Zoonotic helminths parasites in the digestive tract of feral dogs and cats in Guangxi, China

Background In Guangxi, a province of southern China, an important number of dogs and cats roam freely in rural settings, and the presence of these animals in proximity of people may represent a risk of parasitic zoonoses. The objective of the present study was to investigate the presence and identify gastrointestinal helminths in feral carnivores in Guangxi province. Therefore, post mortem examination was performed in 40 dogs and in 39 cats. Results The Gastrointestinal helminths were found in all the necropsied dogs and in 37 out of 39 cats. Fifteen species were identified including 7 trematodes, 3 cestodes and 5 nematodes. Most of them may be responsible for zoonotic infections. Conclusions Major zoonotic gastrointestinal helminths, including liver and intestinal flukes, Toxocara spp., and Ancylostoma spp., are present in feral dogs and cats in Guangxi, and may represent a significant risk for public health.


Background
The potential role of carnivores as reservoirs for zoonotic pathogens has been recognized as a significant public health concern worldwide [1 -3]. Among zoonotic agents, helminths of dogs and cats constitute a diversified group including trematodes, cestodes and nematodes. Carnivores usually act as definitive hosts and they contribute to the transmission of zoonotic infections by disseminating infective eggs or larvae in the environment (in the case of Toxocara spp., Ancylostoma spp., Strongyloides stercoralis or Echinococcus spp.) or by contaminating intermediate hosts that may be further consumed by humans (especially in the case of fishborne zoonotic trematodes like Clonorchis sinensis). Moreover, in some Chinese regions, dogs and cats may be eaten and represent a source of human infection by Trichinella spp. In a recent review, Chen et al. mentioned that canine and feline trichinellosis was reported in 11 and 10 endemic Chineses provinces, respectively [2].
In Southern China, a large number of dogs and cats roam freely in rural settings and the presence of these animals in proximity with people may represent a risk of parasitic zoonoses. The objective of the present study was to investigate the presence and identify gastrointestinal helminths in feral dogs and cats in Guangxi province.

Methods
Gastrointestinal helminths were identified in 40 dogs and 39 cats. The study was conducted from March to October 2012. All of the dogs were collected from Binyang county (near the city of Nanning) and examined at Guangxi Zhuang autonomous region center for disease control and prevention. All of the cats were bought from markets in Nanning. Based on the legislation to protect the welfare of animals and taking into consideration the 3Rs, the animals were sacrificed according to the agreed policy and principles for animal euthanasia and following the guidelines of the Ethical Committee of Guangxi University, which provided a formal approval to the study. The liver, stomach, small and large intestine were separated into four Petri dishes. Each of the portions was cut longitudinally and only the larger parasites were collected. The remaining content was collected in a sediment cup. After several cycles of sedimentation and suspension, the final sediment was poured into a Petri dish and examined under a stereoscopic microscope. All the gastrointestinal helminths were collected and fixed in 70 % alcohol or 10 % formalin. The number of individuals of each species was recorded. Cestodes count was based on the number of scoleces. For further identification, the trematodes and the cestodes were flatten and stained with hydrochloric acid carmine. The nematodes were cleared with lactophenol. All the parasites (trematodes, cestodes and nematodes) were identified morphologically to species according to identification keys [3][4][5][6].

