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In endemic areas, Rift Valley fever virus (RVFV) is a significant threat to both human and animal health. Goals of this study were to measure human anti-RVFV seroprevalence in a high-risk area following the 2006-2007 Kenyan Rift Valley Fever (RVF) epidemic, to identify risk factors for interval seroconversion, and to monitor individuals previously...
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Citations
... Several previous studies have reported endemic RVF transmission during inter-epidemic/ epizootic periods. 5,8,9,11,12,[15][16][17][18][19][20][21][22][23][24][25][26][27] The mechanisms for RVFV maintenance have been described in previous studies. 2,12,[28][29][30][31] Climate is known to affect the geographic, temporal distribution, life cycles of arthropod vectors, and the spread and evolution of the viruses they transmit. ...
Background: Rift Valley Fever (RVF) is a zoonotic disease that affects both animals and humans. Under reporting, misdiagnosis caused by the broad spectrum of symptoms presented by the disease, and limited access to rapid and accurate laboratory confirmation have led to an undefined burden of RVF. Reports are available that show the circulation of the virus during inter-epidemic periods, implying an endemic circulation of RVFV. This study aimed to determine RVFV transmission across annual seasons and demographic factors that are independently associated with exposure to RVFV. Methodology: Repeated serosurveys were performed during the long rainy, short rainy, and dry seasons in Lower Moshi area of Moshi district, Kilimanjaro region from January to December 2020. The goal was to determine seroprevalence against RVFV antibodies in humans and factors associated with seropositivity. Detection of RVF antibody was performed by competitive Enzyme-Linked Immunosorbent Assays (cELISA) using serum samples. Stata statistical software version 15 was used for data analysis. Descriptive statistics was carried out, whereby categorical variables were summarised using frequencies and percentages. Numeric variables were summarised using median and interquartile range. Logistic regression was used to assess factors associated with RVF seropositivity. Results: A total of 446 individuals were involved in the analysis. RVF seroprevalence was highest during rainy season (20.4%) and lowest in the dry season (4%). The overall annual seroprevalence of RVF was 12.8%. Season, participant age, and large number of residents in a given household were found to be significantly associated with RVF seropositivity (p<.05). Conclusion: RVFV demonstrates an endemic circulation in Lower Moshi area of Kilimanjaro region, suggesting the site is a potential RVF hotspot. Based on this study's findings, we recommend close surveillance of RVF in the study area and other areas with similar ecology in Tanzania as a means of preparedness for future unpredicted RVF outbreaks.
... Consumption or handling of sick animal products, interaction with livestock as herders and handling of aborted fetuses, milking, skinning, butchering, sleeping with animals, touching blood, and caring for animals during childbirth are all risk factors for humans (21,22). Human infection has a high risk of movement of livestock during the viremic phase of infection to locations with high mosquito density and naive animal populations, especially among those who handle livestock (23)(24). ...
... Consumption or handling of sick animal products, interaction with livestock as herders and handling of aborted fetuses, milking, skinning, butchering, sleeping with animals, touching blood, and caring for animals during childbirth are all risk factors for humans (21,22). Human infection has a high risk of movement of livestock during the viremic phase of infection to locations with high mosquito density and naive animal populations, especially among those who handle livestock (23)(24). ...
... As outbreaks are infrequent and infection often does not elicit treatment-seeking behavior, serological data provide an objective indicator of historic exposure in humans or other mammals and can be used to generate epidemiological estimates. Contemporary serological assays for RVFV have utilized different antigenic targets, including: nucleocapsid protein (N) (13,14), glycoprotein (Gn) (15), non-structural proteins NSs and NSm (12), and complete virus particles (16,17). Estimates within human populations are typically low for IgM or IgG antibody seropositivity and have rarely exceeded 10% (18,19), except following an RVFV outbreak (16). ...
... Contemporary serological assays for RVFV have utilized different antigenic targets, including: nucleocapsid protein (N) (13,14), glycoprotein (Gn) (15), non-structural proteins NSs and NSm (12), and complete virus particles (16,17). Estimates within human populations are typically low for IgM or IgG antibody seropositivity and have rarely exceeded 10% (18,19), except following an RVFV outbreak (16). Seroprevalence among ruminants is generally higher and can exceed 50%, but is highly variable among species, location, and immunoassay utilization (20)(21)(22). ...
... At this same time period of 2013-2014, RVFV outbreaks were identified in human (18) and ruminant (30) populations in Mozambique, though these were all identified in southern districts of the country. The 60% increased odds for seropositivity in males differs from other serostudies which have generally found no differences in seroprevalence by sex (6,18,19), though a 2009 Kenya study did find over 2-fold increase in seroprevalence in males (16). Increased odds in males in this Mozambique study population may be due to behavioral differences leading to increased exposure to both ruminants and mosquitoes. ...
