Ecology of rabies

Sheep scrapie and deer rabies in England prior to 1800

Eighteenth-century England witnessed the emergence of two neurological diseases in animals. Scrapie, a transmissible spongiform encephalopathy, is a fatal neurodegenerative disease of sheep and goats that appears in classical and atypical forms. Reports of classical scrapie in continental Europe with described symptoms date back to 1750 in what is now western Poland. However, two major outbreaks of scrapie appeared in England prior to the 1800s. References to a sheep disease with a resemblance to scrapie first appear in Southwestern England between 1693 and 1722 and in the East Midlands between 1693 and 1706. Concurrent with the descriptions of scrapie in sheep was a neurological disease of deer first appearing in the East of England. Two 18th-century writers remarked on the symptomatic similarities between the sheep and deer neurological diseases. Multiple outbreaks of the unknown deer disease existing as early as 1772 are examined and are identified as rabies.

RABIES DIAGNOSIS AND RESPONSE TO VACCINATION IN SOUTHERN TAMANDUA (TAMANDUA TETRADACTYLA)

Rabies has rarely been described in Xenarthra, and rabies vaccine response has not been documented. A southern tamandua (Tamandua tetradactyla) presented with nonspecific clinical signs and was euthanatized. Subsequently, immunohistochemistry and RT-PCR confirmed a rabies diagnosis. Following these tests, a group of eight captive tamanduas were vaccinated with a killed rabies vaccine, and titers were measured at the time of vaccination and 23 d later. One animal had day 0 titers suggestive of previous vaccination or exposure. All animals had detectable neutralizing rabies virus antibody titers after vaccination, but one animal failed to meet the World Organization for Animal Health's definition for adequate vaccination (≥0.5 IU/ml), and two other animals had low antibody titers (0.56 and 0.6 IU/ml). Rabies should be considered as a possible cause of illness in tamanduas, and rabies vaccination may be a useful preventative measure when anthropic interaction through medical care or ambassador roles is occurring.

Do open garbage dumps play a role in canine rabies transmission in Biyem-Assi health district in Cameroon?

BACKGROUND

Rabies is a neglected enzootic disease which represents a serious public health problem. In Cameroon, efforts to prevent human deaths caused by rabies are often thwarted by the lack of community awareness. The community knowledge, as well as attitudes and perception on rabies, is therefore important for both prevention of human deaths and control in animals.

METHODS

A cross-sectional study was carried out to evaluate the level of community knowledge as well as the role of open garbage dumps (OGDs) in the epidemiology of human rabies. Overall 420 heads of household were interviewed in the Biyem-Assi health district of Yaoundé. OGDs were identified through a systematic check, and household wastes they contained were characterized.

RESULTS

Although 66.9% of respondents have knowledge on stray dogs, only 35% of respondents knew the role of OGDs in the increase of stray dog population. Overall OGDs consisted of fermentable wastes. Nutrition places for stray dogs were wild garbage dumps (68.1%), markets (18.3%), and houses (13.6%). The feeding behavior of stray dogs correlated significantly with the human rabies transmission (χ (2)=154.12, df=4, p<0.05).

CONCLUSION

Most participants knew that rabies could be transmitted by a dog bite as well as the measures to be taken in this type of situation. Increased knowledge of respondents on rabies showed OGDs and stray dogs as significant risk factors for canine rabies in Biyem-Assi health district.

Bayesian phylogeography finds its roots

As a key factor in endemic and epidemic dynamics, the geographical distribution of viruses has been frequently interpreted in the light of their genetic histories. Unfortunately, inference of historical dispersal or migration patterns of viruses has mainly been restricted to model-free heuristic approaches that provide little insight into the temporal setting of the spatial dynamics. The introduction of probabilistic models of evolution, however, offers unique opportunities to engage in this statistical endeavor. Here we introduce a Bayesian framework for inference, visualization and hypothesis testing of phylogeographic history. By implementing character mapping in a Bayesian software that samples time-scaled phylogenies, we enable the reconstruction of timed viral dispersal patterns while accommodating phylogenetic uncertainty. Standard Markov model inference is extended with a stochastic search variable selection procedure that identifies the parsimonious descriptions of the diffusion process. In addition, we propose priors that can incorporate geographical sampling distributions or characterize alternative hypotheses about the spatial dynamics. To visualize the spatial and temporal information, we summarize inferences using virtual globe software. We describe how Bayesian phylogeography compares with previous parsimony analysis in the investigation of the influenza A H5N1 origin and H5N1 epidemiological linkage among sampling localities. Analysis of rabies in West African dog populations reveals how virus diffusion may enable endemic maintenance through continuous epidemic cycles. From these analyses, we conclude that our phylogeographic framework will make an important asset in molecular epidemiology that can be easily generalized to infer biogeogeography from genetic data for many organisms.

