INTRODUCTION

Canine filariasis is the disease that gives name to the infestation by the parasite Dirofilaria in dogs, also known as heartworm, cardiac verminosis, heartworm disease, worm disease in the heart (^{Rawlings and Calvert, 1997}, ^{Montoya-Alonso et al., 2011}; ^{Alho et al., 2018}). In the world there are two species of Dirofilaria, of interest for human and veterinary medicine (D. repens and D. immitis) (^{Liotta et al., 2013}). D. repens is a disease present in Europe, Africa and Asia; on the other hand DI or heartworm present in mammals, mainly carnivores and primates: dogs, cats, foxes, coyotes, ferrets and sea lions (^{Vezzani et al., 2006}, ^{Orihel et al., 1998}, ^{Genchi et al., 2011}; ^{Alho et al., 2018}).

DI is a cosmopolitan nematode, originally considered of strict veterinary importance; subsequently it was recognized as zoonotic; in humans it causes skin and lung lesions. Cases of dirofilariasis have been reported in large mesenteric vessels, peritoneal vessels, spermatic cord and "right" heart (^{Chinapa et al., 2004}, ^{Sánchez-Klinge et al., 2011}, ^{Wang et al., 2019}).

Clinically ill animals show few signs of infestation; although these depend on the severity of the disease, the location of the filaria, the time that has been present (^{Knight, 1980}, ^{Ceribasi and Simsek, 2012}, ^{Dearsley et al., 2019}), and the amount of damage to the heart; as well as the lungs, liver and other organs; but always the affected animal will show less tolerance to exercise (^{Fox et al., 1999}, Ceribasi and Simsek, 2012, ^{Wang et al., 2019}). The adult worms, in the canine, form a mass in the right ventricle causing a congestive heart failure in the pulmonary artery; while microfilariae circulate in the blood (^{Knight, 1980}, ^{Fox et al., 1999}, ^{Montoya-Alonso et al., 2011}, ^{Alho et al., 2018}).

Microfilaria circulates in the bloodstream, but cannot develop adult worms without passing through an intermediate and transmitting host, the "hematophagous" mosquito that belong to the Phylum Arthropoda, Insecta Class, Diptera Order, Nematocera Suborder, Culicidae Family (^{Christensen, 1978}; ^{Liotta et al., 2013}; ^{Alho et al., 2018}) and the genera: Aedes, Anopheles, Culex and Taeniohynchus; the family has 3,000 species included in 34 genera, receptive as intermediate hosts and biological DI vectors (^{Sánchez-Klinge et al., 2011}, ^{Urquhart et al., 2001}, ^{Simón et al., 2012}, ^{Dearsley et al., 2019}) .

For the biological cycle to occur in the mosquito, it is necessary that in the infected mosquito a series of transformations take place in larval stages (L1, L2 and L3), all this happens between 13 to 16 days (^{Kittleson and Kienle, 2000}; ^{Bowman and Lynn, 1999}; ^{Montoya-Alonso et al., 2011}; ^{Dearsley et al., 2019}). On the other hand, the development in the host mammal occurs after 2 days to 3 months, reaching lengths of 3.2 to 11 cm (L4 and 5; ^{Bowman and Lynn, 1999}; ^{Liotta et al., 2013}; ^{Wang et al., 2019}). The number of adult worms harbored varies from 1 to more than 250 in the dog (^{Dillon, 2000}; ^{Dearsley et al., 2019}). The survival of DI in the dog is from 3 to 8 years (^{Atkins, 1994}, ^{Dillon, 2000}, ^{Newton, 1968}, ^{Liotta et al., 2013}, ^{Dearsley et al., 2019}).

In Mexico epidemiological studies have been conducted to determine the presence of DI in dogs, and its prevalence varies according to the living conditions of the animals and the climatic variations of the region (^{Bautista-Garfias et al., 2001}). Indeed, the highest prevalences are found in tropical and subtropical regions (^{Labarthe and Guerrero, 2005}, ^{Liotta et al., 2013}, ^{Wang et al., 2019}). In a prevalence study conducted in the 11 municipalities of Nayarit state, they found a prevalence range of 2.5 to 33.33 % (^{González-Morteo et al., 2015}, ^{Wang et al., 2019}). ^{Rodríguez-Vivas et al. (1994)}, conducted a study in Mérida city, Yucatán, and found a prevalence of 12.5 %.

