Transovarial Transmission Research Articles

A comparison of horizontal and transovarial transmission efficiency of Borrelia miyamotoi by Ixodes scapularis

Borrelia miyamotoi is a relapsing fever spirochete carried by Ixodes spp. ticks throughout the northern hemisphere. The pathogen is acquired either transovarially (vertically) or horizontally through blood-feeding and passed transtadially across life stages. Despite these complementary modes of transmission, infection prevalence of ticks with B. miyamotoi is typically low (<5%) in natural settings and the relative contributions of the two transmission modes have not been studied extensively. Horizontal transmission of B. miyamotoi (strain CT13–2396 or wild type strain) was initiated using infected Ixodes scapularis larvae or nymphs to expose rodents, which included both the immunocompetent CD-1 laboratory mouse (Mus musculus) and a natural reservoir host, the white-footed mouse (Peromyscus. leucopus), to simulate natural enzootic transmission. Transovarial transmission was evaluated using I. scapularis exposed to B. miyamotoi as either larvae or nymphs feeding on immunocompromised SCID mice (M. musculus) and subsequently fed as females on New Zealand white rabbits. Larvae from infected females were qPCR-tested individually to assess transovarial transmission rates. Tissue tropism of B. miyamotoi in infected ticks was demonstrated using in situ hybridization. Between 1 and 12% of ticks were positive (post-molt) for B. miyamotoi after feeding on groups of CD-1 mice or P. leucopus with evidence of infection, indicating that horizontal transmission was inefficient, regardless of whether infected larvae or nymphs were used to challenge the mice. Transovarial transmission occurred in 7 of 10 egg clutches from infected females. Filial infection prevalence in larvae ranged from 3 to 100% (median 71%). Both larval infection prevalence and spirochete load were highly correlated with maternal spirochete load. Spirochetes were disseminated throughout the tissues of all three stages of unfed ticks, including the salivary glands and female ovarian tissue. The results indicate that while multiple transmission routes contribute to enzootic maintenance of B. miyamotoi, transovarial transmission is likely to be the primary source of infected ticks and therefore risk assessment and tick control strategies should target adult female ticks.

Examination of vertical transmission of Bartonella quintana in body lice following multiple infectious blood meals.

Bartonella quintana is a re-emerging louse-borne pathogen. Horizontal transmission from the body louse vector (Pediculus humanus humanus) to a human host occurs through contact with infectious louse feces containing a high concentration of the bacteria. However, questions have remained about whether vertical transmission from infected vectors to their progeny, which could significantly influence the dynamics of transmission to humans, occurs in body lice. To address this subject, we performed a series of controlled laboratory experiments that examined the presence of B. quintana on the surface of and within eggs produced by female body lice that were provisioned multiple infectious blood meals to recapitulate the natural pathogen acquisition process. Our results demonstrate that B. quintana DNA can be detected from the surface of eggs by qPCR due to vertical transfer of infectious feces to the egg sheath during or after oviposition. However, viable B. quintana could not be cultured from the hemolymph of adult female lice or from within eggs that were surface sterilized, indicating a lack of true transovarial transmission. Based on this evidence, vertical transfer of B. quintana from infected adult lice to their eggs probably has a limited impact on the dynamics of transmission to humans.

Spotted Fever Group Rickettsia spp. Diversity in Ticks and the First Report of Rickettsia hoogstraalii in Romania.

