservoir hosts and insect hosts
6) Rumours about vaccines
7) Unsatisfactory vaccines
4) Vaccine design.
Some viruses have a protein structure that means
vaccines work badly or never e.g. African swine fever,
HIV.
Other viruses have vaccines that only work to a
particular strain of a subtype e.g. influenza virus.
These strains change each year and so the WHO
advises on which strains to use in vaccines for a
particular country.
5) Reservoir hosts and insect hosts.
The virus exists in reservoirs hosts e.g. rabies in dogs
that bite man, or other dogs, when the rabies
encephalitis makes them become furious.
The virus replicates in insects as well as man and
animals e.g. yellow fever virus and West Nile virus are
transferred to man by mosquito bites.
Blue tongue virus infects midges that bite sheep and
cattle.
Obstacles to the control of viruses.
1) Poor infrastructure
2) Global transport
3) Mutation
4) Vaccine design
5) Reservoir hosts and insect hosts
6) Rumours about vaccines
7) Unsatisfactory vaccines
6) Rumours about vaccines.
These include:
autism from the combined mumps, measles and
rubella (MMR) vaccine,
infertility from polio vaccines,
aborted calves and lambs from inactivated blue
tongue vaccines.
7) Unsatisfactory vaccines.
These include:
counterfeit vaccines,
homeopathic vaccine,
little or no viral content, i.e. poor quality
control .
Ways to improve the control of viruses.
1) More vaccine coverage
2) New vaccines
3) Hygiene
4) Cheaper easier vaccines
5) Better reporting
6) Maths
7) Cheaper antiviral drugs
8) Global targets
9) Communication
1) More vaccine coverage.
To establish more universal vaccination programmes
using the licensed existing vaccines that work e.g.
MMR against mumps, measles and rubella and also
those against rabies of reservoir hosts.
2) New vaccines.
To develop vaccines against viruses that have no
working vaccine e.g. HIV, Dengue fever.
3) Improved hygiene.
To improve communal hygiene and well being e.g.
drains, clean water, spacious housing, nutrition,
discouraging intravenous drug use and unprotected
sex.
Ways to improve the control of viruses.
1) More vaccine coverage
2) New vaccines
3) Hygiene
4) Cheaper easier vaccines
5) Better reporting
6) Maths
7) Cheaper antiviral drugs
8) Global targets
9) Communication
4) More useful vaccines
cheaper working dose,
less loss by heat during storage
easier administration.
5) Better reporting and feedback.
To have diagnostic and surveillance teams in place to warn
how outbreaks are spreading and to inform vaccine
manufacturers of how many doses to make of the vaccine
against the correct virus or even subtype of virus.
They also advise the general public, medics and vets on how
to recognise signs of the disease(s).
6) Maths.
To develop mathematical models to establish the cheapest
and best ways of controlling diseases of man and animals e.g.
by public health measures and vaccination.
Ways to improve the control of viruses.
1) More vaccine coverage
2) New vaccines
3) Hygiene
4) Cheaper easier vaccines
5) Better reporting
6) Maths
7) Cheaper antiviral drugs
8) Global targets
9) Communication
7) Cheaper antiviral drugs.
These also must not get out of date as result of viruses
mutating to escape their effects.
8) Global targets
To fund international and national schemes to rid
countries of a particular virus by a particular time, see
below for polio of man and rinderpest of animals.
Ways to improve the control of viruses.
1) More vaccine coverage
2) New vaccines
3) Hygiene
4) Cheaper easier vaccines
5) Better reporting
6) Maths
7) Cheaper antiviral drugs
8) Global targets
9) Communication
9) Communication
To educate the general public about methods of
reducing virus spread such as:
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reporting disease e.g. FMDV and measles,
disinfection of hands and surfaces e.g. in the
kitchen, hospital and infected farm,
becoming more aware of how some viruses, e.g.
HIV and hepatitis B, are transferred by blood
such as during needle sharing and unprotected
sex.
avoiding insect bites e.g. mosquito nets and
insecticides,
isolating infected people and animals e.g.
those with rabies,
receiving vaccinations at the recommended
times e.g. MMR.
Summary
The control of viral diseases
must block their transfer
from infected to uninfected zones
by hygiene and vaccination
schemes.
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