Vector-Borne and Zoonotic Diseases

Powassan virus (POWV, Flaviviridae) is the only North American member of the tick-borne encephalitis serogroup of flaviviruses. It is transmitted to small- and medium-sized mammals by Ixodes scapularis, Ixodes cookei, and several other Ixodes tick species. Humans become infected with POWV during spillover transmission from the natural transmission cycles. In humans, POWV is the causative agent of a severe neuroinvasive illness with 50% of survivors displaying long-term neurological sequelae. POWV was recognized as a human pathogen in 1958 when a young boy died of severe encephalitis in Powassan, Ontario, and POWV was isolated from the brain autopsy of this case. Two distinct genetic lineages of POWV are now recognized: POWV (lineage I) and deer tick virus (lineage II). Since the index case in 1958, over 100 human cases of POWV have been reported, with an apparent rise in disease incidence in the past 16 years. This recent increase in cases may represent a true emergence of POWV in regions where the tick vector species are prevalent, or it could represent an increase in POWV surveillance and diagnosis. In the past 5 years, both basic and applied research for POWV disease has intensified, including phylogenetic studies, field surveillance, case studies, and animal model development. This review provides an overview of POWV, including the epidemiology, transmission, clinical disease, and diagnosis of POWV infection. Recent research developments and future priorities with regard to the disease are emphasized.

Powassan/Deer Tick Virus (POWV/DTV) is an emerging cause of arboviral neuroinvasive disease in the upper Midwest. These studies describe the prevalence and geographic distribution of Wisconsin ticks carrying POWV/DTV as well as the high frequency of Ixodes scapularis ticks coinfected with both POWV/DTV and Borrelia burgdorferi, the causative agent of Lyme disease. These findings suggest that concurrent transmission of POWV/DTV and B. Burgdorferi from coinfected ticks is likely to occur in humans.

Maintenance of sylvatic plague in prairie dogs (Cynomis spp.) was once thought unlikely due to high mortality rates; yet more recent findings indicate that low-level enzootic plague may be maintained in susceptible prairie dog populations. Another hypothesis for the maintenance of sylvatic plague involves small mammals, other than prairie dogs, as an alternative reservoir in the sylvatic plague system. These hypotheses, however, are not mutually exclusive, as both prairie dogs and small mammals could together be driving sylvatic cycles of plague. The concept of a bridging vector has been used to explain the transmission of pathogens from one host species to another. In the case of sylvatic plague, this would require overlap in fleas between small mammals and prairie dogs, and potentially other species such as carnivores. Our goal was to evaluate the level of flea sharing between black-tailed prairie dogs (Cynomis ludovicianus) and other small mammals in a mixed-grass prairie in South Dakota. We investigated the species richness of small mammals and small-mammal fleas in a mixed-grass prairie system and compared findings with previous studies from a short-grass ecosystem in Colorado. Over the summer field seasons 2014–2016 we live-trapped small mammals, collected fleas, and showed differences between both the flea and small mammal composition of the two systems. We also recorded higher densities of deer mice and lower densities of northern grasshopper mice in mixed versus shortgrass prairies. We confirmed, as is the case in shortgrass prairies, a lack of substantial flea species overlap on small mammal hosts and fleas from prairie dogs and their burrows. Moreover this study demonstrates that although small mammals may not play a large part in interepizootic plague cycling in shortgrass prairie ecosystems, their role in mixed-grass prairies requires further evaluation.

Mycoplasma pulmonis is a naturally occurring respiratory pathogen in rodents. To date, this pathogen was not isolated from humans. This study aimed to evaluate the prevalence and seropositivity to M. pulmonis in humans who have had direct contact with rats. Moreover, the prevalence of M. pulmonis in pet and laboratory rats was assessed. Overall, 131 and 235 oropharyngeal swab samples were collected from human individuals and rats, respectively. In humans, M. pulmonis was detected by PCR in 21 of 86 pet rat keepers (24.42%), 10 of 13 technicians (76.32%), and 8 of 32 (25.0%) veterinarians. In rats, M. pulmonis was identified by PCR in 86 of 122 pet rats (70.49%) and 56 of 113 (49.56%) laboratory rats. Seroprevalence in humans was examined by screening sera from 44 individuals for M. pulmonis-specific IgG using ELISA. In total, 26 out of 44 (59.09%) humans were seropositive to M. pulmonis (4 out of 9 technicians, 8 of 12 veterinarians, and 15 of 23 pet rat keepers).The high antibody titer was found in 4 individuals (2 pet rat keepers and 2 veterinarians), whereas the moderate and low antibody titers were found in 8 and 14 individuals, respectively. The high antibody titer found in humans might indicate an active infection. However, it is unknown whether the presence of M. pulmonis in humans might be associated with disease and whether the foreign Mycoplasma can survive for long in its new environment.

