Horizontal Transmission Routes Research Articles

Detection of Enterococcus cecorum to identify persistently contaminated locations using faecal and environmental samples in broiler houses of clinically healthy flocks

ABSTRACT Worldwide outbreaks make infections with pathogenic strains of Enterococcus cecorum (EC) one of the most important diseases in the broiler industry. Although research has increased knowledge about the pathogen, the transmission is not fully understood. Samples from different locations were collected from two broiler farms in Germany over a total of six production cycles. Samples were collected at days 1, 5, 10, 15, 21, 27, 34, 41 post-hatch and after cleaning and disinfection (C&D). A total of 1017 samples were collected from 25 different locations on the farms. Samples were analysed in the laboratory for EC by quantitative real-time PCR. Overall, 7.5% of the samples were positive. The probabilities for positive and negative samples did not differ between the farms. The number of findings differed significantly between the cycles. Compared to other samples, the chances of detecting EC in faecal samples were significantly higher. Most positive samples were found in the last week of the production periods, indicating an accumulation of EC in the barn environment. After C&D, positive PCR results were obtained in four out of 14 locations. A re-introduction from contaminated environment seemed possible. However, one pooled faecal sample was positive 1 day post-hatch. The locations that showed positive results after C&D and the positive faecal sample 1 day post-hatch indicated the persistence of EC in broiler houses of clinically healthy flocks that could lead to potential horizontal transmission routes. The present study detected potential EC sources and may help to improve hygienic measures to avoid transmissions. RESEARCH HIGHLIGHTS Methodology is suitable to detect EC during production and after C&D. Locations were detected that may serve as a reservoir for EC. Cycles with fewer positive samples were observed. Cleaning and disinfection had a major impact on the detection of EC.

Selective replication and vertical transmission of Ebola virus in experimentally infected Angolan free-tailed bats

The natural reservoir of Ebola virus (EBOV), agent of a zoonosis burdening several African countries, remains unidentified, albeit evidence points towards bats. In contrast, the ecology of the related Marburg virus is much better understood; with experimental infections of bats being instrumental for understanding reservoir-pathogen interactions. Experiments have focused on elucidating reservoir competence, infection kinetics and specifically horizontal transmission, although, vertical transmission plays a key role in many viral enzootic cycles. Herein, we investigate the permissiveness of Angolan free-tailed bats (AFBs), known to harbour Bombali virus, to other filoviruses: Ebola, Marburg, Taï Forest and Reston viruses. We demonstrate that only the bats inoculated with EBOV show high and disseminated viral replication and infectious virus shedding, without clinical disease, while the other filoviruses fail to establish productive infections. Notably, we evidence placental-specific tissue tropism and a unique ability of EBOV to traverse the placenta, infect and persist in foetal tissues of AFBs, which results in distinct genetic signatures of adaptive evolution. These findings not only demonstrate plausible routes of horizontal and vertical transmission in these bats, which are expectant of reservoir hosts, but may also reveal an ancillary transmission mechanism, potentially required for the maintenance of EBOV in small reservoir populations.

Autogenous reproduction by Ornithodoros turicata (Ixodida: Argasidae) females and vertical transmission of the tick-borne pathogen Borrelia turicatae (Spirochaetales: Borreliaceae).

Previous research has implicated Ornithodoros ticks, including Ornithodoros turicata, as long-term reservoirs of relapsing fever (RF) spirochetes. Considering the tick's long lifespan and their efficiency in maintaining and transferring spirochetes within the population, the infection could persist in a given enzootic focus for decades. However, little is known about the relative importance of horizontal and vertical transmission routes in the persistence and evolution of RF Borrelia. Our observations on the reproductive biology of O. turicata in the absence of vertebrate hosts indicate an additional mechanism by which Borrelia turicatae can be maintained in the environment. This work establishes the foundation for studying O. turicata reproduction and spirochete-vector interactions, which will aid in devising control measures for Ornithodoros ticks and RF spirochetes.

Revisiting Porcine Circovirus Infection: Recent Insights and Its Significance in the Piggery Sector.

