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West Nile fever in Volgograd Oblast: features of the epidemic process’s manifestations at the present stage

https://doi.org/10.21886/2219-8075-2021-12-4-74-82

Abstract

Objective: To study the regional features of the West Nile fever (WNF) epidemic process manifestations using the example of the territory with stable and long-term pathogen circulation (Volgograd Oblast).

Materials and Methods: We used the data of the Reference Center for monitoring the WNF pathogen based on the Volgograd Research Anti-Plague Institute of Rospotrebnadzor over 1999–2021. The main method is a comprehensive epidemiological method.

Results: The long-term changes in the WNF incidence in Volgograd Oblast is characterized by a cyclical nature with an interval of 1–8 years and a tendency to decrease. The maximum risk of infection occurs in August (58.8%), but there is an increase in the number of cases in September. The average duration of the epidemic season is 8.4 weeks. Case fatality rate is at the level of 4.3%; the prevalence of the number of deaths in the group of 70 years and older (75%), as well as among men (63.6%) has been established. The greatest contribution to the incidence rate is made by the age group of 60 years and older (37.7%). Features of the clinical presentation include the dominance of forms without damage to the central nervous system (91.1%) and moderate clinical course (72.3%). The prevalence of the urban population among the infected was noted (85.5%).

Conclusion: A comparative analysis of the clinical and epidemiological WNF manifestations in Volgograd Oblast, territories with a stable circulation of the pathogen (Astrakhan and Rostov Oblasts) and, in overall, the Russian Federation, established differences in the duration of cyclical fluctuations in incidence, seasonality (Rostov Oblast), age structure of incidence (Astrakhan Oblast), distribution of cases by the severity of the clinical course, the site of the alleged infection and social status.

For citation:


Nikitin D.N., Udovichenko S.K., Putintseva E.V., Viktorov D.V., Toporkov A.V. West Nile fever in Volgograd Oblast: features of the epidemic process’s manifestations at the present stage. Medical Herald of the South of Russia. 2021;12(4):74-82. (In Russ.) https://doi.org/10.21886/2219-8075-2021-12-4-74-82

Introduction

The ongoing tense epidemiological situation of West Nile Fever (WNF) in a number of the Russian Federation subjects (primarily the Southern Federal District [1-3]) determines the relevance of this research. It is aimed at a comprehensive analysis of the epidemic manifestations of this arbovirus infection in order to increase the effectiveness of epidemiological surveillance and a set of preventive measures. However, due to the differences in the intensity of the epidemic process and the peculiarities of the organization of monitoring of the WNF-pathogen in the administrative territories of the Russian Federation, obtaining representative data is possible only with an in-depth incidence analysis in individual subjects of the country. First of all, these studies can be carried out according to the model of the Volgograd region, which occupies a leading place in Russia in terms of the absolute number of WNF-cases [3][4].

To date, with a sufficient number of scientific publications devoted to the analysis of the largest WNF-outbreaks and the study of the morbidity dynamics in the Volgograd region [4-9], the regional features of the epidemic process remain unconsecrated. This can only be established by a comparative analysis of the epidemic situation with WNF -manifestations in other territories with stable circulation of the pathogen (primarily Astrakhan and Rostov regions) and the Russian Federation as a whole. Obtaining such objective data opens up prospects for improving the monitoring system for the causative WNF-agent, studying the complex of factors influencing the epidemiological risk, as well as developing a mathematical model for predicting the development of the epidemiological situation.

This research aims to study the regional features of the epidemic process WNF-manifestations on the example of a territory with a stable and long-term pathogen circulation (Volgograd region).

Materials and methods

The work uses data taken from the Reference Center for monitoring the causative WNF-agent on the basis of the Rospotrebnadzor Federal State Institution “Volgograd Research Anti-Plague Institute”. A comprehensive epidemiological method was used in this study [10], according to which the temporal characteristics of epidemiological risk, the structure of morbidity and the territorial timing of epidemic WNF-manifestations were studied. Statistical data processing was carried out using the means of the Microsoft Excel 2016 processor, 2109 14430.20234 version (Microsoft Corporation, USA).

