This study reports the first comprehensive, island-wide investigation of CVBDs comparatively among the privately-owned and free-roaming community dogs and the military working dogs of the SLAF. Even though all the parasites species have been previously recorded in Sri Lanka, those studies are either confined to one or a few sites or focused on particular species of parasites. Blood parasites of military working dogs in SLAF have not been studied before. One-fourth of the dogs (25.3%) examined were infected with haemoparasites, mostly as single infections and some mixed infections. There was no difference in the prevalence of infection among the three dog categories from the SLAF, free-roaming and privately-owned dogs. A study with 2,104 dogs comprising a stray dog population in Asam, India and a hospital population including privately-owned pet dogs and working dogs of the Central Parliamentary Forces reported 57.31% infected with hemoparasites comprising 58.03% in pets, 54.54% in the working dogs and 63.64% in stray dogs . Similarly, there is no difference of infection among the three dog categories, although the percentages of infected dogs are higher than those reported in the present study.
Among the infected dogs, a significantly higher number of free-roaming dogs were asymptomatic compared to the other two dog categories (SLAF and Privately-owned) but there was no difference in the asymptomatic cases between the SLAF dogs and privately-owned dogs. This is anticipated since better natural resistance against hemoparasites in stray dogs compared to privately-owned dogs or pure breeds of dogs has been established long ago . The absence of clinical signs indicates that these dogs may be chronically or subclinically infected with these haemoparasites or as Dantas-Torres and Ontranto (2014)  point out, they may be having clinical pathological abnormalities and organ dysfunctions. Although chronic infections may not pose an immediate threat to the animals, these dogs do remain possible reservoirs for infections, stressful conditions, concurrent illnesses and parturition may precipitate clinical signs in chronically infected animals . The free-roaming dogs are sub-clinically infected and may provide a continuous source of infection for these pedigree dogs. Arthropod vectors can transmit these infections from the free-roaming dogs to owned dogs which are mostly pedigreed dogs. Pedigree dogs are selectively bred to conform to the aesthetic value of the dog rather than its health and therefore frequently suffer from the effects of inbreeding as the gene pool available is highly limited. Studies have shown that such breeding practices could have increased the expression of inherited defects and thus compromised the health and welfare of many breeds [28–31]. The reduced heterozygosity of a highly inbred population can contribute to the frequency of occurrence of inherited disease in the population [30, 32]. The top 50 most popular breeds of pedigree dogs in the UK are predisposed to 312 inherited disorders, with German shepherd dogs and Golden retrievers associated with the most significant number of ailments . Many vector-borne bacteria and protozoa in healthy hunting dogs from Central Italy and confirmed that dogs infected by these pathogens often develop asymptomatic or subclinical forms . Another study in Turkey  reported a lower percentage of 5.4% out of 757 asymptomatic domestic dogs being infected with vector-borne rickettsia and protozoans. The presence of hemoparasites in asymptomatic dogs is relevant from an epidemiological point of view as the transmission potential of symptomatic and asymptomatic dogs can vary depending on the parasite species. For example, some studies have shown that asymptomatic dogs are unable to infect vectors with Leishmania [36,37], others demonstrate that transmission occurs in similar proportion as that for oligosymptomatic animals, but to a lesser extent than for symptomatic dogs [38–43]. It is important to investigate whether these asymptomatic dogs serve as reservoirs. However, Dantas-Torres and Otranto argue that although the term “asymptomatic” is still used in the international literature, it is falling into disuse because the classification of dogs as asymptomatic, oligosymptomatic, and polysymptomatic based only on physical examination  and therefore is of limited value, as it does not consider clinical pathological abnormalities and also disregards dogs presenting organ dysfunction but with-out apparent clinical manifestations  especially when the dog is infected by Leishmania infantum.