Simple SummaryTicks are important parasites that feed on the blood of various host species, representing the most important arthropods transmitting diseases in Europe. Continuous changes in both tick distribution and abundance are related to multiple factors, including climate change. These changes have strong implications for both animal and human health; therefore, continuous surveillance of tickborne diseases is required for an appropriate evaluation of the potential risks faced by animals and humans in a given area. The spotted fever group Rickettsia comprises a large number of zoonotic agents with an increasing importance recognized in the last 30 years. The aim of this study was to evaluate these bacteria in ticks in Romania. Five Rickettsia species were identified in different tick species, with new pathogen–tick associations reported. Rickettsia hoogstraalii, one member of this group, was detected for the first time in Romania and in Rhipicephalus rossicus ticks. This species was first described in 2006 in Croatia, and its pathogenicity is not well known. In addition, the detection of R. raoultii and R. monacensis in unfed larvae of Haemaphysalis punctata reinforce the hypothesis of transmission of Rickettsia from female ticks to larvae; therefore the bite of larvae could pose a health risk.Tickborne bacterial pathogens have been described worldwide as risk factors for both animal and human health. Spotted fevers caused by Rickettsiae may cause non-specific symptoms, which make clinical diagnosis difficult. The aim of the current study was to evaluate and review the diversity of SFG Rickettsiae in ticks collected in 41 counties in Romania. A total of 2028 questing and engorged ticks collected in Romania belonging to five species were tested by PCR amplification of Rickettsia spp. gltA and 17-D gene fragments: Ixodes ricinus (n = 1128), Dermacentor marginatus (n = 507), D. reticulatus (n = 165), Rhipicephalus rossicus (n = 128) and Haemaphysalis punctata (n = 100). Five Rickettsia species were identified following DNA sequence analysis: R. helvetica, R. monacensis, R. slovaca, R. raoultii, and R. hoogstraalii. The most common species detected was R. monacensis. Moreover, R. hoogstraalii was detected for the first time in Romania and in R. rossicus ticks. The detection of R. raoultii and R. monacensis in questing larvae of Hae. punctata suggests the possible transovarial transmission of these Rickettsia species in ticks. The detection of R. hoogstraalii for the first time in Romania increases the reported SFG Rickettsia diversity in the country.

Vitellogenin-2 Accumulation in the Fat Body and Hemolymph of Babesia-Infected Haemaphysalis longicornis Ticks.

The protozoan parasite Babesia spp. invades into tick oocytes and remains in the offspring. The transovarial transmission phenomenon of Babesia in ticks has been demonstrated experimentally, but the molecular mechanisms remain unclear. Babesia invasion into oocytes occurs along with the progression of oogenesis. In the present study, to find the key tick factor(s) for Babesia transmission, we focused on molecules involved in yolk protein precursor (vitellogenin, Vg) synthesis and Vg uptake, which are crucial events in tick oogenesis. With a Haemaphysalis longicornis tick–Babesia ovata experimental model, the expression profiles of Akt, target of rapamycin, S6K, GATA, and Vg, Vg synthesis-related genes, and Vg receptor (VgR) and autophagy-related gene 6 (ATG6), Vg uptake-related genes, were analyzed using real-time PCR using tissues collected during the preovipositional period in Babesia-infected ticks. The expression levels of H. longicornis Vg-2 (HlVg-2) and HlVg-3 decreased in the fat body of Babesia-infected ticks 1 day after engorgement. In the ovary, HlVg-2 mRNA expression was significantly higher in Babesia-infected ticks than in uninfected ticks 1 and 2 days after engorgement and decreased 3 days after engorgement. HlVgR expression was significantly lower in Babesia-infected ticks than in uninfected ticks 2 and 4 days after engorgement. HlATG6 had a lower gene expression in Babesia-infected ticks compared to uninfected ticks 2 days after engorgement. Additionally, western blot analysis using protein extracts from each collected tissue revealed that H. longicornis Vg-2 (HlVg-2) accumulate in the fat body and hemolymph of Babesia-infected ticks. These results suggest that Vg uptake from the hemolymph to the ovary was suppressed in the presence of B. ovata. Moreover, HlVg-2 knockdown ticks had a lower detection rate of B. ovata DNA in the ovary and a significant reduction of B. ovata DNA in the hemolymph compared with control ticks. Taken together, our results suggest that accumulated HlVg-2 is associated with Babesia infection or transmission in the tick body. These findings, besides previous reports on VgR, provide important information to elucidate the transovarial transmission mechanisms of pathogens in tick vectors.

