Optimising the surveillance of Aedes aegypti in Brazil by selecting smaller representative areas within an endemic city

OBJECTIVES

Arboviruses, such as dengue (DENV), zika (ZIKV), and chikungunya (CHIKV), constitute a growing urban public health threat. Focusing on Aedes aegypti mosquitoes, their primary vectors, is crucial for mitigation. While traditional immature-stage mosquito surveillance has limitations, capturing adult mosquitoes through traps yields more accurate data on disease transmission. However, deploying traps presents logistical and financial challenges, demonstrating effective temporal predictions but lacking spatial accuracy. Our goal is to identify smaller representative areas within cities to enhance the early warning system for DENV outbreaks.

METHODS

We created Sentinel Geographic Units (SGUs), smaller areas of 1 km2 within each stratum, larger areas, with the aim of aligning the Trap Positivity Index (TPI) and Adult Density Index (ADI) with their respective strata. We conducted a two-step evaluation of SGUs. First, we examined the equivalence of TPI and ADI between SGUs and strata from January 2017 to July 2022. Second, we assessed the ability of SGU's TPI and ADI to predict DENV outbreaks in comparison to Foz do Iguaçu's Early-Warning System, which forecasts outbreaks up to 4 weeks ahead. Spatial and temporal analyses were carried out, including data interpolation and model selection based on Akaike information criteria (AIC).

RESULTS

Entomological indicators produced in small SGUs can effectively replace larger sentinel areas to access dengue outbreaks. Based on historical data, the best predictive capability is achieved 2 weeks after infestation verification. Implementing the SGU strategy with more frequent sampling can provide more precise space-time estimates and enhance dengue control.

CONCLUSIONS

The implementation of SGUs offers an efficient way to monitor mosquito populations, reducing the need for extensive resources. This approach has the potential to improve dengue transmission management and enhance the public health response in endemic cities.

LaSap vaccine: Immunotherapy and immunochemotherapy associated with allopurinol in dogs naturally infected with Leishmania infantum

Canine visceral leishmaniasis is a parasitic zoonosis that has a profound impact on public health in countries where it is endemic. Chemotherapeutic treatments cannot keep dogs stable for long periods, and the risk of generating parasitic resistance must be considered. Forty-four symptomatic and naturally infected dogs with Leishmania infantum were tested with two treatment protocols (i) immunotherapy with LaSap vaccine and (ii) immunochemotherapy with LaSap vaccine plus allopurinol. At 90 days after the end of the treatment, it was verified that, although both protocols had generated significant clinical improvements with a greater production of IFN-γ/IL-10, in relation to the parasite load, mainly in the skin, the dogs treated only with immunotherapy maintained the same profile. These results indicate that LaSap is a good strategy to control dog parasitism.

Bivalent Vaccine against Streptococcus agalactiae and Aeromonas hydrophila in Nile Tilapia (Oreochromis niloticus): A Laboratory-Phase and Large-Scale Study

One of the main factors limiting tilapia's production is the occurrence of infections caused by Aeromonas and Streptococcus species. This work intended to evaluate a bivalent vaccine against A. hydrophila and S. agalactiae by intraperitoneal (i.p) administration in Nile tilapia (Oreochromis niloticus) in Brazil. The study was carried out in two phases: one in the laboratory, on a small scale, and from the results obtained, the study was expanded to a large scale in a production system in cages. The vaccine proved to be safe and effective in laboratory tests, with a vaccine efficacy (VE) of 93.66%. However, in large-scale tests with 12,000 tilapias, the VE was 59.14%, with a better food conversion ratio (1.54 kg) in the vaccinated group compared to the control group (1.27 kg). These results corroborate the efficiency of this tested vaccine; however, they indicate the need for field tests to attest to real protection.

Cross-sectional spatial and epidemiological analysis of canine visceral leishmaniasis cases in the triple border region, Brazil, Argentina and Paraguay, between 2015 and 2020

Visceral Leishmaniasis is one of the most important vector-borne zoonoses in the world. In 2013, the first autochthonous canine case of the disease in the state of Paraná, southern region of Brazil, was reported in Foz do Iguaçu, on the triple border between Brazil, Argentina and Paraguay. In 2015, the first human case was related. Once the endemic was confirmed, the Zoonoses Control Center (ZCC), an agency of the Municipal Health Department, started actions to implement the Human Visceral Leishmaniasis (HVL) Surveillance and Control Program (VLSCP), of the Ministry of Health. Between 2015 and 2020, 12,205 dog samples were analyzed for the diagnosis of the disease. A prevalence of 37.94% (4,630 samples) was found: 2016 had the highest prevalence, with 46.25%, and the year with the lowest prevalence was 2020, with 25.98%. Possible risk factors for dogs were analyzed, and the results obtained were: whether the request for the exam was performed by the ZCC was a significant protective factor, with a lower prevalence (37.5%) than dogs coming from private clinics (OR = 0.89, p-value = 0.016). Males were significantly more infected than females, with 41.1% and 35.7% positivity, respectively (OR = 1.24, p < 0.0001). Companion dogs and mixed breed dogs were significantly less affected than the other groups tested (OR = 0.44, p < 0.001; OR = 0.79, p = 0.012, respectively). The dogs' dark coat color was a significant risk factor with respect to the other color categories. Short and medium coat sizes were significantly considered risk factors, with 41.3% and 31.3% positivity. Long-haired dogs had only 22.7% positivity. In univariate analyses, giant, large and medium dogs were significantly more affected than small dogs. Dogs up to four years of age were significantly less affected than those in other age groups. There was a coincidence of human and canine cases in the spatial distribution. However, according to the literature, a higher incidence would be expected in humans, due to the high prevalence found in dogs. Therefore, further studies should be carried out to understand the dynamics of the disease in this region.

