Seoul Virus Tropism and Pathology in Naturally Infected Feeder Rats

Seoul virus (SEOV) is a zoonotic orthohantavirus carried by black and brown rats, and can cause hemorrhagic fever with renal syndrome in humans. Human cases of SEOV virus infection have most recently been reported in the USA, United Kingdom, France and the Netherlands and were primarily associated with contact with pet rats and feeder rats. Infection of rats results in an asymptomatic but persistent infection. Little is known about the cell tropism of SEOV in its reservoir and most available data is based on experimental infection studies in which rats were inoculated via a route which does not recapitulate virus transmission in nature. Here we report the histopathological analysis of SEOV cell tropism in key target organs following natural infection of a cohort of feeder rats, comprising 19 adults and 11 juveniles. All adult rats in this study were positive for SEOV specific antibodies and viral RNA in their tissues. One juvenile rat was seropositive, but negative in the rRT-PCR. Of the 19 adult rats of which subsequently additional organs were tested, SEOV RNA was detected in all lungs, followed by kidney (79%) and liver (74%). Histopathologic changes associated with SEOV infection were primarily found in the liver, consistent with a pathological diagnosis of a mild hepatitis. In conclusion, natural SEOV infection results in mild inflammation of the liver in the absence of clinical disease

First human case of tick-borne encephalitis virus infection acquired in the Netherlands, July 2016

In July 2016, the first autochthonous case of tick-borne encephalitis was diagnosed in the Netherlands, five days after a report that tick-borne encephalitis virus (TBEV) had been found in Dutch ticks. A person in their 60s without recent travel history suffered from neurological symptoms after a tick bite. TBEV serology was positive and the tick was positive in TBEV qRT-PCR. TBEV infection should be considered in patients with compatible symptoms in the Netherlands

Bayesian Binary Mixture Models as a Flexible Alternative to Cut-Off Analysis of ELISA Results, a Case Study of Seoul Orthohantavirus.

Serological assays, such as the enzyme-linked immunosorbent assay (ELISA), are popular tools for establishing the seroprevalence of various infectious diseases in humans and animals. In the ELISA, the optical density is measured and gives an indication of the antibody level. However, there is variability in optical density values for individuals that have been exposed to the pathogen of interest, as well as individuals that have not been exposed. In general, the distribution of values that can be expected for these two categories partly overlap. Often, a cut-off value is determined to decide which individuals should be considered seropositive or seronegative. However, the classical cut-off approach based on a putative threshold ignores heterogeneity in immune response in the population and is thus not the optimal solution for the analysis of serological data. A binary mixture model does include this heterogeneity, offers measures of uncertainty and the direct estimation of seroprevalence without the need for correction based on sensitivity and specificity. Furthermore, the probability of being seropositive can be estimated for individual samples, and both continuous and categorical covariates (risk-factors) can be included in the analysis. Using ELISA results from rats tested for the Seoul orthohantavirus, we compared the classical cut-off method with a binary mixture model set in a Bayesian framework. We show that it performs similarly or better than cut-off methods, by comparing with real-time quantitative polymerase chain reaction (RT-qPCR) results. We therefore recommend binary mixture models as an analysis tool over classical cut-off methods. An example code is included to facilitate the practical use of binary mixture models in everyday practice

Emergence of tick-borne encephalitis (TBE) in the Netherlands.

Recently, tick-borne encephalitis virus (TBEV) was detected in the Netherlands for the first time, in ticks collected in 2015 in the National Park Sallandse heuvelrug in response to the detection of anti-TBEV antibodies in roe deer. Hereafter, two human cases of autochthonous TBE have been reported, occurring in 2016. One case was geographically linked to the area of the previously reported ticks, which harbored a genetically divergent TBEV-Eu strain variant (TBEV-NL). So far these are the few reported events that point to endemic transmission of TBEV in the Netherlands and the true prevalence of TBEV and TBE disease in the Netherlands and its impact on the human population remains to be determined. We describe the third human case, identified in 2017, which geographically clusters with the aforementioned case and TBEV-positive ticks. We also describe the identification of another TBEV-NL-positive tick in the Netherlands, collected 2 years after the initial find in that same region (in 2017). These observations support the concept of continued circulation of TBEV-NL and the presence of a possible TBEV hot spot in the Sallandse Heuvelrug region

Emergence of tick-borne encephalitis (TBE) in the Netherlands.

