3.2 AUSTRALIAN BAT LYSSAVIRUS INFECTION
Australian bat lyssavirus (ABL) and rabies virus are members of the familyRhabdoviridae, genus Lyssavirus
. There are 7 known genotypes within the genusLyssavirus; ABL (genotype 7) is more closely related to rabies virus (genotype 1)than any of the other 6 genotypes.
Based on the two recognised human cases of ABL infection, it has to be assumed thatABL has the same clinical features as rabies. Typically, in the prodromal phase ofrabies, which lasts up to 10 days, the patient may experience non-specific symptomssuch as anorexia, cough, fever, headache, myalgia, nausea, sore throat, tiredness andvomiting. 1 Paraesthesiae and/or fasciculations at or near the site of the wound maybe present at this stage. Anxiety, agitation and apprehension may also occur.
Most rabies patients present with the furious or encephalitic form.1 In theencephalitic phase, objective signs of nervous system involvement includeaerophobia, hydrophobia, bizarre behaviour, disorientation and hyperactivity. Signsof autonomic instability such as hypersalivation, hyperthermia and hyperventilationmay occur.1 The neurological status of the patient deteriorates over a period of up to12 days, and the patient either dies abruptly from cardiac or respiratory arrest, orlapses into a coma. Rabies is almost invariably fatal.
Rabies is endemic throughout much of Africa, Asia, the Americas and Europe, wherethe virus is maintained in certain species of mammals.1 Australia, New Zealand andPapua New Guinea are free of endemic rabies. Human rabies characteristicallyfollows a bite from a rabid animal, most frequently a dog, but in some parts of theworld other animals, such as jackals and bats, are important sources of exposure. Incountries where rabies vaccination of domestic animals is widespread (NorthAmerica and Europe), wild animals such as raccoons and foxes are importantreservoirs.1
Cases of rabies after animal scratches or the licking of open wounds are extremelyrare. Cases have been recorded after exposure to aerosols in a laboratory and incaves infested with rabid bats, and cases have been reported following cornealtransplants from donors who died with undiagnosed rabies.1
In Australia, 2 cases of a fatal rabies-like illness caused by ABL have been reported,one in 1996 and the other in 1998.2 Both patients had been bitten by bats. Evidence ofABL infection has since been identified in all 4 species of Australian fruit bats (flyingfoxes) and in at least 3 species of Australian insectivorous bats. It should therefore beassumed that all Australian bats have the potential to be infected with ABL.
Mérieux Inactivated Rabies Vaccine – Aventis Pasteur. Each 1.0 mL dose containsat least 2.5 IU viral antigens, neomycin 100-150 μg, and up to 70 mg of humanserum albumin. Presentation is a 1.0 mL single dose vial of lyophilised vaccinewith 1.0 mL distilled water as diluent.
The vaccine is a lyophilised, stabilised suspension of inactivated Wistar rabies virus(strain PM/W1381503-3M) that has been cultured on human diploid cells and theninactivated by beta-propiolactone. The dry vaccine is coloured off-white, but afterreconstitution with the diluent it turns a pinkish colour due to the presence of phenolred. The vaccine does not contain a preservative.
Imogam Rabies – Aventis Pasteur (Human rabies immunoglobulin). Each 1.0 mLcontains IgG class human rabies antibodies with a minimum titre of 150 IU,glycine 22.5 mg and sodium chloride 1 mg.
Human rabies immunoglobulin (HRIG) is prepared by cold ethanol fractionationfrom the plasma of hyperimmunised human donors. It is supplied in 2 mL and 10mL vials.
Transport, storage and handling
The vaccine, diluent and HRIG should be transported and stored at 2°C to 8°C. Theymust not be frozen; do not use either the vaccine or HRIG if either has been exposedto a temperature of less than 0°C. Do not freeze or store either the vaccine or HRIGin direct contact with ice packs. The reconstituted vaccine should be usedimmediately after reconstituting; the HRIG should be used immediately once the vialis opened.
