Natural Vertical Transmission of Ndumu Virus in Culex Pipiens (Diptera: Culicidae) Mosquitoes Collected As Larvae
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SHORT COMMUNICATION Natural Vertical Transmission of Ndumu Virus in Culex pipiens (Diptera: Culicidae) Mosquitoes Collected as Larvae 1,2 3 4 1 JOEL LUTOMIAH, JULIETTE ONGUS, KENNETH J. LINTHICUM, AND ROSEMARY SANG J. Med. Entomol. 51(5): 1091Ð1095 (2014); DOI: http://dx.doi.org/10.1603/ME14064 ABSTRACT Ndumu virus (NDUV) is a member of the family Togaviridae and genus Alphavirus.In Downloaded from https://academic.oup.com/jme/article/51/5/1091/884145 by guest on 23 September 2021 Kenya, the virus has been isolated from a range of mosquito species but has not been associated with human or animal morbidity. Little is know about the transmission dynamics or vertebrate reservoirs of this virus. NDUV was isolated from two pools of female Culex pipiens mosquitoes, IJR37 (n ϭ 18) and IJR73 (n ϭ 3), which were collected as larvae on 15 April 2013 from two dambos near the village of Marey, Ijara District, Garissa County, Kenya, and reared to adults and identiÞed to species. These results represent the Þrst Þeld evidence of vertical transmission of NDUV among mosquitoes. KEY WORDS Culex pipiens, Ijara, Ndumu virus, vertical transmission Ndumu virus (NDUV) is a member of the family habitats. There is little evidence to suggest that ver- Torgaviridae and genus Alphavirus, which comprises tical transmission of alphaviruses does occur (Tesh Ͼ31 viruses (Forrester et al. 2012). NDUV was Þrst 1984). Therefore, the Þnding of vertical transmission isolated in South Africa from Mansonia uniformis here provides important information regarding the (Theobald) in 1959 (Kokernot et al. 1961) and has natural maintenance of NDUV. since been described as widespread in most of Africa. It was recently documented in Kenya for the Þrst time Materials and Methods circulating among mosquitoes (Crabtree et al. 2009; Ochieng et al. 2013). Study Sites. Mosquitoes were sampled as larvae In general, infection with alphaviruses such as chi- from dambos in the villages of Marey and Wakab- kungunya, Ross River, Mayaro, and Sindbis causes Harey sublocations in Sangailu Division, Ijara District, clinical manifestations characterized by fever, rash, Garissa County, Kenya (Fig. 1), during the long rainy and arthralgia, although seroconversion in the ab- season of AprilÐMay and short rainy season of No- sence of clinical disease is uncommon with all alpha- vemberÐDecember in 2013. This site was selected viruses (Schmaljohn and McClain 1996). Although based on prior RVFV activity during the 2006Ð2007 mice experimentally infected with NDUV do not sur- RVF epizootic in Kenya. vive the infection (Kokernot et al. 1961), NDUV has Larval Sampling, Rearing, and Identification. Lar- not been associated with human or animal morbidity. val sampling was conducted using standard larval dip- This is because of lack of affordable diagnostic kits to pers (350 ml) (BioQuip, Inc., Compton, CA), from the test febrile patients for infection with this virus and the beginning to the end of the rainy season. Larvae col- lack of studies looking for evidence that NDUV causes lected from the dambos were transferred, in well la- diseases in humans. beled (date of collection and number collected) There are no studies that have been conducted Whirl-Pak bags (Universal Medical, Norwood, MA), speciÞcally to determine whether the virus can be to a Þeld laboratory where they were reared to adults maintained by vertical transmission in mosquito vec- in 4-liter capacity plastic cages. The emerging adults tors. Even this study did not target NDUV in particular were immobilized using 99.5% triethylamine (Sigma- but was primarily designed to explore vertical trans- Aldrich, St. Louis, MO) and identiÞed to species using mission of Rift Valley fever virus (RVFV), and other the keys of Edwards (1941), Gillies and Coetzee arboivruses occurring in mosquito species in natural (1987), and Jupp et al. (1976) and pooled up to 25 mosquitoes per pool. Pooled mosquitoes were pre- This paper was published with the permission from the Director, served in liquid nitrogen for transportation to the Kenya Medical Research Institute, KEMRI. KEMRI laboratories in Nairobi for virus isolation at- 1 Centre for Virus Research, Kenya Medical Research Institute, PO Box 54628, Nairobi, Kenya. tempts. 2 Corresponding author, e-mail: [email protected]. Sample Preparation and Virus Isolation in Cell Cul- 3 Department of Human Pathology and Laboratory Medicine, Jomo ture. Mosquito pools were homogenized using cop- Kenyatta University of Agriculture and Technology, PO Box 62000, per beads in 1 ml of homogenizing media comprising 00200-Nairobi, Kenya. 