An Investigation of Culicoides (Diptera: Ceratopogonidae) as Potential Vectors of Medically and Veterinary Important Arboviruses in South Africa

Culicoides-borne viruses such as bluetongue, African horse sickness, and Schmallenberg virus cause major economic burdens due to animal outbreaks in Africa and their emergence in Europe and Asia. However, little is known about the role of Culicoides as vectors for zoonotic arboviruses. In this study, we identify both veterinary and zoonotic arboviruses in pools of Culicoides biting midges in South Africa, during 2012–2017. Midges were collected at six surveillance sites in three provinces and screened for Alphavirs, Flavivirus, Orthobunyavirus, and Phlebovirus genera; equine encephalosis virus (EEV); and Rhaboviridae, by reverse transcription polymerase chain reaction. In total, 66/331 (minimum infection rate (MIR) = 0.4) pools tested positive for one or more arbovirus. Orthobunyaviruses, including Shuni virus (MIR = 0.1) and EEV (MIR = 0.2) were more readily detected, while only 2/66 (MIR = 0.1) Middelburg virus and 4/66 unknown Rhabdoviridae viruses (MIR = 0.0) were detected. This study suggests Culicoides as potential vectors of both veterinary and zoonotic arboviruses detected in disease outbreaks in Africa, which may contribute to the emergence of these viruses to new regions.

Detection and Phylogenetic Analysis of a Novel Tick-Borne Virus in Yunnan and Guizhou Provinces, Southwestern China

Dabieshan tick virus (DTV) is a novel tick-borne virus with the potential to infect both animals and humans. It has been confirmed that DTV is widely distributed in Shandong and Zhejiang Provinces. In this study, a total of 389 ticks were sampled from Honghe city of Yunnan Province and Bijie city of Guizhou Province, and then divided into 148 pools according to the location and species. QRT-PCR and nested PCR were performed to confirm the presence of DTV. The results showed a minimum infection rate of 2.43% (5/206) in Yunnan Province and 3.28% (6/183) in Guizhou Province, respectively. Interestingly, DTV was identified in Rhipicephalusmicroplus for the first time besides Haemaphysalis longicornis. Phylogenetic analysis showed that DTV from Yunnan and Guizhou Provinces shared over 94% identity with isolates derived from Hubei and Shandong Provinces, and DTV was relatively conservative in evolutionary dynamics. These findings provide molecular evidence of Dabieshan tick virus in different species of ticks from unrecognized endemic regions and suggest that DTV may be widely prevalent in southwestern China.

Nationwide Temporal and Geographical Distribution of Tick Populations and Phylogenetic Analysis of Severe Fever with Thrombocytopenia Syndrome Virus in Ticks in Korea, 2020

Since 2010, the Korea Disease Control and Prevention Agency has established centers at 16 locations to monitor disease vectors and pathogens. Here, we examined tick populations to understand the geographical and temporal distribution of severe fever with thrombocytopenia syndrome virus (SFTSV) vectors in 2020. From April to November, 63,376 ticks were collected from traps to monitor tick populations, with a trap index of 41.3. Tick incidence varied from April to October, with population peaks observed for nymphs in May, adults in July, and larvae in September. The predominant tick species were Haemaphysalis longicornis, Haemaphysalis spp., H. flava, Ixodes spp., Amblyomma testudinarium, and Ixodes nipponensis. Approximately 50% of the collected ticks were pooled into 2973 groups to detect the rate of SFTSV infection in ticks. The minimum infection rate (MIR) of SFTSV was 0.2%, and Andong had the highest MIR for SFTSV (4.0%). The B3 genotype was the most prevalent (52.2%) followed by B2 (28.6%), B5 (15.9%), B4 (1.6%), and B6 (1.6%). We identified widely distributed tick species and a high degree of diversity in SFTSV strains in ticks from different geographical regions. The results may provide a basis for future epidemiological studies and risk assessments for tick-borne diseases.

