Biting rhythms and infection rates of anthropophilic sand fly species (Diptera: Phlebotominae) in sites with different land use in southern Mexico.

Could tropical forest conversion shape sand fly (Diptera: Phlebotominae) biting rhythms and Leishmania infection rates? Using a Shannon trap, we estimated the bite rate and infection prevalence among anthropophilic sand flies at sites with different land use in southern Mexico. We estimated the expected monthly infection rate of the Leishmania parasite along the gradient and generated information on the biting rhythm of sand flies in a poorly characterized cutaneous leishmaniasis endemic region. We used generalized mixed linear and mixed additives models to evaluate differences in the biting rate, nocturnal activity, and inoculation rate of female sand flies, as well as their relationship with the loss of forest cover and environmental disparities recorded throughout the study area. Our results show that the loss of forest cover influences the biting rhythm of sand fly species and the potential number of infectious bites with Leishmania, but the greatest entomological and potential epidemiological risk continues to be associated with sylvatic areas (amplification events). Despite this, we detected that the effect of forest cover (%) on the entomological exposure seems to be also dependent on the sand fly species, and that, albeit to a lesser extent, Leishmania parasite is circulating in disturbed landscapes through generalist and competent sand fly vector species. We also found that land use change did not affect the nocturnal activity, however we detected that important vector species were active most of the time. Contrary to our expectation, temperature and humidity did not shape the biting rhythm of sand fly species. We discuss the limitations and epidemiological implications of our findings regarding the risk of contracting leishmaniasis in southern Mexico.

Larval habitats, species composition and distribution of malaria vectors in regions with autochthonous and imported malaria in Roraima state, Brazil.

BACKGROUND: Malaria control requires local action. Assessing the vector diversity and abundance provides information on the local malariogenic potential or risk of transmission. This study aimed to determine the Anopheles species composition, habitats, seasonal occurrence, and distribution in areas with autochthonous and imported malaria cases in Roraima State. METHODS: A longitudinal study was conducted from January 2017 to October 2018, sampling larvae and adult mosquitoes in three municipalities of Roraima State: Boa Vista, Pacaraima and São João da Baliza. These areas have different risks of malaria importation. Four to six mosquito larval habitats were selected for larval sampling at each municipality, along with two additional sites for adult mosquito collection. All larval habitats were surveyed every two months using a standardized larval sampling methodology and MosqTent for adult mosquitoes. RESULTS: A total of 544 Anopheles larvae and 1488 adult mosquitoes were collected from the three municipalities studied. Although the species abundance differed between municipalities, the larvae of Anopheles albitarsis s.l., Anopheles nuneztovari s.l. and Anopheles triannulatus s.l. were collected from all larval habitats studied while Anopheles darlingi were collected only from Boa Vista and São João da Baliza. Adults of 11 species of the genus Anopheles were collected, and the predominant species in Boa Vista was An. albitarsis (88.2%) followed by An. darlingi (6.9%), while in São João da Baliza, An. darlingi (85.6%) was the most predominant species followed by An. albitarsis s.l. (9.2%). In contrast, the most abundant species in Pacaraima was Anopheles braziliensis (62%), followed by Anopheles peryassui (18%). Overall, the majority of anophelines exhibited greater extradomicile than peridomicile-biting preference. Anopheles darlingi was the only species found indoors. Variability in biting times was observed among species and municipalities. CONCLUSION: This study revealed the composition of anopheline species and habitats in Boa Vista, Pacaraima and São João da Baliza. The species sampled differed in their behaviour with only An. darlingi being found indoors. Anopheles darlingi appeared to be the most important vector in São João da Baliza, an area of autochthonous malaria, and An. albitarsis s.l. and An. braziliensis in areas of low transmission, although there were increasing reports of imported malaria. Understanding the diversity of vector species and their ecology is essential for designing effective vector control strategies for these municipalities.

Vector-Borne Disease Models with Active and Inactive Vectors: A Simple Way to Consider Biting Behavior.