Porcine circovirus (PCV), a member of the Circoviridae family within the genus Circovirus, poses a significant economic risk to the global swine industry. PCV2, which has nine identified genotypes (a-i), has emerged as the predominant genotype worldwide, particularly PCV2d. PCV2 has been commonly found in both domestic pigs and wild boars, and sporadically in non-porcine animals. The virus spreads among swine populations through horizontal and vertical transmission routes. Despite the availability of commercial vaccines for controlling porcine circovirus infections and associated diseases, the continuous genotypic shifts from a to b, and subsequently from b to d, have maintained PCV2 as a significant pathogen with substantial economic implications. This review aims to provide an updated understanding of the biology, genetic variation, distribution, and preventive strategies concerning porcine circoviruses and their associated diseases in swine.

Maternal transmission gives way to social transmission during gut microbiota assembly in wild mice

BackgroundThe mammalian gut microbiota influences a wide array of phenotypes which are relevant to fitness, yet knowledge about the transmission routes by which gut microbes colonise hosts in natural populations remains limited. Here, we use an intensively studied wild population of wood mice (Apodemus sylvaticus) to examine how vertical (maternal) and horizontal (social) transmission routes influence gut microbiota composition throughout life.ResultsWe identify independent signals of maternal transmission (sharing of taxa between a mother and her offspring) and social transmission (sharing of taxa predicted by the social network), whose relative magnitudes shift as hosts age. In early life, gut microbiota composition is predicted by both maternal and social relationships, but by adulthood the impact of maternal transmission becomes undetectable, leaving only a signal of social transmission. By exploring which taxa drive the maternal transmission signal, we identify a candidate maternally-transmitted bacterial family in wood mice, the Muribaculaceae.ConclusionOverall, our findings point to an ontogenetically shifting transmission landscape in wild mice, with a mother’s influence on microbiota composition waning as offspring age, while the relative impact of social contacts grows.

Host and transmission route of Enterocytozoon hepatopenaei (EHP) between dragonfly and shrimp

Enterocytozoon hepatopenaei (EHP) is a shrimp pathogen that causes huge economic losses. In the present study, the hosts of EHP were investigated using polymerase chain reaction (PCR) in an aquaculture farm located in Maoming, China. EHP was detected in Litopenaeus vannamei, Penaeus monodon, Varuna litterata, Mytilopsis leucophaeata, and three dragonfly species (Anax parthenope, Pantala flavescens, and Ischnura senegalensis). In the histopathological examination using hematoxylin–eosin (HE) staining, EHP spores were found in nymphs and adult dragonflies naturally infected with EHP that were collected from the shrimp farm. Fluorescence in situ hybridization (FISH) results showed a positive signal for EHP infection in the fat body of dragonfly nymphs. Immature and mature microsporidian spores and late sporogonial plasmodium were observed in the cytoplasm of dragonfly nymphs using transmission electron microscopy (TEM). The transmission of EHP from shrimp to dragonfly nymphs was confirmed via cohabitation challenge experiments in which EHP-free dragonfly nymphs were cohabited with EHP-infected shrimp, and the transmission of EHP from dragonfly nymphs to shrimp was demonstrated via the cohabitation of EHP-infected dragonfly nymphs with EHP-free shrimp and oral administration challenge experiments. This study confirms that dragonflies can act as natural EHP hosts, and a novel EHP horizontal transmission route exists between dragonflies and shrimp.

The Prevalence of Aliarcobacter Species in the Fecal Microbiota of Farm Animals and Potential Effective Agents for Their Treatment: A Review of the Past Decade.