An Updated Review Of the Invasive Aedes Albopictus in the Americas; The Minimum Infection Rate Suggests That Is More Efficient in the Vertical Than Horizontal Transmission of Arboviruses

The aim of the work was to update the distribution range of Aedes (Stegomyia) albopictus Skuse in the Americas, review the blood feeding patterns and compare the minimum infection rate (MIR) between studies of vertical and horizontal transmission of arboviruses. The current distribution of Ae. albopictus encompasses 21 countries in the Americas. In eleven published papers on the blood feeding pattern of Ae. albopictus, DNA from 16 species of mammals and five species of avian species was found. The most common host is humans, and dogs. We found 24 published papers on the identification of arboviruses in wild populations of Ae. albopictus with the potential to infect humans and animals. Eight arboviruses have been isolated in different studies carried out in Brazil, USA, Mexico, Colombia, and Costa Rica. Fifty-eight percent (14/24) of the publications reported vertical transmission of arbovirus. Positive pools were higher in vertical (8.45%) compared to horizontal transmission (0.97%). This was supported by the MIR, which was 3 times greater in vertical (MIR=3.21) than horizontal transmission (MIR= 1.08). In conclusion, Ae. albopictus is an invasive mosquito with wide phenotypic plasticity to adapt to broad and new areas, high vectorial competence to transmit several arboviruses mainly by transovarial transmission, it can participate in the endemic transmission, and serve as a bridge vector for emerging arboviruses between sylvan, rural, and urban areas.

Dengue-2 and Guadeloupe Mosquito Virus RNA Detected in Aedes (Stegomyia) spp. Collected in a Vehicle Impound Yard in Santo André, SP, Brazil

In 2018–2019, we conducted mosquito collections in a municipal vehicle impound yard, which is 10 km from the Serra do Mar Environmental Protection Area in Santo André, SP, Brazil. Our aim is to study arboviruses in the impound yard, to understand the transmission of arboviruses in an urban environment in Brazil. We captured the mosquitoes using human-landing catches and processed them for arbovirus detection by conventional and quantitative RT-PCR assays. We captured two mosquito species, Aedes aegypti (73 total specimens; 18 females and 55 males) and Ae. albopictus (34 specimens; 27 females and 7 males). The minimum infection rate for DENV-2 was 11.5 per 1000 (CI95%: 1–33.9). The detection of DENV-2 RNA in an Ae. albopictus female suggests that this virus might occur in high infection rates in the sampled mosquito population and is endemic in the urban areas of Santo André. In addition, Guadeloupe mosquito virus RNA was detected in an Ae. aegypti female. To our knowledge, this was the first detection of the Guadeloupe mosquito virus in Brazil.

Detection of Multiple Intracellular Bacterial Pathogens in Haemaphysalis flava Ticks Collected from Hedgehogs in Central China

Tickborne intracellular bacterial pathogens including Anaplasma, Coxiella burnetti, Ehrlichia, and Rickettsia cause emerging infectious diseases worldwide. PCR was used to amplify the genes of these pathogens in Haemaphysalis flava ticks collected from hedgehogs in Central China. Among 125 samples including 20 egg batches, 24 engorged females, and 81 molted male and female adult ticks, the DNA sequences and phylogenetic analysis showed that the minimum infection rate of the ticks was 4% (5/125) for A. bovis, 3.2% (4/125) for C. burnetti, 9.6%, (12/125) for E. ewingii, and 5.6% for Rickettsia including R.japonica (3.2%, 4/125) and R. raoultii (2.4%, 3/125), respectively. The prevalence of these pathogens was significantly higher in dead engorged females (83.3%, 20/24) than in eggs (5%, 1/20) and molted ticks (8.6%, 7/81). Our study indicated that H. flava ticks could be infected with multiple species of tickborne pathogens including Anaplasma, C. burnetti, Ehrlichia, and Rickettsia in Central China, and the prevalence of these pathogens was reduced during transovarial and transstadial transmission in ticks, suggesting that ticks may not be real reservoirs but only vectors for these tickborne pathogens.

First Record of Mosquito-Borne Kyzylagach Virus in Central Europe

RNA of Kyzylagach virus (KYZV), a Sindbis-like mosquito-borne alphavirus from Western equine encephalitis virus complex, was detected in four pools (out of 221 pools examined), encompassing 10,784 female Culex modestus mosquitoes collected at a fishpond in south Moravia, Czech Republic, with a minimum infection rate of 0.04%. This alphavirus was never detected in Central Europe before.