Dosage and administration
(i) Pre-exposure prophylaxis
The dose of rabies vaccine for pre-exposure prophylaxis is 1.0 mL by IM or SCinjection, on days 0, 7 and 28.
(ii) Post-exposure treatment
The dose of rabies vaccine for post-exposure treatment is 1.0 mL by IM or deep SCinjection on days 0, 3, 7, 14 and 30. Also administer HRIG (human rabiesimmunoglobulin) 20 IU/kg body mass, by infiltration around wounds (may giveremainder of dose by IM injection).
(i) Pre-exposure prophylaxis for Australian bat lyssavirus infection
Rabies vaccine is effective and safe when used for pre-exposure prophylaxis foreither ABL3 or rabies1 (level IV evidence)
. The rationale for pre-exposure prophylaxis isthat: (i) vaccination may provide protection to people with inapparent exposure toeither ABL infection or rabies; (ii) it may protect people whose post-exposuretreatment may be delayed or inadequate; and (iii) it simplifies post-exposuretreatment. Patients should be advised that the main reason for pre-exposure
prophylaxis is to prime the immune system for a secondary response, and that if apossible ABL or rabies exposure occurs, booster doses of vaccine may still berequired.
Pre-exposure prophylaxis with rabies vaccine is strongly recommended for people inAustralia liable to receive bites or scratches from bats (this includes bat handlers,veterinarians, wildlife officers and others who come into direct contact with bats).
Pre-exposure prophylaxis is strongly recommended for expatriates and travellerswho will be spending prolonged periods (ie. more than a month) in rural parts ofrabies endemic areas.4 The World Health Organization (WHO) maintains data onrabies infected countries, the most recent of which can be accessed at the followingweb site – http://www.who.int/emc/diseases/zoo/rabies.html
Pre-exposure prophylaxis for both ABL infection and rabies, for all ages, consists of atotal of 3 IM or deep SC injections of 1 mL of rabies vaccine, the second given 7 daysafter the first, and the third given 28 days after the first. For pre-exposureprophylaxis, the vaccine can be obtained from CSL Vaccines. Costs of pre-exposureprophylaxis have to be met by the individual or the employer.
Inadvertent prolongation of the intervals does not impair the response. Doses shouldbe given in the deltoid area, as rabies neutralising antibody titres may be reducedafter administration in other sites. In particular, vaccine should never be given in thebuttock, as failure of pre-exposure prophylaxis has been reported when given by thisroute.
Because the antibody response is reported as satisfactory after the pre-exposureprophylaxis regimen, routine serological testing to confirm seroconversion is notnecessary. However, immunosuppressed people who are at risk of exposure to ABLor rabies should have their antibody titres determined 2 to 3 weeks after the thirddose of vaccine.
Booster doses of rabies vaccine should be considered for immunised people whohave ongoing exposure to either ABL or rabies. People who work with livelyssaviruses in research laboratories are at risk of inapparent exposures, and shouldhave rabies antibody titres measured every 6 months. If the titre is reported asinadequate, they should have a booster dose. Other laboratory workers who performABL or rabies diagnostic tests, those with occupational exposures to bats inAustralia, and those who are likely to be exposed to potentially rabid animals inendemic countries should have rabies antibody titres measured every 2 years. If thetitre is reported as inadequate, they should have a booster dose. Alternatively abooster dose may be offered every 2 years without determining the antibody titre.
Intradermal pre-exposure prophylaxis:
There are no data on the protection provided
by intradermal rabies vaccination for ABL exposures. Therefore intradermal pre-
exposure administration of rabies vaccine should not be used for pre-exposure
prophylaxis of ABL.
Antibody titres are lower after intradermal compared to either IM or SC
administration of rabies vaccine,1 and there may be an impaired anamnestic response
following exposure to rabies virus in those given intradermal rabies vaccine. 5,6 For
these two reasons it is strongly recommended that either the IM or SC route be used
for pre-exposure prophylaxis for potential future exposures to rabies virus.