There is an endless demand for livestock-originated food, so it is necessary to elucidate the hazard points for livestock breeding. Pathogens are one of the hazard points that threaten the biosecurity of farm-animal breeding and public health. As a potential foodborne pathogen, Aliarcobacter is a member of the intestinal microbiota of farm animals with and without diarrhea. Aliarcobacter spp. are capable of colonizing livestock intestines and are transmitted through the feces. Hence, they endanger slaughterhouses and milk products with fecal contamination. They also have other, rarer, vertical and horizontal transmission routes, including the offspring that abort in farm animals. Gastrointestinal symptoms and abort cases demonstrate potential financial losses to the industry. Viewed from this perspective, the global circulation of farm-animal products is a significant route for zoonotic agents, including Aliarcobacter. In the last decade, worldwide prevalence of Aliarcobacter in fecal samples has ranged from 0.8% in Italy to 100% in Turkey. Furthermore, antibiotic resistance is recognized as a new type of environmental pollutant and has become a hot topic in animal breeding and the food industry. Increasing antibiotic resistance has become a significant problem impacting productivity. The increase in antimicrobial resistance rates in Aliarcobacter is caused by the misuse of antimicrobial drugs in livestock animals, leading to the acquiring of resistance genes from other bacteria, as well as mutations in current resistance genes. The most resistant strains are A. butzleri, A. cryaerophilus, and A. skirrowii. This review analyzes recent findings from the past decade on the prevalence of Aliarcobacter in the intestinal microbiota and the current effective antibiotics against Aliarcobacter. The paper also highlights that A. cryaerophilus and A. skirrowii are found frequently in diarrheal feces, indicating that Aliarcobacter should be studied further in livestock diarrheal diseases. Moreover, Aliarcobacter-infected farm animals can be treated with only a limited number of antibiotics, such as enrofloxacin, doxycycline, oxytetracycline, and gentamicin.

Tick-borne Diseases Transmission Research: Co-Feeding in Ticks

Tick-borne Diseases Transmission Research: Co-Feeding in Ticks Tick-borne diseases such as Lyme disease and tick-borne encephalitis are primarily transmitted during the blood feeding process, through systemic and co-feeding horizontal transmission routes. In this article, Research Professor Jianhong Wu explores transmission routes explaining that systemic transmission involves the transmission of the pathogen from infectious ticks to susceptible hosts, and the transmission of pathogen from infectious hosts back to susceptible feeding ticks. Co-feeding transmission provides an exchange of tick-borne pathogens between co-feeding infected and susceptible ticks (perhaps at different stages) directly even though pathogens have not been established within the reservoir host.

Some topical issues of prevention of salmonella infection in the production and consumption of chicken eggs: the role of disinfection in the context of antiepidemic measures

Chicken eggs and their processed products are food products that have valuable nutritional and dietary properties.However, the shell and the food eggs themselves can be infected with Salmonella pathogens — Salmonella Enteritidis and Salmonella Typhimurium. The prevalence of salmonella infection associated with the production and consumption of chicken eggs, economic losses from the diagnosis and treatment of patients predetermine the need for a comprehensive study of risk factors, the development and improvement of a set of measures to prevent this anthropozoon infection. An analytical review of the scientific literature and regulatory documents allowed us to conclude that for the prevention of salmonellosis, it is necessary to develop and implement a set of sanitary and veterinary measures aimed at breaking the vertical and horizontal transmission routes of infection, covering all links of the food chain (from laying hens to eating eggs), among which disinfection measures play an important role.

Neosporosis in sheep: A systematic review and meta-analysis of global seroprevalence and related risk factors

