Failure to demonstrate experimental vertical transmission of the epidemic strain of Chikungunya virus in Aedes albopictus from La Réunion Island, Indian Ocean

Abstract

Aedes albopictus was responsible for transmission in the first outbreak of chikungunya (CHIK) on La Réunion Island, Indian Ocean, in 2005-2006. The magnitude of the outbreak on this island, which had been free of arboviral diseases for over 30 years, as well as the efficiency of Ae. albopictus as the main vector, raises questions about the maintenance of the CHIK virus (CHIKV) through vertical transmission mechanisms. Few specimens collected from the field as larvae were found to be infected. In this study, Ae. albopictus originating from La Réunion were orally infected with a blood-meal containing 10 8 pfu/mL of the CHIKV epidemic strain (CHIKV 06.21 Chikungunya virus (CHIKV) is a vector-borne alphavirus transmitted to humans by mosquitoes belonging to the genus Aedes. It was first isolated in 1953 in Tanzania (Ross 1956) and until recently outbreaks had only been observed in Africa, Asia and India. In Africa, CHIKV is maintained within a sylvatic cycle with wild mosquitoes as vectors (Jupp & Kemp 1996, Diallo et al. 1999. In Asia and India, a sylvatic cycle has never been demonstrated and CHIKV is mainly transmitted within an urban cycle primarily involving the human-biting Aedes aegypti and the less anthropophilic Aedes albopictus (Jupp & McIntosh 1988 (Salvan & Mouchet 1994). Interestingly, the sequencing of viral strains from La Réunion demonstrated the emergence of a mutation in the course of the outbreak and the mutation was detected in the majority of the viral population (Schuffenecker et al. 2006). This mutation was shown to be associated with a better transmission rate by Ae. albopictus (Tsetdatkin et al. 2007, Vazeille et al. 2007). Furthermore, viral particles could be detected in the salivary glands at day 2 post-infection and high densities of viral particles were observed in eggs at day 6 post-infection. This last observation raised con--infection. This last observation raised concerns of possible maintenance of the virus on the island through vertical transmission, a mechanism by which arboviruses can be maintained in nature when climate conditions are unfavourable to the activity of adults: infected females die but the virus can survive in their desiccated eggs. The frequency of this phenomenon is extremely variable depending on the mosquito species and the virus. Vertical transmission of CHIKV has not yet been demonstrated in the laboratory (Jupp et al. 1981, Mourya 1987, but has been proven to occur in the field in Ae. albopictus, in La Réunion (Delatte et al. 2008) and in Madagascar (Ratsitorahina et al. 2008). However, the transmission rate was low and only viral RNA was detected, with no virus isolated. Therefore, we attempted to demonstrate vertical transmission under laboratory conditions with Ae. albopictus from La Réunion and the epidemic viral strain in order to assess the potential risk of maintenance of CHIKV on the island. MATERIALS AND METHODS Mosquitoes 633± 1°C with 80% relative humidity and a 16:8 h photoperiod. Adults were given 10% sucrose solution and females fed on a mouse...

Detection of Persistent Chikungunya Virus RNA but not Infectious Virus in Experimental Vertical Transmission in Aedes aegypti from Malaysia

“…For comparison, previous studies of vertical transmission of CHIKV in Aedes mosquitoes were summarized ( Table 2). RT-PCR was the most common method used to detect CHIKV, in seven of nine studies, 8,9,14,18,[20][21][22] and only one of those failed to detect CHIKV RNA. 22 RNA detection rates otherwise ranged between 0.4% and 100%, in both experimentally and naturally infected samples.…”

“…RT-PCR was the most common method used to detect CHIKV, in seven of nine studies, 8,9,14,18,[20][21][22] and only one of those failed to detect CHIKV RNA. 22 RNA detection rates otherwise ranged between 0.4% and 100%, in both experimentally and naturally infected samples. Notably, only five studies used methods to detect either viral protein expression (immunofluorescence staining 17,22 ) or viable infectious virus (cell culture 9,20 and in vivo inoculation 19 ).…”

“…22 RNA detection rates otherwise ranged between 0.4% and 100%, in both experimentally and naturally infected samples. Notably, only five studies used methods to detect either viral protein expression (immunofluorescence staining 17,22 ) or viable infectious virus (cell culture 9,20 and in vivo inoculation 19 ). Only one of these studies demonstrated the presence of infectious virus, in Ae.…”

Chikungunya Virus: A Novel and Potentially Serious Threat to New Zealand and the South Pacific Islands

“…1 However, vertical transmission of CHIKV within mosquito vectors has not been demonstrated in laboratory conditions. 29,30 The range of vertebrate reservoir hosts in areas where CHIKV is endemic is also poorly known. 31 Primary reservoirs for the virus in Africa are likely to be human and non-human primates, 31,32 but the latter primates are not found in New Zealand except for those captive in zoologic parks.…”

A patchy model for Chikungunya-like diseases

“…The principal vector of the Chikungunya in Réunion Island and in Italy is Aedes albopictus (sometimes called the Asian tiger because it originated from Asia and it is an agressive mosquito), which is also a prospective vector for Dengue transmission. In a recent period, there has been a tremendous progress in our knowledge about the vector and the relationships between the virus and the vector (see, for instance, [12], [13], [14], [15], [27], [34], [35]). One of the first models for the Chikungunya epidemic of [2005][2006] in Réunion Island was proposed in [18].…”