However, the cost of either IM or SC rabies vaccination may be prohibitive for sometravellers. In this circumstance intradermal rabies vaccination, using a dose of 0.1 mLon days 0, 7 and 28, may be considered provided that:
it is given by those with not only expertise in, but also regular practice of, theintradermal technique (because intradermal vaccination is reliable only if thewhole of the 0.1 mL dose is properly given into the dermis);
it must not be administered to anyone known to be immunocompromised in anyway;
it must not be administered to those taking either chloroquine or otherantimalarials structurally related to chloroquine (eg. mefloquine) at either thetime of, or within a month following vaccination;
any remaining vaccine is discarded at the end of the session during which thevial is opened; and
the rabies antibody level should be checked 2 to 3 weeks following completion ofthe pre-exposure course of intradermal vaccine.1
The use of the intradermal route for rabies vaccination is the practitioner ’s ownresponsibility as the vaccine is not licensed for use via this route in Australia. Theintradermal route should never be used to administer rabies vaccine by practitionerswho only occasionally provide travel medicine services.
(ii) Post-exposure treatment for Australian bat lyssavirus and rabies
Rabies vaccine and HRIG are effective and safe when used for post-exposuretreatment following either ABL3 or rabies exposures1 (level IV evidence)
. The essentialcomponents of post-exposure treatment for either ABL or rabies exposures areprompt local wound management and, for people who have not previously beenvaccinated, administration of HRIG and rabies vaccine. Both HRIG and rabiesvaccine are available for post-exposure treatment, without charge, from the relevantState/Territory health authorities (see Appendix 1 for contact phone numbers).
Post-exposure treatment should be considered whenever a bite, scratch or mucousmembrane exposure to saliva from any Australian bat has occurred, regardless of:
the extent of the bite or scratch – even very minor bites overseas have beenknown to transmit rabies;1
the time lapsed since the bite or scratch – although treatment should begin assoon as practicable after a bite or scratch, incubation periods of several yearshave been recorded for both ABL and rabies;1
the species of bat – ABL has been detected in all 4 species of flying fox, and in atleast 3 species of Australian insectivorous bats; and
the bat being apparently normal in appearance and behaviour – although ABL ismore likely to be found in bats that either appear unwell or are behavingabnormally7 it has to be assumed that any bat is potentially infected with ABL.
However, exposure to bat blood, urine or faeces, or to a bat that has been dead formore than 4 hours does not warrant post-exposure treatment.
Where post-exposure treatment for a potential exposure to ABL is indicated the batshould, if possible without placing other persons at risk of exposure, be kept andarrangements made immediately for testing by the relevant State/Territory veterinaryor health authority. Following the wound management, the administration of HRIG
and rabies vaccine can be withheld if the result (concerning the bat’s ABL status) willbe available within 48 hours of the exposure; if the result will not be available within48 hours full post-exposure treatment should be commenced immediately.
An assessment must be made of the potential risk of transmission of rabies as soonas possible after exposure to a possibly infected animal. Dogs and monkeys comprisethe usual exposures in Asia, Africa and Central and South America, but exposures toother animals must also be assessed for potential rabies transmission. Advice shouldbe sought from the relevant State/Territory health authority before advising againstrabies post-exposure treatment.
Post-exposure treatment of a patient presenting after possible rabies exposure shouldbe commenced as soon as possible; treatment should not be withheld even if therehas been a considerable delay in recognising the exposure. Unless the animal hasbeen tested and found to be negative for rabies, the course should be completedirrespective of the clinical outcome in the animal.
Immediate and thorough washing of all bite wounds and scratches with soap andwater, and the application of a virucidal preparation such as povidone-iodinesolution after the washing, is an important measure in the prevention of ABLinfection and rabies.1 Consideration should be given at this stage of woundmanagement to the possibility of tetanus and other wound infections, andappropriate measures taken. Primary suture of a bite from a potentially rabid animalshould be avoided. Bites should be cleaned, debrided and well infiltrated with HRIG(see below). Secondary suture, if necessary, should be performed after 1 to 2 weeks,when it can be assumed that the patient has circulating neutralising antibodies.