Stability and Bifurcation Analysis of a Discrete Severe Fever with Thrombocytopenia Syndrome Model

Severe fever with thrombocytopenia syndrome (SFTS) is an acute tick-borne disease caused by SFTS virus (SFTSV). In this paper, we use difference equations to establish a discrete tick-borne disease model with systemic and transovarial transmission. Using the method of the next generation of matrix, we get the basic reproduction number [Formula: see text] to determine whether SFTS will die out. Furthermore, we analyze the existence and stability of equilibrium points by [Formula: see text]. In addition, the transcritical bifurcation property at the disease-free equilibrium point is discussed by deriving a equation describing the flow on the center manifold. Finally, we perform numerical simulations to verify the theoretical results.

Natural Aedes-Borne Virus Infection Detected in Male Adult Aedes aegypti (Diptera: Culicidae) Collected From Urban Settings in Mérida, Yucatán, México.

Aedes-borne viruses (ABVs) such as dengue (DENV), chikungunya (CHIKV), and Zika (ZIKV) contribute significantly to the global burden of infectious diseases, disproportionately affecting disadvantaged populations from tropical and subtropical urban areas. ABVs can be transmitted from female mosquitoes to their progeny by vertical transmission via transovarial and/or trans-egg vertical transmission and contribute to the maintenance of infected-mosquito populations year-round in endemic regions. This study describes the natural infection rate of DENV, CHIKV, and ZIKV in field-caught male Aedes (Sergentomyia) aegypti (Linnaeus) mosquitoes from Mérida, Yucatán, México, as a proxy for the occurrence of vertical virus transmission. We used indoor sequential sampling with Prokopack aspirators to collect all mosquitoes inside houses from ABV hotspots areas. Collections were performed in a DENV and CHIKV post-epidemic phase and during a period of active ZIKV transmission. We individually RT-qPCR tested all indoor collected Ae. aegypti males (1,278) followed by Sanger sequencing analysis for final confirmation. A total of 6.7% male mosquitoes were positive for ABV (CHIKV = 5.7%; DENV = 0.9%; ZIKV = 0.1%) and came from 21.0% (30/143) houses infested with males. Most ABV-positive male mosquitoes were positive for CHIKV (84.8%). The distribution of ABV-positive Ae. aegypti males was aggregated in a few households, with two houses having 11 ABV-positive males each. We found a positive association between ABV-positive males and females per house. These findings suggested the occurrence of vertical arbovirus transmission within the mosquito populations in an ABV-endemic area and, a mechanism contributing to viral maintenance and virus re-emergence among humans in post-epidemic periods.

A periodic Chikungunya model with virus mutation and transovarial transmission

In this paper, a Chikungunya dynamical model with virus mutation and transovarial transmission is developed, which incorporates the effect of seasonal temperature changes on disease transmission through time-dependent parameters. Firstly, the threshold parameter R0m that determines the persistence and extinction of mosquito populations is given, and then the disease reproduction number R0 is defined. Secondly, it is proved that if R0m > 1 and R0 < 1, the disease disappears; if R0m > 1 and R0 > 1, then Chikungunya with mutants and non-mutants will persist simultaneously. Finally, a case study is carried out with the data in Kerala, India, where the virus mutation causes the outbreak of Chikungunya. Data on newly confirmed human cases in the state between 2007 and 2010 is fitted and the theoretical results obtained in the previous section are validated. In addition, the effects of seasonal temperature change, virus mutation and transovarial transmission on the prevalence of the disease are studied by numerical simulations from different aspects.2020 MSC: 34K13; 37N25; 92D30.

Dengue virus transovarial transmission detection in Aedes aegypti from dengue hemorrhagic fever patients' residences in Denpasar, Bali.

