Vector competence of Aedes albopictus (Skuse) and Aedes aegypti (Linnaeus) for Plasmodium gallinaceum infection and transmission

A Literature Review on the Role of the Invasive Aedes albopictus in the Transmission of Avian Malaria Parasites

The Asian tiger mosquito (Aedes albopictus) is an invasive mosquito species with a global distribution. This species has populations established in most continents, being considered one of the 100 most dangerous invasive species. Invasions of mosquitoes such as Ae. albopictus could facilitate local transmission of pathogens, impacting the epidemiology of some mosquito-borne diseases. Aedes albopictus is a vector of several pathogens affecting humans, including viruses such as dengue virus, Zika virus and Chikungunya virus, as well as parasites such as Dirofilaria. However, information about its competence for the transmission of parasites affecting wildlife, such as avian malaria parasites, is limited. In this literature review, we aim to explore the current knowledge about the relationships between Ae. albopictus and avian Plasmodium to understand the role of this mosquito species in avian malaria transmission. The prevalence of avian Plasmodium in field-collected Ae. albopictus is generally low, although studies have been conducted in a small proportion of the affected countries. In addition, the competence of Ae. albopictus for the transmission of avian malaria parasites has been only proved for certain Plasmodium morphospecies under laboratory conditions. Therefore, Ae. albopictus may play a minor role in avian Plasmodium transmission in the wild, likely due to its mammal-biased blood-feeding pattern and its reduced competence for the development of different avian Plasmodium. However, further studies considering other avian Plasmodium species and lineages circulating under natural conditions should be carried out to properly assess the vectorial role of Ae. albopictus for the Plasmodium species naturally circulating in its distribution range.

Infectivity of Plasmodium parasites to Aedes aegypti and Anopheles stephensi mosquitoes maintained on blood-free meals of SkitoSnack

BACKGROUND

Aedes and Anopheles mosquitoes are responsible for tremendous global health burdens from their transmission of pathogens causing malaria, lymphatic filariasis, dengue, and yellow fever. Innovative vector control strategies will help to reduce the prevalence of these diseases. Mass rearing of mosquitoes for research and support of these strategies presently depends on meals of vertebrate blood, which is subject to acquisition, handling, and storage issues. Various blood-free replacements have been formulated for these mosquitoes, but none of these replacements are in wide use, and little is known about their potential impact on competence of the mosquitoes for Plasmodium infection.

METHODS

Colonies of Aedes aegypti and Anopheles stephensi were continuously maintained on a blood-free replacement (SkitoSnack; SS) or bovine blood (BB) and monitored for engorgement and hatch rates. Infections of Ae. aegypti and An. stephensi were assessed with Plasmodium gallinaceum and P. falciparum, respectively.

RESULTS

Replicate colonies of mosquitoes were maintained on BB or SS for 10 generations of Ae. aegypti and more than 63 generations of An. stephensi. The odds of engorgement by SS- relative to BB-maintained mosquitoes were higher for both Ae. aegypti (OR = 2.6, 95% CI 1.3-5.2) and An. stephensi (OR 2.7, 95% CI 1.4-5.5), while lower odds of hatching were found for eggs from the SS-maintained mosquitoes of both species (Ae. aegypti OR = 0.40, 95% CI 0.26-0.62; An. stephensi OR = 0.59, 95% CI 0.36-0.96). Oocyst counts were similar for P. gallinaceum infections of Ae. aegypti mosquitoes maintained on SS or BB (mean ratio = [mean on SS]/[mean on BB] = 1.11, 95% CI 0.85-1.49). Similar oocyst counts were also observed from the P. falciparum infections of SS- or BB-maintained An. stephensi (mean ratio = 0.76, 95% CI 0.44-1.37). The average counts of sporozoites/mosquito showed no evidence of reductions in the SS-maintained relative to BB-maintained mosquitoes of both species.

CONCLUSIONS

Aedes aegypti and An. stephensi can be reliably maintained on SS over multiple generations and are as competent for Plasmodium infection as mosquitoes maintained on BB. Use of SS alleviates the need to acquire and preserve blood for mosquito husbandry and may support new initiatives in fundamental and applied research, including novel manipulations of midgut microbiota and factors important to the mosquito life cycle and pathogen susceptibility.

Avian Plasmodium in invasive and native mosquitoes from southern Spain

BACKGROUND

The emergence of diseases of public health concern is enhanced by factors associated with global change, such as the introduction of invasive species. The Asian tiger mosquito (Aedes albopictus), considered a competent vector of different viruses and parasites, has been successfully introduced into Europe in recent decades. Molecular screening of parasites in mosquitoes (i.e. molecular xenomonitoring) is essential to understand the potential role of different native and invasive mosquito species in the local circulation of vector-borne parasites affecting both humans and wildlife.