The treatment subsequent to the wound management is the same for both ABL andrabies exposures, except that consideration may be given to omitting the HRIG if it ismore than one year after an exposure to ABL. This is because the risk of infection atthis time is considered to be low. Advice should be sought from the relevant State/Territory health authorities.
a) Use of rabies vaccine in post-exposure treatment
Following the local wound management, the subsequent post-exposure treatment foreither ABL or rabies exposures consists of: (i) a total of 5 doses of 1.0 mL of rabiesvaccine given by IM or SC injection; and (ii) HRIG (see below). The volume ofvaccine administered to infants and children is the same as that given to adults (ie.
1.0 mL). The first dose of vaccine is given immediately (day 0), and subsequent dosesare given on days 3, 7, 14 and 30. In adults and children the vaccine should beadministered into the deltoid area, as administration in other sites may result inreduced neutralising antibody titres. In infants less than 12 months of age,administration into the anterolateral aspect of the thigh is recommended.
Serological testing to measure response is unnecessary except in unusualcircumstances, such as when the patient is known to be immunocompromised. Insuch cases, the antibody titre should be measured 2 to 3 weeks after the dose givenat 28 days and a further dose given if the titre is reported as inadequate.
b) Use of rabies immunoglobulin in post-exposure treatment
Rabies has occurred in people who have received post-exposure rabies vaccine
without rabies immunoglobulin being infiltrated in and around the wound. 8,9
Therefore post-exposure treatment should always include the infiltration of HRIG in
and around wounds at the same time as the first dose of rabies vaccine
, the only
exceptions being people with documented evidence of either completion of the pre-exposure prophylaxis regimen or adequate rabies antibody titres. These peopleshould receive vaccine only.
A single dose of HRIG is given to provide localised anti-rabies antibody protectionwhile the patient responds to the rabies vaccine. It should be given at the same timeas the first post-exposure dose of vaccine (day 0). If not given with the first vaccinedose, it may be given up to day 7, but should not be given any later in the course ofthe vaccination program. From day 8 onwards, an antibody response to rabiesvaccine is presumed to have occurred.
The dose of HRIG for all age groups is 20 IU per kg body mass. HRIG should beinfiltrated in and around all wounds using as much of the calculated dose aspossible, and the remainder administered intramuscularly at a site away from theinjection site of rabies vaccine. Although the value of administering the remainingHRIG intramuscularly is uncertain,10 it must not be omitted. Rather, it must beemphasised that as much as possible of the HRIG be infiltrated in and around thewounds, so that as little HRIG as possible needs to be given intramuscularly.
If the wound has healed, the HRIG should be administered in the vicinity of thehealed wound (eg. around a scar). If the wounds are severe and the calculatedvolume of HRIG is inadequate for complete infiltration (eg. extensive dog bites in ayoung child), the HRIG should be diluted in saline to make up an adequate volumefor the careful infiltration of all wounds.
However, many bat bites occur as small puncture wounds on the fingers;11 suchexposures are probably high-risk exposures because of the extensive nerve supply tothe fingers and hand.1 Therefore, although infiltration of HRIG into finger wounds islikely not only to be technically difficult but also to be painful for the recipient, itmust be undertaken. As much of the calculated dose of HRIG as possible should beinfiltrated into finger and hand wounds using either a 25 or a 26-gauge needle. Toavoid the development of a compartment syndrome, the HRIG should be infiltratedvery gently, and should not cause the adjacent finger tissue to go frankly pale orwhite. If necessary a ring-block using a local anaesthetic may be required.
There is a theoretical risk that HRIG may suppress the patient’s response to rabiesvaccine, and no more than the recommended dose should be given.
Summary of Australian bat lyssavirus and rabies post-exposure treatment for non-
c) Post-exposure treatment of previously vaccinated people
People who have either completed a recommended course of pre-exposureprophylaxis, or previous post-exposure treatment, or who have documentedadequate rabies neutralising antibodies, require a modified post-exposure treatmentregimen if potentially exposed to either rabies virus or ABL. Local wound
management as described above must be carried out, and a total of 2 doses of rabiesvaccine (1.0 mL each) should be given by IM injection on day 0 and day 3. HRIG isnot necessary in these cases.