Results

It is necessary to remember that the history of the WNF-manifestations in the Volgograd region dates back to 1999, when medical workers drew attention to a sharp increase in the number of complaints from the population about serous meningitis and meningoencephalitis, accompanied by an increase in the incidence of a febrile (flu-like) disease course. The assumption about the West Nile-virus as a possible etiological factor of the outbreak arose on the basis of the registration of sporadic cases in epidemic foci, which excluded aspiration and fecal-oral mechanisms of the infection transmission, an anamnesis indication of contact with mosquitoes, as well as the pathogen circulation in the Volga delta established since the 1960s [5][8]. Therefore, among 826 patients hospitalized in medical institutions of the city and the region, 380 had the diagnosis confirmed by laboratory research methods (288 cases occurred in the form of serous meningitis, 44 – in the form of meningoencephalitis and 48 – without damage to the nervous system) [9]. In addition to the Volgograd region, in 1999, WNF -cases were reported in the Astrakhan region (95 patients) and the Krasnodar Territory (85 cases not included in official statistics) [11]. The morbidity analysis in the Volgograd region over the previous years revealed an increase in the number of cases of diseases with lesions of the central nervous system in July-August 1997 (mainly among children) and August-early September 1998. During the examination of 111 Volgograd residents who had been ill with serous meningitis and meningoencephalitis during this time period, 40 (36%) had antibodies to WNF (IgG class). These data confirmed that the contact of the population with the pathogen was quite intense even before the official registration of the incidence in 1999 [3][5].

In total, since the registration of the first epidemic outbreak (1999) to the present (September 2021), 1.324 cases of WNF have been confirmed in the laboratory, while the incidence has not been recorded annually. Manifestations of the epidemic WNF-process were detected in 32 of the 39 administrative territories of the region. In general, the highest incidence is observed in the cities of Volgograd and Volzhsky (Figure 1). Multiple cases of the disease have been confirmed in Gorodishchensk, Sredneakhtubinsky, Mikhailovsky and Svetloyarsky districts. In other areas, cases of the disease are isolated or have not been registered at all. The results of seroepidemiological monitoring indicate the presence of an immune layer to WNF in the population of all the Volgograd region districts, which indicates the spread of the pathogen and, probably, insufficiently effective detection of disease cases. It should be emphasized that 3 out of 7 districts where the incidence has not been officially registered are the suspected place of infection of cases diagnosed in other administrative territories of the Volgograd region.

Figure 1. Zoning of Volgograd Oblast by the number of registered WNF cases

The average long-term WNF-incidence in the Volgograd region is 2.18 cases per 100 thousand population (95% CI: 0.36-3.99; p=0.02). The incidence above the average annual level was registered in 1999, 2007 and 2010-2013, the largest outbreaks were in 1999, 2010 and 2012. A large spread of morbidity values in some years is characterized by a standard deviation of 4.35, which confirms the cyclical course of the epidemic process. Cyclical fluctuations in morbidity in the Volgograd region are observed at intervals of 1 to 8 years (Figure 1). The rise in morbidity is accompanied by a sharp decrease in the number of cases in subsequent years, indicating only a temporary regression of the epidemic process.

Figure 2. Changes in WNF incidence in Volgograd Oblast and the Russian Federation over 1997–2021.

It should be noted that the duration of cyclic fluctuations in morbidity differs in other subjects with stable WNF -manifestations: in the Rostov region it is 5-7 years, in the Astrakhan region — 6-7 years. However, in general, there is a coincidence of the incidence rises in 1999 in the Astrakhan and Volgograd regions, in 2010 — in the Volgograd and Rostov regions, and in 2007 and 2012 — in all of the above-mentioned regions. This indicates the simultaneous action of factors (abiotic and biotic) in different territories that contribute to the activation of epizootic and epidemic processes.