METHODS

The presence of avian Plasmodium parasites was molecularly tested in mosquitoes trapped in five localities with different environmental characteristics in southern Spain from May to November 2022. The species analyzed included the native Culex pipiens and Culiseta longiareolata and the invasive Ae. albopictus.

RESULTS

Avian Plasmodium DNA was only found in Cx. pipiens with 31 positive out of 165 mosquito pools tested. None of the Ae. albopictus or Cs. longiareolata pools were positive for avian malaria parasites. Overall, eight Plasmodium lineages were identified, including a new lineage described here. No significant differences in parasite prevalence were found between localities or sampling sessions.

CONCLUSIONS

Unlike the invasive Ae. albopictus, Cx. pipiens plays a key role in the transmission of avian Plasmodium in southern Spain. However, due to the recent establishment of Ae. albopictus in the area, further research on the role of this species in the local transmission of vector-borne pathogens with different reservoirs is required.

Automatic identification of medically important mosquitoes using embedded learning approach-based image-retrieval system

Mosquito-borne diseases such as dengue fever and malaria are the top 10 leading causes of death in low-income countries. Control measure for the mosquito population plays an essential role in the fight against the disease. Currently, several intervention strategies; chemical-, biological-, mechanical- and environmental methods remain under development and need further improvement in their effectiveness. Although, a conventional entomological surveillance, required a microscope and taxonomic key for identification by professionals, is a key strategy to evaluate the population growth of these mosquitoes, these techniques are tedious, time-consuming, labor-intensive, and reliant on skillful and well-trained personnel. Here, we proposed an automatic screening, namely the deep metric learning approach and its inference under the image-retrieval process with Euclidean distance-based similarity. We aimed to develop the optimized model to find suitable miners and suggested the robustness of the proposed model by evaluating it with unseen data under a 20-returned image system. During the model development, well-trained ResNet34 are outstanding and no performance difference when comparing five data miners that showed up to 98% in its precision even after testing the model with both image sources: stereomicroscope and mobile phone cameras. The robustness of the proposed-trained model was tested with secondary unseen data which showed different environmental factors such as lighting, image scales, background colors and zoom levels. Nevertheless, our proposed neural network still has great performance with greater than 95% for sensitivity and precision, respectively. Also, the area under the ROC curve given the learning system seems to be practical and empirical with its value greater than 0.960. The results of the study may be used by public health authorities to locate mosquito vectors nearby. If used in the field, our research tool in particular is believed to accurately represent a real-world scenario.

Molecular detection of avian haemosporidian parasites in biting midges (Diptera: Ceratopogonidae) from Thailand

Culicoides biting midges are vectors of many haemosporidian parasite species. These parasites are found in several wild and domestic avian species in Thailand but knowledge of the insect vectors is very limited. In this study, a molecular approach was used to detect haemosporidian parasites in six biting midge species in Thailand. A total of fifteen cytochrome b haplotypes of three haemosporidian parasites were detected from 1,165 specimens of six different Culicoides species. Comparisons of these sequences with those recorded in a public database revealed that they were comprised sequences of three species, Leucocytozoon sp., Plasmodium juxtanucleare and P. gallinaceum. All of these haemosporidian parasite species were detected in Culicoides mahasarakhamense Pramual, Jomkumsing, Piraonapicha, & Jumpato while P. juxtanucleare was also detected in C. huffi Causey and C. guttifer Meijere and Leucocytozoon sp. were also detected in C. guttifer. All of these parasites are commonly found in chickens in agreement with information that these biting midge species will bite chickens. Detection DNA of Leucocytozoon sp. in biting midges reported here provides the second record of this parasitic genus infecting Culicoides. This study also provides the first records of P. juxtanucleare and P. gallinaceum in biting midge species. Further investigation is required to determine whether Culicoides biting midge species are competent vectors of these parasites.

Diversity of midgut microbiota in laboratory-colonized and field-collected Aedes albopictus (Diptera: Culicidae): A preliminary study