Spreading in time and space, rapidly evolving viruses can accumulate a considerable amount of genetic variation. As a consequence, viral genomes become valuable resources to reconstruct the spatial and temporal processes that are shaping epidemic or endemic dynamics. In molecular epidemiology, spatial inference is often limited to the interpretation of evolutionary histories with respect to the sampling locations of the pathogens. To test hypotheses about the spatial diffusion patterns of viruses, analytical techniques are required that enable us to reconstruct how viruses migrated in the past. Here, we develop a model to infer diffusion processes among discrete locations in timed evolutionary histories in a statistically efficient fashion. Applications to Avian Influenza A H5N1 and Rabies virus in Central and West African dogs demonstrate several advantages of simultaneously inferring spatial and temporal processes from gene sequences.

Epidemiology and control of fox rabies in Europe

During recent years, most of the research on the control of sylvatic rabies has concentrated on developing methods of oral vaccination of wild rabies vectors. In order to improve both the safety and the stability of the vaccine used, a recombinant vaccinia virus which expresses the immunizing glycoprotein of rabies virus (VRG) has been developed and extensively tested in the laboratory as well as in the field. From 1989 until 1995, several million VRG vaccine doses have been dispersed in western Europe for vaccination of red foxes. In Europe, the use of VRG has lead to the elimination of sylvatic rabies from large areas, which have consequently been freed from vaccination. This may have consequences on the regulation of pets movements within the whole European Union.

Epidemiology and elimination of rabies in western Europe

In recent years, most of the research on the control of sylvatic rabies has concentrated on developing methods of oral vaccination of wild rabies vectors. In order to improve both the safety and the stability of the vaccine used, a recombinant vaccinia virus, which expresses the immunizing glycoprotein of rabies virus (VRG), has been developed and extensively tested in the laboratory as well as in the field. Between 1989 and 1995, several million VRG vaccine doses have been dispersed in Western Europe for the vaccination of red foxes, leading to the elimination of sylvatic rabies from large areas, which have consequently been freed from the need for vaccination. This approach may have consequences for the regulation of pet movement within the whole European Union.

Rabies

The practicing veterinarian has a key role to play in rabies control in the maintenance of protection in the companion animal populations, in the education of the pet-owning community on rabies, and in the decision-making process that accompanies human exposure to potentially rabid animals. This role encompasses far more than the routine maintenance of health and well-being in pet animal populations. Although it is important to remain diligent in the immunization of domestic pets against rabies to provide a barrier between wildlife, the main reservoir of infection, and man, it is also important to be aware of the current trends in wildlife rabies within a region. Research is currently underway to investigate methods of immunizing wildlife populations, but the effective and widespread control of rabies in these species is still a long way off; in the meantime, there will be an increasing demand for practicing veterinarians to take the lead in the control of this most fearful zoonotic disease.

Zoonotic diseases of cats

As veterinarians, our responsibilities do not end with the care of our patients. The welfare of our clients and their families depends on our ability to detect and control potentially zoonotic diseases in their pets. Because some of these zoonoses can have devastating effects on the development of the unborn fetus or on family health in general, discussion about these diseases between veterinarian and client is often emotionally charged. Under such circumstances, the offering of inaccurate and erroneous information by the veterinarian can have drastic consequences. It is likely that other zoonotic diseases of domestic pets will be identified in the future, especially those that can cause opportunistic infections in debilitated and immunodeficient persons. In the meantime, the potential hazards of cat ownership can be significantly reduced through an increased understanding of feline diseases and an improved level of health care for our feline patients.

Population dynamics of fox rabies in Europe

A simple mathematical model for the overall dynamics of the interaction between fox populations and rabies is presented. The model helps to explain epidemiological patterns observed in Europe, including the 3 to 5 year cycle in fox populations infected with rabies, threshold densities and average levels of prevalence of infection. We give a quantitative discussion of the possibilities of controlling rabies by culling or vaccinating foxes (or by a mixture of the two).

Wildlife rabies in Europe and the British situation

The red fox is considered to be the main reservoir of the present European rabies epizootic which began in Poland in 1939-40. Its usual rate of spread is 20 to 60 km a year. Mortality among rabies-infected fox populations is estimated variously to be 20 to 60%. The infection spreads more rapidly among foxes in the autumn and winter and its occurrence is dependent on fox populations is estimated variously to be 20 to 60%. The infection spreads more rapidly among foxes in the autumn and winter and its occurrence is dependent on fox population densities, it being readily transmitted in populations numbering over one fox to a square kilometre. Subsequently it recurs with a periodicity of three to five years. Though it was described in continental Europe in historic times there is no evidence of dramatic outbreaks among wild carnivores in Britain at any time. Aspects of the behaviour and life history of the fox, pertinent to rabies control are described. Potentially, oral antirabies vaccination of foxes in the wild may be a useful control technique, but there are problems in achieving this. In Britain, quarantine evasion with domestic animals is a significant rabies hazard, which could worsen as the five-sixth area of France still free from rabies becomes infected.

The vaccination of man and other animals against rabies

Rabies vaccines and their use in man and other animals are described. Safe and reliable vaccines are available for veterinary use, but many of the problems associated with the vaccination of humans remain unsolved.