While comparing the dynamics of the WNF-incidence in the Volgograd region with that in the Russian Federation, it is necessary to note that the excess of the average long-term morbidity level over the all-Russian one was found to be 28 times (95% CI: 9.21-32.94; p <0.001). In the Russian Federation, periodic fluctuations in morbidity are recorded at intervals from 1 to 4 years. There is a coincidence in the timing of three major increases in morbidity in 1999, 2010, 2012, when the outbreak WNF-incidence in the Volgograd region determined a problem due to this infectious disease in Russia (Figure 1). In these years, the Volgograd Region accounted for 80%, 78.8% and 46.6% of all registered WNF-cases in the Russian Federation, respectively. Since 2013, the contribution of the Volgograd Region to the all-Russian morbidity has significantly decreased, which is due both to a decrease in the number of identified patients in the region, and to the expansion of the pathogen's range and the registration of epidemic WNF-manifestations in the territories of other subjects of the country.

Thus, the analysis of the long-term dynamics of the WNF-incidence indicates the presence of cyclicity, which may be associated with climatic changes, the number and activity of carriers and vectors, as well as the effect of social factors. The significant influence of social factors on the registered morbidity can be judged based on the epidemiological situation that developed in 2020, when no cases of WNF were officially reported in the Volgograd region. This was probably due to the lack of work on the active identification and examination of WNF-patients among those who sought medical help. At the same time, the presence of a broad immune layer (13.2%) among a sample group of a healthy population, as well as the identification of the pathogen markers in the material from the main carriers and vectors, testified to the intensive WNF-circulation in the region during the past epidemic season.

During the study period in the Volgograd region, a slight trend towards a decrease in morbidity was established: the regression equation corresponding to the linear trend Y = -0.136x + 3.8077. To compare it is important to give the following data: in the Astrakhan region, the dynamics of morbidity is also characterized by a tendency to decrease (Y = -0.0363x + 3.3118), and in the Rostov region — to increase (Y = 0.0276x + 0.0621). In the Russian Federation, on the contrary, there is a tendency for a morbidity increase in the long-term aspect (Y = 0.0014x + 0.0655).

The intra-annual dynamics of morbidity has a pronounced seasonality. WNF-cases are registered mainly from July to October, and the peak incidence occurs in August (778 cases; 58.8%; 95% CI: 56.15-61.45%; p <0.001) and September (432 cases; 32.6%; 95% CI: 30.08-35.12%; p <0.001). It should be emphasized that during the entire analyzed period there was a change in the ratio between the number of identified patients: in the first years of observation, most cases of the disease were diagnosed in August (72.2% – 1999, 71.8% – 2000, 86.6% – 2001), and later the distribution of cases in August and September became approximately equal. In the opinion of the authors of this particular study, this fact may be associated with a change in climatic conditions, namely, an increase in the average air temperature in September, which contributes to the preservation of a sufficiently high number and activity of carriers of high-cost nosologies (HCN), and, consequently, increases the duration of their contact with humans. The dynamics of the WNF epidemic process in the Russian Federation has a seasonal character (from June to October), and since 2014 there has been a tendency to shift the peak incidence from July-August to August-September. In other subjects with stable HCN circulation (Astrakhan and Rostov regions), a similar trend is observed, but the ratio of the number of identified patients in the above months on the territory of these subjects differs. The Astrakhan region is characterized by the highest incidence of WNF in August (51.4% of all registered cases), and in the Rostov region, a significant part of the cases (54.1%) was diagnosed in September.

The average duration of the epidemic season in the Volgograd region is 8.4 weeks (95% CI: 3.80-12.92; p <0.001), and the maximum is 17 weeks (2018). The earliest start of the epidemic season was noted in 2013 (the first case of the disease was registered in the third decade of June), the latest case was confirmed in November 2018: infection is presumably associated with contact of the patient with basement mosquitoes. The tendency to increase the duration of the epidemic season is noteworthy: in 1999 it was 9 weeks, in 2010 and 2012 – 15 and 14 weeks, in 2018 – 17 weeks. In the Russian Federation, the duration of the HCN transmission season is higher: 13.55 weeks (95% CI: 9.72–17.37), but in the whole country, there is a tendency to reduce this indicator (Y = -0.8727x + 18.782). There were no significant differences in the duration of the epidemic seasons in the Volgograd, Astrakhan (9.2 weeks, 95% CI: 5.93–12.44; p <0.001) and Rostov (7.9 weeks, 95% CI: 4.79–11.02; p<0.001) regions, as well as in the duration of the season in Russia as a whole.