Background and Aim:To effectively control dengue hemorrhagic fever (DHF), it is necessary to assess the risk of vertical virus transmission in Aedes aegypti mosquitoes. This study aimed to detect dengue virus (DENV) transovarial transmission in A. aegypti collected from DHF patients’ residences in Denpasar, Bali.Materials and Methods:A. aegypti samples were acquired by rearing A. aegypti eggs collected from ovitraps placed in the homes of DHF patients. Ovitraps were installed for 7 days and viewed using a loupe to determine whether there were Aedes spp. eggs present. An immunocytochemical method was utilized with 200 samples, and virus detection was performed using a reverse transcriptase-polymerase chain reaction (RT-PCR).Results:Of the 10 DHF patient houses fitted with ovitraps, four produced positive ovitraps from which larvae developed (house index=40%). Of the 50 ovitraps mounted in the 10 homes, 14 ovitraps were positive and contained A. aegypti eggs (ovitrap index=28%). Of these 14 positive ovitraps containing A. aegypti eggs, 10 ovitraps produced larvae. Immunocytochemical tests were conducted on A. aegypti eggs from the four houses under study. It was found that from the 200 samples collected, 197 samples could be observed, and 11 samples (5.6%) were positive for DENV antigen. RT-PCR examination conducted on mosquitoes reared from the four houses studied obtained a negative virus content result.Conclusion:This study found the presence of DENV antigen to be as high as 5.6%. This means that potential for transovarial transmission exists within DHF patients’ homes in Denpasar, Bali. Aedes control strategy in Denpasar should address this finding, in addition to the current approaches which have focused primarily on the elimination of larval breeding habitats and control of adults using insecticidal fogging during outbreaks.

Detection of Dengue Virus Transovarial Transmission in Dengue Hemorrhagic Fever Endemic Areas

Dengue virus is a group of RNA viruses that are highly pathogenic in humans and spread quickly through the bites of Aedes aegypti and Aedes albopictus mosquitoes, especially in tropical countries. More than half a billion out of 100 countries worldwide are at serious risk of dengue virus infection. Vector surveillance activities with Ovitrap and detection of dengue virus types in Aedes aegypti and Aedes albopictus have never been carried out in Pontianak City. It is important in early alert systems at transmission foci. The purpose of this study was to prove the transovarial transmission of dengue virus in Aedes aegypti and Aedes albopictus mosquitoes with a transovarial transmission index (TTI) in endemic areas in Pontianak City, West Kalimantan. The method used in this research is descriptive observational, viral examination method with immunocytochemistry streptavidin-biotin peroxidase complex (ISBPC) and Polymerase Chain Reaction Transcription Reaction (PCR) aimed at proving the presence of transovarial transmission of dengue virus in the same period. The conclusion in this study is that there is evidence of transovarial transmission of dengue virus in Aedes mosquitoes in endemic areas by 29.3% in Sungai Jawi Dalam sub-district, West Pontianak sub-district, and 39.6% in Batu Layang sub-district, North Pontianak sub-district, mosquito density from the results of the Ovitrap Index measurement (OI) in Batu Layang Village is denser, namely 41.3%, compared to Sungai Jawi Village, which is 38.22% and has succeeded in identifying the type of dengue virus, namely the Dengue virus strain, in the two research locations.

The gut commensal bacterium Enterococcus faecalis LX10 contributes to defending against Nosema bombycis infection in Bombyx mori.