Vector-borne diseases are a serious public health problem, mosquitoes being one of the most important vectors. To analyze the dynamics of this type of disease, Ross-Macdonald models are commonly used. In its simplest formulation and the most common in scientific literature, it is assumed that all mosquitoes are biting at a given rate. To improve this general assumption, we developed a vector-borne disease model with active and inactive vectors as a simple way to incorporate the more general characteristics of mosquito feeding behavior into disease dynamics. Our objective is to obtain an estimate of the Ross-Macdonald biting rate from the feeding parameters that reproduce the same dynamics as the model with active and inactive vectors. Two different cases were analyzed: a SIS-SI model and a SIR-SI model with a single epidemic. Different methods to estimate the biting rate in the Ross-Macdonald model were proposed and analyzed. To compare the results of the models, different epidemiological indicators were considered. When the biting rate is estimated considering that both models have the same basic reproduction number, very similar disease dynamics are obtained. This method is a simple way to incorporate the mosquito feeding behavior into the standard Ross-Macdonald model.

Integrating Parasitological and Entomological Observations to Understand Malaria Transmission in Riverine Villages in the Peruvian Amazon.

BACKGROUND: Remote rural riverine villages account for most of the reported malaria cases in the Peruvian Amazon. As transmission decreases due to intensive standard control efforts, malaria strategies in these villages will need to be more focused and adapted to local epidemiology. METHODS: By integrating parasitological, entomological, and environmental observations between January 2016 and June 2017, we provided an in-depth characterization of malaria transmission dynamics in 4 riverine villages of the Mazan district, Loreto department. RESULTS: Despite variation across villages, malaria prevalence by polymerase chain reaction in March 2016 was high (>25% in 3 villages), caused by Plasmodium vivax mainly and composed of mostly submicroscopic infections. Housing without complete walls was the main malaria risk factor, while households close to forest edges were more commonly identified as spatial clusters of malaria prevalence. Villages in the basin of the Mazan River had a higher density of adult Anopheles darlingi mosquitoes, and retained higher prevalence and incidence rates compared to villages in the basin of the Napo River despite test-and-treat interventions. CONCLUSIONS: High heterogeneity in malaria transmission was found across and within riverine villages, resulting from interactions between the microgeographic landscape driving diverse conditions for vector development, housing structure, and human behavior.

Temporal and Microspatial Heterogeneity in Transmission Dynamics of Coendemic Plasmodium vivax and Plasmodium falciparum in Two Rural Cohort Populations in the Peruvian Amazon.

BACKGROUND: Malaria is highly heterogeneous: its changing malaria microepidemiology needs to be addressed to support malaria elimination efforts at the regional level. METHODS: A 3-year, population-based cohort study in 2 settings in the Peruvian Amazon (Lupuna, Cahuide) followed participants by passive and active case detection from January 2013 to December 2015. Incidence and prevalence rates were estimated using microscopy and polymerase chain reaction (PCR). RESULTS: Lupuna registered 1828 infections (1708 Plasmodium vivax, 120 Plasmodium falciparum; incidence was 80.7 infections/100 person-years (95% confidence interval [CI] , 77.1-84.5). Cahuide detected 1046 infections (1024 P vivax, 20 P falciparum, 2 mixed); incidence was 40.2 infections/100 person-years (95% CI, 37.9-42.7). Recurrent P vivax infections predominated onwards from 2013. According to PCR data, submicroscopic predominated over microscopic infections, especially in periods of low transmission. The integration of parasitological, entomological, and environmental observations evidenced an intense and seasonal transmission resilient to standard control measures in Lupuna and a persistent residual transmission after severe outbreaks were intensively handled in Cahuide. CONCLUSIONS: In 2 exemplars of complex local malaria transmission, standard control strategies failed to eliminate submicroscopic and hypnozoite reservoirs, enabling persistent transmission.

Ingestive Behavior of Young Lambs on Contrasting Tropical Grass Sward Heights.

The efficiency of grazing ruminant production systems is directly associated to the animals' ingestive behavior, and to structural characteristics of the pastures. The objective of this study was to evaluate the ingestive behavior of young lambs grazing three different heights of Capim Aruana (Panicum maximum). The experiment was carried out in two consecutive years, in which 30 tester lambs (4-5 months old) were equally divided into three paddocks (treatments) corresponding to different average sward heights of Aruana grass: (1) Tall-75 cm; (2) Medium-50 cm; and (3) Short-25 cm in a randomized block design. Ingestive behavior assessments were carried out every 28 days through 10-min observations of the main activities of the animals (grazing, ruminating, idling) and biting rate, from sunrise to sunset. In addition, the productive and qualitative characteristics of the pastures were assessed. Despite differences in pasture structure, grazing time (GT) and idling time were similar among treatments (P = 0.4266 and P = 0.2939, respectively). The shortest ruminating time (RT, P = 0.0181) was recorded in the treatment of lowest sward height. Lambs grazing on this treatment also showed 23% more bites per minute (P= < 0.0001) than animals in the Tall and Medium treatments. A Decision Tree analysis was performed for GT, identifying in a hierarchical order that the initial weight of the animals and sward height explained 62% (R 2 = 0.621) of the variation, representing the variables with the greatest influence on GT. Initial body weight explained 48% of the model. Thus, our research shows that the different sward heights of Capim Aruana mainly alter the lamb's RT and biting rate, and that the animals' initial body weight is a key factor influencing GT, given that this variable makes lambs more susceptible to changes in sward height.

