A mosquito survey along a transect of urbanization in Dschang, West Region of Cameroon, reveals potential risk of arbovirus spillovers

BackgroundWith the advance of globalization and the decline of wild habitats, mosquito-borne viruses are no longer confined to their original sylvatic environments and are emerging or remerging worldwide. However, little is known about the mosquito species implicated in the spillovers of these viruses from their enzootic cycles.MethodWe conducted an entomological field survey to catalogue the relative abundance of the Culicidae fauna in rural, peri-urban and urban areas in the Dschang locality in West Cameroon. Mosquitoes were collected from March-April and July-August 2019 at both aquatic and adult stages, and identified using stereomicroscopes and morphological identification keys.ResultsA total of 1,401 mosquitoes belonging to 4 genera and 26 species were collected (n=427, 470 and 504 in rural, peri-urban and urban areas respectively). The most abundant species Aedes africanus (45.47%) as well as Culex moucheti (8.92 %) were encountered in peri-urban and rural environments. Species like Culex duttoni (14.49%), Culex quinquefasciatus (2.35%) and Aedes aegypti (1.36%) were solely found in urban area. Aedes albopictus (14.42%), Culex (Culiciomyia) (6.57%), Culex tigripes (1.43%) and Eretmapodites chrysogaster (0.64%) on the other hand were collected in the three study sites. Importantly, all these species have been suspected or incriminated as vectors of many arboviruses.ConclusionThis study identified potential sylvatic, urban and bridge-vectors that can play a role in current or future virus emergence in Cameroon. Further investigations are needed to assess if arboviruses are circulating in these areas and to study the vector role of each mosquito species in arbovirus transmission.

Analisis Stabilitas Model SIR (Susceptibles, Infected, Recovered) Pada Penyebaran Penyakit Demam Berdarah Dengue di Provinsi Maluku

Health is an investment to support economic development and has an important role in efforts to reduce poverty and improve the quality of human resources. One of the diseases that often become serious problem in health sector that is Dengue Hemorrhagic Fever (DHF). In Indonesia, many mosquitoes cause dangerous DHF such as Aedes aegypti, Aedes albopictus, Aedes africanus, anopheles and others. In this study, we analyzed and applied SIR (Susceptible, Infection, Recovered) mathematical models and their interpolation to determine whether a contagious disease (DHF) can become endemic or not. Therefore, in this study aimed to determine the a special form of model of SIR to analyze the spread of DHF in Maluku Province and the stability analysis of this model and also interpolating the data of DHF transmission in Maluku Province. Furthermore, it can be obtained the characteristics of equilibrium point of each sub population. Based on the research conducted it can be concluded that from the entire population of Maluku Province is 1.686.469 vulnerable people infected with DHF and endemic disease with the basic reproduction value is 3,44.

Now is the time for the Zika virus

In April 1947 it was discovered through an experimental animal model a jungle fever. During the experiment, monkeys (macaques) were placed in cages and left exposed in the Zika forest (Uganda); one of the monkeys became ill and died. They filtered postmortem monkey tissues were inoculated into mouse brain and from there, a virus called Zika (ZIKV) was cultured. In 1948 ZIKV was also isolated from mosquitoes Aedes africanus captured in the Zika forest. In 1956 ZIKV transmission in mosquitoes Ae. aegypti was found, as well as a monkey. Between 1968 and 1975, ZIKV was subsequently isolated from humans (Nigeria); 40% of those patients analized by PRNT shown antibodies.

Interactions between immature Aedes africanus (Theobald) and larvae of two predatory species of Toxorhynchites (Diptera: Culicidae) in Zika Forest, Uganda

Studies conducted in Zika Forest, Uganda, on the breeding interactions between Aedes africanus (Theo.) and two mosquito predators, Toxorhynchites brevipalpis conradti Grünb. and T. kaimosi (van Som.), revealed a significant reduction in the numbers of A. africanus larvae and pupae in tree holes that were also inhabited by the predator larvae. There was a tendency for seasonal peaks in numbers of A. africanus to be followed two months later by peaks in Toxorhynchites spp. Cannibalism appeared to play an important role in the regulation of the population size of the two species of Toxorhynchites. The implications of these results in relation to the possible use of Toxorhynchites mosquitoes for biological control of A. africanus and other mosquitoes breeding in tree holes are discussed.