Toxoplasma gondii is a protozoan parasite with both public health and veterinary importance. The aims of our study were to estimate the T. gondii seroprevalence in sheep in Latvia and to evaluate potential risk factors for seropositivity. The blood samples investigated were collected from 1039 sheep from 84 farms between January 2012 and April 2013. The sera were tested for immunoglobulin G antibodies against T. gondii using an in-house enzyme-linked immunosorbent assay. Antibodies against T. gondii were detected in 179 (17.2%) of the sheep, and at least one seropositive sheep was found on 37 (44.0%) of the farms. The seroprevalence was significantly higher in adult (over 1 year old) sheep than in juveniles—the adult sheep had 1.8 times higher odds to test seropositive than did the juveniles. The seroprevalence was significantly higher in Latvian Dark Headed sheep than in crossbreed and German Merino sheep. Sheep from large herds (with more than 100 sheep), as well as those from farms with cattle, had higher odds to test seropositive, whereas the presence of poultry on the farm appeared as a protecting factor. The results show that sheep in Latvia are commonly exposed to T. gondii.

Bartonella spp. are parasites of mammalian erythrocytes and endothelial cells, transmitted by blood-feeding arthropod ectoparasites. Different species of rodents may constitute the main hosts of Bartonella, including several zoonotic species of Bartonella. The aim of this study was to identify and compare Bartonella species and genotypes isolated from rodent hosts from the South Sinai, Egypt. Prevalence of Bartonella infection was assessed in rodents (837 Acomys dimidiatus, 73 Acomys russatus, 111 Dipodillus dasyurus, and 65 Sekeetamys calurus) trapped in 2000, 2004, 2008, and 2012 in four dry montane wadis around St. Katherine town in the Sinai Mountains. Total DNA was extracted from blood samples, and PCR amplification and sequencing of the Bartonella-specific 860-bp gene fragment of rpoB and the 810-bp gene fragment of gltA were used for molecular and phylogenetic analyses. The overall prevalence of Bartonella in rodents was 7.2%. Prevalence differed between host species, being 30.6%, 10.8%, 9.6%, and 3.6% in D. dasyurus, S. calurus, A. russatus, and A. dimidiatus, respectively. The phylogenetic analyses of six samples of Bartonella (five from D. dasyurus and one from S. calurus) based on a fragment of the rpoB gene, revealed the existence of two distinct genetic groups (with 95–96% reciprocal sequence identity), clustering with several unidentified isolates obtained earlier from the same rodent species, and distant from species that have already been described (90–92% of sequence identity to the closest match from the GenBank reference database). Thus, molecular and phylogenetic analyses led to the description of two species: Candidatus Bartonella fadhilae n. sp. and Candidatus Bartonella sanaae n. sp. The identification of their vectors and the medical significance of these species need further investigation.

Toxoplasma gondii is a protozoan parasite with a broad ecological valence, which has been detected in a wide range of hosts and landscapes. Although the genus is considered monospecific, in recent years it has been demonstrated to exhibit more genetic variability than previously known. In Mexico, there are few genotyping studies, which suggest that classical, autochthonous, and atypical strains are circulating. The goal of this study was to describe T. gondii genetic diversity in naturally infected sheep from Colima, Mexico. This is a good site to study ecological aspects of this parasite since it is located between the Nearctic and Neotropical ecozones and it includes domestic and wild risks for transmission. We analyzed 305 tissue samples of semicaptive sheep from six coastal and central zones of Colima and border zones of Michoacán. We used an 803 bp amplicon of the B1 gene to genotype T. gondii and seroprevalence was determined by ELISA. Indexes for genetic diversity and genetic differentiation were calculated and compared with reference strains from North America (NA) and South America (SA). Twenty-three tissue samples were positive for the B1 gene by PCR, which were sequenced. Crude prevalence was 24.4%. The genetic analysis showed 16 variable sites along the 803 bp region that grouped all sequences into 13 haplotypes in the phylogenetic tree. Bayesian and haplotype network analysis showed nine new B1-types, of which three were frequent and six had unique alleles. Comparisons among sequence sets revealed that the Mexican population had lower differentiation than SA and an intermediate genetic variability between South America and North America. The B1 gene analysis showed new T. gondii haplotypes in naturally infected sheep; therefore, this marker could be initially used in molecular screening studies to identify potentially virulent genotypes of this parasite using natural host samples directly.

