Deteksi Transmisi Transovarial Virus Dengue PadaAedes AegyptiPada Wilayah Endemis Kota Pontianak

Dengue virus is highly pathogenic in humans and spreads rapidly through Aedes aegypti and Aedes albopictus mosquitoes. More than half a billion people from 100 countries in the world are at serious risk of dengue virus infection. The purpose of this study was to prove the existence of transovarial transmission of dengue virus in Aedes aegypti mosquitoes with a transovarial transmission index (TTI) in endemic areas in Pontianak, West Kalimantan. This research method is descriptive observational with a cross-sectional study. The results of the Microscopic Examination of Head Squash Preparations on the Aedes aegypti mosquito, showed the Transovarial Transmission Index in Batulayang Village was 39.60% higher, compared to Sungai Jawi Village, which was 29.30%, but both were still lower than ITT in 2012. The results of the Aedes mosquito examination aegypti using the Polymerase Chain Reaction Transcription Reaction (PCR-TR) method found the dengue virus strain. The conclusion of this study proves that the transovarial transmission of dengue virus in Aedes aegypti mosquitoes in Sungai Jawi Village is 29.30% lower than in Batulayang Village by 39.60%, and the dengue virus serotype, DENV-3, has been found.Keywords: transovarial transmission; dengue virus; Aedes aegypti AbstrakVirus Dengue sangat patogen pada manusia dan menyebar dengan cepat melalui nyamuk Aedes aegypti dan Aedes albopictus. Lebih dari setengah miliar penduduk dari 100 negara di dunia berada pada risiko serius infeksi virus dengue. Tujuan dari penelitian ini adalah untuk membuktikan adanya penularan virus dengue transovarial pada nyamuk Aedes aegypti dengan indeks transmisi transovarial (TTI) di daerah Endemis di Pontianak, Kalimantan Barat. Metode penelitian ini adalah deskriptif observasional dengan studi potong lintang. Hasil Pemeriksaan Mikroskopis Sediaan Head Squash pada nyamuk Aedes aegypti, menunjukan Indeks Transmisi Transovarial pada Kelurahan Batulayang lebih tinggi yaitu 39,60%, dibandingkan dengan Kelurahan Sungai Jawi yaitu 29,30%, tetapi keduanya masih lebih rendah dibandingkan ITT pada Tahun 2012. Hasil pemeriksaan nyamuk Aedes aegypti dengan metode Polymerase Chain Reaction Transcription Reaction(PCR-TR) ditemukan strain virus Dengue-3. Kesimpulan penelitian ini membuktikan adanya transmisi transovarial virus dengue pada nyamuk Aedes aegypti di Kelurahan Sungai Jawi sebesar 29,30% lebih rendah dibandingkan di kelurahan Batulayang sebesar 39,60%, serta berhasil ditemukan serotipe virus Dengue yaitu DENV-3.Kata Kunci : transmisi transovarial; virus dengue; Aedes aegypti

Investigation of Transovarial Transmission of Bartonella henselae in Rhipicephalus sanguineus sensu lato Ticks Using Artificial Feeding

Bartonella henselae is a slow-growing, Gram-negative bacterium that causes cat scratch disease in humans. A transstadial transmission of the bacteria from larvae to nymphs of Rhipicephalus sanguineus sensu lato (s.l.) ticks, suspected to be a potential vector of the bacteria, has been previously demonstrated. The present study aims to investigate transovarial transmission of B. henselae from R. sanguineus s.l. adults to their instars. Adult ticks (25 males and 25 females) were fed through an artificial feeding system on B. henselae-infected goat blood for 14 days, and 300 larvae derived from the experimentally B. henselae-infected females were fed on noninfected goat blood for 7 days. Nested PCR and culture were used to detect and isolate B. henselae in ticks and blood samples. Bartonella henselae DNA was detected in midguts, salivary glands, and carcasses of the semi-engorged adults and pooled tick feces (during feeding and post-feeding periods). After the oviposition period, B. henselae DNA was detected in salivary glands of females (33.3%), but not in pooled eggs or larvae derived from the infected females. However, B. henselae DNA was detected by nested PCR from the blood sample during larval feeding, while no viable B. henselae was isolated by culture. According to our findings, following infected blood meal, B. henselae could remain in the tick midguts, move to other tissues including salivary glands, and then be shed through tick feces with limited persistency. The presence of bacterial DNA in the blood during larval feeding shows the possibility of transovarial transmission of B. henselae in R. sanguineus s.l. ticks.

