Eurosurveillance

ECDC

Leptospirosis in North-West Russia

 Rediger
 1 Published: 27.07.04 Updated: 27.07.2004 14:36:09
N. Stoyanova, N. Tokarevich, L.Gracheva, G.Volkova, N.Gracheva, S.Kravchenko, N.Kuzina, T.Liseeva, E.Matsievskaya, V.Pyanukh, V.Snegiriov, V.Sosnitsky, Saint-Petersburg Pasteur Institute and State Centre for Sanitary and Epidemiological Surveillance in Saint-Petersburg, Arkhangelsk, Murmansk, Novgorod, Pskov, and Republic of Karelia, Russia
Surveillance data from North-West Russia indicate a prevalence of antibodies to Leptospira in 5.2% of small mammals, 20% of farm animals and 19-40% of dogs. In 1992-2001, the mean annual incidence in humans varied between regions from 0.2 in the Pskov region to 1.6 in Saint-Petersburg per 100 000 population. In some regions the case fatality was 25%. Rodents and dogs have become important sources of human infections.

Introduction

Leptospirosis is an important zoonosis worldwide and is well known in the Baltic countries and Russia (1, 2, 3). The disease is caused by Leptospira interrogans, which is subdivided into serovars. Both wild and domestic animals may be carriers of Leptospira and excrete bacteria in urine. The aim of this work was to study the epidemiology of leptospirosis in North-West Russia.

Materials and methods

We analysed notification data of leptospirosis for humans and the veterinary service data for farm animals in the Pskov, Novgorod, Arkhangelsk and Murmansk regions, in Saint- Petersburg and in the Republic of Karelia of North-West Russia. Leptospirosis in humans was confirmed by laboratory analysis in 91% of patients and by clinical and epidemiological data in 9%. Antibody levels in sera from 53 230 patients with influenza, 630 healthy blood donors, 10 500 dogs and 13 686 small mammals were examined by the Leptospira microscopic agglutination test using a standard method including live cultures of  13 leptospires serovars.

Results

Twelve species of small mammals, predominantly moisture-liking rodents, were found to carry Leptospira. The seroprevalence was 12 % in Arvicola terrestris (water vole), 11% in Ondatra zibetica (muskrat) and 4.9% in Microtus oeconomus (tundra vole). The prevalence varied from 2.7% to 12% in the different regions, the mean value being 5.2% (Table 1).
 The seroprevalence among farm animals amounted to 20% for the North-Western region in general, varying from 15% in pigs to 25% in cattle. L. grippotyphosa and sejroe serovars were predominant among cattle while L. pomona and icterohaemorrhagiae were most common among pigs. The circulation of the Leptospira icterohaemorrhagiae serovar was due to the presence of Rattus norvegicus (grey rats) on pig farms (Table 1).

Table 1. Prevalence of antibodies to Leptospira among animals in North-West Russia

 

Species

 

Seroprevalence

Serogroup distribution

Serogroup

Proportion

 

Wild small mammals

 

5.2 %

Grippotyphosa

Javanica
Pomona

Australis

Other

65%

21%

12%

1%

1%

 

Sinanthropic rodents

 

12.0 %

Icterohaemorrhagiae

Pomona

Grippotyphosa

Other

60%

20%

12%

8%

 

Farm animals

 

19.6 %

Sejroe

Grippotyphosa

Pomona

Icterohaemorrhagiae

Tarassovi

55%

26%

10%

6%

3%

 

Dogs

 