Aedes (Ae.) albopictus is an important vector for many pathogens. Previous studies have revealed a role for midgut bacteria during pathogen infection in mosquitoes; however, studies of Ae. albopictus midgut bacteria are limited. We examined the diversity of midgut bacteria in female laboratory-colonized and field-collected Ae. albopictus. A total of 31 bacterial genera were identified representing 10 and 28 genera of laboratory-colonized and field-collected Ae. albopictus, respectively. The predominant bacterial genera in the laboratory-colonized Ae. albopictus were Staphylococcus and Micrococcus, whereas the bacterial diversity in the field-collected Ae. albopictus exhibited a higher proportion of Rhizobium and Agrobacterium as the dominant genera. However, only Staphylococcus showed a significant difference between laboratory-colonized and field-collected Ae. albopictus. The midgut bacterial species were identified from 30 laboratory-colonized Ae. albopictus mosquitoes. A total of 16 bacterial species were identified and the predominant bacterial species was Micrococcus luteus, followed by Staphylococcus epidermidis and Agrobacterium tumefaciens. Field mosquitoes were collected from the Sing Buri, Chumphon, and Yala Provinces of Thailand. The midgut bacterial species identified from the 10 Ae. albopictus collected from the Sing Buri Province included Bacillus subtilis, Staphylococcus haemolyticus, Staphylococcus hominis, and Serratia marcescens. Serratia marcescens was the only bacteria identified from this area. Midgut bacterial species were identified from 40 filed-collected Ae. albopictus from Chumphon Province. A total of 25 bacterial species were identified and the predominant species were Enterobacter cloacae, Micrococcus luteus, and Providencia rettgeri. Only 15 bacterial species were identified from the mosquitoes collected from Chumphon Province. A total of 18 bacterial species were identified from 30 Ae. albopictus collected from Yala Province and the predominant species were Rhizobium pusense and Agrobacterium tumefaciens. Only 12 bacterial species were found in mosquitoes collected from Yala Province. These findings indicate changes in the midgut bacteria population in Ae. albopictus from various locales, which may result from variability in the blood-meal source, diet, or habitat. A comprehensive survey of the midgut bacteria community prevalence in wild populations is critical for not only gaining a better understanding of the role of this bacterium in shaping the microbial community in Ae. albopictus, but also for informing current and future mosquito and disease control programs.

Classification for avian malaria parasite Plasmodium gallinaceum blood stages by using deep convolutional neural networks

The infection of an avian malaria parasite (Plasmodium gallinaceum) in domestic chickens presents a major threat to the poultry industry because it causes economic loss in both the quality and quantity of meat and egg production. Computer-aided diagnosis has been developed to automatically identify avian malaria infections and classify the blood infection stage development. In this study, four types of deep convolutional neural networks, namely Darknet, Darknet19, Darknet19-448 and Densenet201 are used to classify P. gallinaceum blood stages. We randomly collected a dataset of 12,761 single-cell images consisting of three parasite stages from ten-infected blood films stained by Giemsa. All images were confirmed by three well-trained examiners. The study mainly compared several image classification models and used both qualitative and quantitative data for the evaluation of the proposed models. In the model-wise comparison, the four neural network models gave us high values with a mean average accuracy of at least 97%. The Darknet can reproduce a superior performance in the classification of the P. gallinaceum development stages across any other model architectures. Furthermore, the Darknet has the best performance in multiple class-wise classification, with average values of greater than 99% in accuracy, specificity, and sensitivity. It also has a low misclassification rate (< 1%) than the other three models. Therefore, the model is more suitable in the classification of P. gallinaceum blood stages. The findings could help us create a fast-screening method to help non-experts in field studies where there is a lack of specialized instruments for avian malaria diagnostics.

Development and application of a novel multiplex PCR assay for the differentiation of four haemosporidian parasites in the chicken Gallus gallus domesticus

Haemosporidian infections in domestic chickens (Gallus gallus domesticus) are not only widely prevalent but also cause economic loss. Diagnosis is usually made by microscopic examination; however, the method has several drawbacks such as requiring an experienced microscopist, being unreliable when parasitemia is low and being unable to accurately differentiate between co-infections from multiple parasite species. Therefore, the current extent of haemosporidian infections might be underestimated and neglected. We have developed a novel multiplex PCR assay to simultaneously detect and differentiate between four haemosporidian parasites: Leucocytozoon caulleryi, Leucocytozoon sabrazesi, Plasmodium juxtanucleare and Plasmodium gallinaceum. Primers in the present study specifically amplified the corresponding targets with no cross-species amplification detected. The multiplex PCR exhibited a significantly greater detection rate when compared with microscopic examination (p =  0.0001). The results demonstrate that the detection rate of multiplex PCR for L. sabrazesi, P. juxtanucleare, and P. gallinaceum are all greater than that of microscopic examination with p =  0.002, 0.0001 and 0.004, respectively. Co-infections were also detected more effectively by multiplex PCR. We applied the current method to field samples originating from Nan, Prachinburi, and Chachoengsao Provinces. The current study revealed that positive rates of haemosporidian parasites in chickens in the three study sites ranging from 39.5%-93.8%. The present assay offers a timesaving option for molecular diagnosis instead of using singleplex PCRs for detecting the parasites individually. Within a single reaction, this assay would be a useful tool for the detection of avian haemosporidian parasites either single or under co-infection conditions and for large-scale epidemiology studies.