Rats as Indicators of the Presence and Dispersal of Pathogens in Cyprus: Ectoparasites,Parasitic Helminths,Enteric Bacteria,and Encephalomyocarditis Virus

Introduction

R odents have a world-wide distribution as they are able to adapt to a big variety of environments and food availability. They cause great economic losses and play a very important role in the spreading of zoonoses in time and space because they are known to transmit more than 24 different pathogens to humans (Seguin et al. 1986, Webster 1996). Despite the fact that zoonoses constitute a primary health hazard, mainly for people living in rural areas, their importance has been underestimated. During the last 25 years, new pathogens have been identified, most of which are responsible for zoonoses, and old ones reemerged in areas where they have been thought to be wiped out. Factors such as changes in the environment, climatic conditions, and globalization favor the increase of rodent populations and their ectoparasites (arthropod vectors of zoonoses), which aid in the amplification of the problem.

Cyprus, situated in the eastern Mediterranean at the crossroads of three continents Europe, Asia, and Africa (Fig. 1), has played a very important role in history and commerce through the ages. An island, a close ecosystem, with a temperate climate and rich wildlife with the agricultural and stock-raising sectors forming the backbone of the economy is ideal for the manifestation of zoonoses. Rodent populations are large and widespread. Rattus rattus, known to inhabit the island since ancient times, and the recently introduced Rattus norvegicus (Hoppe 1985) are the two species of rats established in Cyprus, which play an important role in the epidemiology of the zoonoses found there. In this role they are aided by blood-sucking arthropods, found in all prefectures of the island (Spyridaki et al. 2002, Psaroulaki et al. 2006), and by migratory birds stopping in Cyprus during their journey from Africa to Europe and vice versa, importing new pathogens and ectoparasites to the ecosystem (Kaiser et al. 1970, Harrus and Baneth 2005).

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FIG. 1.

The geographic distribution of Rattus rattus (RR) and Rattus norvegicus (RN) in Cyprus. Helminth parasites found in rats in the five prefectures of the island and the two high-risk areas for Salmonella spp. (Kofinou and Palaiometocho). Both locations were near abattoirs and dumps.

The object of this study was to investigate the presence and distribution of a number of pathogens, important for public health in Cyprus, using rodents as sentinels. These were Echinococcus granulosus, a cestode widespread in Cyprus before the 1970s, with an annual surgical incidence rate of 12.9 per 100,000 inhabitants (Economides et al. 1998). After it was successfully eradicated, consumable animals and people stayed clean of the parasite for over 30 years. However, changed political and economic conditions present this cestode the opportunity to reemerge. Autochthonous echinococcosis has been diagnosed in a number of sheep and goats during the last 10 years (Economides and Christofi 2000, Christofi 2007). The reestablishment of this parasite would be indicated by its presence in the food chain, in which infected rodents play an important role. The same would be true for Encephalomyocarditis (EMC) virus, which when introduced in the island in 1994 caused great economic losses in the pig-raising industry (Loucaides et al. 1996). At the same time, the incidence and dispersal of a number of pathogens carried by rodents was also studied. The survey involved the capture of rodents from representative areas of the island and the study of their ectoparasites. Their tissues and intestinal contents were examined for parasites and cultured for the isolation of bacteria and viruses. The results were analyzed using the Geographical Information System (GIS) technology to identify high-risk areas.

