Evaluation of the effect of sample suspension concentration and viral load on the outcome of the rabies tissue culture infection test.

In this study, we examined various brain suspension concentrations and viral loads in Neuro-2a cell cultures using 20 rabies-positive bovine samples. The reproducibility of results varied: 65% showed consistent outcomes across all concentrations, while 35% disagreed in at least one. Viral titers ranged from less than 25 × 101 to 25 × 103.50 TCID50/mL, with 20% below 25 × 101 TCID50/mL. Concentrations between 5% and 20% yielded over 90% agreement in positive results, but at 30%, agreement dropped from 85% to 50%. Cell confluence was successfully maintained at 5%, 10%, and 20%, while concentrations of 30% and above led to confluence loss. Low viral loads also negatively impacted reproducibility. These results suggest that sample concentration has a direct influence on preservation of cell confluence and that low viral loads may influence the reproducibility of the rabies tissue culture infection test (RTCIT).

Phylogenetic analysis of rabies virus isolated from canids in North and Northeast Brazil.

Cases of canine rabies continue to occur in North and Northeast Brazil, and the number of notifications of rabies cases in wild canids has increased as a result of the expansion of urban areas at the expense of areas with native vegetation. In light of this, we performed molecular characterization of rabies virus isolates from dogs and Cerdocyon thous from various states in North and Northeast Brazil. In all, 102 samples from dogs (n = 56) and Cerdocyon thous (n = 46) collected between 2006 and 2012 were used. The nucleotide sequences obtained for the N gene of rabies virus were analyzed, and phylogenetic analysis revealed the presence of two distinct genetic lineages, one associated with canids and one with bats, and, within the canid cluster, two distinct sublineages circulating among dogs and Cerdocyon thous. In addition, phylogenetic groups associated with geographic region and fourteen cases of interspecific infection were observed among the isolates from canids. Our findings show that analysis of rabies virus lineages isolated from reservoirs such as canids must be constantly evaluated because the mutation rate is high.

Delayed progression of rabies transmitted by a vampire bat.

Here, we compared the growth kinetics, cell-to-cell spread, and virus internalization kinetics in N2a cells of RABV variants isolated from vampire bats (V-3), domestic dogs (V-2) and marmosets (V-M) as well as the clinical symptoms and mortality caused by these variants. The replication rate of V-3 was significantly higher than those of V-2 and V-M. However, the uptake and spread of these RABV variants into N2a cells were inversely proportional. Nevertheless, V-3 had longer incubation and evolution periods. Our results provide evidence that the clinical manifestations of infection with bat RABV variant occur at a later time when compared to what was observed with canine and marmoset rabies virus variants.

Seroprevalence to Rabies Virus in Wildlife in Brazil.

Serum samples of 638 free-ranging wild mammals from São Paulo state, Brazil, were tested for neutralizing antibodies against rabies virus by the rapid fluorescent focus inhibition test. Overall seroprevalence was 1.7% among 24 species surveyed, with individuals of six species having positive results indicating exposure to rabies virus.

Detection of rabies virus in cranial cavity lavage of naturally infected bats.

The rabies virus (RABV) has been isolated in several bats species in the world, and among them, hematophagous, frugivorous and insectivorous species. Bats found in Brazil are small, which can lead to situations in which there are limitations in the collection of the central nervous system (CNS) and the amount of material may be insufficient to carry out laboratory diagnostic techniques for rabies. The objective of this work was to evaluate an alternative sample collection for the diagnosis of rabies in bats. A total of 92 bat samples, 82 positives and 10 negatives were selected. The cranial cavity was scraped with the aid of sterile tips and a virus diluent was added to create a suspension. All samples were submitted to Rabies Tissue Culture Infection Test (RTCIT) and reverse transcription polymerase chain reaction (RT-PCR). The diagnostic sensitivity and specificity of the RTCIT and RT-PCR using the cranial cavity lavage were calculated in comparison with the results of the laboratory routine (DFAT and RTCIT) performed with the CNS (considered gold standard). The results of the RTCIT show that the cranial cavity lavage is not an adequate sample for viral isolation, since the diagnostic sensitivity was low (37.8 %) when compared with the tests with the CNS. However, the RT-PCR of the cranial cavity lavage may be a tool to assist in the diagnosis, since it presented a sensitivity of 76.8 %. The results of this study suggest that cranial cavity lavage is an interesting alternative to enable the diagnosis of rabies in bats and increases the possibility of diagnosis contributing to rabies surveillance and control.