The blood test is the most practical and simple method for the diagnosis of DI; although it is a qualitative test, it does not indicate the number of microfilariae and the severity of the lesions. In fact, the diagnosis is usually established from regular blood tests (^{Paras, 2011}, ^{Wang et al., 2019}), such as blood count, cases of chronic cough in individuals living in endemic areas and to detect worms adults in the heart through radiographic plates, especially in cases of vena cava syndrome (^{García et al., 2011}; ^{Alho et al., 2018}). In sick animals, a clinical diagnosis is made by several methods for the identification of microfilariae of infected dogs: a) method of direct observation of serum, b) serum concentration method; c) immunological methods to detect antigens and d) modified Knott technique (^{Ferrer -Montaño et al., 2002}; ^{Fernández et al., 2017}; ^{Dearsley et al., 2019}).

In Guerrero state and particularly in the municipalities of Acapulco de Juárez and Cuautepec, there is no information on the prevalence of DI in domestic canines. Therefore, the objective of the present study was to determine the prevalence of Dirofilaria immitis in domestic canines in the municipalities of Cuautepec and Acapulco de Juárez, Guerrero, Mexico.

MATERIAL AND METHODS

RESULTS AND DISCUSSION

In the municipality of Cuautepec, 15.68 % of positive canines were found in microfilariae. The highest percentage of positive animals was found in males than in females and animals> 3 years of age (P <0.05). The canines that presented the highest percentage were those of CC of 4 and 5 that the minors on this scale. On the other hand, a higher percentage of positive animals was found in small and medium size canines (P <0.05). A higher percentage was also found in canines of an indefinite mestizo breed, who lived outside the home, in coexistence with other congeners and who spent more time caring for the home (P <0.05) (Table 1).

The results of the present study show that a high prevalence of ID in canines was found in Cuautepec municipality. Results consistent with this study were similar to those found in the municipalities of Bahía de Banderas Nayarit (12.7 % prevalence) (^{González-Morteo et al., 2015}) and Chontalpa Tabasco (17.5 % prevalence) (^{Torres-Chable et al., 2018}); but different from those reported by ^{Rodríguez-Vivas et al. (1994)} in Yucatán state (6.54 % prevalence). These same investigations (^{Rodríguez-Vivas et al., 1994}, ^{González-Morteo et al., 2015}, ^{Torres-Chable et al., 2018}), mention not having found an effect between the sexes (males and females), age, height, race, place where they lived (inside or outside the house) and coexistence with other dogs.

However, in the present study the animals where the microfilaria were found were males, with high CC (3 and 5 points), small size and medium size. This can be explained as follows: working dogs are generally of an indefinite mestizo breed, medium size, they inhabit outside the home, they have the possibility of interacting more with other dogs and due to the location they are more exposed to mosquito bites host of the DI parasite.

On the other hand, in the municipality of Acapulco de Juárez, 7.44 % of domestic dogs positive for microfilaria were found. The highest percentage of positive animals was found in small animals, with CC from 1 to 3 and living with congeners in the home (P <0.05). Likewise, a higher percentage of positive females was found, with an age> 3 years of age, of an indefinite mestizo race and living outside the home (P <0.05, Table 2).

The results of the present study show that, in the city of Acapulco de Juárez, Guerrero, a low prevalence of DI was found in domestic dogs. Results similar to those of this study were reported by ^{Rodríguez-Vivas et al. (1994)} in the state of Yucatán (6.54% prevalence). Contrary to these results, they were different from those found in the municipality of San Blas Nayarit by ^{González-Morteo et al.} (2015; 33.33% prevalence) and by ^{Torres-Chable et al. (2018)} in Chontalpa Tabasco (17.5% prevalence). These same investigations (^{Rodríguez-Vivas et al., 1994}, ^{González-Morteo et al., 2015}, ^{Torres-Chable et al., 2018}), mention not having found an effect between the sexes (males and females), age, height, race, place where they lived (inside or outside the house) and coexistence with other dogs.

However, in the present study the animals where the microfilaria were found were male, of low CC (1 to 3 points), small size and medium size; this can be explained as follows: most pets are of medium size, live outside the home, have the possibility of interacting more with other dogs and have a greater exposure to mosquito bites intermediate host of the parasite.

In the present study it can be mentioned that at least in the sampled municipalities, DI disease prevails; due to this and by some particular characteristics to consider it as an enzootia to the disease (Dirofilariasis). As the authors mentioned in their localities have considered it; It is possible to use this term because in this specific geographical area of the state of Guerrero the dog populations that live outside the home are continuously affected by mosquitoes and consequently by DI.

CONCLUSION

The results of the present study allow us to conclude that, in the domestic dogs of the municipalities of Cuautepec and Acapulco de Juárez, Guerrero, a high prevalence of DI was found (average: 11.56 %), and the males had a higher percentage of infestation (21 %; Cuautepec). Likewise, it was found that canines of medium size and those with high CC were positive in the parasite detection tests.