Dengue Infection Susceptibility of Five Aedes aegypti Populations from Manaus (Brazil) after Challenge with Virus Serotypes 1-4

Abstract

The successful spread and maintenance of the dengue virus (DENV) in mosquito vectors depends on their viral infection susceptibility, and parameters related to vector competence are the most valuable for measuring the risk of viral transmission by mosquitoes. These parameters may vary according to the viral serotype in circulation and in accordance with the geographic origin of the mosquito population that is being assessed. In this study, we investigated the effect of DENV serotypes (1-4) with regards to the infection susceptibility of five Brazilian Ae. aegypti populations from Manaus, the capital of the state of Amazonas, Brazil. Mosquitoes were challenged by oral infection with the DENV serotypes and then tested for the presence of the arbovirus using quantitative PCR at 14 days post-infection, which is the time point that corresponds to the extrinsic incubation period of Ae. aegypti when reared at 28 °C. Thus, we were able to determine the infection patterns for DENV-1, -2, -3 and -4 in the mosquito populations. The mosquitoes had both interpopulation and inter-serotype variation in their viral susceptibilities. All DENV serotypes showed a similar tendency to accumulate in the body in a greater amount than in the head/salivary gland (head/SG), which does not occur with other flaviviruses. For DENV-1, DENV-3, and DENV-4, the body viral load varied among populations, but the head/SG viral loads were similar. Differently for DENV-2, both body and head/SG viral loads varied among populations. As the lack of phenotypic homogeneity represents one of the most important reasons for the long-term fight against dengue incidence, we expect that this study will help us to understand the dynamics of the infection patterns that are triggered by the distinct serotypes of DENV in mosquitoes.

Keywords: DENV; antiviral response; infection rate; mosquito population; vector competence; vector-borne disease; viral load.

Figure 1

Infection rate (IR), disseminated infection rate (DIR), and assumed vector competence (VC) of Ae. aegypti populations from Manaus (Brazil) for DENV serotypes 1–4.

Figure 2

Variability in the infection rate (IR), disseminated infection rate (DIR) and the assumed vector competence (VC) of the Ae. aegypti populations for DENV serotypes 1–4. (A): Map of the urban area of Manaus showing the mosquito VC for each population (derived from distinct geographic districts), considering the order of decreasing values. The south-central and west-central districts were combined and named the central district to avoid inconsistency in the size of the collection areas. (B): IR, DIR, and VC averages of all populations show similarity in infection patterns between DENV-1 and DENV-4. The error bars on the graph are the standard deviations. The standard deviations of the IRs, DIRs, and VCs, respectively, were 28.7%, 10.6%, and 23.3% for DENV-1; 2.7%, 4.1%, and 4.7% for DENV-2; 12%, 4.9%, and 3.1% for DENV-3; and 18.2%, 7.5%, and 13.1% for DENV-4.

Figure 3

Body and head/SG viral loads of five Ae. aegypti populations from different districts of the municipality of Manaus, Brazil after infection with DENV-1 (A), DENV-2 (B), DENV-3 (C), and DENV-4 (D). p values > 0.05 [non-significant (ns)] are not represented. p values ≤ 0.05, ≤0.01, ≤0.001, and ≤0.0001 are summarized with one (*), two (**), three (***), and four (****) asterisks, respectively.

Figure 4

Interpopulation variability in the body (A) and head/SG (B) viral-load patterns of Ae. aegypti in the northern, southern, eastern, western, and central populations (different colored symbols). Each bar represents a median viral load in the data. In (A), we represent only the non-significant results (more results were statistically distinct) to simplify the demonstration and facilitate comparisons. In (B), we represent only the significant results. All p values were listed for the 10 possible comparisons among the mosquito populations to each DENV serotype. N = northern; E = eastern; W = western; S = southern; C = central. p values > 0.05 (non-significant) are represented as “ns”. p values ≤ 0.05, ≤0.01, ≤0.001, and ≤0.0001 are summarized with one (*), two (**), three (***), and four (****) asterisks, respectively.

Figure 5

Body and head/SG viral loads of Ae. aegypti for the four DENV serotypes in the northern (A), southern (B), eastern (C), western (D), and central (E) populations; and the overall body and head/SG viral loads (F). p values > 0.05 [non-significant (ns)] are not represented. p values ≤ 0.05, ≤0.01, ≤0.001, and ≤0.0001 are summarized with one (*), two (**), three (***), and four (****) asterisks, respectively.

Figure 6

Inter-serotype variability of the patterns of body (A) and head/SG (B) viral loads for DENV serotypes 1–4 (different colored symbols) in each of the five Ae. aegypti populations. Each bar in the figures represents a median viral load in the data. In (A), we represent only the non-significant results (more results were statistically distinct) to simplify the demonstration and facilitate comparisons. In (B), only the significant results are represented. All p values are listed for the six possible comparisons among the DENV serotypes to each population. D1 = DENV-1; D2 = DENV-2; D3 = DENV-3; D4 = DENV-4. p values > 0.05 (non-significant) are represented as “ns”. p values ≤ 0.05, ≤0.01, ≤0.001, and ≤0.0001 are summarized with one (*), two (**), three (***), and four (****) asterisks, respectively.