Results and discussion
Gastrointestinal helminths were found in all the dogs. Eleven species of helminths were identified, including 5trematodes, 3 cestodes, and 3 nematodes ( Fig. 1 and Table 1). The predominant parasite was the cestode Dipylidium caninum, detected in 72.5 % of the examined dogs. The overall infection rate of dogs with more than one helminth species was 77.5 %.
Gastrointestinal helminths were found in 37 out of 39 cats. Twelve species of helminths were identified, including 6 trematodes, 3 cestodes and 3 nematodes ( Fig. 1 and  Table 2). The Predominant parasites were the cestode Dipylidium caninum (in 72.5 % of the cats), the liver fluke Clonorchis sinensis (33.9 %) and the cestode Spirometra erinaceieuropaei (33.3 %). The overall infection rate of cats with more than one helminth species was 73.0 %.
Among the 14 species of helminths identified in the present survey, Echinochasmus liliputanus, Pharyngostomum cordatum and Ancylostoma ceylanicum were reported for the first time in Guangxi province. The main characteristics concerning the morphology and biology of these parasites are presented in Table 3.
Nematodes of the genus Strongyloides and cestodes of the genus Echinococcus were not detected in the present study.
In China, only little information is available about the prevalence of gastrointestinal parasites in dogs and cats. Andrews [7] first reported the presence of helminths in dogs and cats in Shanghai. Wang et al. [8] and Dai et al. [9] identified helminths in 178 dogs from Heilongjiang province, and in 438 dogs from Hunan province, respectively. The present study demonstrated for the first time that gastrointestinal helminths are common in feral carnivores in Guangxi province. In dogs, the infection rate was 100 %, the same value as that reported by Wang et al. [8] in Heilongjiang and Dai et al. [9] in Hunan. In feral cats, the infection rate was 94.9 %, a value similar to that reported by Yang [10] in Sichuan (95 %) and Wang et al. [11] in Guizhou (88.6 %).
The most important result of the present study is that most of the detected helminths can infect humans. In both dogs and cats, the most frequently identified parasite was the cestode Dipylidium caninum, suggesting a high density of flea intermediate hosts in feral carnivores. Humans, normally children, acquire the infection by accidentally ingesting infected fleas [12].
The prevalence of the cestode Spirometra erinaceieuropaei infection in cats (33.3 %) was higher than in dogs (10.0 %). This may be due to the fact that cats hunt amphibians, reptiles, and small mammals (which represent intermediate or paratenic host for S. erinaceieuropaei) more frequently than dogs do. During 1927-2009, more than 1000 cases in humans in 25 Chinese provinces were reported; most cases were in southern China, where human infections were mainly acquired by eating raw or insufficiently cooked meat of frogs and snakes or by placing frog or snake flesh on open wounds for treatment of skin ulcers or on eyes to treat inflammation [13,14]. The high infection rate in definitive hosts probably maintains a high level of contamination in frogs and snakes and consequently a high risk of sparganosis in local residents who have the habit of eating meat of frogs and snakes and some superstitious beliefs in medical properties of raw frog or snake meat [14].
The trematode species Echinochasmus liliputanus was found only in dogs with an infection rate of 10.0 %. This parasite can infect animals and humans as definitive hosts via both metacercariae and cercariae. Through 2002, more than 2500 human cases have been reported in Anhui province, China. Drinking unboiled pond water containing cercariae is the main route of human infection [15][16][17].  Clonorchis sinensis, Echinochasmus perfoliatus, Metagonimus yokogawai, Haplorchis taichui and H. pumilio are liver or intestinal flukes, which can infect both carnivores and humans as definitive hosts. Humans become infected through ingestion of raw or undercooked freshwater fish or shrimp infected with metacercariae [17,18]. Since raw fish is a popular dish in Guangxi, the high prevalence and intensity of liver and intestinal flukes in feral carnivores is of real concern. According to a recent survey based on coproscopic examinations, 59.6 % (428/ 718) of Guangxi inhabitants are infected by Clonorchis sinensis and intestinal flukes [19].
The trematode species Pharyngostomum cordatum is a feline parasite, mainly distributed in Southern China (Fig. 2) [20]. In the present survey the frequency in feral cats (20.5 %) was greater than that reported by Yang [10] in Sichuan (15.0 %). According to Shin [21], humans are likely to be infected with P. cordatum as paratenic host. However, no human infection has been reported so far.
Both hookworms Ancylostoma caninum and A. ceylanicum can infect humans [3]. In the present study, the predominant species was A. ceylanicum, with an infection rate of 17.5 % in dogs and 28.2 % in cats, and it was the only hookworm species found in the examined cats. Human infections with A. ceylanicum were reported in Fujian where the high prevalence of hookworm infections in dogs and cats was identified as a significant risk factor for human contamination [22]. According to Xu et al. (2005), the species Necator americanus and A. duodenale are found to be the most prevalent hookworms distributed in provinces of southern China (including Guangxi), with a mean prevalence of 6.12 % nationwide [23]. Infected people mainly live in less developed rural areas, where dogs and cats may roam freely and farmers often walk barefoot [24].
Toxocara canis infection rate (30 %) reported in the present study in dogs was lower than that previously reported from Heilongjiang (36.5 %) and Hunan (45.2 %), respectively [8,9]. In cats, infection rates with Toxocara cati (5.1 %) and Toxascaris leonina (7.7 %) were relatively low in comparison to previous surveys [10,11]. Toxocarosis is considered as one of the most common parasitic zoonoses in the world and a high incidence has been reported in developing countries. However a few investigations have been made in China and there is only one report indicating that contact with infected dogs is the risk factor for human toxocarosis in China [25]. With regard to Toxocara in cats, Li et al. [26] mentioned the presence of a new Toxocara species (T. malaysiensis) in Guangzhou, China. This parasite seems to be remarkably different from T. canis, T. cati and T. leonina of dogs and cats by molecular characterization [26]. However, the role of T. malaysiensis as a zoonotic parasite has yet to be confirmed. A row of 24 collar spines is present; the vitellaria are distributed from the posterior end of acetabulum to terminal; the body surface is covered with spines from the collar to the posterior testis (Fig. 1a) IH: snails, bivalves, crustaceans, fishes, and amphibians [14] Pharyngostomum cordatum (Trematode, Diplostomidae) 1.40-2.10 × 1.02-1.52 mm DH: cats, lions [16] Indistinctly bipartite body, a huge holdfast organ, cordiform, and irregular oval testes (Fig. 1c) IH: snails, tadpoles Reservoir host: toad, snakes, tortoises and shrews [17] Ancylostoma ceylanicum (Nematode, Ancylostomatidae) Male: 5.26-6.50 × 0.23-0.26 cm Dog, cats, humans [3] Female: 5.79-6.70 × 0.25-0.31 cm The anterior edge of the buccal capsule is armed with a pair of large hook-like teeth (Fig. 1d & e) Fig. 2 Adults of the trematode species Pharyngostomum cordatum on the pharynx of a cat