Neosporosis is recognized as the main cause of abortions in cattle worldwide and there is an increasing concern about its role in ovine reproductive losses; however, epidemiological studies regarding neosporosis in sheep are still limited. This meta-analysis aimed to estimate the global pooled seroprevalence and associated risk factors of ovine neosporosis. In the current report, a comprehensive strategy of search and data collection from 7 worldwide databases was performed. A final set of 73 studies (80 datasets) published from 2000 to 2021 were selected based on inclusion criteria, comprising data on 35,740 sheep (corresponding to 37,565 evaluated samples) from 30 countries worldwide. The global pooled seroprevalence of Neospora caninum infection in sheep estimated by the random-effects model was 13% (95% CI, 10-15) and showed high heterogeneity (Q = 5147.15, I2 = 98%, p< 0.001). Furthermore, by meta-analyses of subgroups it was demonstrated for the first time that seroprevalence significantly varied between continents (highest in Africa; 20%, 95% CI, 4-44), WHO regions (highest in African Region; 42%, 95% CI, 36-48), countries (highest in Colombia; 79%, 95% CI, 61-92%) and diagnostic methods (highest by IFAT; 17%, 95% CI, 12-23). Meta-regression indicated significant increasing trends in the prevalence of ovine neosporosis with decrease in geographical latitude (coefficient = -0.013; p<0.001), whereas longitude did not influence it (coefficient = -0.001; p=0.365). Regarding associated risk factors, older sheep were more likely to be infected with N. caninum than younger ones (OR 1.42; 95% CI 1.08–1.87), and sheep bred under intensive or semi-intensive systems resulted less susceptible to be seropositive than those bred under extensive system (OR 0.65; 95% CI 0.42-0.99 and OR 0.74; 95% CI 0.62–0.89, respectively). Conversely, no apparent association was found between seroprevalence and other variables, such as sex (OR 1.06; 95% CI 0.9–1.24), the presence of dogs on the farm (OR 1.15; 95% CI 0.63–2.12) or the presence of abortion (OR 1.80; 95% CI 0.87–3.74). In conclusion, the seroprevalence of ovine neosporosis is widely and heterogeneously distributed throughout the world, and it is negatively associated with increasing geographical latitude. In addition, age and extensive production system represent risk factors, which suggest that the horizontal transmission route is relevant for this host species. It is recommended to pay more attention to this disease and emphasize the global need for more indexed studies concerning the seroprevalence and risk factors of ovine neosporosis to better understand the epidemiology of this coccidian infection.

Microbiomes of the Sydney Rock Oyster are acquired through both vertical and horizontal transmission

BackgroundThe term holobiont is widely accepted to describe animal hosts and their associated microorganisms. The genomes of all that the holobiont encompasses, are termed the hologenome and it has been proposed as a unit of selection in evolution. To demonstrate that natural selection acts on the hologenome, a significant portion of the associated microbial genomes should be transferred between generations. Using the Sydney Rock Oyster (Saccostrea glomerata) as a model, we tested if the microbes of this broadcast spawning species could be passed down to the next generation by conducting single parent crosses and tracking the microbiome from parent to offspring and throughout early larval stages using 16S rRNA gene amplicon sequencing. From each cross, we sampled adult tissues (mantle, gill, stomach, gonad, eggs or sperm), larvae (D-veliger, umbo, eyed pediveliger, and spat), and the surrounding environment (water and algae feed) for microbial community analysis.ResultsWe found that each larval stage has a distinct microbiome that is partially influenced by their parental microbiome, particularly the maternal egg microbiome. We also demonstrate the presence of core microbes that are consistent across all families, persist throughout early life stages (from eggs to spat), and are not detected in the microbiomes of the surrounding environment. In addition to the core microbiomes that span all life cycle stages, there is also evidence of environmentally acquired microbial communities, with earlier larval stages (D-veliger and umbo), more influenced by seawater microbiomes, and later larval stages (eyed pediveliger and spat) dominated by microbial members that are specific to oysters and not detected in the surrounding environment.ConclusionOur study characterized the succession of oyster larvae microbiomes from gametes to spat and tracked selected members that persisted across multiple life stages. Overall our findings suggest that both horizontal and vertical transmission routes are possible for the complex microbial communities associated with a broadcast spawning marine invertebrate. We demonstrate that not all members of oyster-associated microbiomes are governed by the same ecological dynamics, which is critical for determining what constitutes a hologenome.

Reproduction and pathogenesis of short beak and dwarfish syndrome in Cherry Valley Pekin ducks infected with the rescued novel goose parvovirus

