How we control viral diseases of man and animals

How we control viral diseases of man and animals Outline

How we control viral diseases of man and animals. by Peter Russell prussell@rvc.ac.uk http://www.rvc.ac.uk/Staff/prussell.cfm

BackgroundI 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.

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.

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.

9) Communication To educate the general public about methods of reducing virus spread such as:  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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