30.6 %

Canicola

Icterohaemorrhagiae

Grippotyphosa

Pomona

54%

40%

5%

1%

In the Pskov region, 40% of dogs had antibodies to Leptospira, in the Murmansk region 38 % and in Saint-Petersburg 19%. The predominant serovars in dogs were L. canicola and icterohaemorrhagiae (Table 1).
In 1992-2001, 1157 patients with leptospirosis were reported, of which 840 from Saint-Petersburg. The mean annual incidence per 100 000 population was 1.6 in Saint-Petersburg, 1.0 in the Novgorod region, 0.8 in the Arkhangelsk region, 0.7 in the Murmansk region, 0.2 in the Pskov region and 0.3 in the Republic of Karelia as compared to 1.0 in Russia as a whole. The highest incidence values were recorded in the Novgorod region in 1990 (2.6 per 100 000) and in Saint-Petersburg in 1992 (3.3 per 100 000).
Eighty percent of the cases were among persons between 20-60 years. Only 2% of cases were among children less than 15 years of age. Fifty-seven percent of the patients were men. In the Arkhangelsk region, 79% of the patients were men.
Most cases occurred in the summer and autumn. In the Arkhangelsk region, 58% of cases occurred in June and July and 76% of cases were infected through contact with small rodents. The main route of leptospirosis transmission was reported to be through direct contacts (78%), while only 8% were thought to have been infected through food or water. Transmission through water is more typical for the southern regions of Russia (5). Rodents were thought to be the main source of Leptospira infection (52%) including the synanthropic ones (44%). The role of farm animals as the source of Leptospira infection decreased to 7 % during the last decade. Farm animals were the probable source of infection for 19 % of patients with leptospirosis in the Murmansk region, 14%  in the Pskov region, 7 % in the Novgorod region and 0% in the Arkhangelsk region.
During the 1990s, the number of cattle in the area decreased while the size of domestic dog population, including stray dogs, increased dramatically. Leptospira infected dogs were thought to be the cause of infection for 35% of human cases in the Pskov, Novgorod and Murmansk regions, in Saint-Petersburg and in the Republic of Karelia. In the last years, the role of L. canicola increased in several regions of North-Western Russia and in Saint-Petersburg. In the Murmansk region, the etiological agent for 54% of cases of leptospirosis was L.canicola. Dogs were revealed as the source of infection for 48% of patients.
The serovar distribution among human cases was L. icterohaemorrhagiae (48%), canicola (33%), grippotyphosa (12%), pomona (4%) and sejroe (2%). The distribution varied in different regions of North-Western Russia. The L. grippotyphosa serovar predominated in the Arkhangelsk region, pomona in the Murmansk and Novgorod regions, and icterohaemorrhagiae in the Novgorod region and in Saint-Petersburg.
 A total of 23% of cases were thought to have contracted the disease at work. During the mid 1980s in the Murmansk region, 80% of cases were registered among stock-breeders and meat reprocessing industry workers. In the 1990s, however, this proportion decreased to 19 %. In some regions, especially in the cities, the number of persons with rodent contact (yard-keepers, sanitary equipment workers, rubbish chute cleaners, storehouse and shop workers) increased dramatically. For example, in Saint-Petersburg, 19% of patients with leptospirosis were from this risk group.
Moderate and severe forms of the disease were registered among 93% of patients. The case fatality in some regions of North-West Russia was approximately 25 % (for instance, in Saint-Petersburg) as compared to 5% in Russia as a whole. No deaths were registered in the Arkhangelsk region where most leptospirosis cases (56%) were caused by the L. grippotyphosa serovar.
Seventy-four percent of patients were admitted to the hospital during the first week of illness. Only 39 % of the patients received an etiological diagnosis at this stage. The diagnosis of leptospirosis was confirmed by laboratory analysis after the second week of disease for 46 % of the patients.
The seroprevalence among healthy blood donors was 9.6 % in the Pskov region, 5.9% in the Murmansk region and 4.7% in Saint-Petersburg.

Discussion

Leptospirosis is widespread in wild animals and dogs in North-West Russia. The disease is emerging among humans.
The landscape and climatic conditions in North-West Russia, the variety of plants, the abundance of reservoirs and waterlogged territories, and the diversity of species of small rodents favour the existence and development of natural foci of leptospirosis. Human modification of landscapes has contributed to the situation. Most of the Murmansk region lies above the Arctic circle. The severe climate in this part of Russia seems to protect wildlife against Leptospira infection. In the Arkhangelsk region, most cases seem to be associated with wildlife reservoirs and there is a clear seasonal pattern. The higher proportion of male patients may be explained by their frequent contact with natural wildlife during hunting, fishing and haymaking.
In the 1990s, leptospirosis in dogs became epidemiologically significant in Russia as a whole (4) and in North-West Russia in particular, especially in urban areas with the increasing number of dogs. In the cities of North-West Russia, the epidemiology of leptospirosis has changed significantly over the last few years. Stable and active foci of leptospirosis developed under the influence of human activity. Urban rodent populations increased and had a high infection rate. In Saint-Petersburg, 12% of synathropic rodents were seropositive. Furthermore, the size of the dog population and the seroprevalence among dogs increased. The situation was reflected in the distribution of serogroups among human cases. L. icterohaemorrhagiae and canicola serovars dominated, and aggravated the clinical course of the infection.
The high case fatality of leptospirosis may result partly from late diagnosis. The wide spectrum of clinical manifestations and the inaccessibility of methods for early laboratory diagnosis may lead to dangerous delays in diagnosis. However, incomplete recording of the less severe cases may lead to an overestimation of the case fatality of the disease. The high seroprevalence among blood donors indicates that Leptospira infections are indeed under- diagnosed in North-West Russia.

Conclusions

Leptospirosis is widespread in humans and animals in North-Western Russia. The true incidence is probably higher than the recorded incidence due to an under-diagnosis of mild cases. During the last decade, rodents and dogs have become more important sources for human cases while farm animals have become less important. Two serovars, L. icterohaemorrhagiae and canicola, seem to be associated with a more serious clinical course of infection and higher case fatality. Workers in housing and municipal services with possible contacts with Leptospira infected rodents seem to be a new risk group for leptospirosis.


References

1. Kariv R, Klempfner R, Barnea A et al. The changing epidemiology of leptospirosis in Israel. Emerg Infect Dis 2001; 7: 990-2.
2. Jasulaitiene V, Jociene R, Asokliene L et al. Leptospirosis morbidity in Lithuania 1989-1999. EpiNorth 2002; 3: 5-7.
3. Tokarevich N, Stoyanova N, Kozhukhova E et al. Wild small mammals and domestic dogs infected with zoonotic agents in Saint-Petersburg and its suburbs. EpiNorth 2002; 3: 12-15.
4. Goldenstein ZA, Kalashnikov IA, Mkrtchan MO et al. Causes of leptospirosis morbidity in the Krasnodar Territory. Zh Mikrobiol (Moscow) 2001; (6): 77-9.
5. Popov VA, Efemenko VI, Antonenko AD et al. Epidemic peculiarities of leptospirosis in the Stavropol region. Zh Microbiol (Moscow) 2001; (6): 74-6.

 


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