Spatial and Temporal Description of Laboratory Diagnosis of Bovine Rabies in the State of Rio Grande do Sul, Brazil

Abstract

Background: Rabies remains one of the most important zoonosis worldwide and in Brazil. In the Brazilian state of Rio Grande do Sul (RS) the disease is one of the main causes of death in bovine herds. The confirmation of suspected rabies cases upon clinical examination depends on specific laboratory diagnosis. The Instituto de Pesquisas Veterinárias Desidério Finamor (IPVDF) is the reference laboratory in RS to diagnose rabies. The objective of the present study was to present a spatial-temporal description of diagnostic procedures of rabies in cattle in the years 2011 to 2015 in RS.Materials, Methods & Results: The results of diagnosis procedures of rabies in cattle carried out in the Laboratory of Virology, IPVDF, between January 2011 and December 2015 were listed. Direct immunofluorescence (DIF) and biological assays for confirming rabies cases were used. Cattle population density per area of a municipality, as well as date, species involved, location of suspected case, and diagnosis were obtained from exams and from official rabies record, and input to a spreadsheet file. Spatial distribution maps of cattle rabies confirmed in laboratory and cattle population density per municipality were constructed using the software TerraView 4.2.2 (INPE). In the study period, 998 samples of brains of cattle presenting neurological symptoms compatible with rabies, of which 582 (58%) were confirmed in the laboratory. The frequency of positive cases on a yearly basis varied between 41 and 65%, with statistically lower number of positives in 2011 (P > 0.05). The annual incidence of rabies for a population of 10,000,000 bovines was 33, 88, 112, 108, and 79, respectively, for the years 2011 to 2015, in that order. A positive correlation was observed between the number of samples analyzed and the incidence of positive cases in the study period, and statistically significant difference in incidence between years (P > 0.05). Samples were from 175 municipalities, of which 114 (65%) had at least one confirmed rabies case and 61 did not have any. The five municipalities that sent most samples for analysis were Viamão (n = 66), Montenegro (n = 40), Camaquã (n = 39), Gravataí (n = 38), and São Lourenço do Sul (n = 37). The spatial distribution of rabies in cattle in a year did not follow a defined pattern, though most cases confirmed in the laboratory occurred in the greater Porto Alegre region and in southeast RS.Discussion: High incidence of rabies was observed in 2012 and 2013, and in the two following years the number of cases confirmed in laboratory remained high, compared with 2011. The high incidence of rabies cases confirmed in laboratory correlated with the number of samples analyzed. The fall in vaccine coverage during the study period may also have prompted the increase in suspected cases and in the number of samples examined in the laboratory. A large number of the municipalities presenting rabies cases in cattle was in the greater Porto Alegre region and in southeast RS, which are areas of high and intermediate risk for the disease, according to a previous epidemiological modeling study. The spatial distribution of positive cases was not associated with the cattle population density. The large number of rabies in cattle in RS underscores the importance of the disease and the high risk of exposure, both to humans and animals. The results presented herein may help define control and prevention actions against rabies in RS.

Temporal and spatial distributions of animal and human rabies cases during 2012 and 2018, in Tunisia

“…On the other hand, the number of samples submitted to the rabies diagnostic laboratory has doubled, going from an average of 452 samples/year, before 2012, to an average of 995 samples/year after 2012. It was demonstrated in a study on bovine rabies in Brazil that the increase by one unit in the number of samples submitted raises incidence by 0.57 (Rodenbusch et al., 2016).…”

Bovine rabies in Rio Grande do Sul: positivity rates, geographical distribution, and seasonal occurrence

“…Meanwhile, the regions of Ijuí, Passo Fundo, Santa Maria, and Caxias do Sul showed the lowest percentages (Figure 7). This is concerning because sampling practices relate to positivity rates: the more municipalities send in samples, the higher the number of diagnosed and positive samples (RODENBUSCH et al, 2016). Since regions and municipalities with more efficient surveillance had higher positivity rates, in non-sampled areas the occurrence of rabies in cattle might still be underestimated.…”

“…Although cattle production is largely concentrated in the west and south regions of RS in the Pampa biome, as they are more suitable environments for livestock (IBGE, 2018), the west region of RS sent in fewer bovine samples for diagnosis in the early 2010s (RODENBUSCH et al, 2016). This is still true today.…”

“…However, bovine rabies is endemic. It continues to cause economic losses and is still a risk factor for public health (RODENBUSCH et al, 2016). Results from the Brazilian institute that coordinates national geographic and statistical data (Instituto Brasileiro de Geografia e Estatística -IBGE) show that the state of RS has the seventh-largest bovine population in Brazil (IBGE, 2018), with an average of approximately 12.6 million heads counted between 2016 and 2020 (RIO GRANDE DO SUL, 2020).…”

Spatiotemporal analysis of rabies in cattle in central Mexico

“…While the number and quality of epidemiological spatial applications of rabies are increasing, the full potential of these methods has not yet been achieved (Rodenbusch et al, 2016). The main critical control point observed in spatial distribution of rabies in cattle is that municipalities that send high numbers of biological material for analysis to the laboratory are those that also present the highest number of cases (Hayes and Piaggio, 2018), i.e.…”