Induction of humoral and cellular immune responses to COVID-19 mRNA and vector vaccines: A prospective cohort study in Bulgarian healthcare workers.

Installing efficient protective immunity by anti-SARS-CoV-2 vaccines is the only current means to overcome coronavirus disease 2019 pandemics. The cellular and humoral immune responses induced with an messenger RNA (mRNA) (BNT162b2) or with a vector (ChAdOx1nCoV-19) vaccine among Bulgarian healthcare workers (n = 123, aged 23-71 years) were studied in the course of 16 weeks after priming. Receptor-binding domain (RBD)-blocking Abs and SARS-CoV-2 RBD immunoglobulin A  (IgA) were evaluated in parallel with interferon gamma (IFNγ)-producing virus-specific T cells. Both vaccines induced RBD-blocking Abs in 100% of the participants after complete immunization while the levels of protection after a single dose largely varied (22%-98%). Advanced age had a negative impact on the level and longevity of virus-neutralizing activity induced by one dose mRNA, but not by the vector vaccine. RBD-binding IgA was detected in 100% of tested donors from the mRNA vaccine cohort, and in 67% of tested from the vector vaccine cohort, at least 1 month after completed immunization. One month after completing mRNA immunization, the number of IFNγ-producing T cells correlated significantly with the levels of RBD-specific IgA and virus-neutralizing activity induced after priming. Enumeration of circulating virus-specific IFNγ+ T cells is not recommended for evaluation of protective immunity as their detection may require longer stimulation beyond the firstmonth postimmunization. In conclusion, BNT162B2 and ChAdOx1nCoV-19 induced potent and comparable humoral and cellular anti-SARS-CoV-2 immune responses, peaking between 10 and 30 days after complete immunization. A single dose of any vaccine did not induce adequate protection in a great part of donors, making the shorter interval between mRNA vaccine doses preferable in the settings of increased risk of infection.

A nationwide seroprevalence screening for West Nile virus and Tick-borne encephalitis virus in the population of Bulgaria.

To assess local circulation and risk for human infections with West Nile virus (WNV) and Tick-borne encephalitis virus (TBEV) in Bulgaria, a nationwide seroprevalence study was conducted. In total, 1451 residents of all 28 districts in Bulgaria were tested for WNV-specific and TBEV-specific IgG antibodies. The survey found overall seroprevalence of 1.5% and 0.6%, respectively. The highest WNV seroprevalence was found in Sofia Province and districts near the river Danube. TBEV circulation was detected among residents of six districts. The results showed that the two virus infections seem to be more wide-spread in the country as has been described.

Detection of Dobrava hantavirus RNA in Apodemus mice in Bulgaria.

Several Hantaviruses cause hemorrhagic fever with renal syndrome (HFRS) in Europe: Dobrava-Belgrade virus (DOBV), Puumala, Saaremaa, Sochi, and Seoul virus. Although HFRS is endemic in Bulgaria, genome sequences of hantaviruses have never been detected in wild rodents. To identify rodent reservoirs, a total of 691 rodents from three endemic regions were trapped in 2011-2012 and screened by TaqMan RT-PCR for detection of hantaviral genomic RNA. Partial small (S) and/or large (L)-segment sequences were recovered from six Apodemus mice: five of the species A. flavicollis and one A. agrarius. Phylogenetic analysis revealed that all recovered sequences belonged to DOBV. On the phylogenetic trees, the novel Bulgarian hantavirus sequences clustered together with sequences of established previously DOBV variants recovered from Bulgarian HFRS patients and also with variants found in wild rodents trapped in Slovenia, Greece, and Slovakia. One of the novel Bulgarian DOBV S-sequences from A. agrarius was related closely to DOBV sequences recovered from A. flavicollis, suggesting a spillover of DOBV from its natural host to A. agrarius mice. The results of this study confirmed the circulation of DOBV in wild rodents in Bulgaria. The complexity of the epidemiological situation in the Balkans requires further studies of hantaviruses in rodent hosts and human HFRS cases.

Seroprevalance of Crimean-Congo haemorrhagic fever in Bulgarian livestock.