Recently, tick-borne encephalitis virus (TBEV) was detected in the Netherlands for the first time, in ticks collected in 2015 in the National Park Sallandse heuvelrug in response to the detection of anti-TBEV antibodies in roe deer. Hereafter, two human cases of autochthonous TBE have been reported, occurring in 2016. One case was geographically linked to the area of the previously reported ticks, which harbored a genetically divergent TBEV-Eu strain variant (TBEV-NL). So far these are the few reported events that point to endemic transmission of TBEV in the Netherlands and the true prevalence of TBEV and TBE disease in the Netherlands and its impact on the human population remains to be determined. We describe the third human case, identified in 2017, which geographically clusters with the aforementioned case and TBEV-positive ticks. We also describe the identification of another TBEV-NL-positive tick in the Netherlands, collected 2 years after the initial find in that same region (in 2017). These observations support the concept of continued circulation of TBEV-NL and the presence of a possible TBEV hot spot in the Sallandse Heuvelrug region

Occurrence of <i>Rickettsia</i> spp., <i>Hantaviridae</i>, <i>Bartonella</i> spp. and <i>Leptospira</i> spp. in European Moles (<i>Talpa europaea</i>) from the Netherlands

The European mole (Talpa europaea) has a widespread distribution throughout Europe. However, little is known about the presence of zoonotic pathogens in European moles. We therefore tested 180 moles from the middle and the south of the Netherlands by (q)PCR for the presence of multiple (tick-borne) zoonotic pathogens. Spotted fever Rickettsia was found in one (0.6%), Leptospira spp. in three (1.7%), Bartonella spp. in 69 (38.3%) and Hantaviridae in 89 (49.4%) of the 180 moles. Infections with Anaplasma phagocytophilum, Babesia spp., Neoehrlichia mikurensis, Borrelia spp., Spiroplasma spp. and Francisella tularensis were not found. In addition, in a subset of 35 moles no antibodies against Tick-borne encephalitis virus were found. The obtained sequences of Bartonella spp. were closely related to Bartonella spp. sequences from moles in Spain and Hungary. The Hantaviridae were identified as the mole-borne Nova virus, with high sequence similarity to sequences from other European countries, and Bruges virus. Though the zoonotic risk from moles appears limited, our results indicate that these animals do play a role in multiple host-pathogen cycles

Occurrence of spp., , spp. and spp. in European Moles () from the Netherlands.

The European mole (Talpa europaea) has a widespread distribution throughout Europe. However, little is known about the presence of zoonotic pathogens in European moles. We therefore tested 180 moles from the middle and the south of the Netherlands by (q)PCR for the presence of multiple (tick-borne) zoonotic pathogens. Spotted fever Rickettsia was found in one (0.6%), Leptospira spp. in three (1.7%), Bartonella spp. in 69 (38.3%) and Hantaviridae in 89 (49.4%) of the 180 moles. Infections with Anaplasma phagocytophilum, Babesia spp., Neoehrlichia mikurensis, Borrelia spp., Spiroplasma spp. and Francisella tularensis were not found. In addition, in a subset of 35 moles no antibodies against Tick-borne encephalitis virus were found. The obtained sequences of Bartonella spp. were closely related to Bartonella spp. sequences from moles in Spain and Hungary. The Hantaviridae were identified as the mole-borne Nova virus, with high sequence similarity to sequences from other European countries, and Bruges virus. Though the zoonotic risk from moles appears limited, our results indicate that these animals do play a role in multiple host-pathogen cycles

Detection of tick-borne encephalitis virus in ear tissue and dried blood spots from naturally infected wild rodents.

