A.Bartulienė1, Ž. Milišiūnaitė1, S.Čaplinskas1
1 Centre for Communicable Diseases and AIDS
Citation: Bartulienė A, Milišiūnaitė Ž, Čaplinskas S. Human trichinellosis in Lithuania, 2001 – 2010. EpiNorth 2012;13:44-9.
Trichinellosis infection poses an important public health problem in Lithuania. In 2010, trichinellosis incidence remained relatively high (2.3 cases per 100,000 population). Trichinella infection rates were higher among adults, although infection cases among children were not rare. Infection incidence was higher in rural populations than in urban populations.
According to the results of epidemiological investigations, people become infected by eating undercooked infected meat of domestic or wild animals. Human trichinellosis outbreaks (2 or more cases that are epidemiologically linked) are registered annually in Lithuania. The data for the period 2001-2010 showed that 55.5% of outbreaks were caused by consuming domestic pork that had not been examined for trichinellosis.
Trichinellosis is an acute disease of humans and animals caused by Trichinella genus roundworms. People become infected by eating raw or insufficiently cooked infected meat of domestic or wild animals.
Each year about 11 million people are infected by Trichinella globally (1). According to medical statistics, on average 46 cases of trichinellosis are registered in Lithuania annually (2). The incidence of trichinellosis is variable and depends on eating habits, meat preparation, infection diagnostics, reporting and people’s awareness about the infection.
In 2001-2010, the trichinellosis morbidity in Lithuanian was the highest of all Baltic countries. The data for 2001-2010 showed that the infection reached the highest rates in 2001, 2009 and 2010, with 105, 115 and 77 infection cases, respectively (2). During this period only three cases were reported in Estonia. In Latvia, the incidence of trichinellosis was low, except in 2005 with 62 cases registered (3,4).
The objective of this study is to provide an overview of the current epidemiological situation and trends of trichinellosis infection in Lithuania in 2001-2010.
Materials and Methods
Surveillance data from the national communicable diseases register and urgent reports were used for a retrospective descriptive epidemiological analysis of human trichinellosis. Probable and confirmed human trichinellosis case definitions are used in Lithuania (5).
Following an urgent report from a health care institution, the territorial public health centre specialists start an epidemiological investigation by interviewing patients, their family members and other individuals who have consumed the suspected meat. The suspected individuals are referred to health care facilities for laboratory testing, medical monitoring and treatment (6).
According to the data from the Centre for Communicable Diseases and AIDS, 465 cases of human trichinellosis were reported in Lithuania during 2001-2010, including 33 sporadic cases and 45 outbreaks. During the decade the incidence of trichinellosis increased from 0.4 to 3 cases per 100,000 population. The incidence was highest in 2001, 2009 and 2010, and lowest in 2005-2007 (Fig. 1).
Fig. 1. Human trichinellosis incidence in Lithuania, 2001-2010
People of any profession and age can be affected by trichinellosis but the highest incidence rate of infection was recorded among adults (Fig. 2). Nevertheless, trichinellosis infection is not rare among children. During 2001-2010, 80 cases (17.2 %) were reported among children under the age of eighteen years.
Fig. 2. Cumulative annual incidence of human trichinellosis by age group, Lithuania, 2001–2010
The trichinellosis incidence among the rural population was higher than among the urban population during 2001-2010. The average incidence of human trichinellosis was 1.5 and 1.2 cases per 100,000 population in rural and urban populations, respectively.
Results of epidemiological outbreak investigation indicates that human trichinellosis in Lithuania is spread by the consumption of infected domestic pig and wild boar meat. During 2001-2010 the majority of trichinellosis cases (53.1 %) were caused by infected domestic pig meat, wild boar (23.9 %) while 23 % of the infection sources were unknown (Fig. 3).
Fig. 3. Proportion of trichinellosis by infection source in Lithuania, 2001–2010
Outbreaks of human trichinellosis (2 or more epidemiologically linked cases) are registered in Lithuania annually. According to the from the Public Health Centres in Lithuania, during 2001-2010 55.5 % of trichinellosis outbreaks occurred in family farms where pig meat had not been examined, approximately 17.8 % by consuming infected wild boar and the source of infection in 26.7 % of cases was unknown.