First Record of Natural Transovarial Transmission of Dengue Virus in Aedes albopictus from Cuba

Transovarial transmission (TOT) of dengue virus (DENV) in Aedes spp. is an important mechanism for DENV maintenance in nature and may be important in initiating outbreaks. The objective of this study was to explore the occurrence of TOT in wild Aedes albopictus populations in Cuba. Mosquito larvae were collected in Cotorro municipality, Havana, Cuba, and identified to species. Fifteen pools of Ae. albopictus each containing 30 larvae were processed for DENV detection by using conventional RT-PCR and nested PCR. Four out of 15 pools processed were positive for DENV-3, but no other DENV serotype was detected. This is the first time TOT of DENV detected in Cuban field populations of Ae. albopictus, and this suggests that this species may be an important vector of DENV in Cuba.

Transovarial Transmission of Borrelia hermsii by Its Tick Vector and Reservoir Host Ornithodoros hermsi

Transovarial passage of relapsing fever spirochetes (Borrelia species) by infected female argasid ticks to their progeny is a widespread phenomenon. Yet this form of vertical inheritance has been considered rare for the North American tick Ornithodoros hermsi infected with Borrelia hermsii. A laboratory colony of O. hermsi was established from a single infected female and two infected males that produced a population of ticks with a high prevalence of transovarial transmission based on infection assays of single and pooled ticks feeding on mice and immunofluorescence microscopy of eggs and larvae. Thirty-eight of forty-five (84.4%) larval cohorts (groups of larvae originating from the same egg clutch) transmitted B. hermsii to mice over four and a half years, and one hundred and three single and one hundred and fifty-three pooled nymphal and adult ticks transmitted spirochetes during two hundred and fourteen of two hundred and fifty-six (83.6%) feedings on mice over seven and a half years. The perpetuation of B. hermsii for many years by infected ticks only (without acquisition of spirochetes from vertebrate hosts) demonstrates the reservoir competence of O. hermsi. B. hermsii produced the variable tick protein in eggs and unfed larvae infected by transovarial transmission, leading to speculation of the possible steps in the evolution of borreliae from a tick-borne symbiont to a tick-transmitted parasite of vertebrates.

Transovarial transmission of a core virome in the Chagas disease vector Rhodnius prolixus

Triatomine assassin bugs comprise hematophagous insect vectors of Trypanosoma cruzi, the causative agent of Chagas disease. Although the microbiome of these species has been investigated to some extent, only one virus infecting Triatoma infestans has been identified to date. Here, we describe for the first time seven (+) single-strand RNA viruses (RpV1-7) infecting Rhodnius prolixus, a primary vector of Chagas disease in Central and South America. We show that the RpVs belong to the Iflaviridae, Permutotetraviridae and Solemoviridae and are vertically transmitted from the mothers to the progeny via transovarial transmission. Consistent with this, all the RpVs, except RpV2 that is related to the entomopathogenic Slow bee paralysis virus, established persistent infections in our R. prolixus colony. Furthermore, we show that R. prolixus ovaries express 22-nucleotide viral siRNAs (vsiRNAs), but not viral piRNAs, that originate from the processing of dsRNA intermediates during viral replication of the RpVs. Interestingly, the permutotetraviruses and sobemoviruses display shared pools of vsiRNAs that might provide the basis for a cross-immunity system. The vsiRNAs are maternally deposited in the eggs, where they likely contribute to reduce the viral load and protect the developing embryos. Our results unveil for the first time a complex core virome in R. prolixus and begin to shed light on the RNAi-based antiviral defenses in triatomines.