Materials and Methods

Results

Animals and their ectoparasites

Of the 625 rodents captured, 402 (64.6%) were R. norvegicus, 220 (35.4%) R. rattus frugivorus, and 3 Mus musculus. The majority were females (329, 52.4%). Most of the rodents appeared healthy with satisfactory weight for their age, species, and sex: 11 were not in good health (low weight, dermatological ulcers, poor quality of hair, skin lesions, and many had problems with eyes); 94 in moderate health (low weight, poor quality of hair, and skin lesions); 253 in good health (expected weight and no obvious problems); 234 in very good health (higher than expected weight and no obvious problems); 30 in perfect health (a lot higher than expected weight and no obvious problems). The number of rodents captured varied according to the time of the year: the greatest numbers caught in August (101 animals), September (95 animals), and October (82 animals), although the same effort was put each month. The majority of the rats were captured in Nicosia prefecture, the center of the island (33.3%). A high percentage of the rodents (40.5%) harbored arthropods. A total of 1038 ectoparasites were collected from 252 animals (59 from R. rattus and 193 from R. norvegicus) (Table 1), 1035 fleas, and 3 ticks. The number of fleas per rat ranged from 1 to 25 (mean, 4 fleas/rat). Five flea species were identified: Xenopsylla cheopis (70.34%), Ctenocephalides felis (24.22%), Ctenocephalides canis (0.48%), Leptopsylla segnis (4.36%), and Nosophylla fasciatus (0.67%). A higher proportion of ectoparasites were found on R. norvegicus (48% cf. 27% on R. rattus, p < 0.0001) (Table 4), on males (47% cf. 35% on females, p = 0.002), in Ammochostos and Larnaca prefectures (68% and 62% respectively, compared with other prefectures, p < 0.0001), and on healthy animals (50% of those in perfect health cf. 18% of those not in good health, p < 0.0001) (Table 4 and Fig. 2).

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FIG. 2.

The geographic distribution of arthropod ectoparasites on R. rattus (RR) and R. norvegicus (RN) in Cyprus.

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Table 1.

The Ectoparasite Species Collected from the 622 Rodents Caught (220 Rattus rattus and 402 Rattus norvegicus)

Ectoparasite species found	No. (%) of infested rodents	No. (%) of infested Rattus rattus	No. (%) of infested Rattus norvegicus
Any ectoparasite	252 (40.5)	59 (23.4)	193 (76.6)
Xenopsylla cheopis	189 (30.4)	27 (12.3)	162 (40.3)
Ctenocephalides felis	75 (12.1)	33 (15.0)	42 (10.4)
Leptopsylla segnis	17 (2.7)	3 (1.4)	14 (3.5)
Ctenocephalides canis	2 (0.3)	1 (0.5)	1 (0.2)
Nosophylla fasciatus	4 (0.6)	0	4 (1.0)
Ticks	3 (0.5)	0	3 (0.7)

Discussion

The distribution of the two rat species, R. rattus and R. norvegicus, appears to have changed during the last years, indicating a movement and rearrangement of populations. The recently introduced R. norvegicus has established itself in niches previously occupied by the black rat, which was introduced in Europe during the Roman times bringing the cholera epidemic (Audoin-Rouzeau 1999). The movement of rodents is important in the spread of diseases in time and space, affecting the local population, livestock, and wild animal health (Fèvre et al. 2006) and causing great economic losses to animal husbandry and agriculture.

Cyprus, an island ecosystem of 9455 km² with over half a million inhabitants, has succeeded in the elimination of a number of zoonoses, such as echinococcosis and brucellosis (Steele et al. 1976, Economides et al. 1998, Economides 2000). However, it appears that these, as well as other zoonoses, are reemerging/emerging because of changing conditions.

Rodents play an important role in the maintenance and spread of Echinococcus because they can be eaten by canines, the final host. Before 1970 the parasite caused great economic losses with 40–100% of sheep, 4–50% of lambs, 20–50% of cattle, 27–93% of goats, and 5–22% of pigs infected (Polydorou 1982). The control program carried out by the Department of Veterinary Services in 1971–1985 successfully eradicated the parasite (Polydorou 1977, 1984). At that time, the number of dogs dropped from 46,000 to 6000. However, this number is estimated to be over 100,000 presently and consumable animals are known to be illegally transported to the Republic from the non–government-controlled area. This, as well as the fact that stray dogs and rodents freely cross the boarder from the North to the South, where the parasite is still found (Sadjjadi 2006), can result in the reemergence of the problem. Recognizing the danger, the Department of Veterinary Services reintroduced the control program in 1994 and the absence of cysts in rodents shows that the measures taken are successful. Trichinella larvae were not found in any of the rodents examined. The veterinary services are carrying out trichinoscopic tests on biological samples from wild and livestock animals since 1970. Our results confirm that the island is free of this Nematode because rodents are important in the epidemiological chain of the parasite (Oivanen et al. 2000).