Rift Valley fever virus (RVFV) is endemic in sub-Saharan Africa (SSA), with outbreaks reported in the Arabian Peninsula and throughout SSA. The natural reservoir for RVFV are ruminants, with livestock populations exceeding 50% exposure rates in some areas of SSA. Transmission to humans can occur through exposure to infected livestock products or multiple species of mosquito vectors. In 2013 and 2014, cross-sectional surveys occurred in two districts of Nacala-a-Velha and Mecubúri in northern Mozambique, and participants provided blood samples for later serological assays. IgG against the N protein of RVFV was detected through multiplex bead assay (MBA). Of the 2,278 persons enrolled between the two surveys and study sites, 181 (7.9%, 95% confidence interval (CI): 6.9%-9.1%) were found to be IgG seropositive with increasing seroprevalence with older age and significantly higher seroprevalence in Nacala-a-Velha (10.5%, 8.8%-12.5%) versus Mecubúri (5.7%, 4.5%-7.1%). Seroprevalence estimates were not significantly different between the 2013 and 2014 surveys. Significant spatial clustering of IgG positive persons were consistent among surveys and within the two districts, pointing toward the consistency of serology data for making population-level assumptions regarding RVFV seroprevalence. A subset of persons (n = 539) provided samples for both the 2013 and 2014 surveys, and a low percentage (0.81%) of these were found to seroconvert between these two surveys. Including the RVFV N protein in an MBA antigen panel could assist elucidate RVFV exposure in SSA. IMPORTANCE Due to sporadic transmission, human contact with Rift Valley Fever Virus (RVFV) is difficult to ascertain at a population level. Detection of antibodies against RVFV antigens assist in estimating exposure as antibodies remain in the host long after the virus has been cleared. In this study, we show that antibodies against RVFV N protein can be detected from dried blood spot (DBS) samples being assayed by multiplex bead assay. DBS from two districts in northern Mozambique were tested for IgG against the N protein, and 7.9% of all enrolled persons were seropositive. Older persons, males, and persons residing closer to the coast had higher RVFV N protein seroprevalence. Spatial clustering of IgG positive persons was noted in both districts. These results show low exposure rates to RVFV in these two northern districts in Mozambique, and the ability to perform serology for the RVFV N protein from dried blood samples.
... During large outbreaks, RVFV causes mass mortality of young livestock and near 100 percent abortion in pregnant animals [1]. As livestock succumb to RVF disease, the humans that rely on them to support their livelihoods attempt to mitigate their losses by assisting in the removal of abortion tissues, slaughtering, or selling sick animals, and sometimes consuming these animal sourced foods (ASFs), all of which put them at high risk of severe disease or even death from RVF disease [5,6]. Thus, risk of RVFV exposure is highly connected to livestock rearing activities, human behavior, cultural norms, and the ever-changing ecosystems in which susceptible hosts live [7,8]. ...
... Because of the current global distribution of RVFV, the risk of more widespread risk factors such as consumption, and handling of raw milk has not been disentangled from livestock rearing activities. There is also very little field data on the infectious nature of milk which, highlights a mechanism for RVFV transmission without owning or working with livestock [5,9]. ...
... We hypothesize that an urban transmission cycle of RVFV is indeed possible and that the first urban infections may not occur as a detectable outbreak, but rather through cryptic transmission from infected livestock or infected animal products. In this study, we aimed to document the human community burden of RVFV in two areas of Kenya and describe how risk factors may vary in the urban setting compared to what we have collectively learned previously about RVFV studies conducted primarily in rural areas [5,[25][26][27]. ...
The Rift Valley fever virus (RVFV) is a zoonotic arbovirus that can also transmit directly to humans from livestock. Previous studies have shown consumption of sick animal products are risk factors for RVFV infection, but it is difficult to disentangle those risk factors from other livestock rearing activities. Urban areas have an increased demand for animal source foods, different vector distributions, and various arboviruses are understood to establish localized urban transmission cycles. Thus far, RVFV is an unevaluated public health risk in urban areas within endemic regions. We tested participants in our ongoing urban cohort study on dengue (DENV) and chikungunya (CHIKV) virus for RVFV exposure and found 1.6% (57/3,560) of individuals in two urban areas of Kenya had anti-RVFV IgG antibodies. 88% (50/57) of RVFV exposed participants also had antibodies to DENV, CHIKV, or both. Although livestock ownership was very low in urban study sites, RVFV exposure was overall significantly associated with seeing goats around the homestead (OR = 2.34 (CI 95%: 1.18–4.69, p = 0 . 02 ) and in Kisumu, RVFV exposure was associated with consumption of raw milk (OR = 6.28 (CI 95%: 0.94–25.21, p = 0 . 02 ). In addition, lack of piped water and use of small jugs (15–20 liters) for water was associated with a higher risk of RVFV exposure (OR = 5.36 (CI 95%: 1.23–16.44, p = 0 . 01 ) and this may contribute to interepidemic vector-borne maintenance of RVFV. We also investigated perception towards human vaccination for RVFV and identified high acceptance (91% (97/105) at our study sites. This study provides baseline evidence to guide future studies investigating the urban potential of RVFV and highlights the unexplored role of animal products in continued spread of RVFV.