Seasonal population dynamics of the immature stages of Aedes africanus (Theobald) (Diptera: Culicidae) in Zika Forest, Uganda

The seasonal population trends of the immature stages of Aedes africanus (Theo.), an important vector of yellow fever virus and other arboviruses, were studied in Zika Forest, Uganda, for two years during 1974–75. Data were collected from natural breeding places in tree holes and from bamboo pots placed 80 cm above the ground. Developing larvae and pupae were present at all times of year, and there were monthly, seasonal and annual fluctuations in density. These fluctuations followed the seasonal distribution of rainfall and were more marked in the natural breeding places, which were subject to irregular fluctuations in water level, than in the bamboo pots, which were constantly supplied with water. Thus, in addition to the drought-resistant eggs whose erratic hatching by instalments could ensure the presence of A. africanus throughout the year, there are probably also present at any given time females that are capable of ovipositing. As a measure of the seasonal population changes, it was found that both the percentage of positive containers index and the mean number per container index were almost equally sensitive.

Natural selection and feeding speed in a blood-sucking insect

When a blood-sucking insect 'bites’ a sensitized host it must, if it is to survive, depart before the host is alerted by the irritation that accompanies or precedes the 'immediate’ reaction. There is a safety period between initial salivary injection by the insect and onset of irritation in the host during which the insect’s meal must be completed; immunity from attack by the host must, therefore, depend partly on the speed at which the insect can tap the blood supply and complete its meal, and partly on an adequate delay in the onset of irritation in the host. In mosquitoes, and other insects that depend on a blood meal for egg production, only those that complete the meal within the safety period can lay a full complement of eggs; the others will either be killed or injured by the host before egg development begins, or they will be disturbed before completion of the meal and so lay fewer eggs. Thus, fast feeders and those producing a delay in the onset of irritation will tend to lay more eggs, and these two properties will be maintained by natural selection, with the onset of irritation in the host acting as the main selection force. Experiments were made comparing a population of wild mosquitoes ( Aëdes africanus ) with that of a colonized species ( A. aegypti ), which had been protected from retaliatory action by the host during the previous 3 years. They showed that while the period between salivary injection and the onset of irritation was the same in both species ( ca . 3 min), feeding was usually fast in the wild species, which had presumably been subjected to rigorous selection against slow feeding, but variable and often slow in the captive species, which had been reared for generations in the absence of this pressure. The results also indicated a slight compensatory delay in the onset of irritation following slow feeding in the wild mosquitoes; presumably a difference in antigenic properties of the saliva affects the speed at which the insect can take up blood, and provides what appears to be a remarkable alternative path way to successful feeding, and so to maximum egg output and thus to survival.

Studies on mosquitos (Diptera, Culicidae) biting birds, using twenty-four-hour catches, in the Entebbe area, Uganda

Series of 24-hour catches at different levels were made at Zika and Lunyo in the Entebbe area, Uganda, using fowls (White Leghorn cocks) as bait, and some comparative catches were made with man as bait.Thirty-seven different mosquito species (including five species groups) were taken on the avian bait.The vertical distributions and biting cycles of each of nine species (including one species group), Anopheles implexus (Theo.), Mansonia (Coquillettidia) aurites (Theo.) gp., M. (C.) fuscopennata (Theo.), M. (Mansonioides) africana (Theo.), Hodgesia cyptopus Theo., Aedes africanus (Theo.), A. apicoargenteus (Theo.), A. ingrami Edw. and Culex annulioris Theo. were similar on human and avian bait.At Lunyo both A. africanus and C. annulioris had a marked diurnal peak, which had not been described previously.Comparison of the numbers coming to avian and human bait indicate that species of Culex, H. cyptopus and most of the species of Mansonia (Coquillettidia) have a preference for birds.