Dengue and Zika virus infection patterns vary among Aedes aegypti field populations from Belo Horizonte, a Brazilian endemic city

Abstract

Dengue virus (DENV) and Zika virus (ZIKV) belong to the same viral family, the Flaviviridae. They cause recurring threats to the public health systems of tropical countries such as Brazil. The primary Brazilian vector of both viruses is the mosquito Aedes aegypti. After the mosquito ingests a blood meal from an infected person, the viruses infect and replicate in the midgut, disseminate to secondary tissues and reach the salivary gland (SG), where they are ready to be transmitted to a vertebrate host. It is thought that the intrinsic discrepancies among mosquitoes could affect their ability to deal with viral infections. This study confirms that the DENV and ZIKV infection patterns of nine Ae. aegypti field populations found in geographically separate health districts of an endemic Brazilian city vary. We analyzed the infection rate, disseminated infection, vector competence, and viral load through quantitative PCR. Mosquitoes were challenged using the membrane-feeding assay technique and were tested seven and fourteen days post-infection (early and late infection phases, respectively). The infection responses varied among the Ae. aegypti populations for both flaviviruses in the two infection phases. There was no similarity between DENV and ZIKV vector competencies or viral loads. According to the results of our study, the risk of viral transmission overtime after infection either increases or remains unaltered in ZIKV infected vectors. However, the risk may increase, decrease, or remain unaltered in DENV-infected vectors depending on the mosquito population. For both flaviviruses, the viral load persisted in the body even until the late infection phase. In contrast to DENV, the ZIKV accumulated in the SG over time in all the mosquito populations. These findings are novel and may help direct the development of control strategies to fight dengue and Zika outbreaks in endemic regions, and provide a warning about the importance of understanding mosquito responses to arboviral infections.

Fig 1. IR, DIR, and VC for the nine Ae. aegypti populations infected with DENV and ZIKV, at 7 and 14 days post-infection (dpi).

A-B: Values of IR, DIR, and VC for the Ae. aegypti populations infected with DENV (A) and ZIKV (B). C: Comparison of the pattern of IR, DIR, and VC sets for each population, previously described in A-B, between DENV and ZIKV at 7 and 14 dpi. The bars represent the rates and were disposed of in a model that highlights each population’s specific patterns. No association is detected between DENV and ZIKV infection patterns of the populations, neither in 7 nor in 14 dpi. IR: Infection rate, the proportion of infected mosquitoes of the total number of mosquitos tested. DIR: Disseminated infection rate, the proportion of infected head/salivary gland (SG) of the total number of infected mosquitos. VC: vector competence, the proportion of infected head/SG of the total number of tested mosquitoes.

Fig 2. The graph shows the mean values of the infection rate (IR), disseminated infection rate (DIR), and vector competence (VC) for DENV and ZIKV at early infection (7 days post-infection—dpi), and late infection (14 dpi), considering the Aedes aegypti mosquitoes from all regions of Belo Horizonte.

The schematic maps show the rates that increased, decreased or remained unaltered from 7 to 14 dpi. (The schematic maps were adapted from a previously published map [28], source: https://parasitesandvectors.biomedcentral.com/articles/10.1186/1756-3305-7-320/figures/2).

Fig 3. DENV viral load per body and head/salivary gland (SG) of Ae. aegypti at 7 and 14 days post-infection (dpi).

A: DENV viral load per head/SG and body at 7 dpi in A. aegypti females from each district of Belo Horizonte. Each dot represents a tested female. B: DENV viral load per head/SG and body at 14 dpi in A. aegypti females from each district of Belo Horizonte. Each dot represents a tested female. C-D: Representation of the previous data (A-B) in another layout model to highlight the differences in DENV viral load between 7 and 14 dpi in the body (C) and head/SG (D) of the Ae. aegypti mosquitoes from each of the nine populations of Belo Horizonte. Fully filled and half-filled squares represent viral load in the mosquito bodies at 7 and 14 dpi, respectively. Fully filled and half-filled circles represent viral load in the mosquito head/SG at 7 and 14 dpi, respectively. P values > 0.05 (not significative) are not represented. P values ≤ 0.05, ≤ 0.01, ≤ 0.001, ≤ 0.0001 are summarized with one, two, three, and four asterisks, respectively.

