Introduction
1.1 Dog populations
Humans and dogs share a long history and were probably associated with European early-modern humans [1], coexisting indoors and outdoors and colonising new environments, often in cooperation [2].
From ancient times dogs have been used by humans as tools for different purposes, such as hunting, gathering food, caring for livestock, protection, and more recently as detectors of explosives and drugs, as companion animals, or as assistants for people with various types of disease or disability [3-5]. Therefore, their coexistence has been wide-ranging, and has generated numerous opportunities for around 260 zoonotic diseases to emerge between dogs and humans [2, 6].There are almost one billion dogs worldwide [7], but the relationship between the numbers of people and dogs varies according to the geographic area and socioeconomic conditions of each country or region [8]. In developed countries the human to dog ratio varies from 6 to 10:1 according to the World Health Organisation [9]; in Italy the human:dog ratio is 9:1 [10], and in the United States it is 3.6:1
[11]. The dog population in South America is very large, around 87.6 million. In Brazil in particular there are 44.9 million children aged under 14 years, and an estimated total of 52.2 million dogs, which means there are more dogs than children
[12]. In Argentina, a survey carried out for food companies determined that there are approximately 9 million dogs, and that 78% of households have a dog, whose function is mainly exclusively companionship [13]. The situation in Chile is similar, where the dog population is around 3.5 million and 64% of households have at least one [14], while in Uruguay the dog population is 1.75 million and 72% of households own a dog [15].
To encourage responsible ownership of this large number of dogs, it was necessary to enact laws indicating what responsible dog care implies (Argentina: Decree 1088/11; Chile: No.
21.020/17; Uruguay: No. 1189/14). Animal welfare thus imposes obligations on the owner, which include vaccinations, deworming, neutering, adequate food, and keeping pets confined to the household or taking them outside on a lead, thus preventing them from roaming freely. It should be noted that in most localities of these countries these laws are not enforced effectively [16].1.2 Dog care
Although national laws have been promulgated several years ago, knowledge of them and the care received by dogs is far from adequate [17-20]. The biggest problem in these countries is that dogs are allowed to roam freely in public areas, and this is associated with education, socio-economic level, the idiosyncrasy and customs of each country, the role the dog plays within the family, and the low importance that people give to how their dog can affect other people or animals [21]. In addition, allowing dogs to roam freely is strongly correlated with other aspects of dog care, such as a lack of appropriate vaccination and deworming treatment [21]. The care given to dogs that roam freely is poorer than for dogs which are confined, and they are rarely taken to the vet due to the high cost that this represents [22]. In Chile, the average cost spent per pet for annual veterinary checkups, diagnoses, vaccines and treatment is US$ 330 [4], while in Argentina this cost is around US$ 100 annually (personal observation). The percentage of vaccinated dogs is low, even when there is a possibility of rabies contagion [14, 23], and the frequency of deworming is in most cases inadequate considering that dogs can roam freely on public roads, becoming reinfected [23-25]. The percentage of animals that are neutered is also insufficient, despite the national or local neutering programs run in the three countries [21, 26, 27]. Neutered animals represent less than half the dog population [21, 23, 28] and the majority are older than 3 years; in many cases dogs are allowed to have at least one litter of offspring [23].
1.3 Dogs, parasites and diseases
One Health is recognised as a valuable paradigm for global health management, and seeks the integration of human and animal health.
The risk of transmission of a zoonotic disease from dogs to humans is related to the abundance of infectious forms in the environment, climatic conditions, whether dogs roam freely, and theThe State of Knowledge on Intestinal Helminths in Free-Roaming Dogs in Southern...
DOI: httpd∕dx.doi.org∕1o.∣5772∕ΓTexLi.9612ζ
behaviour of humans that exposes them to infective sources [29, 30]. It has been observed that free-roaming dogs are more exposed and prone to acquiring parasites [24, 31-33]. In Chile, rural dogs are associated with agricultural and livestock activities. They are unsupervised, have freedom to roam and are given limited veterinary care [34]. In Argentina, parasite richness and prevalence are positively associated with free-roaming animals, and only a small proportion of dogs (17%) is subjected to some degree of movement restriction [20]. In the cities of Argentinian Patagonia, another important factor that promotes infection by zoonotic parasites, mainly cystic echinococcosis, is the domestic slaughter of small ruminants for human consumption. This practice occurs frequently in rural areas and the peripheral low-income neighbourhoods of cities, where dogs are fed with the raw offal of sheep and goats [35, 36]. The vast majority of parasites registered in South America are cosmopolitan zoonotic parasites transmitted through dog faeces, such as Toxocara canis, Ancylostoma caninum, Toxascaris leonina, Echinococcus spp., and Dipylidium caninum, which are common parasites in dogs worldwide [12]. Zoonotic parasitic infections in dogs are a public health issue not only in developing countries but also in developed nations, such as in the USA and European countries [37, 38]. Other parasites like Trichuris vulpis are distributed worldwide, but are rarely transmitted to humans [39]. Some human parasites like Ascaris lumbricoides and Strongyloides stercoralis are occasionally reported in dogs [40, 41]. Therefore, worldwide, dogs may harbour zoonotic parasites that affect the health and wellbeing of humans, their distribution being linked to poverty, poor knowledge of sanitary practices, insufficient hygiene and problems with unconfined and untreated dogs [42].
Pet diseases may pose risks to human health but are rarely included in surveillance systems. Although pet-borne infections have become increasingly relevant to human health, systematic notification of these infections is not currently conducted, except for rabies and Echinococcosis in some countries [22, 43].Southern South America is a region with varied geography and climate and marked altitudinal and latitudinal differences; for example, plains (Pampas in Argentina and Uruguay), arid plateaus (Patagonia), forests (Patagonia and northeastern Argentina), and mountains of high altitude between Argentina and Chile (the Andes). The climate ranges from humid tropical in northern Argentina and Uruguay, arid in northern Chile, to humid cold in the south of Argentina and Chile. This climatic variety favours the distribution and occurrence of different parasites. On the other hand, the socio-economic condition of a large part of the population is characterised by poverty and a low-income economy. This scenario is accompanied by a lack of parasitological studies, surveillance and zoonosis control plans on the part of public health organisations [44].
The objective of this work is to describe, through bibliographic analysis, the occurrence, prevalence, species richness, and distribution of intestinal helminth parasites found in dog faeces in urban and rural areas of southern South America (Argentina-Chile-Uruguay).
2.