BACKGROUNDMicrosporidia, a group of obligate intracellular fungal‐related parasites, have been used as efficient biocontrol agents for agriculture and forestry pests due to their host specificity and transovarial transmission. They mainly infect insect pests through the intestinal tract, but the interactions between microsporidia and the gut microbiota of the host have not been well demonstrated.RESULTSBased on the microsporidia–Bombyx mori model, we report that the susceptibility of silkworms to exposure to the microsporidium Nosema bombycis was both dose and time dependent. Comparative analyses of the silkworm gut microbiome revealed substantially increased abundance of Enterococcus belonging to Firmicutes after N. bombycis infection. Furthermore, a bacterial strain (LX10) was obtained from the gut of B. mori and identified as Enterococcus faecalis based on 16S rRNA sequence analysis. E. faecalis LX10 reduced the N. bombycis spore germination rate and the infection efficiency in vitro and in vivo, as confirmed by bioassay tests and histopathological analyses. In addition, after simultaneous oral feeding with E. faecalis LX10 and N. bombycis, gene (Akirin, Cecropin A, Mesh, Ssk, DUOX and NOS) expression, hydrogen peroxide and nitric oxide levels, and glutathione S‐transferase (GST) activity showed different degrees of recovery and correction compared with those under N. bombycis infection alone. Finally, the enterococcin LX protein was identified from sterile LX10 fermentation liquid based on liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis.CONCLUSIONAltogether, the results revealed that E. faecalis LX10 with anti‐N. bombycis activity might play an important role in protecting silkworms from microsporidia. Removal of these specific commensal bacteria with antibiotics and utilization of transgenic symbiotic systems may effectively improve the biocontrol value of microsporidia. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Ticks on the Run: A Mathematical Model of Crimean-Congo Haemorrhagic Fever (CCHF)-Key Factors for Transmission.

Crimean-Congo haemorrhagic fever (CCHF) is a zoonotic disease caused by the Crimean-Congo hemorrhagic fever virus (CCHFV). Ticks of the genus Hyalomma are the main vectors and represent a reservoir for the virus. CCHF is maintained in nature in an endemic vertebrate-tick-vertebrate cycle. The disease is prevalent in wide geographical areas including Asia, Africa, South-Eastern Europe and the Middle East. It is of great importance for the public health given its occasionally high case/fatality ratio of CCHFV in humans. Climate change and the detection of possible CCHFV vectors in Central Europe suggest that the establishment of the transmission in Central Europe may be possible in future. We have developed a compartment-based nonlinear Ordinary Differential Equation (ODE) system to model the disease transmission cycle including blood sucking ticks, livestock and human. Sensitivity analysis of the basic reproduction number R0 shows that decreasing the tick survival time is an efficient method to control the disease. The model supports us in understanding the influence of different model parameters on the spread of CCHFV. Tick-to-tick transmission through co-feeding and the CCHFV circulation through transstadial and transovarial transmission are important factors to sustain the disease cycle. The proposed model dynamics are calibrated through an empirical multi-country analysis and multidimensional plot reveals that the disease-parameter sets of different countries burdened with CCHF are different. This information may help decision makers to select efficient control strategies.

Transovarial Transmission of Heartland Virus by Invasive Asian Longhorned Ticks under Laboratory Conditions.

We demonstrated experimental acquisition and transmission of Heartland bandavirus by Haemaphysalis longicornis ticks. Virus was detected in tick salivary gland and midgut tissues. A total of 80% of mice exposed to 1 infected tick seroconverted, suggesting horizontal transmission. H. longicornis ticks can transmit the virus in the transovarial mode.

Rickettsia africae infection rates and transovarial transmission in Amblyomma hebraeum ticks in Mnisi, Bushbuckridge, South Africa.

Rickettsia africae is a gram-negative bacterium, which causes African tick bite fever (ATBF) in humans. ATBF is a febrile disease mainly affecting travellers to southern Africa. This bacterium is known to be transmitted by Amblyomma hebraeum and Amblyomma variegatum ticks. In southern Africa, the principal vector is A. hebraeum. Febrile disease is a serious issue in the study area. There is a high prevalence of non-malaria illness caused by Rickettsia, so there is a need to have more knowledge on these species. Infection rates and transovarial transmission efficiency of R. africae in A. hebraeum ticks were investigated in a rural area of Mpumalanga province, South Africa. Adult and engorged A. hebraeum female ticks were collected from cattle. Larvae were collected by dragging a cloth at ground level using 100 steps, equivalent to an area of 100 m2. Tick identification was performed according to standard taxonomic keys using a microscope. Engorged ticks were incubated to oviposit and egg masses were collected. DNA was extracted from the ticks, larvae and egg masses, and screened for gltA and ompA genes, using quantitative real-time PCR and conventional PCR, respectively. Positive ompA amplicons were sequenced and phylogenetic analysis showed 99.8-100% identity with R. africae. Infection rates were 13.7 and 12.7% for adults and larvae, respectively. Transovarial transmission of R. africae in A. hebraeum from this study was 85.7%. The results provide a clear indication that people living in the study area and travellers that visit the area are at risk of contracting ATBF.