Adaptation of a Human Diagnostic Kit to Detect Dengue, Zika, and Chikungunya Viruses in Mosquito Samples (Aedes aegypti and Aedes albopictus): A Contribution to Public Health in the International Triple Border (Brazil, Paraguay, and Argentina)

Objective: The objective of this work was to adapt a diagnostic kit developed for humans to identify Dengue (DENV1, DENV2, DENV3, DENV4), Zika (ZIKV) and Chikungunya virus (CHIKV) in females of Aedes aegypti and Aedes albopictus and to verify if the occurrence of mosquitoes infected with these three arboviruses are being found in regions with high occurrence of these diseases in humans. Materials and Methods: For this purpose, live mosquitoes were captured between January and June 2020 using 3,476 traps permanently installed in the field were used. After capture, the species were identified, then the females were placed in a pool of 2 to 10 specimens and sent to the laboratory for detection of DENV1, DENV2, DENV3, DENV4, ZIKV and CHIKV by RT-PCR using a commercial human kit for arboviruses. Results: Of the 76 mosquito pools collected, six (7.9%) pools tested positive for the DENV2 virus. The DENV-positive mosquitoes were collected in regions with a high incidence of reported cases of Dengue or in adjacent areas. Conclusion: The absence of kits for the detection of these arboviruses in Aedes is a limiting factor and the adequacy of commercial kits, already used for the diagnosis of arboviruses in humans, the results presented demonstrate that it is possible to identify the presence of DENV2 in mosquitoes with the respective kit, reinforcing the use of RT-qPCR as a robust diagnostic tool for epidemiological surveillance allowing managers to receive timely results for decision-making regarding prevention and control actions.

Malathion insecticide resistance in Aedes aegypti: laboratory conditions and in situ experimental approach through adult entomological surveillance

OBJECTIVE

In Brazil, the most common method of controlling outbreaks of arbovirus is by the use of chemical sprays, which kill the insect vector, Aedes aegypti. The main objective of this study was to evaluate the resistance of Ae. aegypti to the insecticide, malathion, in situ. The location of this study was the municipality of Foz do Iguaçu, in the state of Paraná, Brazil.

METHODS

Ultra-low-volume (ULV) fogging equipment was used, by vehicle, to apply the insecticide in situ, and mosquito populations after treatment were compared with those of control areas. The resistance of strains collected from the municipality was compared to the Rockefeller strain under laboratory conditions.

RESULTS

We found 220 adult female specimens and 7423 eggs of Ae. aegypti in the areas subjected to UBV treatment, whereas 245 adult females and 10 557 eggs were found in the control areas. The UBV treatment area showed no significant difference compared to the control area, for all the indices. Mortality of the Rockefeller colony varied more quickly when there were slight variations in malathion concentration than the Foz do Iguaçu population.

Immunogenicity of HLA-DR1 and HLA-A2 peptides derived from Leishmania major Gp63 in golden hamsters

AIMS

This study aimed to evaluate the toxicity and humoral and cellular immune response of three heterologous vaccines against Leishmania infantum, yet containing synthetic peptides from Leishmania major in the experimental model in hamsters.

METHODS AND RESULTS

Through bioinformatics analyses, two Leishmania major Gp63 peptides were predicted and selected for vaccine formulations. Hamsters were divided into four groups, with each group receiving doses of three vaccine formulations containing HLA-DR1 or HLA-A2 peptides plus Montanide^TM or both associated with the adjuvant. The animals received three vaccine doses and were evaluated for toxicity after each dose, in addition to being analysed for the production of antibodies and lymphoproliferation on day 211 after the last vaccine dose. Peptides predicted in association with oily adjuvant induced a humoral response and strong lymphoproliferation to Leishmania infantum antigen-specific stimulation.

Molecular Detection of Dengue Virus in Mosquitoes as an Early Indicator to Aid in the Prevention of Human Infection in Endemic Areas

Human cases of dengue virus based on the National Dengue Control Plan were compared with the molecular detection of the dengue virus in trapped mosquitoes, verifying the prediction and efficacy potentials of vector control between the two methodologies in a city with three endemic frontiers. Molecular detection of dengue virus in trapped mosquitoes was significantly higher than in human cases (p = 0.0435). Thus, molecular detection could be used as an early indicator to help prevent more human cases of dengue.