The present study reported seven hemoparasites: Babesia gibsoni, Babesia cani, Ehrlichia canis, Hepatozoon canis, Leishmaia sp., Anaplasma platys and microfilariae. Out of these, B. gibsoni, E. canis and A. platys were recorded in all three dog categories. Among these, B. gibsoni was the most prevalent canine hemoparasite island-wide (13.8%). Only one case of B. canis was reported from a privately-owned dog. It is interesting to study why B. canis, which is clinically more important due to its ability to cause lethal nervous signs in dogs, is rare when the vector is the same as B gibsoni. There was no difference in the prevalence of B. gibsoni among the three dog categories: SLAF, free-roaming and privately-owned dogs. Globally, babesiosis is a common vector-borne disease among domestic and wild canines . A recent study from the Anuradhapura district in Sri Lanka reported B. gibsoni and B. canis (with a prevalence of 15.0% and 1.3%, respectively) in addition to mixed infections in three Divisional Secretariat Divisions (DSDs): Rambewa, Tirappane, and Galenbidunuwewa . A more recent study investigated canine babesiosis in dogs brought to the Veterinary Teaching Hospital in the University of Peradeniya and showed a high prevalence of B. gibsoni (78.6%) in the Kandy district . The study conducted in stray dog population in Asam, India also reported B. gibsoni as the highest prevalent infection with an infection rate of 47.16% in hospital dogs and 47.72% in stray dogs . In the present study, all the free-roaming dogs (100%) that were smear-positive for babesiosis (31dogs) were asymptomatic, while 46.7% of the SLAF dogs and 27.5% of the privately-owned dogs were asymptomatic. Asymptomatic babesiosis has been reported elsewhere with a prevalence of 3.42% (29 of 848) cases of asymptomatic dogs in Croatia . The prevalence of babesiosis could be higher in these dogs as Ranatunga et al.  reported that 33.3% of blood smear negative dogs were PCR positive for Babesia DNA.
Ehrlichiosis or infection with Ehrlichia canis was the second most prevalent canine hemoparasite, and its prevalence among the SLAF dogs was as same as that of B. gibsoni infection (15 dogs). Most were asymptomatic. None of the smear-positive, free-roaming dogs (12) showed any signs, while 62.5% SLAF dogs and 50% privately-owned dogs were also asymptomatic. Infection with E. canis in dogs may result in acute disease, chronic disease or remain clinically silent . Moreover, due to the non-specific and variable symptoms of ehrlichiosis, dogs are often misdiagnosed or diagnosed past the point of recovery and such cases can be fatal . A higher prevalence of E. canis infections (56.1%)  compared to the previously reported prevalence of 14% in dogs in the Western Province . A previous study carried out in Sri Lanka observed E. canis in imported dogs . In Asam, India, dogs infected with E. canis was much less (< 3%), comparatively . Ehrlichia canis has a worldwide distribution, and dogs and other canids are the natural hosts. It is generally not considered as a zoonotic agent, but some cases of human infection have been reported in Venezuela .
Anaplasmosis or Anaplasma platys infection was also reported from all three dog categories with a higher prevalence among the SLAF dogs (6.4%) compared to other dog categories. The first record of A. paltys (formerly known as Ehrlichia canis) in Sri Lanka was in 2005 from Colombo used buffy coat analysis and confirmation by PCR . This study reported 18% owned dogs and 12% stray infected while 75% with no clinical signs. The study carried out in three DSDs in the Anuradhpura district didn't report A. platys in their sample . Anaplasma platys is also more common (8.49%) among the working dogs in Asam, India (Bhattacharjee and Sarmah, 2013). Anaplasmosis is an emerging infectious diseases affecting dogs in many parts of the world and can be manifested as acute or non-clinical infections .
