Vertical transmission of dengue virus in Aedes aegypti and its role in the epidemiological persistence of dengue in Central and Southern Mexico.

BACKGROUND: Aedes aegypti and Aedes albopictus are the main mosquito species responsible for dengue virus (DENV) transmission to humans in the tropical and subtropical regions of the world. The role of vertical transmission in the epidemiology of dengue and the maintenance of this arbovirus in nature during interepidemic periods remain poorly understood, and DENV vertical transmission could sustain the existence of virus reservoirs within Aedes populations. METHODS: Between April 2011 and October 2012, we monitored vertical transmission of DENV in Ae. aegypti and Ae. albopictus in 9 cities of 4 Mexican states. Aedes eggs were collected in ovitraps, then adults were reared under laboratory conditions and their heads were used to infect C6/36 cells. The presence of flavivirus was detected by immunofluorescence assays (IFA), and DENV infection was confirmed by RT-PCR. RESULTS: About 96% of reared adults were Ae. aegypti and 4.0% were Ae. albopictus. No infection was detected in Ae. albopictus, whereas 54 of 713 (7.8%) of Ae. aegypti pools tested positive. A minimum infection rate (MIR) of 2.52 per 1000 mosquitoes was estimated for Ae. aegypti. DENV-1, DENV-2 & DENV-3 serotypes were detected even during interepidemic periods. CONCLUSIONS: This study reports the evidence of vertical transmission of dengue virus with viral isolation and molecular confirmation in Ae. aegypti eggs collected in four endemic regions of Central and Southern Mexico. Vertical transmission may play a role as a reservoir mechanism during mosquito dormancy in interepidemic periods but with minor participation in transmission during epidemic periods.

TRANSMISSION VERTICALE DU VIRUS DE LA DENGUE CHEZ AEDES AEGYPTI ET SON RÔLE DANS LA PERSISTANCE ÉPIDÉMIOLOGIQUE DE LA DENGUE DANS LE CENTRE ET LE SUD DU MEXIQUE: OBJECTIF: Aedes aegypti et Aedes albopictus sont les principales espèces de moustiques responsables de la transmission du virus de la dengue (DENV) à l'homme dans les régions tropicales et subtropicales du monde. Le rôle de la transmission verticale dans l'épidémiologie de la dengue et le maintien de cet arbovirus dans la nature pendant les périodes d'inter-épidémiques restent mal compris, et la transmission verticale du DENV pourrait maintenir l'existence de réservoirs de virus au sein des populations d'Aedes. Notre objectif était d'évaluer la transmission verticale du DENV au Mexique. MÉTHODES: Entre avril 2011 et octobre 2012, nous avons surveillé la transmission verticale du DENV chez Ae. aegypti et Ae. albopictus dans 9 villes de 4 états mexicains. Les œufs d'Aedes ont été collectés dans des ovitraps, puis les adultes ont été élevés dans des conditions de laboratoire et leur tête a été utilisée pour infecter les cellules C6/36. La présence de flavivirus a été détectée par des tests d'immunofluorescence (IFA) et l'infection par DENV a été confirmée par RT-PCR. RÉSULTATS: 96% des adultes élevés étaient Ae. aegypti et 4,0% étaient Ae. albopictus. Aucune infection n'a été détectée chez Ae. albopictus, alors que 54 des 713 (7,8%) des pools d'Ae. aegypti ont été testés positifs. Un taux d'infection minimum (MIR) de 2,52 pour 1000 moustiques a été estimé pour Ae. aegypti. Les sérotypes DENV-1, DENV-2 et DENV-3 ont été détectés même pendant les périodes inter-épidémiques. CONCLUSIONS: Cette étude rapporte les preuves de transmission verticale du virus de la dengue avec isolement viral et confirmation moléculaire dans les œufs d'Ae. Aegypti collectés dans quatre régions d'endémie du centre et du sud du Mexique. La transmission verticale pourrait jouer un rôle de mécanisme réservoir lors de la dormance des moustiques en période inter-épidémique, mais avec une participation mineure à la transmission en période d'épidémie.

Plasmodium vivax CSP-Pvs25 variants from southern Mexico produce distinct patterns of infectivity for Anopheles albimanus versus An. pseudopunctipennis, in each case independent of geographical origin.

