The veterinary care in the Nepal-Indian border is considerably inadequate so, husbandry and domestic animals and stray dogs as well as the wildlife might be a potential source of parasitic infections. Large populations of stray dogs are present in the urban districts of Nepal/India. The present study reported the first occurrence of dirofilariosis at a prevalence of 19.33% in Nepal. In the closely related areas, in the eastern boundary, Borthakur et al. (2015) have reported that the prevalence rate of 11.38% in Assam and Mizoram. Similarly, Ranjbar-Bahadori et al. (2010) reported that the prevalence of D. immitis was 12.29% in Garmsar area, the central part of Iran.
The mosquito is the main vector for Dirofilaria spp. The larval development to the infective third stage in mosquito vectors, like Anopheles, Culex and Aedes, depends on several factors. The ability of an invertebrate host to survive, invasion of microfilariae and the consequent development is essential for evaluating the vector competence (Kartman 1953; Taylor 1960; Montarsi et al. 2015). The overall hygiene, the improper disposal of garbage, and the inadequate animal welfare, all contribute the dispersal of mosquito vectors, the intermediate host, as well as stray dogs, the definitive host. In Nepal, huge populations of stray dogs are present, and there are no adequate preventive measures.
Currently, the occurrence of dirofilarioids in the blood of stray dogs was evident by the use of blood examinations tests. It is known that traditional methods for detecting filarial parasites is by observing and identifying their larvae (microfilariae) in the blood/skin specimens, usually after application of various staining techniques (McCall et al., 2008; Siwila et al. 2015). Unfortunately, morphological characters including the length and width of each filarioid species greatly vary among commonly released literature as well as they are closely associated to the fixation techniques used. Such variation might lead to misidentification of the recovered microfilariae, particularly when several Dirofilaria spp. or Acanthocheilonema spp. are detected in the surveyed district (Magnis et al. 2013; Little et al. 2018). Both direct smear and the modified Knott’s methods are used for identification of microfilariae, particularly for the heartworm, Dirofilaria immitis, but the later is more reliable as it is more sensitive test depending on the concentration of microfilariae, while the direct smear is a quick test but non-concentrative. Therefore, the priority of choice is for the modified Knott’s method (Watanabe et al. 2004)
The duration of the life cycle of Dirofilaria species in stray dogs is approximately 3–7 months, with the diagnosis was often late and the primary symptoms pass unnoticed, therefore, veterinary health problems evoke when clear clinical symptoms appear. In the present work, a significant relationship between dirofilariosis and the respiratory rate [χ2 (1, N = 150, 7.73, P = o.o21)] of infected dogs was given. This might be attributed to that microfilariae pass within the peripheral circulation and gain access to lungs producing the heartworm associated respiratory disease (HARD). The adult Dirofilaria spp. can survive up to 6 years inside the infected dog, and this might explain the significant higher infection rate [χ2 (1, N = 150, 12.44, P = 0.006)] in old-aged dogs and the lower prevalence in dogs aged less than one year. It is worthy to mention that the sex of dogs had no significant effect [χ2 (1, N = 150, o.474, P = 0.491)] relative to dirofilariosis. Clinically, the alteration in the body temperature was non-significant [χ2 (1, N = 150, 0.985, P = 0.611)].
Hematologically, values of the PCV was non-significant [χ2 (1, N = 150, 2.571, P = 0.277)]. Biochemically, it has been found that SGPT and SGOT were significantly elevated with unclear clinical symptoms indicating that the infected dogs were subclinically infected. Such enzymatic alteration might be suggested to be due to the predominant intracellular activity which occurs as a result of the damaged tissue cells. Similar findings were obtained by Niwetpathomwat et al. (2007) in Thailand. With the progress of the disease, more cellular damage takes place and the typical clinical picture of the disease evokes. To the best of our knowledge, this is the first report denoting the occurrence of dirofilariosis in stray dogs in Siddharthanagar sub-metropolitan (Indo-Nepal Border), Lumbini, Nepal. Due to being a mosquitoes-transmitted disease, strict hygienic measures regarding eradication of stray dogs, with the proper disposal, as well as adequate control of mosquitoes are urgently demanded in terms of zoonosis and hygiene.