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 reverse transcription polymerase chain reaction (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.

The Piroplasmida Babesia, Cytauxzoon, and Theileria in farm and companion animals: species compilation, molecular phylogeny, and evolutionary insights.

The order Piroplasmida, including the genera Babesia, Cytauxzoon, and Theileria is often referred to as piroplasmids and comprises of dixenous hemoprotozoans transmitted by ticks to a mammalian or avian host. Although piroplasmid infections are usually asymptomatic in wild animals, in domestic animals, they cause serious or life-threatening consequences resulting in fatalities. Piroplasmids are particularly notorious for the enormous economic loss they cause worldwide in livestock production, the restrictions they pose on horse trade, and the negative health impact they have on dogs and cats. Furthermore, an increasing number of reported human babesiosis cases are of growing concern. Considerable international research and epidemiological studies are done to identify existing parasite species, reveal their phylogenetic relationships, and develop improved or new drugs and vaccines to mitigate their impact. In this review, we present a compilation of all piroplasmid species, isolates, and species complexes that infect domestic mammals and which have been well defined by molecular phylogenetic markers. Altogether, 57 taxonomic piroplasmid entities were compiled, comprising of 43 piroplasmid species, 12 well-defined isolates awaiting formal species description, and two species complexes that possibly mask additional species. The extrapolation of the finding of at least 57 piroplasmid species in only six domestic mammalian groups (cattle, sheep, goat, horse, dog, and cat) allows us to predict that a substantially higher number of piroplasmid parasites than vertebrate host species exist. Accordingly, the infection of a vertebrate host species by multiple piroplasmid species from the same and/or different phylogenetic lineages is commonly observed. Molecular phylogeny using 18S rRNA genes of piroplasmids infecting domestic mammals results in the formation of six clades, which emerge due to an anthropocentric research scope, but not due to a possibly assumed biological priority position. Scrutinizing the topology of inferred trees reveals stunning insights into some evolutionary patterns exhibited by this intriguing group of parasites. Contrary to expectations, diversification of parasite species appears to be dominated by host-parasite cospeciation (Fahrenholz's rule), and, except for piroplasmids that segregate into Clade VI, host switching is rarely observed. When only domestic mammalian hosts are taken into account, Babesia sensu lato (s.l.) parasites of Clades I and II infect only dogs and cats, respectively, Cytauxzoon spp. placed into Clade III only infect cats, Theileria placed into Clade IV exclusively infect horses, wheras Theileria sensu stricto (s.s.) of Clade V infects only cattle and small ruminants. In contrast, Babesia s.s. parasites of Clade VI infect all farm and companion animal species. We outline how the unique ability of transovarial transmission of Babesia s.s. piroplasmids of Clade VI facilitates species diversification by host switching to other host vertebrate species. Finally, a deterioration of sequence fidelity in databases is observed which will likely lead to an increased risk of artifactual research in this area. Possible measures to reverse and/or avoid this threat are discussed.

Biology and Transmission Dynamics of Aedes flavivirus.