Mortality is 4.3% on average (57 deaths; 95% CI: 3.21-5.4%; p <0.001), the highest values were observed in 1999 (38 cases; 10%; 95% CI: 6.98-13.02%; p <0.001). During the outbreak of 1999, along with high mortality, the registration of deaths in young and middle-aged patients attracted attention. Thus, persons under 50 years of age accounted for 8 deaths (21% of the total number of deaths), of which the groups of 15-20 years and 21-30 years — 5.3%, 31-40 years – 7.9% [12]. Subsequently, fatal outcomes were noted only in patients older than 50 years, mainly among people aged 70 and over (75%). The causes of deaths for the elderly were the presence of an unfavorable premorbid background in the form of chronic concomitant diseases and later seeking medical help. Of the total number of deaths, 63.6% of males and 36.4% of females accounted for. The established fact of the prevalence of the number of deaths among the male population over the female population by 2 times requires further study. A higher mortality rate among men was also reported during outbreaks of WNF in European countries (69.7% of the total number of deaths) [13]. The mortality rate in the Astrakhan region (18 cases; 2.6%; 95% CI: 1.41-3.79%; p=0.01) is relatively lower than that in the Volgograd region, but the differences between them are not statistically significant. The mortality rate from WNF disease in the Rostov region was 1.2% (4 cases). At the same time, the assessment of the gender and age structure of deaths from WNF in these subjects of the country is difficult due to the incompleteness of the information provided to the Reference Center, as well as an unrepresentative sample of data. Therefore, 67% of deaths in Russia were observed in people over 70 years of age, the same amount falls on men of this age group, and in other age groups (0-14, 50-59, 60-69 years), cases of the disease are isolated and therefore do not lend themselves to statistical processing.

The analysis of data on the incidence distribution of WNF by sex showed that the proportion of men is 54.16% (95% CI: 51.46-56.86; p <0.001), women – 45.84% (95% CI: 43.14-48.54; p <0.001). A similar situation is observed in the Russian Federation (men – 56.94%, 95% CI: 54.99-58.88, p <0.001; women – 43.06%, 95% CI: 41.12-45.01, p <0.001). The prevalence among male patients can be explained by their more frequent trips to natural biotopes, where there is a higher probability of contact with infected vectors (fishing, agricultural activities, etc.).

In general, the distribution by age groups is characterized by dominance among the patients aged 60 years and older (499 cases; 37.7%; 95% CI: 35.09-40.31; p <0.001), which, in the opinion of the authors, is associated with a more severe course of the disease in this age group and, accordingly, better detectability of such patients. The proportion of cases aged 50-59 years is 18.4% (244 cases; 95% CI: 16.31-20.49; p <0.001), the age groups 30-39 years and 40-49 years are represented in approximately equal proportions (170 cases; 12.8%; 95% CI: 11-14.6; p <0.001 and 188 cases; 14.2%; 95% CI: 12.32-16.08; p <0.001, respectively). Persons aged 20-29 years account for 9.2% (122 cases; 95% CI: 7.64-10.76; p <0.001) of all cases of the disease. Children and adolescents who have a mild clinical course of the disease and who are often diagnosed with acute respiratory infection have the lowest proportion in the structure of morbidity: age groups 0-14 years and 15-19 years account for 4.8% (64 cases; 95% CI: 3.65-5.95; p <0.001) and 2.8% (37 cases; 95% CI: 1.91-3.69; p <0.001) of the total number of cases. In the Astrakhan region, on the contrary, these age groups make a more significant contribution to morbidity (12.3% and 4.7%), differences in the group of children under 14 years old are significant (p <0.001). The distribution of older patients is generally similar to that in the Volgograd region, there were no significant differences between individual groups in these subjects. The absence of differences between them is also characteristic when compared with the Rostov region, with the exception of the 0-14-year-old group, the analysis of which is difficult due to the small number of identified patients of this age (2 cases, 0.8%). In general, in Russia there is a predominance in the structure of morbidity of persons aged 50-59 years (19.05%) and 60 years and older (31.14%), the share of children and adolescents (under 14 years) accounts for 4% of all the WNF-cases.