... In endemic areas, this cumulative exposure is usually estimated from cross-sectional surveys based on the population prevalence of human anti-RVFV IgG seropositivity at different ages. Among the 25 well-designed population-based serosurveys (scored as having low risk-of-bias) among our included reports (n = 44), IgG seroprevalence during interepidemic periods ranged from (0.15%) in Madagascar in 2014-2015 [40] to 22% in eastern Kenya in early 2006 [103] and again in 2013-2014 [104], with an overall median intra-epidemic value of 5.2% (IQR 1.8% -13%) seropositivity across all 25 surveys. ...
... As a result of these factors and the irregular frequency of disease outbreaks, the epidemiology of RVFV transmission and the risk factors for RVFV-related human disease are not well defined. In some endemic areas, post-epidemic serosurveys have shown high community exposure to RVFV [69,104,[153][154][155][156][157][158], even though symptomatic RVF had been only rarely reported by local health care services. Based on our consolidated picture of recent RVFV epidemiology and the knowledge gaps we have identified, future operational research and clinical trial design should consider the factors discussed below, with the understanding that currently available data have some significant limitations in accurately defining human risk for RVF. ...
Background
Rift Valley fever virus (RVFV) is a lethal threat to humans and livestock in many parts of Africa, the Arabian Peninsula, and the Indian Ocean. This systematic review’s objective was to consolidate understanding of RVFV epidemiology during 1999–2021 and highlight knowledge gaps relevant to plans for human vaccine trials.
Methodology/Principal findings
The review is registered with PROSPERO (CRD42020221622). Reports of RVFV infection or exposure among humans, animals, and/or vectors in Africa, the Arabian Peninsula, and the Indian Ocean during the period January 1999 to June 2021 were eligible for inclusion. Online databases were searched for publications, and supplemental materials were recovered from official reports and research colleagues. Exposures were classified into five groups: 1) acute human RVF cases, 2) acute animal cases, 3) human RVFV sero-surveys, 4) animal sero-surveys, and 5) arthropod infections. Human risk factors, circulating RVFV lineages, and surveillance methods were also tabulated. In meta-analysis of risks, summary odds ratios were computed using random-effects modeling. 1104 unique human or animal RVFV transmission events were reported in 39 countries during 1999–2021. Outbreaks among humans or animals occurred at rates of 5.8/year and 12.4/year, respectively, with Mauritania, Madagascar, Kenya, South Africa, and Sudan having the most human outbreak years. Men had greater odds of RVFV infection than women, and animal contact, butchering, milking, and handling aborted material were significantly associated with greater odds of exposure. Animal infection risk was linked to location, proximity to water, and exposure to other herds or wildlife. RVFV was detected in a variety of mosquito vectors during interepidemic periods, confirming ongoing transmission.
Conclusions/Significance
With broad variability in surveillance, case finding, survey design, and RVFV case confirmation, combined with uncertainty about populations-at-risk, there were inconsistent results from location to location. However, it was evident that RVFV transmission is expanding its range and frequency. Gaps assessment indicated the need to harmonize human and animal surveillance and improve diagnostics and genotyping. Given the frequency of RVFV outbreaks, human vaccination has strong potential to mitigate the impact of this now widely endemic disease.
... Consumption or handling of sick animal products, interaction with livestock as herders and handling of aborted fetuses, milking, skinning, butchering, sleeping with animals, touching blood, and caring for animals during childbirth are all risk factors for humans (21,22). Human infection has a high risk of movement of livestock during the viremic phase of infection to locations with high mosquito density and naive animal populations, especially among those who handle livestock (23)(24). ...
Rift Valley fever is an emerging viral disease that has been reported from several countries including Kenya,
... Consumption or handling of sick animal products, interaction with livestock as herders and handling of aborted fetuses, milking, skinning, butchering, sleeping with animals, touching blood, and caring for animals during childbirth are all risk factors for humans (21,22). Human infection has a high risk of movement of livestock during the viremic phase of infection to locations with high mosquito density and naive animal populations, especially among those who handle livestock (23)(24). ...
