Leptospirosis Morbidity in Lithuania, 1989 - 1999
Published: 17.11.04 Updated: 17.11.2004 10:52:30
V. Jasulaitiene, R. Jociene, L. Asokliene, J. Antanavicius
National Centre for Communicable Diseases Prevention and Control, Lithuania
Leptospirosis incidence was 0.5-1.1 per 100 000 population in 1989-1999 in Lithuania. Seasonal distribution was characterised by high incidence in August-October and age distribution by highest involving of persons 50-59 years old. 71% of cases were laboratory confirmed and 29% – diagnosed by clinical symptoms. Etiologically were dominating Leptospira icterohaemorrhagiae and Leptospira grippotyphosa. Main leptospira carriers in nature foci were wild rodents Microtus arvalis, Apodemus agrarius and Clethriomonys glareolus
Leptospirosis is a worldwide zoonosis caused by pathogenic Leptospira species, for which humans are accidental hosts. Humans can became infected through contact with an environment contaminated by the urine of shedder hosts, predominantly rodents. The severity of this acute febrile illness varies considerably from mild to fatal, and the wide spectrum of symptoms make clinical diagnosis unreliable. First cases of leptospirosis in Lithuania were diagnosed in 1945 in Klaipeda district. Leptospirosis natural foci exist in some districts of Lithuania, especially in the central part of the country where Microtus arvalis is more common.
Materials and Methods
Leptospirosis is a notifiable disease in Lithuania. Every suspected case is investigated by an epidemiologist of the local Public Health Centre. After a laboratory confirmation of diagnoses data about case is reported to the National Centre for Communicable Diseases Prevention and Control.
Patient’s blood samples for serological examination were collected twice - one blood sample as soon as suspected as having leptospirosis; 14 days later the second blood samples were collected. Sera of patients were examined by the Leptospira microscopic agglutination test (MAT) using a standard microtitre technique with live culture.
In the period 1989 - 1999 280 cases of leptospirosis were reported in Lithuania, with the incidence from 19 0.51 to 1.1 per 100 000 population per year (fig 1).
Fig 1. Leptospisrosi in Lithuania, 1989-1999
Leptospirosis cases are being registered in the whole territory of Lithuania, but in this period the highest number of cases (65%) were observed in the central part of Lithuania, where moist and alkaline soils create favorable conditions for formation of leptospirosis natural foci. The highest incidence has been registered in Joniskis district - 43 cases and Kaunas district - 32 cases (fig 2).
Fig 2. The geographical distribution of leptospirosis cases reported during 1989-1999
Leptospirosis incidence rate among rural population is 1.3 times higher than among urban population since rural population is more often exposed to leptospirosis risk factors: taking care of cattle, agriculture work and etc.
Forms of medium seriousness and severe forms of the disease have been diagnosed. Leptospirosis mortality rate in Lithuania has been from 5% in 1993 to 21% in 1997. The majority of cases have been registered in August - October (fig 3). Such seasonal distribution depended on the increase of number of rodents and increase of their migration, so the risk of population and cattle to contract the disease has been higher.
The age distribution shows the highest incidence in the age group 50-59 years old (73 cases; 26%). Male predominance is noted (52%).
Leptospirosis diagnosis was confirmed serologically in 198 (71%) cases by MAT with live cultures of leptospiras. In most cases diagnostic antibody titres were detected against L. icterohaemorrhagiae - in 46% cases and L. grippotyphosa - 26% (fig 4). For 29% of patients leptospirosis was diagnosed only by clinical symptoms.
Only to 31% of patients leptospirosis was suspected while taking medical advice. In the remaining cases other primary diagnosis was made: viral hepatitis - 28%, acute viral respiratory infection or influenza - 12%, meningococcal infection - 4%, gastroenterocolitis - 6%.
56% of the patients for whom risk factors of the disease were determined, had a contact with cattle while taking care of them at the job or at their own farm, others were veterinarians or employees of meat - packing plants. Rodents were found in 73% of foci.
Microbiological investigation of wild rodents had showed that Microtus arvalis, Apodemus agrarius and Clethriomonys glareolus were most infected.
Figu 3. Leptospirosis seasonality, 1989-1999
Numbers of leptospirosis cases in Lithuania should be higher since clinical course of the disease often shows only flu - like symptoms, and after 2 - 3 weeks patients recover. For such patients leptospirosis is suspected rarely, and the disease remains unrecognized. Other cause, which should increase the leptospirosis incidence - developing of laboratory diagnostics in Lithuania.