4 USDA/ARS Center for Medical, Agricultural and Veterinary En- Minimum Essential Medium Eagle (MEM), with tomology, 1600/1700 SW 23rd Dr., Gainesville, FL 32608. EarleÕs salts and reduced NaHCO3 (Sigma-Aldrich, 0022-2585/14/1091Ð1095$04.00/0 ᭧ 2014 Entomological Society of America 1092 JOURNAL OF MEDICAL ENTOMOLOGY Vol. 51, no. 5 Downloaded from https://academic.oup.com/jme/article/51/5/1091/884145 by guest on 23 September 2021 Fig. 1. Map of Kenya showing the study sites in Marey and Wakab-Harey sublocations in Sangailu Division, Ijara District, Garissa County, where larval sampling was conducted. St. Louis, MO) supplemented with 15% heat-inac- (Invitrogen, Carlsbad, CA) using random hexamers tivated fetal bovine serum (FBS; Sigma-Aldrich), 2% followed by RT-PCR using AmpliTag Gold PCR Mas- L-glutamine (Sigma-Aldrich), and 2% antibioticÐan- ter Mix (Applied Biosystems). The cDNA was tested timycotic solution (Sigma-Aldrich) with 10,000 U using a panel of genera (alphavirus, bunyavirus, and penicillin, 10 mg streptomycin, and 25 g ampho- flavivirus) and speciÞc primers for RVFV, NDUV, tericin B per milliliter. The homogenates were clar- babanki (BBKV), and sindbis (SINV) virus (Table 1). iÞed by centrifugation at 12,000 rpm (Eppendorf A positive control cDNA and a no-template negative Њ centrifuge 5417R) for 10 min at 4 C and the super- control were included during the setting up of all PCR natants transferred into 1.5-ml cryogenic vials. Each mos- reactions. AmpliÞcation products were resolved in quito pool supernatant (50 l) was inoculated per well 1.5% agarose gel in tris-borate-EDTA buffer stained onto conßuent monolayers of Vero cells (CCL81) in with ethidium bromide. 24-well plates grown in MEM, which was supplemented Sequencing. The ampliÞed PCR products were with 10% FBS. The inoculated cultures were incubated puriÞed using ExoSAP-IT (Affymetrix, Inc.). The pu- for 45 min to allow for virus adsorption, and 1 ml of maintenance media comprising MEM supplemented riÞed DNA fragments were sequenced using the Big- with 2% FBS was added to each well. The cultures were Dye 3.1 kit (PE Applied Biosystems, Foster City, CA) Њ and analyzed using ABI 3500xL Genetic analyzer (Ap- incubated at 37 Cin5%CO2 and monitored daily, through day 10, for cytopathic effects (CPE) as an in- plied Biosystems, Foster City, CA). The sequences dication of virus infection. were compared with available sequences of other Total RNA Isolation and Virus Identification by members of the alphavirus genus in the GenBank Reverse Transcription PCR. Total RNA was isolated database (http://www.ncbi.nlm.nih.gov/genbank/) from the supernatant of each culture exhibiting CPE using Basic Local Alignment Search Tool (BLAST, by Trizol-LS-Chloroform method (Chomczynski and http://blast.ncbi.nlm.nih.gov/Blast.cgi) to conÞrm the Sacchi 1987). Extracted RNA was reverse transcribed identity of the virus isolates. The sequences were to cDNA using SuperScriptIII reverse transcriptase aligned using ClustalW (Larkin et al. 2007). September 2014 LUTOMIAH ET AL.: VERTICAL TRANSMISSION OF NDUMU VIRUS IN Culex MOSQUITOES 1093 Results In total, 4,683 adult mosquitoes emerged from larvae (MareyÑ2,565; Wakab-HareyÑ2,118) and were identiÞed into three genera, representing 14 species, and pooled. Overall, Culex pipiens was the most pre- dominant and constituted 59.7% (n ϭ 2,797) of the total collection and 144 pools, followed by Culex uni- vittatus (21.8%; n ϭ 1,022; Table 2). Two pools (IJR37 and IJR73) out of 325 inoculated in Vero cell cultures caused CPE. The Vero cells in- oculated with IJR37 (n ϭ 18) and IJR73 (n ϭ 3), which were both female Cx. pipiens, developed CPE on day Downloaded from https://academic.oup.com/jme/article/51/5/1091/884145 by guest on 23 September 2021 777Ð798 Kuno et al. (1996) 1309Ð1327 3 and 2 post infection (pi), respectively. Analysis of the two positive samples by RT-PCR conÞrmed the virus agent to be NDUV. IJR37 and IJR73 were collected on 15 April 2013, from dambo 9 (01Њ 14Ј46.3Љ S, 040Њ ) 86Ð114 Kuno et al. (1996) Ј 39Ј31.6Љ E) and dambo 2 (01Њ 14Ј45.5Љ S, 040Њ 39Ј29.6Љ E), ) 6971Ð6997 Eshoo et al. (2007) Ј respectively, in the village of Marey. BLAST sequence ) 7086Ð7109 ) 9308Ð9283 Ј Ј for the envelope (E1) gene fragment used to identify ) 9007Ð9032 Bryant et al. (2005) Ј the isolates was 99% identical to previously reported ) 4184Ð4203 ) 3368Ð3388 Bryant et al. (2005) Ј Ј Ј ) 309Ð329 sequences (HM147989.1; AF339487.1; AF398375.1; Ј )-3 Ј JN989958.1). ) 5194Ð5213 Bryant et al. (2005) Ј ) 615Ð632 ) 6482Ð6500 ) 124Ð141 Bryant et al. (2005) Ј Ј Ј Ј Discussion Vertical transmission is a fairly common phenom- enon among arboviruses and is thought to play a role in the maintenance of a number of arboviruses in nature, thus ensuring survival during adverse condi- tions (Tesh 1984). Until this study, vertical transmis- sion of NDUV had not been demonstrated. This Þrst evidence of natural vertical transmission