During the decade, the biggest outbreaks were caused by consumption of wild boar: one outbreak accounted for 69 and 107 cases in 2001 and in 2009, respectively. Outbreaks of trichinellosis caused by pork meat were small, accounting for 2-5 cases in a single outbreak. The largest outbreak caused by pork consumption occurred in 2010 with 25 cases. (Fig. 4).
Fig. 4. Number of trichinellosis outbreaks by infection source in Lithuania, 2001–2010
Human trichinellosis infection outbreaks were primarily reported from the central region of Lithuania. During 2001-2010, more than 4 trichinellosis outbreaks were reported in the Ukmergė and Jurbarkas regions (Fig. 5).
Fig. 5. Cumulative number of human trichinellosis outbreaks (n=45) in Lithuania by region, 2001-2010
During 2001- 2010 the majority of trichinellosis outbreaks associated with pork consumption were registered in January, March, April, and July. Outbreaks were associated with the slaughtering of pigs before major holidays in the spring and winter (Christmas and Easter).
During the last ten years most of trichinellosis outbreaks caused by the consumption of wild boar occurred in June. These outbreaks coincided with the onset of hunting season; wild boar hunting is permitted from May 1st through February of the following year.
Human trichinellosis spreads in Lithuania via infected pork and wild boar meat. One major reason is the inappropriate surveillance and inspection of pork meat in small farms. Consumption of wild boar meat is the second largest cause of trichinellosis in Lithuania. The largest outbreak was registered in 2001 during which 107 persons fell ill with trichinellosis after having eaten infected wild boar meat. Investigations performed in 2000-2002 showed that about 0.5% of wild boars in Lithuania are infected with Trichinella (7). The infected wild boars live throughout the country and therefore the meat of wild boar is an important source of infection in Lithuania.
According to Lithuanian legislation, the meat of all slaughtered pigs and hunted wild boars must be examined for Trichinella. However, in some cases meat from small farms is used for personal consumption and examination is not obligatory. Presently, there are two methods used to detect Trichinella in meat: trichinoscopy (digest compressorium technique) and artificial digestion method. Epidemiological data indicates that despite regulations, consumption of uninspected meat occurs. Pork meat received from small farms just for personal consumption is not produced for trade marketing. However, owners of small farms often supply their neighbours, friends and co-workers with meat, and thus several families may acquire infection. Therefore, information, especially for small pig breeders and hunters, is needed in order to prevent human trichinellosis in Lithuania.
Incidence rate of human trichinellosis remains relatively high.
Incidence of human trichinellosis is higher in rural than in urban populations.
Higher incidence of human trichinellosis is been registered among adults.
The main risk factor of outbreaks of human trichinellosis was infected and uninspected pork meat from small farms (55.5%) during 2001–2010.
Human trichinellosis outbreaks associated with infected pork consumption were primarily registered in January, March, April, and July while outbreaks due to consumption of contaminated wild boar were registered in June.
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2. Lithuanian Centre for Communicable Disease and AIDS. Statistical report form No. 4 Morbidity of infectious diseases. [in Lithuanian]. Available from: http://www.ulac.lt/ataskaitos
3. EpiNorth, EpiNorth Data. Available from: http://www.epinorth.org/eway/default.aspx?pid=230&trg=Area_5279&MainArea_5260=5279:0:15,2937:1:0:0:::0:0&Area_5279=5291:44530::1:5290:1:::0:0&diseaseid=38
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6. Health Minister’s order No. V-599 “Due Health Minister’s order No. V-397 adopted on 28 May, 2004 “Due to list and endorsement of information rendering order of communicable disease and health problems, when epidemiological surveillance should be performed” amendment and addition” [in Lithuanian]. Available from: http://www3.lrs.lt/pls/inter3/dokpaieska.showdoc_l?p_id=376175&p_query=&p_tr2=2
7. Bartulienė A, Jasulaitienė V, Malakauskas A et al. Methodical guideline for trichinellosis epidemiological and epizootological surveillance and control, diagnostics, treatment and monitoring of recovered patients. Vilnius: Lithuanian Centre for Communicable Disease Prevention and Control; 2003. [in Lithuanian]. Available from: http://www.ulac.lt/uploads/tekstai/teises%20aktai/trich.pdf