Arboviral diseases are major global public health threats. Yet, our understanding of infection risk factors is, with a few exceptions, considerably limited. A crucial shortcoming is the widespread ...use of analytical methods generally not suited for observational data--particularly null hypothesis-testing (NHT) and step-wise regression (SWR). Using Mayaro virus (MAYV) as a case study, here we compare information theory-based multimodel inference (MMI) with conventional analyses for arboviral infection risk factor assessment.
A cross-sectional survey of anti-MAYV antibodies revealed 44% prevalence (n = 270 subjects) in a central Amazon rural settlement. NHT suggested that residents of village-like household clusters and those using closed toilet/latrines were at higher risk, while living in non-village-like areas, using bednets, and owning fowl, pigs or dogs were protective. The "minimum adequate" SWR model retained only residence area and bednet use. Using MMI, we identified relevant covariates, quantified their relative importance, and estimated effect-sizes (β ± SE) on which to base inference. Residence area (β(Village) = 2.93 ± 0.41; β(Upland) = -0.56 ± 0.33, β(Riverbanks) = -2.37 ± 0.55) and bednet use (β = -0.95 ± 0.28) were the most important factors, followed by crop-plot ownership (β = 0.39 ± 0.22) and regular use of a closed toilet/latrine (β = 0.19 ± 0.13); domestic animals had insignificant protective effects and were relatively unimportant. The SWR model ranked fifth among the 128 models in the final MMI set.
Our analyses illustrate how MMI can enhance inference on infection risk factors when compared with NHT or SWR. MMI indicates that forest crop-plot workers are likely exposed to typical MAYV cycles maintained by diurnal, forest dwelling vectors; however, MAYV might also be circulating in nocturnal, domestic-peridomestic cycles in village-like areas. This suggests either a vector shift (synanthropic mosquitoes vectoring MAYV) or a habitat/habits shift (classical MAYV vectors adapting to densely populated landscapes and nocturnal biting); any such ecological/adaptive novelty could increase the likelihood of MAYV emergence in Amazonia.
Individuals from three isolated, rural communities in the western Brazilian Amazon were evaluated for serological markers of hepatitis B virus (HBV) infection, HBV genotype, and the presence of risk ...factors for infection and transmission. Of the 225 individuals studied, 79.1% had serological evidence of HBV infection; 10.2% individuals were chronic carriers for HBV surface antigen (HBsAg-positive). Analysis of risk factors indicates that HBV is transmitted mainly horizontally within the family from a chronic "active" carrier for hepatitis B "e" antigen (HBeAg-positive), though a strong possibility of vertical transmission remains. The predominance of HBV genotype F, with a higher genomic similarity between the isolates, indicated a relatively recent introduction of HBV, from a common source, to the area. This study sheds light on the HBV epidemiology in the Brazilian Amazon region and highlights the need for greater emphasis on HBV control and immunization programs.
A infecção pelo VHB e VHD são importantes problemas de saúde na Amazônia. Este estudo avalia a prevalência da infecção por esses agentes em sete grupos indígenas do Estado do Amazonas. A taxa de ...infecção passada pelo VHB encontrada foi de 54,5% e a de portadores do AgHBs de 9,7%. Observa-se variação importante destes marcadores entre as aldeias, inclusive da mesma etnia. Não evidenciamos marcador de infecção aguda, os quatro AgHBe reativos eram todos Apurinã, da mesma aldeia, e três da mesma família. O VHD foi encontrado em 13,4% dos AgHBs reativos. O padrão de infecção pelo VHB e VHD encontrado possui as seguintes características: endemicidade elevada, baixo potencial de infectividade, transmissão marcada em idade precoce, provável transmissão familiar, e pouca importância da transmissão vertical. Entretanto, também sugere que esses vírus não tenham sido ainda introduzidos efetivamente em algumas das etnias estudadas.
HBV and HDV infections are a major health problem in the Amazon. This study evaluates the prevalence of these viruses within Indians groups, measuring the frequency of serological markers. The ...prevalence of past infection was 54.5% and HBsAg was found in 9.7%. An important variation of those markers was detected between villages, inclusively within the same ethnic group. None showed evidence of an acute infection. All HBeAg reactive were Apurinã, living in the same village and three of them from the same family. The prevalence of anti-HDT was 13.4% in HBsAg positive individuals. The authors observed high prevalence of HBV and HDV infection with the following pattern: low degree of infectivity, marked transmission in early ages, intra-familial dissemination, and lack of importance of vertical transmission. However, the results suggest that these viruses were not yet introduced effectively in some of the studied groups.
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