Human embryonic kidney (HEK-293) cell line: An alternative for rabies virus diagnosis and research.

Rabies is a serious public health problem in developing countries and is caused by Rabies lyssavirus (RABV), a neurotropic RNA virus. The gold standard test for rabies diagnosis is the direct fluorescent antibody test (DFAT). Nevertheless, a confirmatory method is recommended, such as rabies tissue culture infection test (RTCIT). Several cell lines have been tested for RTCIT, and the murine neuroblastoma (Neuro-2a) cell line has been shown to be the most permissive for infection. The human embryonic kidney (HEK-293) cell line was recently thought as an option, due to neuronal protein expression and easy maintenance. In the present work, we evaluated the susceptibility of HEK-293 cell line to RTCIT compared to Neuro-2a. We used a total of 93 brain samples, 48 negatives and 45 positives for RABV previously tested by DFAT or RT-PCR and by RTCIT in Neuro-2a. Of the positive samples, 43 were positive in the traditional RTCIT using Neuro-2a. Two protocols of HEK-293 cell line to RTCIT were tested (with and without virus adsorption) with different incubations times: 24, 48 and 72 h. The highest positive rate in HEK-293 (41 positive samples) resulted from the adsorption protocol with 72 h incubation period, in contrast to 43 positive samples with the traditional RTCIT with Neuro-2a. No satisfactory results were observed using the protocol without adsorption, regardless of the incubation time. Despite the slightly higher sensitivity of Neuro-2a cells, the use of the HEK-293 cells still offers positive aspects, such as, more rapid results, with the advantage of fast and easy growth over Neuro-2a cell line. Therefore, our findings confirm that HEK-293 cells are susceptible to RABV and can be an alternative for RTCIT.

Diagnóstico de cinomose canina por RT-PCR em amostras de cães do Estado de São Paulo enviadas para a vigilância laboratorial da raiva

A cinomose canina (CD) é uma das doenças infecciosas mais importantes dos cães domésticos. No Brasil é ainda a principal causa de mortalidade de cães em algumas populações urbanas. Embora sequências de diferentes genes do vírus sejam utilizadas como alvo para detecção do vírus da cinomose canina (CDV), o gene N parece ser o melhor para a amplificação de todas as suas linhagens. Utilizando-se a técnica de RT-PCR direcionada ao gene N do CDV, foram analisadas 190 amostras de sistema nervoso central (SNC) de cães do estado de São Paulo com quadros sugestivos de encefalite e que foram encaminhadas ao Instituto Pasteur para o diagnóstico da raiva, durante o ano de 2014. A positividade foi superior a 50% indicando que a cinomose continua a ser uma importante causa de mortalidade canina.

Canine distemper diagnosis by RT-PCR in dog samples from São Paulo State submitted to rabies laboratory diagnosis / Diagnóstico de cinomose canina por RT-PCR em amostras de cães do estado de São Paulo enviadas para o diagnóstico laboratorial da raiva

Canine distemper (CD) is one of the most important infectious diseases in domestic dogs. In Brazil, CD is still the principal cause of mortality of dogs in some urban populations. Although different viral gene sequences have been identified for detecting the canine distemper virus (CDV), the N gene appears to be a better target for the amplification of specific fragments from all CDV strains. Using RT-PCR targeted to the CDV N gene, during the year 2014 we analyzed 190 central nervous system (CNS) samples of dogs from the state of São Paulo, Brazil, with symptoms suggestive of encephalitis and sent them to the Pasteur Institute for the diagnosis of rabies. Positivity for CD was over 50%, indicating that the disease remains an important cause of canine mortality.