The First Report on the Transovarial Transmission of Microsporidian Nosema bombycis in Lepidopteran Crop Pests Spodoptera litura and Helicoverpa armigera

Microsporidia are ubiquitous fungi-related parasites infecting nearly all vertebrates and invertebrates. Microsporidian Nosema bombycis is a natural pathogen of multiple insects, including the silkworm and many agricultural and forest pests. N. bombycis can transovarially transmit in silkworm and cause huge economic losses to the sericulture. However, it remains unclear whether N. bombycis vertically transmits in the crop pests Spodoptera litura and Helicoverpa armigera. Here, we investigated the infection of N. bombycis in S. litura and H. armigera to illuminate its infectivity and transovarial transmission. In result, tissue examination with light microscopy revealed that the fat body, midgut, malpighian tubules, hemolymph, testis, and ovary were all infected in both pest pupae. Immunohistochemical analysis (IHA) of the ovariole showed that a large number of parasites in maturation and proliferation presented in follicle cell, nurse cell, and oocyte, suggesting that N. bombycis can infect and multiply in these cells and probably transovarially transmit to the next generations in both pests. Microscopic examination on the egg infection rate demonstrated that 50% and 38% of the S. litura and H. armigera eggs were congenitally infected, respectively. IHA of both eggs manifested numerous spores and proliferative pathogens in the oocyte, confirming that N. bombycis can invade into the female germ cell from the parent body. After hatching of the infected eggs, we detected the infection in offspring larvae and found large quantities of proliferative pathogens, confirming that N. bombycis can transovarially transmit in S. litura and H. armigera, and probably persists in both pest populations via congenital infection. In summary, our work, for the first time, proved that N. bombycis is able to vertically transmit in S. litura and H. armigera via infecting the oocyte in the parent, suggesting that N. bombycis could be a biological insecticide for controlling the population of crop pests.

Tick Ecdysteroid Hormone, Global Microbiota/Rickettsia Signaling in the Ovary versus Carcass during Vitellogenesis in Part-Fed (Virgin) American Dog Ticks, Dermacentor variabilis

The transovarial transmission of tick-borne bacterial pathogens is an important mechanism for their maintenance in natural populations and transmission, causing disease in humans and animals. The mechanism for this transmission and the possible role of tick hormones facilitating this process have never been studied. Injections of physiological levels of the tick hormone, 20-hydroxyecdysone (20E), into part-fed (virgin) adult females of the American dog tick, Dermacentor variabilis, attached to the host caused a reduction in density of Rickettsia montanensis in the carcass and an increase in the ovaries compared to buffer-injected controls. This injection initiates yolk protein synthesis and uptake by the eggs but has no effect on blood feeding. Francisella sp. and R. montanensis were the predominant bacteria based on the proportionality in the carcass and ovary. The total bacteria load increased in the carcass and ovaries, and bacteria in the genus Pseudomonas increased in the carcass after the 20E injection. The mechanism of how the Rickettsia species respond to changes in tick hormonal regulation needs further investigation. Multiple possible mechanisms for the proliferation of R. montanensis in the ovaries are proposed.

Vector Transmission of Tomato Yellow Leaf Curl Thailand Virus by the Whitefly Bemisia tabaci: Circulative or Propagative?

Viruses that cause tomato yellow leaf curl disease are part of a group of viruses of the genus Begomovirus, family Geminiviridae. Tomato-infecting begomoviruses cause epidemics in tomato crops in tropical, subtropical, and Mediterranean climates, and they are exclusively transmitted by Bemisia tabaci in the field. The objective of the present study was to examine the transmission biology of the tomato yellow leaf curl Thailand virus (TYLCTHV) by B. tabaci, including virus-infected tissues, virus translocation, virus replication, and transovarial transmission. The results demonstrated that the virus translocates from the alimentary gut to the salivary glands via the hemolymph, without apparent replication when acquired by B. tabaci. Furthermore, the virus was detected in 10% of the first-generation progeny of viruliferous females, but the progeny was unable to cause the viral infection of host plants. There was no evidence of transovarial transmission of TYLCTHV in B. tabaci. When combined with the current literature, our results suggest that B. tabaci transmits TYLCTHV in a persistent-circulative mode. The present study enhances our understanding of virus–vector interaction and the transmission biology of TYLCTHV in B. tabaci.