When assessing the distribution of morbidity in different age and sex groups, significant differences between men and women were revealed only in the group of 60 years and older (Figure 2). In the authors’ opinion, this circumstance can be explained based on the more severe clinical WNF-course in men. Thus, among patients suffering from neuroinvasive manifestations, males account for 79% of all cases. The same pattern can be traced in the Rostov region. However, in the Astrakhan region, there is a statistically significant prevalence of morbidity among men aged 20-29 years and 40-49 years, associated with the peculiarities of the lifestyle of the population, namely actively developed fishing and hunting, which contributes to intensive contact with natural focal areas.

It is important to study the features of the age structure of the WNF-morbidity of the population during the major outbreaks of 1999, 2010 and 2012. During the outbreak of 1999, attention was drawn to the high proportion of sick children under the age of 14 (8.9%), exceeding similar indicators in all subsequent years of epidemic increases in morbidity, which probably indicated the appearance of HCN in a new territory for him. The authors’ assumptions about the active involvement of the children and youth population in the epidemic process in the “new foci” of WNF are confirmed by data in the Voronezh region, where during the first outbreak in 2010, the proportion of cases in the age group of 15-19 years was 11.1%, and the Lipetsk region (in 2012, children under 14 years accounted for 25.7%).

Figure 3. Incidence of WNF in men and women in different age groups in Volgograd Oblast over 2009-2021.

In 2010, while maintaining a high proportion of patients aged 50 years and older (53.8%), there was a 2.1-fold increase in the number of patients aged 20-29 years, as well as an increase in morbidity in groups 30-39 years and 40-49 years. Among the cases, children under 14 years of age accounted for 2.2%, which is significantly lower than in the outbreak of 1999. In 2012, an increase in the proportion of patients aged 20-29 years and 30-39 years was found to be 2.9 and 2.2 times as compared to that in 1999, with a decrease in the proportion of the group of 60 years and older by 32.8%. Taking into account the above-mentioned information, there has been a tendency to involve the active, able-bodied population in the epidemic process, as well as to reduce the proportion of older patients.

The analysis of the social composition of patients made it possible to identify groups at increased risk of infection with WNF. Thus, the greatest contribution to the final morbidity is made by pensioners (474 cases; 36.15%; 95% CI: 33.55-38.76%; p <0.001), workers (239 cases; 18.23%; 95% CI: 16.14-20.32%; p <0.001) and employees (204 cases; 15.56%; 95% CI: 13.59-17.52%; p <0.001). During the years of outbreaks, a number of changes were observed in the social structure. Reliable at the level of reliability of 95% is a decrease in 2012 compared to 1999, the share of pensioners by 36% and an increase in the number of cases among employees by 2.4 times. At the same time, the cumulative distribution of patients across the country in the above groups is characterized by an approximately equal ratio, with the exception of a significant predominance of pensioners (the share of this group is 26.79%, 95% CI: 24.84–28.76, p <0.001; non-working population – 20.44%, 95% CI: 18.62—22.18%, p <0.001; employees – 19.83% 95%, CI: 18.04—21.56%, p <0.001; workers – 19.12%, 95% CI: 17.36-20.84%, p <0.001).

The dominance of pensioners in the incidence structure is also noted in other subjects of the Russian Federation that are disadvantaged by the WNF, of which this indicator is most pronounced in the Rostov region (29.44%, 95% CI: 23.35-34.65%, p <0.001), but lower than in the Volgograd region. In addition, the Rostov region has a high proportion of unemployed persons among the sick (26.21%, 95% CI: 20.54-31.46%, p <0.001). In the Volgograd region, this population group accounts for only 15% (95% CI: 12.5-17.5%, p <0.001). In the Astrakhan region, pensioners are at the greatest risk of infection – 23.97% (95% CI: 19.27-28.67%; p <0.001) and the unemployed population – 22.71% (95% CI: 18.1-27.32%; p <0.001).

