Experimental rabies infection in haematophagous bats Desmodus rotundus.

In order to determine the susceptibility and serum neutralizing antibody response of Desmodus rotundus to rabies virus, bats were inoculated with a virus isolated from a naturally infected haematophagous bat. Bats were divided into four groups of 10 animals each. Dilutions of rabies virus containing 100, 1000, 10,000 and 100,000 MICLD50 (lethal dose 50% for mice inoculated by the intracerebral route) were administrated in the pectoral muscle. The presence of rabies virus was detected in brain and salivary glands by fluorescent antibody, mouse inoculation and RT-PCR. The observed mortality for each virus dose was 0, 20, 20 and 60% respectively. Serum neutralizing antibodies were tested for by the rapid fluorescent focus inhibition test, and antibody titres greater than 0.5 IU/ml were found in 53% of bats 30 days after virus inoculation. Resistance to infection was seen in bats that developed low or no detectable antibody response as well as in bats with high titres. Among the 10 bats that died of rabies, eight showed signs of paralytic rabies and two bats showed no clinical signs.

Indirect oral immunization of captive vampires, Desmodus rotundus.

A vaccinia-rabies glycoprotein recombinant virus (V-RG) vaccine was tested in hematophagous bats (Desmodus rotundus) kept in captivity. The vaccine was applied in a neutral vehicle (Vaseline) spread on the back of one or two vector bats, which were then reintroduced into their groups. Our hypothesis was that, as in the case of vampire bat control by vampiricide paste, the administration of V-RG vaccine through paste to one bat could indirectly protect other bats from the same group. Eight groups were tested. The rabies virus strain used to challenge the bats was isolated from a naturally infected hematophagous bat (Desmodus rotundus). The survival proportion after the virus challenge ranged between 42.8 and 71.4%. The results are encouraging because a significant number of bats that did not receive the vaccine survived the challenge. The vaccine was shown to be safe and immunogenic to hematophagous bats. No adverse effects to vaccinia virus were observed.

A mixed ectoparasite--microparasite model for bat-transmitted rabies.

This paper considers the transmission of rabies to domestic livestock by vampire bats. Vampire bats act as ectoparasites on cattle both by ingesting a small amount of blood every night and by prolonging bleeding by the action of anticoagulant substances in their saliva. In addition to this parasitic action bats may also transmit rabies, inflicting important losses on affected herds by the inevitable mortality due to the infection. We modeled this complex interaction and we also demonstrate that bat control measures are more effective in reducing rabies prevalence and mortality by rabies than cattle vaccination.

Rabies seroprevalence of street dogs from São Paulo City, Brazil.

A sample of 602 street dogs captured by the São Paulo zoonosis-control municipal service was analyzed for the presence of serum antibodies against the rabies virus and compared to a control sample of 37 dogs from the kennel of the police of São Paulo. Data were stratified into 4 age intervals and the age from the street-dog sample was estimated by general aspects and dental observation according to standard techniques. We assumed that seropositivity was due to previous vaccination (no sub-clinical infection). From the prevalence data, we estimated the age-dependent incidence-density rate of vaccination by a simple mathematical model, which also allowed the estimation of the period of antibody protection given by the supposed vaccination. Crude seroprevalence in the street-dog sample was 16.5% and in the sample from the police-kennel dogs was 80%. The average age of first vaccination calculated for the street-dog sample was 5 years of age (if we assumed an average period of vaccine protection of 3 years) - but 5 months of age for the police-kennel sample.