Aedes albopictus (Skuse) and Aedes aegypti (Linnaeus) (Diptera: Culicidae) mosquitoes transmit pathogenic arthropod-borne viruses, including dengue, chikungunya, and Zika viruses, with significant global health consequences. Both Ae. albopictus and Ae. aegypti also are susceptible to Aedes flavivirus (AEFV), an insect-specific flavivirus (ISF) first isolated in Japan from Ae. albopictus and Ae. flavopictus. ISFs infect only insect hosts and evidence suggests that they are maintained by vertical transmission. In some cases, ISFs interfere with pathogenic flavivirus infection, and may have potential use in disease control. We explored the host range of AEFV in 4 genera of mosquitoes after intrathoracic injection and observed greater than 95% prevalence in the species of Aedes and Toxorhynchites tested. Anopheles and Culex species were less permissive to infection. Vertical transmission studies revealed 100% transovarial transmission and a filial infection rate of 100% for AEFV in a persistently-infected colony of Ae. albopictus. Horizontal transmission potential was assessed for adult and larval mosquitoes following per os exposures and in venereal transmission experiments. No mosquitoes tested positive for AEFV infection after blood feeding, and infection with AEFV after sucrose feeding was rare. Similarly, 2% of adult mosquitoes tested positive for AEFV after feeding on infected cells in culture as larvae. Venereal transmission of AEFV was most frequently observed from infected males to uninfected females as compared with transmission from infected females to uninfected males. These results reveal new information on the infection potential of AEFV in mosquitoes and expand our understanding of both vertical and horizontal transmission of ISFs.

Emergence of “urban scrub typhus” during Monsoon season in an urban pocket and biodiversity hotspot of New Delhi, India

Introduction: Scrub typhus is an endemic disease transmitted within the “epidemiological tetrad” of rains, rodents, chigger mites, and scrub vegetation prevalent in “Tsutsugamushi Asia-Pacific triangle,” predisposing one billion population at risk and annual incidence of one million. Scrub typhus is difficult to differentiate clinically from coendemic vector-borne acute undifferentiated febrile illness (AUFI). Untreated scrub typhus may cause disseminated vasculitis, serositis, and hemophagocytic syndrome. Outbreaks of scrub typhus have been reported from Thailand, China, Korea, and rural India. Transmission of scrub typhus in urban areas is relatively rare. Three consequent outbreaks in a urban pocket in New Delhi, India, highlight emergence of urban scrub typhus. Materials and Methods: A cross-sectional, clinicoepidemiological, ambispective outcome surveillance study was conducted among all clinicodemographically homogenous patients presenting with AUFI during 2016–2018. Clinically suspected or intuitively investigated scrub typhus was screened by IgM/IgG immunochromatography and confirmed through IgM enzyme-linked immunosorbent assay and real-time polymerase chain reaction. Spatial, temporal, and vector surveillance through epidemiological mapping, line listing, and mite surveillance was done. Results: Scrub typhus outbreaks affected 161 patients during 2016–2018. Mean age was 31.77 ± 17 years. Most common clinical presentation was fever with headache. Eschar was present in 46.88% patients commonly on abdomen, chest, perineum, and extremities. Coinfections and comorbidities were seen in 3.75% and 14.37% patients, respectively. Seventy percent and 14.8% patients were managed in acute care and intensive care. Mean hospital stay was 8.96 ± 3.86 days. Doxycycline and doxycycline-azithromycin combination were given in 92.5% and 7.5% patients, respectively. All-cause mortality was 6.25%. 126/160 (78.75%) patients were geospatially distributed from urban landscape depicted in epidemiological maps. Temporal-seasonal distribution revealed bell-shaped curve from May to November. Mite carriage was seen in 16% rodents. Conclusion: Urban scrub typhus is emerging in microhabitats fulfilling the epidemiological tetrad and chigger mites undergoing transovarian transmission. Geospatial and temporal mapping are required in urban neighborhoods for risk stratification, outbreak management, vector control, and community education. A high index of suspicion in AUFI and early initiation of doxycycline therapy are required.

