A.P. Rosolovsky, V.A. Pyanykh, V.N. Ignatyeva
Directorate of the Federal Service for Surveillance on Consumer Rights Protection and Human Well-Being in Novgorod Oblast (Rospotrebnadzor in Novgorod Oblast), Veliky Novgorod, Russian Federation
Citation: Rosolovsky AP., Pyanykh VA., Ignatyeva VN. Emergence of Cases of Dirofilariasis in Novgorod Oblast, Russia, in 2010-2012. EpiNorth 2012;13:91-5.
The incidence of dirofilariasis in Novgorod oblast was analyzed. Before November 2010 no cases of dirofilariasis were registered in Novgorod oblast but 8 cases were reported in the region from November 2010 to August 2012.
Dirofilariasis is a disease caused by Dirofilaria repens, a nematode infecting the subcutaneous tissue of various body parts, mucous membranes and conjunctiva of the eye, genitals (scrotum, testicles, etc.), mammary glands as well as the inner coat of tissues and organs in the abdominal cavity of a human being (3). This is a tissue-invasive helminthic infection characterized by slow development and long-term chronicity. People usually get infected with dirofilariasis after being bitten by bloodsucking mosquitoes belonging to the Aedes, Culex and Anopheles genera (1) that carry infectious dirofilaria larvae (6). Mosquitoes acquire the disease from infected dogs (or occasionally cats) and some wild predators (wolves, foxes, etc.). The most widely-spread species of dirofilariasis in Russia – Dirofilaria repens (D. repens) and Dirofilaria immitis (D. immitis) – are obligate parasites of carnivorous animals of the canine and feline families. Mature female dirofilariae (D. repens) are usually 135 – 150 mm in length, while male dirofilariae are typically 50-58 mm long. Dirofilariae development includes change of two hosts. Mature fertilized female dirofilariae excrete microfilariae in the bloodstream of their host. Microfilariae may circulate in the blood of the host without any morphological changes up to 2.5 years or until they are transmitted to a bloodsucking insect.
A human being cannot become the source of infection since the concentration of dirofilariae is usually rather low and there is practically no chance for a human to get infected with female and male parasites simultaneously. Therefore, female dirofilariae usually remain unfertilized and do not excrete any microfilariae in the blood of their host. According to the published data (3), dirofilariasis is diagnosed among patients of different age groups: from 3 to 75 years. Most of patients are between 30 to 39 years; the lowest number of patients is registered in the age group under 9 years. Women get infected with dirofilariasis more often than men.
The true incidence of dirofilariasis is unknown. Since medical specialists often lack knowledge about the infection, it is often incorrectly diagnosed under some other disease of non-parasitic etiology.
The aim of this paper is to analyze cases of dirofilariasis registered in Novgorod oblast.
Materials and Methods
Epidemiological investigation reports on patients infected with dirofilariasis in Novgorod oblast from November 2010 to August 2012 were analyzed. The results of dirofilariasis tests conducted among domestic and service dogs by specialists of the veterinary service in Novgorod oblast since 2005 were also taken into consideration.
Parasites were identified morphologically at the laboratory of medical parasitology and immunology of the Federal Budgetary Scientific Institution “Rostov Research Institute of Microbiology and Parasitology” (Rostov-on-Don).
Novgorod oblast is located in the northwest of the Great Russian plain (Fig. 1). It covers 385 km from east to west and 250 km from north to south. The region borders Pskov oblast in the southwest, Leningrad oblast in the northwest and the north, Vologda oblast in the northeast and Tver oblast in the east and the southeast. The total area is 55.3 thousand square kilometers. As of January 1, 2012 the population of Novgorod oblast was 630 thousand people. The central city of the region is Veliky Novgorod, located at latitude 580 31’N.
The climate of the region is moderate continental with considerable humidity: winters are comparatively warm and summers are not hot. The average temperature in January is -10ºС and the average temperature in July is between +16.5º С and +18º С. The average precipitation level is from 500 to 650 mm per year (4).
