Integrative models of bat rabies immunology, epizootiology and disease demography

Bats are natural reservoirs of rabies. We address the maintenance of the disease in bat colonies by developing individual and population models that generate indicators of risk of rabies to bats, that provide dynamic estimates of effects of rabies on population densities, and that suggest consequences of viral exposures and infections in bats relative to physiological and ecological characteristics of bats in different habitats. We present individual models (within host) for the immune responses to a rabies virus challenge, an immunotypic disease model that describes the evolution of the disease and a disease demographics model, which is structured by immunotypic response governed by immune system efficiency. Model simulations are consistent with available data, characterized by relatively low prevalence of the virus in colonies and much higher prevalence of rabies virus-neutralizing antibodies. Under model conditions, there is a robust non-clinical state that can be attained by the exposed individual that allows persistence of the disease in the population.     

Molecular epidemiology of rabies in Vietnam

The present study was done to determine the molecular epidemiology of rabies virus (RV) in Vietnam. The nucleoprotein (N) and glycoprotein (G) genes of RVs were amplified from the brains of ten rabid dogs of Ho Chi Minh City, Vietnam. The nucleotide sequences of these genes were compared with those of other Asian strains to find the possible relationship among them. Phylogenetic analysis revealed that the Asian N gene segregated into three main branches, namely South-East Asia 1 (SEA 1), South-East Asia 2 (SEA 2) and Indian subcontinent (ISC) genotypes. The SEA 1 genotype comprised RVs from Malaysia, Vietnam and Thailand. The SEA 2 genotype contained strains from the Philippines, and the ISC genotype comprised strains from Sri Lanka and India. Phylogenetically G genes of RVs from Vietnam and Thailand were clustered together. Our study suggests that Vietnamese and Thai RVs are closely related and might have originated from a common ancestor.     

Molecular epidemiology of rabies in the United States

Changes in demographics, land use, recreation and hunting practices in the last 50 years dramatically increased the public health importance of reservoirs for rabies in wild species in the United States. This article focuses on attributes of host natural history to interpret the molecular phylogenies of the rabies variant transmitted within a particular animal population and the threat to human health presented by this reservoir.     

Role of gamasids in the epizootiology of tularemia]

10 strains of Francisella tularensis were isolated from 4 species of gamasid mites, Laelaps muris, L. multispinosus, Hyperlaelaps amphibius and Haemolaelaps glasgowi, in natural nidi of tularemia in the Tumen district. Under experimental conditions L. muris is often infected with tularemia agent on sick animals but preserves it at an indoor temperature not more than a week and does not transmit it transovarially. Haemogamasus ambulans preserve the agent within the same period. L. muris and Hirstionyssus isabellinus do not transmit the tularemia agent to healthy animals through a bite.     

Molecular epidemiology of rabies in Thailand.

For the purpose of making clear the dynamics of rabies viruses that are prevalent among dogs in Asia, especially Thailand, nucleoprotein (N) genes of isolates derived from Thailand were partially sequenced, and a phylogenetic analysis was performed on the basis of the sequencing data. Firstly, all 27 isolates from Thailand belonged to one group that was distantly related to an isolate from China and was separated into at least six lineages. On the other hand, the isolate from Japan was related to viruses from the Arctic. Secondly, in order to analyze the diversity of the N gene more conveniently, restriction fragment length polymorphism (RFLP) analysis was performed on the N gene of 27 isolates from Thailand. The RFLP analysis could distinguish the lineages of each isolate, and the lineages of additional 34 isolates were deduced by this method. On examination of the geographical distribution of the six lineages, based on the results of phylogenetic and RFLP analyses, it was clear that infection cycles of the rabies virus in Thailand have tended to be maintained endemically.     

The role of the Badger (Meles meles) in rabies epizootiology and the implications for Great Britain

The occurrence of a wildlife rabies epizootic in Britain remains a very unlikely event, but it is important to examine all the possible consequences of such an event. Here, I examine the possible role of the European Badger (Meles meles) in such an epizootic. The population density of Badgers in Britain is much higher than that in Europe, and appears to have increased substantially over the last decade or so. The population parameters and epizootiology of rabies in the Badger are reviewed in comparison with the Fox (Vulpes vulpes) and other species. Mustelids appear to be very susceptible to rabies, with the smaller mustelids becoming aggressive, although Badgers do not appear to show heightened aggression when infected. Badger populations on the continent become severely reduced when rabies arrives in the area, and circumstantial evidence strongly suggests that Badgers can easily transmit the virus. Preliminary models support the idea that the Badger could be a very significant secondary host, especially in the initial rabies outbreak. The population recovery rate of the Badger suggests that it is unlikely to become a primary host, although short‐term epizootics in the Badger population are likely. The potential for controlling rabies in the Badger is also examined.     