Tick-borne encephalitis virus (TBEV) can cause severe neurological disease in humans. Its geographical distribution is expanding in Western Europe with unresolved causes and spatial patterns, necessitating enhanced surveillance. Monitoring the virus in the environment is complicated, as it usually relies on destructive sampling of small rodents to test organs for TBEV, which in addition to ethical considerations also raises issues for long-term monitoring or longitudinal studies. Moreover, even when the virus is not detected in the blood or organs of the rodent, TBEV can still be transmitted from an infected tick to uninfected ticks feeding nearby. This is due to the ability of TBEV to replicate and migrate locally within the epidermis of small mammals, including those that do not appear to have systemic infection. This suggests that the virus may be detectable in skin biopsies, which has been confirmed in experimentally infected laboratory rodents, but it remains unknown if this sample type may be a viable alternative to destructively obtained samples in the monitoring of natural TBEV infection. Here we test ear tissue and dried blood spot (DBS) samples from rodents to determine whether TBEV-RNA can be detected in biological samples obtained non-destructively. Methods: Rodents were live-trapped and sampled at three woodland areas in The Netherlands where presence of TBEV has previously been recorded. Ear tissue (n = 79) and DBSs (n = 112) were collected from a total of 117 individuals and were tested for TBEV-RNA by real-time RT-PCR. Results: TBEV-RNA was detected in five rodents (4.3% of tested individuals), all of which had a TBEV-positive ear sample, while only two out of four of these individuals (for which a DBS was available) had a positive DBS. This equated to 6.3% of ear samples and 1.8% of DBSs testing positive for TBEV-RNA. Conclusions: We provide the first evidence to our knowledge that TBEV-RNA can be detected in samples obtained non-destructively from naturally infected wild rodents, providing a viable sampling alternative suitable for longitudinal surveillance of the virus. Graphical Abstract: [Figure not available: see fulltext.]

Seoul Virus in Pet and Feeder Rats in The Netherlands.

Seoul virus (SEOV) is a zoonotic orthohantavirus carried by rats. In humans, SEOV can cause hemorrhagic fever with renal syndrome. Recent human SEOV cases described in the USA, United Kingdom, France and the Netherlands were associated with contact with pet or feeder rats. The prevalence of SEOV in these types of rats is unknown. We collected 175 pet and feeder rats (Rattus norvegicus) from private owners, ratteries and commercial breeders/traders in the Netherlands. Lung tissue of the rats was tested using a SEOV real-time RT-qPCR and heart fluid was tested for the presence of antibodies against SEOV. In all three investigated groups, RT-qPCR-positive rats were found: in 1/29 rats from private owners (3.6%), 2/56 rats from ratteries (3.4%) and 11/90 rats from commercial breeders (12.2%). The seroprevalence was largely similar to the prevalence calculated from RT-qPCR-positive rats. The SEOV sequences found were highly similar to sequences previously found in domesticated rats in Europe. In conclusion, SEOV is spread throughout different populations of domesticated rats

Seoul Virus in Pet and Feeder Rats in The Netherlands.

Seoul virus (SEOV) is a zoonotic orthohantavirus carried by rats. In humans, SEOV can cause hemorrhagic fever with renal syndrome. Recent human SEOV cases described in the USA, United Kingdom, France and the Netherlands were associated with contact with pet or feeder rats. The prevalence of SEOV in these types of rats is unknown. We collected 175 pet and feeder rats (Rattus norvegicus) from private owners, ratteries and commercial breeders/traders in the Netherlands. Lung tissue of the rats was tested using a SEOV real-time RT-qPCR and heart fluid was tested for the presence of antibodies against SEOV. In all three investigated groups, RT-qPCR-positive rats were found: in 1/29 rats from private owners (3.6%), 2/56 rats from ratteries (3.4%) and 11/90 rats from commercial breeders (12.2%). The seroprevalence was largely similar to the prevalence calculated from RT-qPCR-positive rats. The SEOV sequences found were highly similar to sequences previously found in domesticated rats in Europe. In conclusion, SEOV is spread throughout different populations of domesticated rats