The Optimal Age of Vaccination Against Dengue with an Age-Dependent Biting Rate with Application to Brazil.

In this paper we introduce a single serotype transmission model, including an age-dependent mosquito biting rate, to find the optimal vaccination age against dengue in Brazil with Dengvaxia. The optimal vaccination age and minimal lifetime expected risk of hospitalisation are found by adapting a method due to Hethcote (Math Biosci 89:29-52). Any number and combination of the four dengue serotypes DENv1-4 is considered. Successful vaccination against a serotype corresponds to a silent infection. The effects of antibody-dependent enhancement (ADE) and permanent cross-immunity after two heterologous infections are studied. ADE is assumed to imply risk-free primary infections, while permanent cross-immunity implies risk-free tertiary and quaternary infections. Data from trials of Dengvaxia indicate vaccine efficacy to be age and serostatus dependent and vaccination of seronegative individuals to induce an increased risk of hospitalisation. Some of the scenarios are therefore reconsidered taking these findings into account. The optimal vaccination age is compared to that achievable under the current age restriction of the vaccine. If vaccination is not considered to induce risk, optimal vaccination ages are very low. The assumption of ADE generally leads to a higher optimal vaccination age in this case. For a single serotype vaccination is not recommended in the case of ADE. Permanent cross-immunity results in a slightly lower optimal vaccination age. If vaccination induces a risk, the optimal vaccination ages are much higher, particularly for permanent cross-immunity. ADE has no effect on the optimal vaccination age when permanent cross-immunity is considered; otherwise, it leads to a slight increase in optimal vaccination age.

Ingestive behavior and movement patterns of steers grazing sorghum and supplemented with concentrate / Comportamento ingestivo e padrões de deslocamento de novilhos suplementados em pastagem de sorgo forrageiro

The present study was developed at the Beef Cattle Laboratory of the Federal University of Santa Maria and evaluated the effect of three levels of concentrate supplementation (S 0.8, S 1.0, and S 1.2, corresponding to 0.8%, 1.0%, and 1.2% of bodyweight, respectively) on the ingestive behavior and movement patterns of 24 steers grazing on sorghum. The experiments were performed using a completely randomized block design in a 3 x 3 factorial arrangement (three levels of supplementation - three experimental periods), and the grazing time was evaluated using a 3 x 24 factorial arrangement (three levels of supplementation - 24 hours of observation). The steers fed S 0.8 presented longer (P=0.009) grazing time in the morning (241 min day-¹) compared to animals fed S 1.2 (172 min day-¹). The number of bites per feeding station was higher (4.05) during the second experimental period, and the number of bites min-¹ increased from 25.4 to 31.4 from the first to the second experimental period. The changes in sward structure during the growth stages of sorghum affected the number of bites per feeding station and the number of bites per minute.

O presente estudo foi desenvolvido no Laboratório de Bovinocultura de Corte da Universidade Federal de Santa Maria e teve como objetivo avaliar a influência de três níveis de suplementação energética (S0,8; S 1,0 ou S 1,2% do peso corporal) sobre o comportamento ingestivo e os padrões de deslocamento de 24 novilhos mantidos em pastagem com sorgo forrageiro. Foi utilizado o delineamento experimental inteiramente casualizado em fatorial 3 x 3 (três níveis de suplementação x três períodos de avaliação da pastagem) e para análise dos dados da frequência de pastejo um fatorial 3 x 24 (três níveis de suplementação e 24 horas de observação). Os novilhos do tratamento S 0,8 apresentaram maior (P=0,009) tempo de pastejo durante o turno da manhã (241 min. dia-¹) comparado aos animais do tratamento S1,2, que despenderam 172 min.dia-¹ nesta atividade. O maior número de bocados estação-¹(4,05) foi registrado durante o segundo período experimental, enquanto a taxa de bocados min.-1 aumentou de 25,4 (primeiro período) para 31,4 (segundo período). O fornecimento do equivalente a 1, 2% do peso corporal em suplementação energética promove a diminuição do tempo de pastejo durante o turno da manhã comparado a oferta de 0,8%. A variação estrutural da pastagem de sorgo forrageiro ao longo do seu ciclo produtivo promove variação no número de bocados por estação alimentar e taxa de bocadosmin.-¹ de novilhos suplementados.