Dirofilariasis in the Russian Federation
From 1996 to 2001 there were 152 cases of dirofilariasis registered in the Russian Federation. Most of the cases were reported from the southern regions of the country that are traditionally endemic for the infection. The distribution area of dirofilariasis covers the whole territory of the Russian Federation, to the south from the 58th parallel in the western part of the country and from the 50th parallel in the Far East of Russian Federation. The major factor restricting the distribution area of this parasite is the lack of warm summer seasons necessary for the vector and parasite to develop in a vector (2). In recent years the infection foci with local transmission were also revealed in areas with moderate climate up to the latitude of 55-57º N, among residents of Moscow, Ryazan, Tambov, Tula, Voronezh, Lipetsk and other regions of Russia.
Dirofilariasis in Novgorod oblast
There were no cases of dirofilariasis reported in Novgorod oblast prior to November 2010. In 2010 – 2011, the summer was extraordinarily warm with very high temperatures (over +30ºС) registered over a long period of time.
From November 2010 to August 2012 there were 8 cases of the infection (with D. repens as pathogen) diagnosed among the population of the oblast. All cases of the disease were sporadic with no relation between the cases (Table 1, Fig. 2).
Five of eight patients (62.5%) were women, 3 (37.5%) were men including 1 child.
The patients complained that they felt something “crawling” in their belly and suffered from painful and itchy bumps. In 5 of 8 cases (62.5%) the parasites were found in the conjunctiva and periorbital area of the eye; one woman had 2 worms extracted from subcutaneous tissue of the belly and the thigh, one patient had parasites under the skin of the left hand and the child had helminthes in the scrotum area. All patients had been bitten by mosquitoes and none of them had left the Novgorod oblast. In 7 cases helminthes were extracted surgically, in one case a patient retrieved the parasite on her own from the opened bump on the skin of the little finger on her hand.
There are 2 species of malarial mosquitoes Anopheles, 16 species of the Culex genus, 4 species of the Culiseta genus, and 1 species of Mansonia mosquitoes found in Novgorod oblast.
The average quantity of mosquitoes on observer per 20 accounting minutes in the area of Veliky Novgorod in 2009 was 30 mosquitos, in 2010 - 61.7, in 2011 - 66.7 mosquitos and in 2012 - 42 specimens. The active period of mosquitoes starts in the middle or end of May with peak activity lasting approximately 1.5-2 months (5).
We analyzed the test results for dirofilariasis among dogs conducted by specialists of the veterinary service. According to the data, 15.2% of dogs tested were already infected with D. repens in 2005. In contrast, from 2006 to 2010 the extent of infection among service dogs was not high (about 3.2%). In 2011 the frequency of infection among service dogs increases to 11.3% (12 out of 106 dogs were tested positive for microfilariae). Dirofilariasis was first revealed among private-owned dogs in 2008. Testing of private-owned dogs is conducted in accordance with the order of the Veterinary Committee of Novgorod oblast on a voluntary basis with permission from the dogs’ owners.
Discussion and Conclusion
The results of epidemiological investigations indicate that dirofilariasis may have been imported to Novgorod oblast by service dogs that had been regularly sent to the Northern Caucasus to participate in specific missions during the previous years. The abnormally hot summers of 2010 and 2011 with the temperature over +30ºС created favorable conditions for the development of parasites in their vectors. At the same time the population of mosquitoes also increased twofold during these years from 30 mosquitoes per 20 minutes of monitoring in 2009 to 66.7 in 2011. These circumstances may contribute to the formation of the focus of dirofilariasis in Novgorod oblast and result in domestic cases of infection among the population.
The appearance of domestic cases of dirofilariasis in Novgorod oblast located in the northern part of Russia demonstrates how the incidence of infectious and parasitic diseases can be influenced by climate changes. To prevent further spread of the infection among the population, a comprehensive plan for the prophylaxis of parasitic diseases for 2010-2012 has been developed in cooperation with the Veterinary Committee of Novgorod oblast. The measures include reducing the population of stray dogs and cats, preventive dehelminthisation treatment of domestic animals in the spring and summer, dehelminthisation treatment of infected domestic animals, control of mosquitoes that carry the infection (extermination of imago and larvae) and information and public health education campaigns devoted to the prevention of dirofilariasis.
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