Rift Valley fever is an emerging viral disease that has been reported from several countries including Kenya,
... However, 1-3% of cases develop more severe symptoms of haemorrhagic fever, neurological disorders or blindness, which could be lethal [7,13]. Mosquitoes transmit RVFV to humans, but direct contact with infected animals, aborted foetal material, and consumption of raw milk also have been shown to correlate with transmission in endemic RVFV regions [14][15][16]. As in livestock, RVFV, transmitted to pregnant women, has been associated with miscarriage and foetal disease [17]. ...
The mosquito-borne Rift Valley fever (RVF) is a prioritised disease that has been listed by the World Health Organization for urgent research and development of counteraction. Rift Valley fever virus (RVFV) can cause a cytopathogenic effect in the infected cell and induce hyperimmune responses that contribute to pathogenesis. In livestock, the consequences of RVFV infection vary from mild symptoms to abortion. In humans, 1–3% of patients with RVFV infection develop severe disease, manifested as, for example, haemorrhagic fever, encephalitis or blindness. RVFV infection has also been associated with miscarriage in humans. During pregnancy, there should be a balance between pro-inflammatory and anti-inflammatory mediators to create a protective environment for the placenta and foetus. Many viruses are capable of penetrating that protective environment and infecting the foetal–maternal unit, possibly via the trophoblasts in the placenta, with potentially severe consequences. Whether it is the viral infection per se, the immune response, or both that contribute to the pathogenesis of miscarriage remains unknown. To investigate how RVFV could contribute to pathogenesis during pregnancy, we infected two human trophoblast cell lines, A3 and Jar, representing normal and transformed human villous trophoblasts, respectively. They were infected with two RVFV variants (wild-type RVFV and RVFV with a deleted NSs protein), and the infection kinetics and 15 different cytokines were analysed. The trophoblast cell lines were infected by both RVFV variants and infection caused upregulation of messenger RNA (mRNA) expression for interferon (IFN) types I–III and inflammatory cytokines, combined with cell line-specific mRNA expression of transforming growth factor (TGF)-β1 and interleukin (IL)-10. When comparing the two RVFV variants, we found that infection with RVFV lacking NSs function caused a hyper-IFN response and inflammatory response, while the wild-type RVFV suppressed the IFN I and inflammatory response. The induction of certain cytokines by RVFV infection could potentially lead to teratogenic effects that disrupt foetal and placental developmental pathways, leading to birth defects and other pregnancy complications, such as miscarriage.
... This finding is similar to other studies [44] that have reported Ae. aegypti to be more susceptible to RVFV infection compared with other known RVFV vectors. Evidence for RVFV transmission during IEPs has previously been reported among humans, livestock, and wild animals in Tanzania and elsewhere [1][2][3][4]6,23,30,[32][33][34][35]37,42,[45][46][47][48]. ...
Background
Rift Valley Fever virus (RVFV) is a zoonotic arbovirus of public health impact infecting livestock, wildlife, and humans mainly in Africa and other parts of the world. Despite its public health importance, mechanisms of RVFV maintenance during interepidemic periods (IEPS) remain unclear.
Objective
We aimed to examine comparatively exposure to RVFV between humans and goats and RVFV infection between humans, goats and mosquitoes.
Methods
A cross sectional study was performed in the Lower Moshi area of the Kilimanjaro region from March to June 2020. RVFV exposure was determined by detecting IgG/IgM to RVFV using a competitive enzyme linked immunosorbent assay whereas infection was determined by real time quantitative polymerase chain reaction (RT-qPCR) assay.
Results
Results show that the male gender was related to RVFV seropositivity (χ² = 5.351; p=0.030). Being 50 years and above was related to seropositivity (χ² =14.430; p=0.006) whereas bed net use, larger numbers of persons living in the same house (>7 persons) and RVFV seropositivity in goats were related to higher seropositivity to RVFV among humans χ² =6.003; p=0.021, χ² =23.213; p < 0.001 and χ² =27.053; p < 0.001), respectively. By the use of RT-qPCR, goats exhibited the highest RVFV infection rate of 4.1%, followed by humans (2.6%), Ae. aegypti (2.3%), and Cx. pipiens complex(1.5%). Likewise, a higher proportion of goats (23.3%) were RVFV seropositive as compared with humans (13.2%).
Conclusion
Our findings suggest the Lower Moshi area as a potential hotspot for Rift Valley Fever (RVF), posing the danger of being a source of RVFV spread to other areas. Goats had the highest infection rate, suggesting goats as important hosts for virus maintenance during IEPs. We recommend the implementation of strategies that will warrant active RVF surveillance through the identification of RVF hotspots for targeted control of the disease.