Crimean-Congo haemorrhagic fever (CCHF) is a tick-borne zoonotic disease. Over the past decade, CCHF cases in humans have emerged in Turkey and reemerged in the Balkan countries, Ukraine and Tajikistan. Occupational contact with infected livestock has been recognized as a common cause of the disease. A cross-sectional seroprevalence study in livestock was conducted in farming communities of an endemic area in Bulgaria, southeastern Europe. Overall, 72% of the tested animals were positive for IgG antibodies to CCHF virus. By the time the animals were one-year old almost 50% had serologic evidence of CCHF infection, and by two years already 80% of them had been infected. The data obtained in this study reflect current situation of CCHF virus infection among livestock in Bulgaria. The results showed active CCHF virus circulation that poses risk for humans to be infected during contacts with animals and requires public health awareness.

Patterns of cytokine and chemokine expression in peripheral blood of patients with COVID-19 associated with disease severity.

OBJECTIVES: Cytokine dysregulation has been proposed as one of the main culprits for severe COVID-19 and poor prognosis. We examined the parallel presence of lymphopoietic, proinflammatory, Th1, Th2, regulatory cytokines, and chemokines in the serum of 47 patients with mild, moderate, and severe COVID-19 and evaluated the association between cytokine concentrations and disease severity. METHODS: A multiplex quantitative cytokine analysis ProcartaPlex™ immunoassay was applied, using the LuminexTM 200X detection system (Invitrogen). RESULTS: The concentrations of twelve cytokines: IL-18, IFN-gamma, TNF-alpha; IL-21; IL-1alpha, IL-1beta, IL-6, IL-22; IL-10, IL-1RA; IL-7 and IFN-alpha were consistently elevated in the studied serum samples. All examined chemokines-Eotaxin, GRO-alpha, IL-8, IP-10, MCP-1, MIP-1alpha, MIP-1beta, SDF-1alpha, and RANTES, were detectable in all studied groups, confirming their importance in mediating the adaptive immune response regardless of disease severity. The serum concentrations of six mediators: IL-1beta, IL-6, IL-18, IL-10, IL-8, and IP-10, showed statistically significant differences among the groups with different disease severity. IL-6, IL-1beta, and IL-10 were more significantly elevated in severe cases while milder symptoms were associated with lower levels of IL-8 and IP-10. CONCLUSION: Overall, the studied chemokines demonstrated an associated production in acute COVID-19 infection. A strong correlation was observed between the Th1 mediators IL-18 and IL-10 and the proinflammatory IL-6 in the severe COVID-19 group. Our results indicated that severe COVID-19 was characterized by a dysregulated cytokine pattern whereby the Th1 immune response is outweighed by the immunoregulatory response, while inhibitory signals cannot balance the hyperinflammatory response.

Age and Gender Trends in the Prevalence of Markers for Hepatitis E Virus Exposure in the Heterogeneous Bulgarian Population.

The prevalence of hepatitis E virus (HEV) in the Bulgarian population remains underestimated. The aim of the present study was to evaluate age and gender trends in HEV prevalence in the heterogeneous Bulgarian population. Stored serum samples from blood donors and different patient sub-populations-kidney recipients (KR), patients with Guillain-Barre syndrome (GBS), Lyme disease (LD), patients with liver involvement and a clinical diagnosis other than viral hepatitis A and E (non-AE), hemodialysis (HD) and HIV-positive patients (HIV)-were retrospectively investigated for markers of past and recent/ongoing HEV infection. The estimated overall seroprevalence of past infection was 10.6%, ranging from 5.9% to 24.5% for the sub-populations evaluated, while the seroprevalence of recent/ongoing HEV infection was 7.5%, ranging from 2.1% to 20.4%. The analysis of the individual sub-populations showed a different prevalence with respect to sex. In regard to age, the cohort effect was preserved, as a multimodal pattern was observed only for the GBS sub-population. Molecular analysis revealed HEV 3f and 3e. The type of the population is one of the main factors on which the anti-HEV prevalence depends, highlighting the need for the development of guidelines related to the detection and diagnosis of HEV infection with regard to specific patient populations.

Serologic evidence of widespread Toscana virus infection in Bulgaria.