Among the clinical forms, WNF without CNS-damages prevails (726 cases in 2009-2021; 91.1%; 95% CI: 89.12-93.08%; p <0.001), in some years this indicator was 50-97%. In 1999, the highest proportion of neuroinvasive WNF-forms was observed (332 cases; 87.4%; 95% CI: 84.06-90.74%; p <0.001), which confirms the introduction of the pathogen to a new territory for it. The validity of this assumption is evidenced by the high frequency of neuroinvasive forms of the disease, noted on the territory of other subjects where WNF was diagnosed for the first time. In 2012 the proportion of patients with CNS-damage in the Stavropol Territory was 100%, the Saratov region – 77.3%, the Republic of Adygea – 50%.

In 2010 and 2012, the proportion of neuroinvasive forms in the Volgograd Region decreased significantly compared to 1999 — 5.08% (21 cases; 95% CI: 2.98-7.22%; p=0.003) and 10.48% (22 cases; 95% CI: 6.35–14.65%; p=0.001), respectively. This is probably due to the formation of the immune layer in the population and a milder course of the disease. The assumption that the decrease in the proportion of clinical forms with CNS-damages is due to the change of circulating genotypes of the virus from the first in 1999 to the less virulent second genotype since 2007 has not been confirmed. In particular, in 2010 during the WNF-outbreak in Greece caused by the 2nd genotype of the virus, neuroinvasive manifestations were noted in 197 of 262 (75%) patients [13].

However, in general, since 2010, the authors of this article have observed an increasing trend in the proportion of neuroinvasive forms of infection (Y = 1.2622x + 5.5788). A similar trend was observed on the territory of the Russian Federation (Y = 0.7479x + 17.787). The observed increase in the proportion of WNF-cases with CNS-damage is not an objective indicator and is primarily associated with the predominant detection of severe and moderate (neuroinvasive) forms of the disease, while cases of a mild (flu-like) variant of the course remain undiagnosed.

Figure 4. Changes in the WNF clinical course severity in Volgograd Oblast (2009-2021)

The prevalence of moderate forms of infection is noted in the structure of morbidity according to the severity of the clinical course (Fig. 3). Nevertheless, in 2009-2021, the proportion of mild forms in the incidence structure was 22.94% (181 cases; 95% CI: 20.01–25.87%; p <0.001), moderate — 72.37% (571 cases; 95% CI: 69.25–75.49%; p <0.001), severe — 6.34% (50 cases; 95% CI: 4.64 –8.04%; p <0.001). The cumulative distribution of clinical forms in the Russian Federation is characterized by a smaller proportion of mild forms (17.32%; 95% CI: 15.67–18.97%; p <0.001) and a larger proportion of severe forms (10.39%; 95% CI: 9.06-11.72%; p <0.001). In the Astrakhan region, the predominant WNF is of moderate severity (87.74%; 95% CI: 84.14-91.34%; p <0.001), severe course was noted in 11.64% of cases (95% CI: 8.12-15.16%; p <0.001). The Rostov region, in comparison with the Volgograd region, is characterized by a high incidence of severe WNF – 23.33% (95% CI: 18.54-28.12%; p <0.001), the contribution of mild forms to the structure of morbidity is 26.33% (95% CI: 21.35-31.31%; p <0.001), the moderate course is confirmed in 50.33% of patients (95% CI: 44.67-55.99%; p <0.001).