Information regarding the infection rate and genotype shifts for Japanese encephalitis virus (JEV) are important for JE vaccine application. In Jiangsu province, China, which is one of the provinces with a high prevalence of JE, JEV infection in swine and mosquitoes in certain cities has only been investigated in 2008–2009. Lianyungang City has one of the highest numbers of JE cases in Jiangsu province, and it has a high risk of JEV invasion via migrant birds. JEV infection in vectors in Lianyungang City, which has urban and rural parts, has not been investigated. In 2015–2016, we collected mosquitoes in cowsheds with ultraviolet light traps and detected JEV by reverse transcription-polymerase chain reaction (RT-PCR) method in Culex tritaeniorhynchus in Xintan village, Xuzhuang village, and Xiaogaozhuang village in Lianyungang City, China. The proportion of positive pools, which is calculated by the number of infected pools to the total number of pools tested in these villages, were 16.67%, 20.00%, and 4.17%, respectively, and the minimum infection rates, which is calculated as the ratio of the number of positive pools to the total number of mosquitoes tested, were 3.33‰, 4.00‰, and 0.83‰, respectively. Four JEV strains from positive samples were coded as LYG-1, LYG-2, LYG-3, and LYG-4, and the complete E genes were sequenced. Furthermore, the complete genome of LYG-3 was sequenced. The phylogenetic analysis indicated that all the four JEV strains belonged to genotype I-b. This is the first report of genotype I JEV strain in Jiangsu province. The high JEV infection rate in Culex tritaeniorhynchus indicated a high risk of JE reemergence in Lianyungang. The detected JEV strains may have similar antigenicity to that of SA14-14-2 according to molecular characters. These findings suggest that the vaccine can still be effective in Lianyungang.

In contrast to animals, Crimean–Congo hemorrhagic fever (CCHF) causes a severe disease in humans with a high mortality rate. The etiological agent, CCHF virus (CCHFV), can be transmitted by argasid and ixodid ticks, but arachnids of the genus Hyalomma, followed by Rhipicephalus and Dermacentor serve as the major vectors of this virus. The goal of the study was to assess the epidemiological situation of CCHFV infection in cattle in south-east Poland, and survey for potential tick vector species. A total of 592 bovine blood samples from animals located in the southernmost region in Poland were tested by IgG sandwich enzyme-linked immunosorbent assay. Ticks (n = 993) from south-east Poland were collected from dogs, cats, cattle, and horses and tested by RT-PCR. All 592 serum samples were negative for IgG antibodies to CCHFV. Of the ticks collected, 125 were Dermacentor reticulatus and 868 represented Ixodes ricinus, both species are regarded as potential vectors of CCHFV. All tick samples were negative for the presence of CCHFV. Considering the zoonotic nature, public health importance, and the virus increasing spread, it was prudent to assess the seroprevalence of CCHFV in the south-east area of Poland, bordering with CCHFV endemic areas. It seems unlikely that CCHFV infection will suddenly spread in Poland, but considering the multiple possibilities of the virus introduction, serosurveys and vector biosurveillance should be conducted at regular intervals.

Previous molecular-based studies have identified microorganisms of zoonotic and human nature in surface waters. Contaminated water can lead to human health issues, and the detection of pathogenic microorganisms is a valuable tool for the prevention of their spread. Water samples were taken from the River Tiber in and out of the city of Rome. Genetic analysis of the sequences obtained showed the presence of Coxiella burnetii in both the analyzed sites. Blast analysis showed that two sequences were identical to each other. Sequences from the polluted site showed high homology with different strains of C. burnetii. In this article, we report for the first time the presence of C. burnetii in environmental waters.

Toxoplasma gondii is an important food-borne zoonotic protozoan parasite, which can infect endothermic animals, including pigs. However, data on T. gondii in slaughter pigs in Shaanxi Province were still lacking. To detect the seroprevalence and analyze the risk factors of T. gondii infection in slaughter pigs in Shaanxi Province, Northwestern China, a total of 784 serum samples were collected from four administrative regions and detected by indirect hemagglutination test for T. gondii infection. Antibodies to T. gondii were found in 19.9% (156/784) slaughter pigs. Moreover, the seropositive rate was different among rearing systems (31% in nonintensive pig farms and 6.7% in intensive pig farms), genders (19.8% in male and 20.0% in female), and regions (ranging from 6.7% in Shenmu to 38.2% in Zhouzhi). Rearing system and region were identified as risk factors for T. gondii infection. These results showed that T. gondii is highly prevalent in slaughter pigs in Shaanxi Province, and it could cause a serious risk to public health. This study provided fundamental information for the prevention and control of T. gondii infection in slaughter pigs in China.