BACKGROUND: Toscana virus (TOSV) is an emerging sandfly-borne virus that is endemic in Mediterranean countries. METHODS: In order to detect TOSV circulation among the human population of Bulgaria, serum samples from 459 apparently healthy adult individuals, residing in19 out of 28 districts in the country, were tested for the presence of IgG antibodies to TOSV. RESULTS: An overall seroprevalence rate of 24.4% was observed, ranging from 4.4% to 53.5% in the districts. Rates were highest in persons over 60 years of age and residing in the southern districts. CONCLUSION: The results of the first TOSV seroprevalence study in Bulgaria revealed that infection is widespread. Physicians should be aware of the virus circulation during summer and consider the diagnosis in cases of febrile illness, meningitis or meningoencephalitis.

Molecular identification of Puumala orthohantavirus in Bulgaria.

In Bulgaria, only Dobrava orthohantavirus has been detected in patients and in rodents. In order to elucidate possible Puumala orthohantavirus (PUUV) circulation, 131 bank voles (Myodes glareolus) were captured. PUUV RNA was detected in 14 (10.7%). Partial L segment sequences were recovered from six M. glareolus. Phylogenetic analysis showed that all PUUV sequences from this study clustered together among the Alpe-Adrian lineage. It is the first genetic evidence of the virus circulation in a Balkan country outside north-western Balkans. The findings in this study extended the known edge of virus distribution towards Southeastern Europe.

Prevalence of infection with Francisella tularensis, Borrelia burgdorferi sensu lato and Anaplasma phagocytophilum in rodents from an endemic focus of tularemia in Bulgaria.

The prevalence of Francisella tularensis, Borrelia burgdorferi and Anaplasma phagocytophilum in rodents is a determinant for their role in maintaining pathogens in the environment. A total of 169 rodents, trapped in an endemic focus of tularemia, were examined by PCR to asses the frequency of infection with the etiological agents of tularemia, Lyme borreliosis and human granulocytic anaplasmosis. The overall prevalence of F. tularensis was 22 %. In 6 % of the black rats, F. tularensis was identified in coinfection with B. burgdorferi and in 3 % in coinfection with A. phagocytophilum. B. burgdorferi and A. phagocytophilum were detected in 26 % and 8 % of the trapped rodents. Results obtained show the existence of an active natural focus of tularemia. The high level of coinfections indicated that the endemic focus is mixed and generates risk for multiple infections in humans. Further investigations are needed to reveal interactions between the pathogens in the infected animals.

Hemorrhagic fever with renal syndrome and Crimean-Congo hemorrhagic fever as causes of acute undifferentiated febrile illness in Bulgaria.

Hemorrhagic fever with renal syndrome (HFRS) and Crimean-Congo hemorrhagic fever (CCHF) are the 2 widespread viral hemorrhagic fevers occurring in Europe. HFRS is distributed throughout Europe, and CCHF has been reported mainly on the Balkan Peninsula and Russia. Both hemorrhagic fevers are endemic in Bulgaria. We investigated to what extent acute undifferentiated febrile illness in Bulgaria could be due to hantaviruses or to CCHF virus. Using enzyme-linked immunosorbent assays (ELISAs), we tested serum samples from 527 patients with acute febrile illness for antibodies against hantaviruses and CCHF virus. Immunoglobulin M (IgM) antibodies against hantaviruses were detected in 15 (2.8%) of the patients. Of the 15 hantavirus-positive patients, 8 (1.5%) were positive for Dobrava virus (DOBV), 5 (0.9%) were positive for Puumala virus (PUUV), and the remaining 2 were positive for both hantaviruses. A plaque reduction neutralization test (PRNT) confirmed 4 of the 10 DOBV-positive samples. PRNT was negative for all PUUV-positive samples. Serologic evidence of recent CCHF virus infection was found in 13 (2.5%) of the patients. Interestingly, HFRS and CCHF were not only detected in well-known endemic areas of Bulgaria but also in nonendemic regions. Our results suggested that in endemic countries, CCHF and/or HFRS might appear as a nonspecific febrile illness in a certain proportion of patients. Physicians must be aware of possible viral hemorrhagic fever cases, even if hemorrhages or renal impairment are not manifested.