In cases where the vaccination status is uncertain because the documentation of a fullcourse of rabies vaccine is not available, the standard post-exposure treatmentregimen (HRIG plus 5 doses of rabies vaccine) should be administered.
d) Post-exposure treatment commenced overseas
Australians who are exposed to a potentially rabid animal while travelling abroadmay be given post-exposure treatment whilst abroad with vaccines that are notavailable in Australia.
The Thai Red Cross Rabies Committee considers that the following ‘first’ and‘second’ generation tissue culture vaccines are interchangeable:12
human diploid cell vaccines (eg. Imovax Rabies),
purified chick embryo cell vaccines (eg. Rabipur),
purified duck embryo vaccine (Lyssavac N), and
rhesus lung cell vaccine (Rabies Vaccine Adsorbed).
Therefore, if a person has received one of the above vaccines abroad, the standardpost-exposure treatment regimen should be continued in Australia with the locallyavailable human diploid cell rabies vaccine. If the post-exposure treatment wasstarted overseas with one of the above vaccines but HRIG was not given, and theperson presents in Australia within 7 days of commencing post-exposure treatment,HRIG should be given immediately. If the person presents in Australia after 8 daysthen HRIG should be withheld.
If post-exposure treatment was started abroad using either a primary hamster kidneycell culture vaccine (in widespread use in China) or a nerve tissue vaccine (eg. sheepbrain vaccine), the standard post-exposure treatment regimen (HRIG plus 5 doses ofhuman diploid cell rabies vaccine) should be commenced in Australia as soon aspossible. The full regimen of 5 doses of vaccine should be administered, regardless ofhow many doses of the (suboptimal) hamster kidney or nerve tissue vaccines werereceived overseas.
Adverse events and precautions
In a large (1770 volunteers) study the following adverse events were reported afteradministration of human diploid cell culture rabies vaccines: sore arm (15 to 25%),headache (5 to 8%), malaise, nausea or both (2 to 5%); and allergic oedema (0.1%).1In another study of post-exposure vaccination, 21% had local reactions, 3.6% hadfever, 7% had headache and 5% had nausea. These reactions are not more frequent inchildren.1
Anaphylactic reactions are rare (approximately 1 per 10 000 vaccinations) followingadministration of human diploid cell culture rabies vaccines. However, allergicreactions occur in approximately 6% of people receiving booster doses of some of thehuman diploid cell vaccines.1 The reactions typically occur 2 to 21 days after abooster dose, and are characterised by generalised urticaria, sometimes witharthralgia, arthritis, oedema, nausea, vomiting, fever and malaise. These reactions are
not life-threatening; they have been attributed to the presence of beta-propiolactone-altered human albumin in the implicated vaccines.1 NB: Mérieux Inactivated RabiesVaccine contains human albumin.
Management of adverse events
Once initiated, rabies prophylaxis should not be interrupted or discontinued becauseof local reactions or mild systemic reactions. Such reactions can usually be managedwith either aspirin or paracetamol.
Because ABL infection and rabies are lethal diseases, the recommended vaccinationregimens, in particular the post-exposure treatment regimen, should be continuedeven if a significant allergic reaction occurs following a dose of rabies vaccine.
Antihistamines can be administered in an attempt to ameliorate any subsequentreactions. A patient’s risk of developing either ABL infection or rabies must becarefully considered before deciding to discontinue vaccination.
There are no contraindications to post-exposure treatment in a person with apresumed exposure to either ABL or rabies.
Use of steroids and immunosuppressive agents
Corticosteroids and immunosuppressive agents can interfere with the developmentof active immunity, and therefore if possible should not be administered during post-exposure treatment. A person who either has an immunosuppressing illness or istaking immunosuppressant medications should have his/her rabies antibody titreschecked 2 to 4 weeks after completion of the vaccination regimen (see above).