ABSTRACT Since the outbreak of short beak and dwarfish syndrome (SBDS) in Cherry Valley Pekin ducks in China, novel goose parvovirus (NGPV) has been isolated. Till now, little is known about the NGPV pathogenesis toward Cherry Valley Pekin ducks. Besides, due to detection of duck circovirus co-infection in SBDS clinical cases, whether sole NGPV infection can reproduce all the typical symptoms of SBDS remains unclear. In this study, based on the NGPV isolate SDJN19, an infectious plasmid clone pJNm containing the entire SDJN19 genome was constructed. Transfection of pJNm in embryonated duck eggs resulted in generation of the infectious virus carrying the genetic marker, named rJNm. rJNm infection of 2-day-old Cherry Valley Pekin ducks reproduced all the typical signs of SBDS, including beak atrophy, tongue protrusion, and growth retardation. rJNm can infect Cherry Valley Pekin ducks through the horizontal transmission route, and the infected ducks exhibited the characteristic SBDS symptoms. A high level of serum precipitation antibodies (above 5log2) were induced in the surviving ducks, however, high viral loads were still detected in the duck organs, suggesting persistent NGPV infection in ducks. By incorporating the homologous Rep1 and VP1 gene from classical GPV, two chimeric viruses rJN-cVP1 and rJN-cRep1 were generated. Duck infection tests revealed that the non-structural protein Rep1 played a crucial role in the NGPV pathogenicity. The present result lays a solid foundation for further exploring how the Rep protein contributes to the NGPV pathogenesis.

A Model for Brucellosis Disease Incorporating Age of Infection and Waning Immunity

This paper proposes a model for brucellosis transmission. The model takes into account the age of infection and waning immunity, that is, the progressive loss of immunity after recovery. Three routes of transmissions are considered: vertical transmission, and both direct and indirect routes of horizontal transmission. According to the well-posedness results, we provide explicit formulas for the equilibria. Next, we derive the basic reproduction number R0 and prove some stability results depending on the basic reproductive number. Finally, we perform numerical simulations using model parameters estimated from biological data to confirm our theoretical results. The results of these simulations suggest that for certain values of parameters, there will be periodic outbreaks of epidemics, and the disease will not be eradicated from the population. Our results also highlight the fact that the birth rate of cattle significantly influences the dynamics of the disease. The proposed model can be of a good use in studying the effects of vaccination on the cattle population.

Narrow Genetic Diversity of Wolbachia Symbionts in Acrididae Grasshopper Hosts (Insecta, Orthoptera).

Bacteria of the Wolbachia genus are maternally inherited symbionts of Nematoda and numerous Arthropoda hosts. There are approximately 20 lineages of Wolbachia, which are called supergroups, and they are designated alphabetically. Wolbachia strains of the supergroups A and B are predominant in arthropods, especially in insects, and supergroup F seems to rank third. Host taxa have been studied very unevenly for Wolbachia symbionts, and here, we turn to one of largely unexplored insect families: Acrididae. On the basis of five genes subject to multilocus sequence typing, we investigated the incidence and genetic diversity of Wolbachia in 41 species belonging three subfamilies (Gomphocerinae, Oedipodinae, and Podisminae) collected in Turkey, Kazakhstan, Tajikistan, Russia, and Japan, making 501 specimens in total. Our results revealed a high incidence and very narrow genetic diversity of Wolbachia. Although only the strains belonging to supergroups A and B are commonly present in present, the Acrididae hosts here proved to be infected with supergroups B and F without A-supergroup variants. The only trace of an A-supergroup lineage was noted in one case of an inter-supergroup recombinant haplotype, where the ftsZ gene came from supergroup A, and the others from supergroup B. Variation in the Wolbachia haplotypes in Acrididae hosts within supergroups B and F was extremely low. A comprehensive genetic analysis of Wolbachia diversity confirmed specific features of the Wolbachia allelic set in Acrididae hosts. This result can help to elucidate the crucial issue of Wolbachia biology: the route(s) and mechanism(s) of Wolbachia horizontal transmission.

Stability analysis and optimal control of production-limiting disease in farm with two vaccines