BACKGROUND: The susceptibility of Anopheles albimanus and An. pseudopunctipennis to local Plasmodium vivax has been associated in southern Mexico with two ookinete surface proteins (Pvs25/28) polymorphism. Perhaps parasite population selection (i.e. adaptation to local vectors) contributes to this phenomenon. It is also possible that certain molecular interactions exist between P. vivax and each mosquito species independently of geographical origin. This study aimed to explore the susceptibility of An. albimanus and An. pseudopunctipennis (collected from different geographical sites) to P. vivax cspVk/Pvs25-130 haplotypes from southern Mexico. RESULTS: Of the 120 P. vivax-infected blood samples used to simultaneously feed An. albimanus and An. pseudopunctipennis mosquitoes originating from various geographical sites, 80 produced at least one infected mosquito species. Three parasite haplotypes were identified in infected blood: Vk210/Pvs25-A (12.5%), Vk210/Pvs25-B (20%) and Vk247/Pvs25-B (67.5%). Two parameters (the proportion of infected mosquitoes and number of oocysts/mosquito) showed a similar pattern for each mosquito species (independently of geographical origin). For An. albimanus mosquitoes (from the Pacific coast, Mexican gulf and Lacandon Forest lowlands), these two parameters were higher in specimens infected with P. vivax Vk210/Pvs25-A versus Vk210/Pvs25-B or Vk247/Pvs25-B (P < 0.001). For An. pseudopunctipennis mosquitoes (from the Pacific coast, northeast Mexico and east Guatemala foothills), the same two parameters were higher in specimens infected with Vk247/Pvs25-B or Vk210/Pvs25-B versus Vk210/Pvs25-A (P < 0.001). Higher infection rates were caused by Vk247/Pvs25-B than Vk210/Pvs25-B parasites in An. pseudopunctipennis (P = 0.011) and An. albimanus (P = 0.001). The greatest parasitaemia, gametocytaemia and microgamete formation was observed in Vk247/Pvs25-B infected blood, and each of these parameters correlated with each other and with the number of oocysts in An. pseudopunctipennis from the sympatric colony. CONCLUSIONS: Plasmodium vivax Vk247/Pvs25-B infections were the most prevalent, likely due to the higher parasitaemia produced in the susceptible vector (especially An. pseudopunctipennis). The analysis of mosquito-parasite interactions indicate that An. pseudopunctipennis and An. albimanus each have a unique pattern of transmitting genetic variants of P. vivax, and this is not dependent on geographical origin. The present findings highlight the importance of parasite genotyping to understand transmission dynamics and vectorial participation.

Molecular and Clinical Characterization of Chikungunya Virus Infections in Southeast Mexico.

Chikungunya fever is an arthropod-borne infection caused by Chikungunya virus (CHIKV). Even though clinical features of Chikungunya fever in the Mexican population have been described before, there is no detailed information. The aim of this study was to perform a full description of the clinical features in confirmed Chikungunya-infected patients and describe the molecular epidemiology of CHIKV. We evaluated febrile patients who sought medical assistance in Tapachula, Chiapas, Mexico, from June through July 2015. Infection was confirmed with molecular and serological methods. Viruses were isolated and the E1 gene was sequenced. Phylogeny reconstruction was inferred using maximum-likelihood and maximum clade credibility approaches. We studied 52 patients with confirmed CHIKV infection. They were more likely to have wrist, metacarpophalangeal, and knee arthralgia. Two combinations of clinical features were obtained to differentiate between Chikungunya fever and acute undifferentiated febrile illness. We obtained 10 CHIKV E1 sequences that grouped with the Asian lineage. Seven strains diverged from the formerly reported. Patients infected with the divergent CHIKV strains showed a broader spectrum of clinical manifestations. We defined the complete clinical features of Chikungunya fever in patients from Southeastern Mexico. Our results demonstrate co-circulation of different CHIKV strains in the state of Chiapas.

Chikungunya Virus as Cause of Febrile Illness Outbreak, Chiapas, Mexico, 2014.

Since chikungunya virus (CHIKV) was introduced into the Americas in 2013, its geographic distribution has rapidly expanded. Of 119 serum samples collected in 2014 from febrile patients in southern Mexico, 79% were positive for CHIKV or IgM against CHIKV. Sequencing results confirmed CHIKV strains closely related to Caribbean isolates.

First Report of Aedes aegypti Transmission of Chikungunya Virus in the Americas.

During a chikungunya fever outbreak in late 2014 in Chiapas, Mexico, entomovirological surveillance was performed to incriminate the vector(s). In neighborhoods, 75 households with suspected cases were sampled for mosquitoes, of which 80% (60) harbored Aedes aegypti and 2.7% (2) Aedes albopictus. A total of 1,170 Ae. aegypti and three Ae. albopictus was collected and 81 pools were generated. Although none of the Ae. albopictus pools were chikungunya virus (CHIKV)-positive, 18 Ae. aegypti pools (22.8%) contained CHIKV, yielding an infection rate of 32.3/1,000 mosquitoes. A lack of herd immunity in conjunction with high mosquito populations, poor vector control services in this region, and targeted collections in locations of human cases may explain the high infection rate in this vector. Consistent with predictions from experimental studies, Ae. aegypti appears to be the principal vector of CHIKV in southern Mexico, while the role of Ae. albopictus remains unknown.