Despite the fact that the data for the years 2011 and 2012 are constantly undergoing revisions and updates within the Information System on Diseases Compulsory Declaration (SINAN), the available data allows a deep, unprecedented and wide-ranging analysis.
The observed annual average rate of incidents makes it possible to affirm that the most recent estimate of the Ministry of Health quoting only 26,000 cases of snakebite for the year 2010 [3
] is an underestimation by at least 4,000.
The observed growth in the number of incidents in all the regions between 2001 and 2004 can be attributed not only to a greater occurrence of snakebites, but also to improvements in the Brazilian health information system that tried to document the incidents while providing improved access to health services for victims.
The distinct reduction in the frequency of incidents in the Southeast region in the period from 2005 to 2009 does not appear to be as a result of any preventive measures. It merits a study to determine if there was a reduction in access to health services (which could have reduced the number of victims recorded by the information system) and/or environmental changes, which might have reduced the snake population as a consequence. There was a curve inversion with a growth trend after 2010.
In some states, snakebites represent a significant noticeable health issue for medical services. It is the third most reported medical issue in Tocantins, after dengue and leprosy, and the second most reported in Pará, exceeded only by dengue [14
Waldez & Vogt [15
] report that the highest incidences of snakebites for the Center-West region (33/100,000 inhabitants), followed by the North (24/100,000 inhabitants). The data analyzed in the present study allows for an inversion in the order of these two regions. The states bordering the Amazon Forest and the Pantanal (Acre, Amazonas, Pará, Roraima and Tocantins in the North region and Mato Grosso in the Center-West region) are those, which showed the highest frequency of cases in 2010. The low rates observed in the states of São Paulo and Rio de Janeiro (Southeast region), Paraná (South region), Piauí, Pernambuco and Sergipe (Northeast region) and the Federal District (Center-West region) demonstrate that, an analysis which contains a breakdown by region is important, but it is insufficient to fully explain the phenomenon of snakebite. Urbanization leading to concentration of significant human population reduces the risk of exposure to the snakebite. It is an important factor to note that mechanization of agriculture is also reducing the exposure of rural workers from snakes. Both these factors may contribute to an explanation of the low rates in the Southeast and Southern regions of the country. This logic, however, is not adequate in the case of several states of the Northeast regions. It is likely that difficulties in accessing health services and problems in reporting might have contributed to underreporting.
The high rate of Bothropic incidents may be explained by the enormous capacity of these snakes to adapt to a range of environments, allowing them to equally inhabit in forested areas or those which have been cleared and occupied by humans. Urbanization in Brazil has led to increased physical closeness of the Bothropic group of snakes to areas densely populated by humans. The precarious nature of the infrastructure in these new urban areas has contributed to proliferation of rodents and other pests which are the preferred prey of these snakes [16
]. Urban centers, whether in substandard settlements on the peripheries of cities, or in more affluent neighborhoods alongside areas of natural preservation, offer shelter for snakes. It may be said that parallel to the traditional rural snakebite issue, the conditions have been nurtured for a phenomenon called “urbanization of snakebites”.
The concentration of incidents involving snakes of the genus Lachesis in the North region is due to the fact that this type of snake lives predominantly in the tropical forests, thus favoring the higher frequency of cases in the region which contains the Amazon [17
]. It should be noted that each species of snake is geographically distributed in a particular region andpose challenges to the health-care teams in the identification of the species by attending the victims at various regions of Brazil. Nevertheless, there is an observed tendency in the last few years of the period studied towards a reduction in the proportion of incidents reflecting an improvement in the capacity of healthcare personnel to identify the snake genus, either by mere description given by the victim, or based on the symptoms. Strategies have been developed to assist with identification, such as the establishment of protocols based on the manifested symptoms of the victim, which aid in identifying the type of poisoning and, consequently, in guaranteeing the administration of the appropriate anti- venom [5
]. Another recent strategy is, taking advantage of the advancements of information technology, which provides direct access to snakebite specialists, so that the healthcare teams could attend the victims efficiently.
The monthly frequency of snakebite incidents throughout the period 2001-2012 shows the presence of seasonal variations in the temperature and rainfall in all regions, with the strong influence of periods of rain/dry weather in the North and Northeast regions and of temperature variations in other regions. The snakes are most active in the hot and humid months which correspond to the higher incidence of snakebites. Also to be taken into consideration is the degree of exposition implicit in human activities related to agriculture and ecotourism.
Although incidence rate is an important parameter in the analysis of snakebites, the total number of cases should not be neglected, since it informs policy concerning the production and distribution of antivenom in the country. Seasonal variations suggest the need for concern about the guarantee of antivenom supply, keeping the fluctuations in view related to the number of cases in each region. The production of sufficient serum to deal with the average annual number of cases need not necessarily guarantee its availability during the months when the majority of snakebites take place. Large fluctuations in the number of incidents could generate temporary shortages of serum which might not be detected in an analysis based on average values. A recent study by Machado [5
] points to a high frequency of cases involving the genus Crotalus
, but with the number of doses of serum used below that recommended by the Ministry of Health. One possible explanation for this may be the smaller number of doses available in certain periods, a hypothesis which demands further investigation.
The social and environmental variations between regions are reflected in the observed differences in the time elapsed before medical attention is received for young people between 10 and 19 years of age, and in the evolution of the case. In the South and Southeast, 79.9% and 73.3% of the victims, respectively, received medical attention within three hours. These numbers reflects the better quality of transportation networks and health services in those regions. The higher relative risk to which young people in the North are exposed may be due to their entry at an early age into the rural job market, especially in extractive industries, which tend to exhibit the highest prevalence of snakebites [20
Aspects like the species of the snake, the age of the victim, the site of the bite, and the time elapsed until medical attention is given, are determinants of seriousness and lethality.
Lethality in general is low, in the Northeast and Center and Western regions and a high percentage of them are curable with after-effects. This is due to variety of causes, such as better healthcare access, quality of care, information about the steps to be taken in the event of snakebite, and the genus of the snake. It is worth noting that snakes of the genus Micrurus
are not an aggressive species, and not possessing specialized teeth for venom delivery. The data related to states do not permit an estimation of the underreporting of snakebites which must inevitably take place, especially in the North, where low population density, precarious nature of transportation and huge distances to be traveled are acting as hurdles for victims in accessing health services. Nevertheless, the hypothesis should be raised that the growth in the number of reported incidents may be the result of both improvements in the access to the healthcare services, improving the quality of record keeping.
Current information systems have already produced a large quantity of data, which makes possible an updating of the profile of snakebite in Brazil. Despite this, information is lacking in all the areas as most of the fields are not properly filled and recorded for each snakebite incident so that it is not available on the SINAN site. Such information ought to be shared better and used to support the planning and decision-making process through the entire chain related to the production, storage and distribution of antivenom serum, as well as the education, training and maintenance of teams specialized in the treatment of snakebite. The differing patterns of snakebite presented by Brazil’s various regions suggest that studies of snakebite should make use of disaggregated data, which will permit the incorporation of existing environmental and socio-economic peculiarities into analysis of this serious health issue.