This is the first survey concerning EMC virus on the island since 1994, when it was found responsible for great economic losses in the pig-raising industry (Loucaides et al. 1996). EMC virus is found in different continents associated with the death of pigs (Koenen et al. 1999). Rodents are probably the most common reservoir hosts and the source for the infection of animals and humans (Seaman et al. 1986). The mechanism by which the virus is transferred from reservoir hosts to pigs is probably by the consumption of infected rodents or animal feed contaminated with their urine or feces.

Three helminth parasites were found in 92 rodents; all three, C. fasciolaris, H. diminuta, and Physalloptera spp., were detected for the first time in Cyprus (Table 2 and Fig. 1). These parasites, carried by rodents, although may be transmitted indirectly to humans, do not pose a serious health hazard. H. diminuta was detected in 44 animals scattered all over the island, indicating that this helmith is well established in the ecosystem. C. fasciolaris, the larval stage of Taenia taeniafornis, was found in 55 rats caught along the south cost of the island (Fig. 1). It uses members of the Felidae as final host and rodents as intermediate hosts. It produces a cyst on the liver without obvious impairment. Physaloptera spp. was detected only in one rat in the Paphos district. It uses a number of arthropods as intermediate hosts and may be transmitted to humans causing gastric ulcers. No human infections due to these parasites have been reported on the island. It is interesting that rats of both species were infested with helminth parasites, although a higher proportion was found on R. rattus (p = 0.007); yet, infested rats were found mainly in animal-raising areas (p = 0.0006).

Medical reports show that salmonellosis is a common health problem in Cyprus. Rodents are carriers of a great number of Salmonella spp., thus helping in their distribution (Davies and Wray 1995). This pathogen was isolated from the intestine of 9% of the rats examined and the majority of the infected animals came from areas near abattoirs and garbage disposal. The serotypes found in the rodents are the ones found in patients and poultry in Cyprus. Today, Salmonella enteritidis, the most infectious and most widespread species in the world, has been reported as one of the most frequently identified Salmonella sp. in the island (EFSA Annual Report 2007). More than 50 phage types of S. enteritidis are known, with S. enteritidis phage type 4 being the most hazardous one. In Cyprus the species S. enteritidis, S. typhimurium, S. dublin, S. anatum, S. infantis, S. sainpaul, S. blokley, S. morbificans, S. essen, S. agona, S. hadar, S. bredeney, S. chincol, S. mission, and others have been isolated from biological materials, food staffs, and animal tissues (EFSA Annual Report 2007). Twelve of these species and serotypes were also isolated from the rodents examined (Table 3). Humans and animals, especially pigs and poultry, may be asymptomatic carriers of Salmonella and excrete the bacterium, thus infecting the environment, animals, and humans. GIS indicated 2 out of the 51 study areas as high risk for Salmonella spp. (Kofinou and Palaiometocho), both locations near abattoirs and dumps (Fig. 1).

The use of rodents as epidemiological tool proved valuable for the study of the incidence and dispersal of pathogens on the island and for monitoring the antiechinococcosis campaign. Their use as disease sentinels has the advantage of low cost, shorter latency of disease development, and greater ease of obtaining tissue samples and autopsy material. They could be used as early warning systems because animal and human health is closely related. Although Cyprus is an island, the political problem dividing the island north and south has not allowed common preventive actions for zoonoses. Rodent control measures have been undertaken in the past in Cyprus (Hoppe 1985); yet, a campaign to control zoonotic pathogens, to be effective, must cover the whole of the island and it should be targeted around abattoirs, dumps, and animal farms.