Leishmania was found only in two free-roaming dogs as a single infection with a prevalence of 0.9%. This is consistent with the results of a recent study examining 114 stray dogs in Sri Lanka; only one dog (0.9%) having detectable anti-Leishmania sp. antibodies . Another study examined 151 dogs, of which two showing Leishmania amastigotes in Giemsa-stained smears (prevalence 1.3%), one in the skin and one in peripheral blood . These studies show that the prevalence of canine leishmaniasis may not be a widespread CVDB. However, its zoonotic potential has been highlighted [13,54]. Human leishmaniasis is an emerging infection caused by Leishmania donovani which is traditionally considered a visceralizing anthroponotic species but causes cutaneous leishmaniasis in Sri Lanka . In the present study both infected dogs showed clinical signs. Asymptomatic dogs, some even without skin parasitism, are competent in transmitting Leishmania to the vector, the sandfly . However, some  argue that the term "asymptomatic" is of limited value because it does not consider clinical-pathological abnormalities and those with organ dysfunction  and recommend the LeishVet guidelines of [56, 57] for those who are involved in research in canine Leishmaniasis. In India, the presence of Leishmania has been attributed to domestication of dogs by tribes to protect them from untoward activities of wild animals . Canine leishmaniosis due to L. infantum is enzootic in some countries, and it is an emerging zoonosis in endemic foci.
Only one privately-owned dog was infected with H. canis. Acute hepatozoonosis in five dogs have been characterized by neurological symptoms, ataxia orparesis, emaciation and anaemia . Recently, in Galenbindunuwewa, H. canis has been reported with B. gibsoni infections . Hepatozoon canis is a common CVBD and has been reported from several parts in India  and also is distributed throughout the old world. Disease-associated with the infection is usually asymptomatic, while disease, when present, may range from subclinical and chronic, especially in the absence of concurrent infections, to severe and life-threatening .
Microfilaria was also found in all three dog categories but was always as mixed infections either with B. gibsoni in free-roaming and privately-owned dogs or with B. canis and A. platys in the SLAF dogs. Canine filariasis has been reported previously from Sri Lanka and the species identified include Dirofilaria repens, Brugia ceylonensis and Brugia malayi, and their geographic distribution and prevalence varied from 30 to 68.8% [11,61, 62]. Mallawarachchi et al.  anticipate that the actual rates of infections are even higher. However, the prevalence of microfilaria in the present study was 0.6% with only four dogs being infected. All the canine filaria worms recorded in Sri Lanka are zoonotic (see 11] and have the potential to cause disease in humans. In 2016, Sri Lanka received the WHO certification for the elimination of lymphatic filariasis or the bancroftian filariasis ; however, the emergence of zoonotic canine filariasis may endanger the filariasis-free status of the country due to the potential reservoirs for humans.
The pattern of infection of hemoparasites was similar in the SLAF dogs and the free-roaming dogs, island-wide. However, it varied in the privately-owned dogs. Socio-economic factors of the dog owners and their capability or willingness to afford to use methods to control ectoparasites contribute to the level of infection among the privately-owned dogs . The SLAF veterinarians claim that there are a thorough quarantine and screening process for all the imported dogs, even to detect infections at subclinical levels before introducing them to the military units. It is highly likely that they have acquired the diseases through the tick vectors once they are brought to the country. Stray dogs may act as reservoirs of these diseases as there is a substantially high population of stray dogs found island-wide. As a strategy to suppress the spread of rabies, the Rabies Ordinance of 1893 allowed stray, free-roaming dogs to be seized and disposed of. However, in 2006 a presidential order was passed to implement a “no-kill policy” and with the lobbying of animal activists, a more humane approach of "catch-neuter-vaccinate-release" method (CNVR) was practiced. The statistics show a dramatic decline in reported cases of rabies, but these free-roaming dogs act as constant reservoirs of CVBDs by habouring the vectors of these infections.
Environmental changes have an effect on emerging parasitic diseases . As Dantas Torres reviews in 2015, human developments affect the environment and the climate, which in turn have an effect on biodiversity and alter tick population dynamics and tick-borne pathogen transmission. The present study provides baseline data on the types of infections and prevalence of these diseases in dogs in military kennels, free-roaming, and privately-owned dogs in Sri Lanka. They can be used in future studies of disease dynamics, vectors of infections, seasonality, together with additional knowledge on ticks and other vectors, animals, pathogens, and their interactions with the whole ecosystem.