Molecular evidence of Babesia caballi and Theileria equi in equines and ticks in Nigeria: prevalence and risk factors analysis

Babesia caballi and Theileria equi are biological agents responsible for equine piroplasmosis (EP). We conducted a robust and extensive epidemiological study in Nigeria on the prevalence and risk factors of EP. Blood (468, both horses and donkeys) and ticks (201 pools) were screened using polymerase chain reaction (PCR). DNA of equine piroplasms was observed in tick pools with B. caballi amplified in Rhipicephalus evertsi evertsi only [minimum infection rate (MIR) of 7.6%] while T. equi was observed in R. e. evertsi (MIR, 61.6%), Hyalomma dromedarii (MIR, 23.7%) and H. truncatum (MIR, 50.0%). Overall results showed that 196/468 (41.9%) animals were positive for equine piroplasms (both B. caballi and T. equi). The prevalence for T. equi was 189/468 (40.4%) compared to 7/468 (1.5%) for B. caballi. In the horses and donkeys, respectively, the prevalence for T. equi was (39.9%; 112/281) and (41.2%; 77/187) compared with (1.4%; 4/281) and (1.6%; 3/187) due to B. caballi. Our analysis showed that location (Jigawa state), Talon breed, horses used for work and reproduction, unsatisfactory husbandry practices, contact with other mammals are risk factors that associated positivity to T. equi infection in horses, whilst horses kept on intensive management appeared to be less prone to infection. On the other hand, Jangora breed of donkeys and location (Jigawa state) are risk factors to infection with T. equi in donkeys. Findings suggest the persistence of EP in equids and ticks in Nigeria.

Tick-borne pathogens in Ixodidae ticks collected from privately-owned dogs in Italy: a country-wide molecular survey

Background Ticks and tick-borne diseases are increasingly recognized as a cause of disease in dogs worldwide. The epidemiology of ticks and tick-transmitted protozoa and bacteria has changed due to the spread of ticks to urban and peri-urban areas and the movement of infected animals, posing new risks for animals and humans. This countrywide study reports information on distribution and prevalence of pathogens in ticks collected from privately-owned dogs in Italy. We analyzed 2681 Ixodidae ticks, collected from 1454 pet dogs from Italy. Specific PCR protocols were used to detect i) Piroplasms of the genera Babesia and Theileria , ii) Gram-negative cocci of the family Anaplasmataceae and iii) Borrelia burgdorferi sensu lato. Sequencing of positive amplicons allowed for species identification. Results Babesia / Theileria spp. DNA was detected in 435 homogeneous tick-pools (Minimum Infection Rate (MIR) = 27.6%; 95% confidence interval (CI) = 25.4-29.8%) with higher prevalence in Ixodes ricinus and Rhipicephalus sanguneus group. The zoonotic B. venatorum was the most prevalent species (MIR = 7.5%; 95% CI = 6.3-9.0%). Anaplasma and Ehrlichia species were detected in 165 tick-pools (MIR = 10.5%; 95% CI = 9.3-11.8%) and specifically, A. phagocytophilum was identified with MIR = 5.1% (95% CI = 4.1-6.3%). Borrelia burgdorferi s.l. and B. afzelii were detected with MIR = 0.4% (95% CI = 0.2-0.8%) and MIR = 0.3% (95% CI 0.1-0.7%) respectively. Conclusions Zoonotic pathogens B. venatorum and A. phagocytophilum were the most frequently detected in ticks collected from privately-owned dogs which might be used as markers of pathogens presence and distribution.

Error associated with estimates of Minimum Infection Rate for Endemic West Nile Virus in areas of low mosquito trap density

West Nile Virus (WNV) is a mosquito-borne infection that can cause serious illness in humans. Surveillance for WNV primarily focuses on a measure of infection prevalence in the Culex spp. mosquitos, its primary vectors, known as the Minimum Infection Rate (MIR). The calculation of MIR for a given area considers the number of mosquitos tested, but not the relative effort to collect mosquitos, leading to a potential underestimation of the uncertainty around the estimate. We performed Value of Information analysis on simulated data sets including a range of mosquito trap densities in two well-studied counties in Illinois between 2005 and 2016 to determine the relative error introduced into MIR associated with changing the density of mosquito traps. We found that low trap density increases the potential for error in MIR estimation, and that it does so synergistically with low true MIR values. We propose that these results could be used to better estimate uncertainty in WNV risk.