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Publication - Guidance

Rabies control strategy

Published: 17 Oct 2017

For use in the event of an outbreak of rabies. Information about the disease and what would happen in response to an outbreak.

45 page PDF

704.1kB

45 page PDF

704.1kB

Contents
Rabies control strategy
Chapter 1: Description of Rabies disease

45 page PDF

704.1kB

Chapter 1: Description of Rabies disease

The Virus

1.1 The rabies virus is a lyssavirus, one of a group of viruses responsible for causing encephalitis, which causes acute inflammation of the brain. Other lyssaviruses are considered along with classical rabies as their clinical presentation is indistinguishable. There are currently eleven classified species of lyssavirus.

1.2 Full details of each can be found on the ‘International Convention on taxonomy of viruses [5] and ‘ Rabies Bulletin Europe [6] websites.

1.3 This strategy focuses on Classical rabies virus, as the most prevalent serotype. European Bat Lyssavirus ( EBLV) is subject to separate control measures.

Transmission

1.4 The virus is usually transmitted through the saliva of an infected animal, normally via a bite. Less often, it can be transmitted through an open wound or a mucous membrane such as those in the mouth, nasal cavity or eyes. Person to person transmission does not occur, though there are rare reports of transmission by other routes, such as after transplantation of organs from infected individuals. Aerosol transmission has been documented in special circumstances, such as in laboratories and caves with an extremely high bat density (although such circumstances do not exist in the UK).

Though most animals are susceptible to rabies infection, many are ‘dead end’ hosts who will be unlikely to transmit the infection. Such ‘dead end’ hosts include humans most herbivores: cattle, sheep, goats and horses. This is because viral excretion may be very low in a species for which the viral strain is not well adapted.

European Bat Lyssavirus

European Bat Lyssaviruses ( EBLV1 and 2) have, very occasionally, been confirmed in bats in the UK. These viruses are strains of rabies virus, which are very highly adapted to their bat host. Spill over into humans and other terrestrial mammals is extremely rare.

EBLV2 has been detected at a low prevalence in Daubenton’s bats. These bats are found throughout UK often close to calm water in open wooded areas. Populations are thought to be more dispersed north of the Lake District. Figures estimate Scotland’s Daubenton’s population at around 40,000 (compared to 95,000 in England) (Joint Nature Conservation Committee ( JNCC), 1995).

In Europe, insectivorous bats are known to harbour European EBLV1 and EBLV2.

EBLVs have only rarely been isolated from terrestrial mammals; five isolations from sheep in Denmark (1998, 2002), one (2001) from a Stone Marten in Germany and two from cats in France (2003, 2007). Between 1977 and 2000, 630 cases of EBLV in bats were recorded in Europe, mainly in Demark, Germany and the Netherlands.

Since 1977 there have been five recorded human deaths attributed to EBLVs, one of which was in Scotland in November 2002. All human cases are believed to have been infected as a result of handling bats. Additionally, antibodies to EBLV 1 have been detected in two separate Natterer’s bats in Scotland and in a single Serotine bat in England (notably though, the virus itself was not detected). In mainland Europe, EBLV is most often associated with Serotine bats.

The small likelihood of contact between people and bats (apart from bat handlers) make the human risk from this disease very low and there are no known incidences of bat lyssaviruses becoming established in other, more risk-associated animal populations.

Rabies in bats

It should also be noted that, unlike the typical case in terrestrial mammals, rabies in bats may not always be fatal. Bats may become carriers of the infection and intermittently excrete virus, potentially infecting other bats and any terrestrial mammal with which they may have direct contact.

Further information and guidance on prophylaxis and human health management in relation to bat exposure is contained within ‘ Rabies: Guidance on Prophylaxis and Management in Humans in Scotland’. [7]

Incubation

1.5 Incubation of the Disease in Animals : The incubation period can vary considerably but for dogs and cats it is generally considered to be between two and twelve weeks post-infection though longer incubation periods have been reported. Factors that determine the length of this period include the strain of rabies, the infective dose and the site of the bite.

1.6 Incubation of the Disease in Humans : In human cases, the incubation period is typically two to eight weeks, but may vary from less than a week to more than a year.

1.7 It is only after the virus spreads via the nervous system from the site of the bite to the brain that an animal will become infectious and begin to excrete the virus in its saliva. It is common for an animal to begin to develop clinical signs at this point too. It is possible that the virus may be excreted prior to the onset of such signs. Cats may excrete the virus up to one day prior to the onset of clinical signs and dogs up to 13 days prior to the onset of clinical signs. After infection the virus enters the peripheral nervous system. It travels along the nerves towards the central nervous system. During this phase, the virus cannot easily be detected within the host and vaccination may still confer immunity to prevent symptomatic rabies.

Clinical Signs - Animals

1.8 Rabies cannot be definitively diagnosed on clinical signs alone and must be confirmed in the laboratory. In animals, clinical signs vary considerably, though typically include sudden behavioural changes and progressive paralysis leading to death. In some cases however, an animal may die rapidly without demonstrating significant clinical signs. Animals often exhibit one of the two following forms of rabies:

1.9 Furious rabies : Animals may be anxious and/or aggressive, losing their natural fear of other animals and humans. They may demonstrate sudden behaviour changes and attack without provocation. The animal may attempt to bite objects, other animals and its handler. The eyes take on a staring expression. The lower jaw may droop and there may be copious salivation. There may be a change in voice. Animals may suffer from general itching and increased thirst. Dogs may attempt to break free and run for miles attacking other animals in their way. Muscular weakness and seizures are common. Death results from progressive paralysis.