Molecular epidemiology of terrestrial rabies in the former Soviet Union

Fifty-five rabies virus isolates originating from different regions of the former Soviet Union (FSU) were compared with isolates originating from Eurasia, Africa, and North America according to complete or partial nucleoprotein (N) gene sequences. The FSU isolates formed five distinct groups. Group A represented viruses originating from the Arctic, which were similar to viruses from Alaska and Canada. Group B consisted of "Arctic-like" viruses, originating from the south of East Siberia and the Far East. Group C consisted of viruses circulating in the steppe and forest-steppe territories from the European part of Russia to Tuva and in Kazakhstan. These three phylogenetic groups were clearly different from the European cluster. Viruses of group D circulate near the western border of Russia. Their phylogenetic position is intermediate between group C and the European cluster. Group E consisted of viruses originating from the northwestern part of Russia and comprised a "northeastern Europe" group described earlier from the Baltic region. According to surveillance data, a specific host can be defined clearly only for group A (arctic fox; Alopex lagopus) and for the Far Eastern part of the group B distribution area (raccoon dog; Nyctereutes procyonoides). For other territories and rabies virus variants, the red fox (Vulpes vulpes) is the main virus reservoir. However, the steppe fox (Vulpes corsac), wolf (Canis lupus), and raccoon dog are also involved in virus circulation, depending on host population density. These molecular data, joined with surveillance information, demonstrate that the current fox rabies epizootic in the territory of the FSU developed independently of central and western Europe. No evidence of positive selection was found in the N genes of the isolates. In the glycoprotein gene, evidence of positive selection was strongly suggested in codons 156, 160, and 183. At these sites, no link between amino acid substitutions and phylogenetic placement or specific host species was detected.     

Ichthyophthiriasis: emphases on the epizootiology

Ichthyophthiriasis (white spot disease) is an economically important protozoosis caused by Ichthyophthirius multifiliis in freshwater fish. Medication prevention and curation are the main methods to control this disease with vaccines in laboratory, but the efficacy of drugs practically acts on the free‐living (nonparasitic) stage of I. multifiliis and can be easily impaired by a variety of environmental factors. Thus, study on the biological properties of I. multifiliis and the complicated ecological relationships between I. multifiliis and other biotic or abiotic factors that influence epidemicity of ichthyophthiriasis will contribute to integrated control of ichthyophthiriasis. In this article, some I. multifiliis biological properties, such as systematic position and life cycle of I. multifiliis, are briefly reviewed, and the seemingly abnormal phenomenon associated with in vitro cultures is specially discussed; then, the epizootiology of ichthyophthiriasis is emphasized, which involves various biotic or abiotic factors that impact the life and action of I. multifiliis. The susceptibility and stress reaction of fish to I. multifiliis infection are stated. Also, the pathogenicity and diagnosis of ichthyophthiriasis were covered, and an overall assessment is finally made on ichthyophthiriasis control.     

Contrasting landscape epidemiology of two sympatric rabies virus strains

Viral strain evolution and disease emergence are influenced by anthropogenic change to the environment. We investigated viral characteristics, host ecology, and landscape features in the rabies‐striped skunk disease system of the central Great Plains to determine how these factors interact to influence disease emergence. We amplified portions of the N and G genes of rabies viral RNA from 269 samples extracted from striped skunk brains throughout the distribution of two different rabies strains for which striped skunks were the reservoir. Because the distribution of these two strains overlapped on the landscape and were present in the same host population, we could evaluate how viral properties influenced epidemiological patterns in the area of sympatry. We found that South Central Skunk rabies (SCSK) exhibited intense purifying selection and high infectivity, which are both characteristics of an epizootic virus. Conversely, North Central Skunk rabies (NCSK) exhibited relaxed purifying selection and comparatively lower infectivity, suggesting the presence of an enzootic virus. The host population in the area of sympatry was highly admixed, and skunks among allopatric and sympatric areas had similar effective population sizes. Spatial analysis indicated that landscape features had minimal influence on NCSK movement across the landscape, but those same features were partial barriers to the spread of SCSK. We conclude that NCSK and SCSK have different epidemiological properties that interact differently with both host and landscape features to influence rabies spread in the central Great Plains. We suggest a holistic approach for future studies of emerging infectious diseases that includes studies of viral properties, host characteristics, and spatial features.