Detection of Zika virus in Anopheles stephensi Liston, 1901 (Diptera: Culicidae) in India - First report

Zika virus (ZIKV) a mosquito-borne, causing acute febrile illness associated with rash, arthralgia and conjunctivitis in the patient, was reported from Thiruvananthapuram, Kerala, as an outbreak with 83 cases. Entomological surveillance revealed the presence of aedine mosquitoes viz., Aedes aegypti (Linnaeus, 1762), Ae. albopictus (Skuse, 1894) and Ae. vittatus (Bigot, 1861) and nonaedine mosquitoes viz., Anopheles stephensi Liston,1901, Mansonia uniformis (Theobald, 1901), Culex tritaeniorhynchus Giles, 1901 and Cx. gelidus Theobald,1901. Aedes (Ae. aegypti, Ae. vittatus and Ae. Albopictus) mosquito larvae were high in the Zika affected areas. Moreover ZIKV was detected in An. stephensi mosquitoes collected from Parassala, Thiruvananthapuram (the native place of the first ZIKV confirmed case in the present outbreak in Kerala). Molecular diagnostics of Ae. Aegypti, Ae. vittatu and An. stephensi mosquitoes revealed that the species were loaded with ZIKV. Significantly this is the first ever report of ZIKV detecting in An. stephensi in the world. Aedes adults (male and female) and An. stephensi emerged from fourth instar larvae and pupae were found to have ZIKV, indicating transovarial transmission of the virus.

Molecular investigation on transstadial/transovarial transmission of Hepatozoon canis in Rhipicephalus sanguineus sensu lato ticks

ABSTRACT To investigate the possibility of transovarial and transstadial transmission of Hepatozoon canis, a total of 953 Rhipicehlalus sanguineus sensu lato ticks at different stages were collected from 231 stray dogs housed at Blue cross, and 10 dogs presented at small animal clinics. The engorged nymphs collected from the cracks and crevices of Blue cross were allowed to moult in the laboratory. The ticks collected from the host and moulted ticks were pooled according to their sex and feeding status as fed, unfed males and females. Each tick was dissected individually and examined microscopically, then pooled as H. canis positive and negative. Microscopic examination of the 953 ticks revealed H. canis oocysts in 228 (89.76%) unfed adult males and females which moulted from the nymphs collected from cracks and crevices. Positivity of 74% was observed in unfed females while all unfed males (100%) were positive. Amongst the 213 fed males, 174 (81.69%) were positive, while only 210 (43.20%) of the 486 fed females were positive. No oocyst was detected from ticks collected from dogs presented to clinics. The occurrence of H. canis DNA in the tick was confirmed by PCR assay based on the amplification of 666 bp fragment of partial 18S rRNA gene. Amplification was observed in pooled samples collected from Blue cross, whereas no amplification was observed in ticks collected from dogs presented to clinics. The DNA samples from tick larvae did not show amplification, which indicated that H. canis is not transmitted transovarially.

The Absence of Abdominal Pigmentation in Livestock Associated Culicoides following Artificial Blood Feeding and the Epidemiological Implication for Arbovirus Surveillance.

Culicoides midges (Diptera: Ceratopogonidae), the vectors of economically important arboviruses such as bluetongue virus and African horse sickness virus, are of global importance. In the absence of transovarial transmission, the parity rate of a Culicoides population provides imperative information regarding the risk of virus dispersal. Abdominal pigmentation, which develops after blood feeding and ovipositioning, is used as an indicator of parity in Culicoides. During oral susceptibility trials over the last three decades, a persistent proportion of blood engorged females did not develop pigment after incubation. The present study, combining a number of feeding trials and different artificial feeding methods, reports on this phenomenon, as observed in various South African and Italian Culicoides species and populations. The absence of pigmentation in artificial blood-fed females was found in at least 23 Culicoides species, including important vectors such as C. imicola, C. bolitinos, C. obsoletus, and C. scoticus. Viruses were repeatedly detected in these unpigmented females after incubation. Blood meal size seems to play a role and this phenomenon could be present in the field and requires consideration, especially regarding the detection of virus in apparent “nulliparous” females and the identification of overwintering mechanisms and seasonally free vector zones.