1.10 Dumb/Paralytic rabies : Animals may be depressed or unusually docile, sometimes paralysed in the face, throat and neck, causing abnormal facial expressions, drooling and inability to swallow. The paralysis progresses rapidly to the whole body with subsequent coma and death.

Clinical Signs - Humans

1.11 The first symptoms are likely to be non-specific; headaches, muscular pain, nausea or coughing. The most suggestive early sign of impending rabies is numbness and/or tingling and twitching at the site of the original bite. This is likely to be followed by a phase of agitation and confusion, followed by coma, respiratory failure and death.

Treatment/Disease Risk Mitigation in Humans

Once symptoms have begun the disease is invariably fatal so rapid intervention after a biting incident or other exposure to rabies is vital. Prompt post-exposure vaccination and administration of rabies immunoglobulin together with immediate and appropriate wound cleansing can prevent the risk of rabies developing. Post exposure vaccine needs to be very specifically administered in order to be effective and the World Health Organisation ( WHO) has published recommendations [8] for the use of rabies vaccine.

Initial Response to a bite: The rabies virus is rapidly inactivated by heat, liquid solvents and disinfectants, including warm soapy water and basic detergents. Swift and thorough cleansing of the entry site with these is an effective first measure to reduce the risk of infection. (See Appendix 1).

Vaccination: Modern rabies vaccinations offer a safe and very high level of protection against classical rabies virus and other serotypes including EBLV when give pre-exposure. Vaccination immediately following exposure will also help to reduce the risk of rabies developing. Rabies immunoglobulin is also given as a post exposure treatment to prevent development of the disease. There are vaccines available for human use as well as for use in animal populations. The vaccines are considered both safe and effective.

Confirming Disease

1.12 Rabies can only be confirmed by laboratory testing on the brain after death in animals other than humans. Results can usually be delivered within a few hours. Slower laboratory tests taking around 2-3 days will also be used to confirm earlier results and identify different serotypes.

Risk of Introduction

1.13 Classical rabies was eradicated from the UK in 1922 but is widely distributed across the globe, present on all continents and endemic in most African and Asian countries. Our island status makes it unlikely that rabies will be introduced through natural wildlife spread. There are strict legal controls on the entry of animals into the UK aimed at preventing the introduction of rabies. If you are bringing a pet animal into the UK you must follow the requirements for pet travel [9] . Rabies quarantine [10] in the United Kingdom is now only for dogs, cats and ferrets that do not qualify for entry into the UK under these EU pet movement rules. A new maximum quarantine period of 4 months was introduced on 29 December 2014.

1.14 Experts have assessed that by far the most likely scenario UK might face is:

  • A single pet with rabies entering or re-entering the country from abroad without meeting all legal border controls, which is subsequently diagnosed as having rabies; and as being the initial source of the infection
  • In virtually all cases of rabies brought into Europe in the last decade by illegal pet movements, the initial pet that had brought in rabies was identified.

Risk of Disease Spread

1.15 The Urban Cycle : In countries where rabies is enzootic, the urban cycle, in which dogs are the main reservoir for rabies infection, is a particular danger to human health because of the close contact between dogs and humans. 99% of human deaths from rabies are associated with dog bites. This cycle is maintained when the proportion of unvaccinated and stray dogs is high. Urban rabies is the predominant cycle in Africa, Asia, Central and South America.

1.16 The UK does not have the high levels of stray animals required to perpetuate this cycle but the low levels of dogs vaccinated against the disease would have to be quickly addressed in the event of an outbreak that could not be contained.

1.17 Feral cats are defined as ‘groups of three or more cats which the owner on whose property they occur would be unable to confine if required to do so under the Rabies (Control) Order 1974. Thus, they can be considered wildlife for the purpose of rabies control.

1.18 The Sylvatic Cycle : The sylvatic (or wildlife) cycle is still present in various areas of Europe and North America where rabies is endemic in one or more wildlife species, normally foxes. Scotland’s large fox population and large number of urban foxes could therefore be significant in an outbreak. The loss of innate fear of humans which has been recorded in rabid foxes represents particular problems, especially in urban areas where encounters with humans are more likely. Foxes may enter settlements, approach people and generally behave as if tame. How long such clinical signs last is not known. In this state, such animals are extremely dangerous, as their saliva contains the virus and they remain very unpredictable.

1.19 Badgers have not been a significant host in epidemics in Europe, however, the density of the UK badger population is much greater than in other countries.

1.20 Wildlife rabies has the potential to remain undetected, allowing it to establish itself more widely before it is noticed. Human contact with wild animals, though rarer, still occurs and there is also the possibility of ‘spill over’ infections into the domestic dog or cat populations, once again putting human health at risk.


Contact

Email: Frances Hepburn Frances Hepburn

Telephone: Central Enquiries Unit 0300 244 4000