During the entire observation period, urban population prevailed among the sick (1132 cases; 85.5%; 95% CI: 83.6-87.4%; p <0.001) over rural (192 cases; 14.5%, 95% CI: 12.6-16.4%; p <0.001). Despite the obvious more intensive and constant contact with HCN-vectors of rural residents, the detection of cases of the disease among them is lower. Probably, this can be explained by their “anti-epidemic” at a young age and as a result of a lighter course of infection, as well as low access of the rural population to medical care. Most cases of infection are associated with visits to suburban areas (500 cases; 38.1%, 95% CI: 35.47-40.73%; p <0.001), the proportion of infected in nature and at the place of residence is approximately equal (362 and 356 cases, respectively), and the differences between them are not reliable: 27.6% (95% CI: 25.18-30.02%; p <0.001) and 27.2% (95% CI: 24.79–29.61%; p <0.001). The urban population accounts for 8.45% (95% CI: 6.9–9.9%; p <0.001) of cases of HCN -infection at the place of residence. At the same time, the percentage of such cases in Russia is 19.6% (95% CI: 18.19-21%; p <0.001), and in the Astrakhan and Rostov regions this indicator is approximately equal (31.5% and 35.1%, respectively). The combined contribution of urban and rural populations to the WNF-incidence in the Russian Federation is 76.2% (95% CI: 74.48–77.92%; p <0.001) and 23.8% (95% CI: 22.08–25.52%; p <0.001), Astrakhan Region — 48.7% (95% CI: 43.17–54.23%; p <0.001) and 51.3% (95% CI: 45.77–56.83%; p <0.001), Rostov Region — 70.5% (95% CI: 64.86–76.14%; p <0.001) and 29.5% (95% CI: 23.86–35.14%; p <0.001), respectively.

Conclusion

The epidemic process of WNF in the Volgograd region is characterized by cyclicity in long-term dynamics (epidemic rises with an interval of 1 to 8 years) and vivid seasonality (the peak of morbidity occurs in August). The prevalence of older patients in the structure of morbidity has been established (while men of this age are a group of increased risk due to a more severe clinical course of the disease). However, it should be noted that there is a tendency to increase the proportion of cases among younger people and the able-bodied population. Currently, there is an increase in the proportion of neuroinvasive forms of infection associated with the predominant detection of severe and moderate forms of the disease, which is also confirmed by their predominance in the structure of morbidity according to the severity of the clinical course. These data indicate the omission of cases of WNF-diseases with a mild (flu-like) variant of the course and the need to increase the alertness of doctors of the general medical network to identify and examine patients during the epidemic season. The greatest risk of infection is exposed to urban residents who lead an active lifestyle – traveling to suburban areas and natural recreation areas. The study of the territorial distribution of morbidity showed that cases of the disease are concentrated within Volgograd and the administrative-territorial entities bordering it, which is primarily due to the higher appeal of urban residents for medical care. A comparative analysis of clinical and epidemiological WNF-manifestationsin the Volgograd region, territories with stable circulation of the pathogen (Astrakhan and Rostov regions) and the Russian Federation as a whole revealed differences in the duration of cyclic fluctuations in morbidity, seasonality (Rostov region), age (Astrakhan region) the incidence structure, the distribution of cases according to the severity of the clinical course, the place of suspected infection and social status.

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About the Authors

D. N. Nikitin
Volgograd Plague Control Research Institute
Russian Federation

Dmitry N. Nikitin, researcher

Volgograd



S. K. Udovichenko
Volgograd Plague Control Research Institute
Russian Federation

Svetlana K. Udovichenko, Cand. Sci. (Med.), leading researcher

Volgograd



E. V. Putintseva
Volgograd Plague Control Research Institute
Russian Federation

Elena V. Putintseva, Cand. Sci. (Med.), leading researcher

Volgograd



D. V. Viktorov
Volgograd Plague Control Research Institute
Russian Federation

Dmitry V. Viktorov, Dr. Sci. (Bio.), associate professor, Deputy Director for Scientific and Experimental Work

Volgograd



A. V. Toporkov
Volgograd Plague Control Research Institute
Russian Federation

Andrey V. Toporkov, Dr. Sci. (Med.), associate professor, Director

Volgograd



Review

For citation:


Nikitin D.N., Udovichenko S.K., Putintseva E.V., Viktorov D.V., Toporkov A.V. West Nile fever in Volgograd Oblast: features of the epidemic process’s manifestations at the present stage. Medical Herald of the South of Russia. 2021;12(4):74-82. (In Russ.) https://doi.org/10.21886/2219-8075-2021-12-4-74-82

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