&lt;p style='text-indent:20px;'&gt;The transmission of production-limiting disease in farm, such as Neosporosis and Johne's disease, has brought a huge loss worldwide due to reproductive failure. This paper aims to provide a modeling framework for controlling the disease and investigating the spread dynamics of &lt;i&gt;Neospora caninum&lt;/i&gt;-infected dairy as a case study. In particular, a dynamic model for production-limiting disease transmission in the farm is proposed. It incorporates the vertical and horizontal transmission routes and two vaccines. The threshold parameter, basic reproduction number &lt;inline-formula&gt;&lt;tex-math id="M1"&gt;\begin{document}$ \mathcal{R}_0 $\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt;, is derived and qualitatively used to explore the stability of the equilibria. Global stability of the disease-free and endemic equilibria is investigated using the comparison theorem or geometric approach. On the case study of &lt;i&gt;Neospora caninum&lt;/i&gt;-infected dairy in Switzerland, sensitivity analysis of all involved parameters with respect to the basic reproduction number &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$ \mathcal{R}_0 $\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt; has been performed. Through Pontryagin's maximum principle, the optimal control problem is discussed to determine the optimal vaccination coverage rate while minimizing the number of infected individuals and control cost at the same time. Moreover, numerical simulations are performed to support the analytical findings. The present study provides useful information on the understanding of production-limiting disease prevention on a farm.&lt;/p&gt;

A prevalence survey of Wolbachia in butterflies from southern China

AbstractWolbachia is a maternally inherited endosymbiont of the phylum α‐Proteobacteria that is found widely in arthropods and nematodes. Wolbachia is the most common endosymbiont in butterflies (Lepidoptera) and it manipulates host reproduction mainly by inducing cytoplasmic incompatibility, male killing, and feminization. We studied the prevalence patterns of Wolbachia in 52 butterfly species from five families collected in southern China. A substantial infection incidence was determined in the study region, where 18 out of the 52 butterfly species (35%) were infected, including members of the families Hesperiidae, Lycaenidae, Nymphalidae, Papilionidae, and Pieridae. Based on multi‐locus sequence typing (MLST) and Wolbachia cell surface protein (WSP) profiles, seven unique sequence types (STs) and six wsp alleles were detected. One MLST haplotype was detected for the first time (ST‐wPcau). Most of the identified Wolbachia STs belonged to supergroup B, those found in two Ypthima spp. belonged to supergroup A. Many STs were shared among various insect species; the most widespread strain in our samples, ST‐41, was detected in seven butterfly species from four families. We discuss the potential horizontal transmission routes of Wolbachia, as well as the suitability of the Wolbachia strain typing method.

Defensive Symbionts and the Evolution of Parasitoid Host Specialization

Insect host-parasitoid interactions abound in nature and are characterized by a high degree of host specialization. In addition to their behavioral and immune defenses, many host species rely on heritable bacterial endosymbionts for defense against parasitoids. Studies on aphids and flies show that resistance conferred by symbionts can be very strong and highly specific, possibly as a result of variation in symbiont-produced toxins. I argue that defensive symbionts are therefore an important source of diversifying selection, promoting the evolution of host specialization by parasitoids. This is likely to affect the structure of host-parasitoid food webs. I consider potential changes in terms of food web complexity, although the nature of these effects will also be influenced by whether maternally transmitted symbionts have some capacity for lateral transfer. This is discussed in the light of available evidence for horizontal transmission routes. Finally, I propose that defensive mutualisms other than microbial endosymbionts may also exert diversifying selection on insect parasitoids.

Equine parvovirus hepatitis.

Equine parvovirus hepatitis (EqPV‐H) was first described in 2018 in a fatal case of Theiler's disease which followed the administration of an equine‐origin biological product. The virus has since been frequently identified in serum and liver tissue of horses affected by Theiler's disease—an acute, severe hepatitis characterised by fulminant hepatic necrosis with a fatal outcome in most cases. EqPV‐H is hepatotropic, appears to be associated with subclinical to severe hepatitis in horses, and is a likely cause of Theiler's disease. Although this disease is most frequently reported following the administration of equine‐origin biological products, it can also occur among in‐contact horses. Horizontal transmission may be iatrogenic, via contaminated equine‐origin biological products such as equine serum, botulism or tetanus antitoxin, and mesenchymal stem cells or by means of the oral route of infection. Other horizontal transmission routes, for example, arthropod vectors, warrant further investigation. A worldwide prevalence of EqPV‐H antibodies and DNA has been reported in asymptomatic horses. EqPV‐H‐positive horses suffering from acute, severe hepatitis have reportedly developed clinical signs including icterus, lethargy, inappetence, and neurological abnormalities and have had increased liver‐associated biochemistry parameters recorded. The most common histopathological abnormalities of the liver have been hepatocellular necrosis, collapse of the lobular architecture, and lymphocytic infiltration. Most horses infected experimentally with EqPV‐H have developed subclinical hepatitis, and close temporal associations between peak viraemia, seroconversion, and the onset of hepatitis have been observed. Based on strong evidence indicating that EqPV‐H causes hepatitis in horses, veterinarians should consider this virus an important differential diagnosis in such cases. Potential risks associated with the administration of equine‐origin biological products must be emphasised.