Ingestive behavior and movement patterns of steers grazing sorghum and supplemented with concentrate / Comportamento ingestivo e padrões de deslocamento de novilhos suplementados em pastagem de sorgo forrageiro

The present study was developed at the Beef Cattle Laboratory of the Federal University of Santa Maria and evaluated the effect of three levels of concentrate supplementation (S 0.8, S 1.0, and S 1.2, corresponding to 0.8%, 1.0%, and 1.2% of bodyweight, respectively) on the ingestive behavior and movement patterns of 24 steers grazing on sorghum. The experiments were performed using a completely randomized block design in a 3 x 3 factorial arrangement (three levels of supplementation - three experimental periods), and the grazing time was evaluated using a 3 x 24 factorial arrangement (three levels of supplementation - 24 hours of observation). The steers fed S 0.8 presented longer (P=0.009) grazing time in the morning (241 min day-¹) compared to animals fed S 1.2 (172 min day-¹). The number of bites per feeding station was higher (4.05) during the second experimental period, and the number of bites min-¹ increased from 25.4 to 31.4 from the first to the second experimental period. The changes in sward structure during the growth stages of sorghum affected the number of bites per feeding station and the number of bites per minute.(AU)

O presente estudo foi desenvolvido no Laboratório de Bovinocultura de Corte da Universidade Federal de Santa Maria e teve como objetivo avaliar a influência de três níveis de suplementação energética (S0,8; S 1,0 ou S 1,2% do peso corporal) sobre o comportamento ingestivo e os padrões de deslocamento de 24 novilhos mantidos em pastagem com sorgo forrageiro. Foi utilizado o delineamento experimental inteiramente casualizado em fatorial 3 x 3 (três níveis de suplementação x três períodos de avaliação da pastagem) e para análise dos dados da frequência de pastejo um fatorial 3 x 24 (três níveis de suplementação e 24 horas de observação). Os novilhos do tratamento S 0,8 apresentaram maior (P=0,009) tempo de pastejo durante o turno da manhã (241 min. dia-¹) comparado aos animais do tratamento S1,2, que despenderam 172 min.dia-¹ nesta atividade. O maior número de bocados estação-¹(4,05) foi registrado durante o segundo período experimental, enquanto a taxa de bocados min.-1 aumentou de 25,4 (primeiro período) para 31,4 (segundo período). O fornecimento do equivalente a 1, 2% do peso corporal em suplementação energética promove a diminuição do tempo de pastejo durante o turno da manhã comparado a oferta de 0,8%. A variação estrutural da pastagem de sorgo forrageiro ao longo do seu ciclo produtivo promove variação no número de bocados por estação alimentar e taxa de bocadosmin.-¹ de novilhos suplementados.(AU)

Forage intake and behavior of goats on Tanzania-grass pasture at two regrowth ages / Consumo de forragem e comportamento de caprinos em pasto de capim-tanzânia em duas idades de rebrotação

The forage mass, sward structure, the ingestive and grazing behavior and forage intake by goats grazing on Tanzania-grass at 22 and 37 days of regrowth were evaluated. A completely randomized experimental design was used, with eight replications for evaluating the pasture and bite depth, and six replications for evaluating intake, feeding and grazing behavior. The forage canopy height ranged from 64.1 to 92.7 cm. Higher forage mass was observed at 37 days, and the best leaf/stem ratio, at 22 regrowth days. The bite depth did not differ between regrowth ages. The biting rate for the 22 regrowth days (23.07 bites min. <->1) was higher than at 37 days (19.06 bites min. <->1). The grazing time was longer at the regrowth age of 22 days (5.58h) than at 37 days (4.51h). The average feed intake was 2.75% of the body weight and was not different between regrowth ages.(AU)

