Epidemiologic and ecologic characteristics of some diseases transmitted by arthorpods on the littoral of the Republic of Croatia

Military Medicine, Apr 2002 by Mulic, Rosanda

Objective: To show epidemiologic and ecologic characteristics of some diseases transmitted by arthropods on the littoral of the Republic of Croatia. Methods: The pattern of infectious diseases that are transmitted exclusively by vectors was monitored during the period 1985 to 1999. Data on the incidence of the diseases in the Republic of Croatia as a whole and available data on the presence of the vectors for the diseases on the littoral are presented for comparison. Results: Mediterranean spotted fever, murine typhus, Lyme disease, cutaneous and visceral leishmaniasis, and pappataci fever occur sporadically on the Croatian littoral. Tick-borne meningoencephalitis is endemic in the northwestern part of Croatia but is not present on the littoral. Twelve cases of malaria are imported into Croatia per year on average. Conclusion: Diseases transmitted by arthropods are not a major public health problem in Croatia. The medically relevant entomofauna of Croatia has not yet been adequately investigated.

Introduction

The group of diseases transmitted by arthropods includes the diseases transmitted by live hematophagous insects (Insecta), a class of arthropods (Arthropoda). Seasonal occurrence is one of the characteristics of this group of diseases.1 The islands and coastal area of the Republic of Croatia (Palearctic zone, Mediterranean subregion) are characterized by mild and humid winters, usually without keen frost, and hot and rainless summers.2 The specific climatic and geographic conditions determine the ecologic features of the niches, with the present animal communities playing a major role in maintaining certain infections and potentially serving as reservoirs and/or vehicles of the microorganisms.1

From this group of diseases, tick-borne meningoencephalitis, pappataci fever, hemorrhagic fever with renal syndrome, Lyme disease, Q fever, Mediterranean spotted fever, murine typhus, and leishmaniasis (cutaneous and visceral) occur in Croatia as autochthonous diseases. In addition, some 12 cases of malaria are imported into Croatia per year.3,4 These diseases mostly occur sporadically, implicating no risk for the population at large.3-6 The vectors present in the area include various species of mosquitoes (of the genera Anopheles, Culex, and Phlebotomus), ticks (of the genera Ixodes, Dermacentor, and Haemaphysalis), and fleas, which are animal parasites (of the genus Xenopsylla).7-11

The present study was focused on the diseases transmitted by arthropods potentially associated with the epidemiologic burden of the study area. Although Croatia has a well-developed system of infectious disease surveillance and prevention, thus minimizing the potential risks, the vicinity of the subtropical zone, climatic alterations with a tendency toward average temperature increase, intense international traffic, and the presence of biological vectors call for continuous alertness in the field.12,13 According to World Health Organization estimates, Croatia belongs to a so-called "no-risk zone"; other such zones are other European countries, North America, and Australia.14 The epidemiologic situation concerning diseases transmitted by arthropods is of paramount importance for military forces, because this group is more frequently exposed to the risk of these diseases. This fact has become more relevant with Croatia's joining the Partnership for Peace and the frequent NATO exercises in the Adriatic Sea.

Materials and Methods

For the purpose of this study, the term "littoral of the Republic of Croatia" covers the "epidemiologic zones" on the islands and in the coastal and hinterland drainage area of the rivers flowing into the Adriatic Sea. The pattern of infectious diseases that are transmitted exclusively by vectors was monitored during the period 1985 to 1999. The following diseases were observed: malaria, Mediterranean spotted fever, pappataci fever, murine typhus, Lyme disease, tick-borne meningoencephalitis, and leishmaniasis. Data from the Croatian Institute of Public Health were used in this study. Data on the incidence of these diseases in the Republic of Croatia as a whole and available data on the presence of the vectors for the diseases on the littoral are presented for comparison.

Results

Malaria

The last autochthonous case of malaria in Croatia was recorded in 1958.5,10 Twelve cases of malaria are imported into Croatia per year on average, more than half of them on the littoral. Plasmodium falciparum and Plasmodium vivax are most commonly isolated as the causes of malaria, and transmission of the infection to humans is attributable to the resistance of the microorganism to antimalarial agents or to inappropriate chemoprophylaxis.3,4,14

Mediterranean Spotted Fever

In Croatia, the first laboratory-verified case of this disease was reported in 1984.(15) The disease has been demonstrated by laboratory tests in all Mediterranean countries.15-20 In the Mediterranean basin, and in Croatia as well, the main vector is Rhipicephalus sanguineus.9-11,16-18 The tick shows a worldwide distribution.1,9,10 Epidemiologic data on the incidence of the disease in Croatia show it does not occur north of Zadar (Fig. 1). During the last 15 years, 67 patients with Mediterranean spotted fever have been recorded in Croatia.