Studying the Regional Transmission and Inferring the Local/External Contribution of Fine Particulate Matter Based on Multi-Source Observation: A Case Study in the East of North China Plain

The regional transmission characteristics as well as the local emission and external transmission contribution of fine particulate matter in the eastern North China Plain were investigated using multisource data. Himawari-8 aerosol optical depth can represent the whole layer of air pollution situation; hourly aerosol optical depth were used to reconstruct the route of fine particulate matter horizontal transmission, and the transmission speed was calculated and compared with the near-surface wind speed. A case study conducted on 22 September 2019 showed the pollutant was mainly transmitted from Tangshan to Dezhou, and the transmission speed was greater than the near-surface wind speed. We also found that pollution air mass had 2–3 h of diffusion delay in the near-surface pollutant monitoring results. In addition, the vertical diffusion of pollution mainly occurred at low altitude below 1.8 km. The contribution of local emission and external transmission was inferred in this study with the help of the WRF-Chem model, the pollution in the northeastern portion of the study area mainly derived from local emissions, while the southwestern portion of the study area was mainly affected by external transport. Among them, the local emission accounted for 79.15% of the pollution in Tangshan, while the external transmission contributed 60.28% of the fine particulate matter concentration in Dezhou.

Tissue Tropisms and Transstadial Transmission of a Rickettsia Endosymbiont in the Highland Midge, Culicoides impunctatus (Diptera: Ceratopogonidae).

Rickettsia is a genus of intracellular bacteria which can manipulate host reproduction and alter sensitivity to natural enemy attack in a diverse range of arthropods. The maintenance of Rickettsia endosymbionts in insect populations can be achieved through both vertical and horizontal transmission routes. For example, the presence of the symbiont in the follicle cells and salivary glands of Bemisia whiteflies allows Belli group Rickettsia transmission via the germ line and plants, respectively. However, the transmission routes of other Rickettsia bacteria, such as those in the Torix group of the genus, remain underexplored. Through fluorescence in situ hybridization (FISH) and transmission electron microscopy (TEM) screening, this study describes the pattern of Torix Rickettsia tissue tropisms in the highland midge, Culicoides impunctatus (Diptera: Ceratopogonidae). Of note is the high intensity of infection of the ovarian suspensory ligament, suggestive of a novel germ line targeting strategy. Additionally, localization of the symbiont in tissues of several developmental stages suggests transstadial transmission is a major route for ensuring maintenance of Rickettsia within C. impunctatus populations. Aside from providing insights into transmission strategies, the presence of Rickettsia bacteria in the fat body of larvae indicates potential host fitness and vector capacity impacts to be investigated in the future.IMPORTANCE Microbial symbionts of disease vectors have garnered recent attention due to their ability to alter vectorial capacity. Their consideration as a means of arbovirus control depends on symbiont vertical transmission, which leads to spread of the bacteria through a population. Previous work has identified a Rickettsia symbiont present in several species of biting midges (Culicoides spp.), which transmit bluetongue and Schmallenberg arboviruses. However, symbiont transmission strategies and host effects remain underexplored. In this study, we describe the presence of Rickettsia in the ovarian suspensory ligament of Culicoides impunctatus Infection of this organ suggests the connective tissue surrounding developing eggs is important for ensuring vertical transmission of the symbiont in midges and possibly other insects. Additionally, our results indicate Rickettsia localization in the fat body of Culicoides impunctatus As the arboviruses spread by midges often replicate in the fat body, this location implies possible symbiont-virus interactions to be further investigated.