Avaliou-se a massa de forragem e estrutura do pasto, comportamento ingestivo e de pastejo e o consumo de forragem por caprinos em pasto de capim-tanzânia aos 22 e 37 dias de rebrotação. Foi adotado o delineamento experimental inteiramente casualizado com oito repetições para a avaliação do pasto e da profundidade do bocado, e com seis repetições para a avaliação do consumo e do comportamento ingestivo e de pastejo. As alturas do dossel variaram de 64,1 a 92,7 cm. Maior massa de forragem foi verificada aos 37 dias e a maior relação folha/colmo aos 22 dias de rebrotação. A profundidade de bocado não diferiu nas idades avaliadas. A taxa de bocado aos 22 dias (23,07 bocados minuto-1) foi maior que aos 37 dias (19,06 bocados minuto <->1). Os animais despenderam maior parte do tempo em pastejo, aos 22 dias (5,58h) do que aos 37 dias (4,51h). O consumo médio de forragem foi 2,75% do peso vivo e não diferiu entre dias de rebrotação.(AU)

Forage intake and behavior of goats on Tanzania-grass pasture at two regrowth ages / Consumo de forragem e comportamento de caprinos em pasto de capim-tanzânia em duas idades de rebrotação

The forage mass, sward structure, the ingestive and grazing behavior and forage intake by goats grazing on Tanzania-grass at 22 and 37 days of regrowth were evaluated. A completely randomized experimental design was used, with eight replications for evaluating the pasture and bite depth, and six replications for evaluating intake, feeding and grazing behavior. The forage canopy height ranged from 64.1 to 92.7 cm. Higher forage mass was observed at 37 days, and the best leaf/stem ratio, at 22 regrowth days. The bite depth did not differ between regrowth ages. The biting rate for the 22 regrowth days (23.07 bites min.

Avaliou-se a massa de forragem e estrutura do pasto, comportamento ingestivo e de pastejo e o consumo de forragem por caprinos em pasto de capim-tanzânia aos 22 e 37 dias de rebrotação. Foi adotado o delineamento experimental inteiramente casualizado com oito repetições para a avaliação do pasto e da profundidade do bocado, e com seis repetições para a avaliação do consumo e do comportamento ingestivo e de pastejo. As alturas do dossel variaram de 64,1 a 92,7 cm. Maior massa de forragem foi verificada aos 37 dias e a maior relação folha/colmo aos 22 dias de rebrotação. A profundidade de bocado não diferiu nas idades avaliadas. A taxa de bocado aos 22 dias (23,07 bocados minuto-1) foi maior que aos 37 dias (19,06 bocados minuto

Malaria entomological inoculation rates in gold mining areas of Southern Venezuela

A longitudinal study of malaria vectors aiming to describe the intensity of transmission was carried out in five villages of Southern Venezuela between January 1999-April 2000. The man-biting, sporozoite and entomological inoculation rates (EIR) were calculated based on 121 all-night collections of anophelines landing on humans, CDC light traps and ultra violet up-draft traps. A total of 6,027 female mosquitoes representing seven species were collected. The most abundant species were Anopheles marajoara Galvão & Damasceno (56.7 percent) and Anopheles darlingi Root (33 percent), which together accounted for 89.7 percent of the total anophelines collected. The mean biting rate for An. marajoara was 1.27 (SD + 0.81); it was 0.74 (SD + 0.91) for An. darlingand 0.11 (SD + 0.10) for Anopheles neomaculipalpus Curry and the overall biting rate was 2.29 (SD + 1.06). A total of 5,886 mosquitoes collected by all three methods were assayed by ELISA and 28 pools, equivalent to 28 mosquitoes, yielded positive results for Plasmodium spp. CS protein. An. neomaculipalpus had the highest sporozoite rate 0.84 percent (3/356), followed by An. darlingi 0.82 percent (16/1,948) and An. marajoara 0.27 percent (9/3,332). The overall sporozoite rate was 0.48 percent (28/5,886). The rates of infection by Plasmodium species in mosquitoes were 0.37 percent (22/5,886) for Plasmodium vivax(Grassi & Feletti) and 0.10 percent (6/5,886) for Plasmodium falciparum (Welch). The estimated overall EIR for An. darling was 2.21 infective bites/person/year, 1.25 for An. marajoara and 0.34 for An. neomaculipalpus. The overall EIR was four infective bites/person/year. The biting rate, the sporozoite rate and the EIR are too low to be indicators of the efficacy of control campaigns in this area.