Pregnancy is never a contraindication to rabies vaccination. Follow-up of 202 Thaiwomen vaccinated during pregnancy did not indicate either increased medicalcomplications or birth defects.13
Conflicts with product information
The product information does not mention that the rabies vaccine should be used forboth pre-exposure prophylaxis and post-exposure treatment for ABL exposures.
The product information recommends a routine sixth dose at 90 days in the post-exposure treatment regimen. This dose is not considered necessary on a routine basisbut should be offered to an immunosuppressed person without adequate antibodiesfollowing the standard regimen. It also recommends a pre-exposure booster after ayear; boosters are usually recommended in Australia after 2 years (see above).
The product information for rabies vaccine recommends administration by ’deepsubcutaneous injection, preferably into the infraspinous fossa’. However, NHMRCrecommends that it be given by either IM or SC injection into the usual sites. Thevaccine is not licensed for adminstration by the intradermal route in Australia.
The WHO maintains data on rabies-infected countries, the most recent of which canbe accessed at the following web site: http://www.who.int/emc/diseases/zoo/rabies.
As of March 2003 the Department of Agriculture, Fisheries & Forestry – Australiaadvised that Bali continued to be rabies free. Furthermore, no cases of Bali-acquiredrabies have ever been reported in the medical literature despite many people beingbitten and scratched by animals in Bali every year. Although post-exposure treatmentfollowing animal bites sustained in Bali is therefore not warranted, it must beemphasised that this situation could change at any time.
However, rabies still exists in other parts of Indonesia including the islands of Flores,Sulawesi, Sumatra and parts of Java and Kalimantan. Post-exposure treatment isnecessary for any animal bite sustained in any of these locations. Any doubts orconcerns about the need for post-exposure treatment following animal bites in anypart of Indonesia should be discussed with the State/Territory public healthauthority.
1. Plotkin SA, Rupprecht CE, Koprowski H. Rabies vaccine. In: Plotkin SA, Orenstein
WA, editors. Vaccines. 3rd ed. Philadelphia, PA: WB Saunders; 1999.
2. Hanna JN, Carney IK, Smith GA, et al. Australian bat lyssavirus infection: a
second human case, with a long incubation period. Medical Journal of Australia
3. Hooper PT, Lunt RA, Gould AR, et al. A new lyssavirus - the first endemic rabies-
related virus recognized in Australia. Bulletin de L’Institut Pasteur
4. LeGuerrier P, Pilon PA, Deshaies D, Allard R. Pre-exposure rabies prophylaxis for
the international traveller: a decision analysis. Vaccine
5. Jaijaroensup W, Limusanno S, Khawplod P, et al. Immunogenicity of rabies
postexposure booster injections in subjects who had previously receivedintradermal preexposure vaccination. Journal of Travel Medicine
6. Gherardin AW, Scrimgeour DJ, Lau SC, et al. Early rabies antibody response to
intramuscular booster in previously intradermally immunized travelers usinghuman diploid cell rabies vaccine. Journal of Travel Medicine
7. McCall BJ, Epstein JH, Neill AS, et al. Potential exposure to Australian bat
lyssavirus, Queensland, 1996-1999. Emerging Infectious Diseases
8. Wilde H, Choomkasien P, Hemachudha T, et al. Failure of rabies postexposure
treatment in Thailand. Vaccine
9. Wilde H, Sirikawin S, Sabcharoen A, et al. Failure of postexposure treatment of
rabies in children. Clinical Infectious Diseases
10. Saesow N, Chaiwatanarat T, Mitmoonpitak C, Wilde H. Diffusion and fate of
intramuscularly injected human rabies immune globulin. Acta Tropica
11. Jackson AC, Fenton MB. Human rabies and bat bites. Lancet
12. Wilde H. Rabies, 1996. International Journal of Infectious Diseases
13. Chutivongse S, Wilde H, Benjavongkulchai M, et al. Postexposure rabies
vaccination during pregnancy: effect on 202 women and their infants. ClinicalInfectious Diseases
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