A cinomose canina (CD) é uma das doenças infecciosas mais importantes dos cães domésticos. No Brasil é ainda a principal causa de mortalidade de cães em algumas populações urbanas. Embora sequências de diferentes genes do vírus sejam utilizadas como alvo para detecção do vírus da cinomose canina (CDV), o gene N parece ser o melhor para a amplificação de todas as suas linhagens. Utilizando-se a técnica de RT-PCR direcionada ao gene N do CDV, foram analisadas 190 amostras de sistema nervoso central (SNC) de cães do estado de São Paulo com quadros sugestivos de encefalite e que foram encaminhadas ao Instituto Pasteur para o diagnóstico da raiva, durante o ano de 2014. A positividade foi superior a 50% indicando que a cinomose continua a ser uma importante causa de mortalidade canina.

Canine distemper diagnosis by RT-PCR in dog samples from São Paulo State submitted to rabies laboratory diagnosis / Diagnóstico de cinomose canina por RT-PCR em amostras de cães do estado de São Paulo enviadas para o diagnóstico laboratorial da raiva

Canine distemper (CD) is one of the most important infectious diseases in domestic dogs. In Brazil, CD is still the principal cause of mortality of dogs in some urban populations. Although different viral gene sequences have been identified for detecting the canine distemper virus (CDV), the N gene appears to be a better target for the amplification of specific fragments from all CDV strains. Using RT-PCR targeted to the CDV N gene, during the year 2014 we analyzed 190 central nervous system (CNS) samples of dogs from the state of São Paulo, Brazil, with symptoms suggestive of encephalitis and sent them to the Pasteur Institute for the diagnosis of rabies. Positivity for CD was over 50%, indicating that the disease remains an important cause of canine mortality.(AU)

A cinomose canina (CD) é uma das doenças infecciosas mais importantes dos cães domésticos. No Brasil é ainda a principal causa de mortalidade de cães em algumas populações urbanas. Embora sequências de diferentes genes do vírus sejam utilizadas como alvo para detecção do vírus da cinomose canina (CDV), o gene N parece ser o melhor para a amplificação de todas as suas linhagens. Utilizando-se a técnica de RT-PCR direcionada ao gene N do CDV, foram analisadas 190 amostras de sistema nervoso central (SNC) de cães do estado de São Paulo com quadros sugestivos de encefalite e que foram encaminhadas ao Instituto Pasteur para o diagnóstico da raiva, durante o ano de 2014. A positividade foi superior a 50% indicando que a cinomose continua a ser uma importante causa de mortalidade canina.(AU)

Rabies lyssavirus Isolates from Brazilian Different Reservoirs Species Present Distinct Pattern of Propagation in N2a Cell

Background: Rabies cell culture infection test was developed for the isolation of Rabies lyssavirus and as an alternative for the mouse inoculation test. However, tissue culture for street rabies strains produces low viral titer. Here, we assessed the quantity of brain tissue for successful viral isolation toward increased virus titer in effective way.Methods: Brain tissue isolates from different reservoirs species of Brazil were harvested in different concentration and inoculated in mouse neuroblastoma cells (N2a). These isolates were measured infectious viral titer and cell viability followed by consecutive passages in N2a cells.Results: Inoculum containing were prominent Rabies lyssavirus due to higher viral titer and not significantly dead cell. After consecutive passages in N2a cells Rabies lyssavirus variant maintained by vampire bat had remarkable adaptation to the culture system, while isolates from marmoset presents distinct pattern of propagation in N2a cell when compared with other groups.Conclusion: Based on these results, the isolation followed by viral replication assay may be used in isolates from different reservoirs which enable an effective amplification of the wild type virus strains