Fig 4. ZIKV viral load per body and head/salivary gland (SG) of Ae. aegypti at 7 and 14 days post-infection (dpi).

A: ZIKV viral load per body and head/SG at 7 dpi in Ae. aegypti females from each district of Belo Horizonte. Each dot represents a tested female. B: ZIKV viral load per body and head/SG at 14 dpi in A. aegypti females from each district of Belo Horizonte. Each dot represents a tested female. C-D: Representation of the previous data (A-B) in another layout model to highlight the differences in ZIKV viral load between 7 and 14 dpi in the body (C) and head/SG (D) of the Ae. aegypti mosquitoes from each of the nine populations of Belo Horizonte. Fully filled and half-filled squares represent viral load in the mosquito bodies at 7 and 14 dpi, respectively. Fully filled and half-filled circles represent viral load in the mosquito head/SG at 7 and 14 dpi, respectively. P values > 0.05 (not significative) are not represented. P values ≤ 0.05, ≤ 0.01, ≤ 0.001, ≤ 0.0001 are summarized with one, two, three, and four asterisks, respectively.

Fig 5. Comparison of the pattern of viral load sets for each population, previously described in Figs 3 and 4, between DENV and ZIKV in the body and head/salivary gland (SG) at 7 and 14 days post-infection (dpi).

The bars represent the viral load medians, and were disposed in a model that highlight the specific patterns of each population.

Fig 6. Representation of DENV (red) and ZIKV (green) viral load comparisons for each of the nine Ae. aegypti populations of Belo Horizonte.

Fully filled and half-filled squares represent viral load in the mosquito bodies at 7 and 14 dpi, respectively. Fully filled and half-filled circles represent viral load in the mosquito head/SG at 7 and 14 dpi, respectively. P values > 0.05 (not significative) are not represented. P values ≤ 0.05, ≤ 0.01, ≤ 0.001, ≤ 0.0001 are summarized with one, two, three, and four asterisks, respectively. The p-values of the comparisons between body 7 dpi, head 7 dpi, body 14 dpi, head 14 dpi were, respectively: 0.7004, 0.9109, > 0.9999, 0.1419 (North); 0.0887, ****< 0.0.0001, *0.0133, *0.0349 (Northeast); ***0.0003, *0.115, *0.0232, *0.0286 (East); **0.0021, **0.0011, *0.0147, 0.7243 (Barreiro); 0.0703, 0.3484, 0.6706, 0.1419 (South-Central); ****< 0.0001, 0.3867, **0.0015, 0.4237 (West); ***0.0003, 0.2399, *0.0354, 0.1220 (Northwest); 0.7913, **0.0065, 0.3493, *0.0185 (Pampulha); 0.0008, 0.0734, ***0.0003, 0.2341 (Venda Nova).

Fig 7. DENV (red) and ZIKV (green) viral loads for the total Ae. aegypti population of Belo Horizonte.

The DENV total viral load in the body and head/salivary gland (SG) at 7 days post-infection (dpi) and in the body at 14 dpi is greater than the respective ZIKV total viral loads. At 14 dpi, the DENV total viral load in the head/SG is similar to that of ZIKV total viral load. Fully filled and half-filled squares represent viral load in the mosquito bodies at 7 and 14 dpi, respectively. Fully filled and half-filled circles represent viral load in the mosquito head/SG at 7 and 14 dpi, respectively. P values > 0.05 (not significative) are not represented. P values ≤ 0.05, ≤ 0.01, ≤ 0.001, ≤ 0.0001 are summarized with one, two, three, and four asterisks, respectively.