Ocorrência de microfilaremia em cães (Canis familiaris) em municípios do Rio de Janeiro

Esse trabalho teve como objetivo realizar o levantamento epidemiológico de cães com microfilaremia em Centro Diagnóstico Veterinário localizado no município de Niterói, estado do Rio de Janeiro. A microfilaremia pode ser causada por várias espécies de filarídeos, como a Dirofilaria immitis, Dirofilaria repens e Acanthocheilonema reconditum. Essas espécies liberam microfilárias na corrente sanguínea de seu hospedeiro infectado, sendo a espécie que mais acomete os cães, Dirofilaria immitis, causadora da parasitose denominada dirofilariose canina. Para a realização deste estudo foram analisados 10.996 exames hematológicos, no período de janeiro a setembro de 2020, dos quais 292 foram positivos (2,66%) para microfilaremia, sendo 284 (97,26%) pela técnica do esfregaço sanguíneo, dois (0,70%) pela técnica da gota espessa e seis (2,05%) por ambos os métodos. Os dados foram coletados dos municípios de Niterói (36%), São Gonçalo (30,5%), Maricá (29,5%) e Itaboraí (4,1%). O mês de janeiro teve 42 casos positivos (3,77%), fevereiro 34 (3,48%), março 9 (0,86%), abril 41 (4,15%), maio 42 (3,54%), junho 40 (2,45%), julho 48 (3,45%), agosto 17 (1,12%) e setembro 19 (1,37%). Dentre os animais positivos para microfilaremia 147 eram machos (50,3%), 144 fêmeas (49,3%) e 1 não foi informado (0,3%), com idade média de 6 anos, não tendo sido encontradas diferenças estatísticas entre os gêneros e raças dos animais. Face ao exposto a média de casos positivos para microfilaremia canina foi de 2,65% do total de exames analisados, ressaltando a importância dos achados hematológicos e da solicitação de métodos mais sensíveis na rotina clínica.

Can P-glycoprotein and β-tubulin polymorphisms be used as genetic markers of resistance in Dirofilaria immitis from Rio de Janeiro, Brazil?

OBJECTIVE

Dirofilaria immitis, the causative agent of canine heartworm infection, is worldwide the most important filarid to affect domestic dogs. Prevention of this infection is done by macrocyclic lactones, but some reports on the lack of efficacy have been published. Although the actual cause of resistance is unknown, single nucleotide polymorphisms (SNPs) on a P-glycoprotein ABC transporter and β-tubulin genes have been pointed out as candidates for genetic markers of resistance. We conducted a survey to verify the presence of these suggested genetic markers in microfilariae from 30 naturally infected dogs under macrocyclic lactones treatment living in an endemic area in the state of Rio de Janeiro.

RESULTS

The analysis of these specific SNPs demonstrated no sign of polymorphism on the P-glycoprotein loci, while 72 and 48% of the samples were polymorphic to the first and second SNPs on β-tubulin loci, respectively. This work demonstrates that the P-glycoprotein position 11 and 618 were not polymorphic and, therefore, not suitable as a genetic marker of resistance in Rio de Janeiro whereas both β-tubulin loci were polimorphic. This work points out the difficulty of finding a universal genetic marker for resistance.

Serological evidence of canine exposure to arthropod-borne pathogens in different landscapes in Rio de Janeiro, Brazil

Arthropod-borne infections are dependent on environmental conditions, and several combinations of natural and human-related variables play an important role in vector populations as well as the life cycle of agents carried by the arthropods. The top 5 canine arthropod-transmitted agents, Dirofilaria immitis, Leishmania spp., Ehrlichia canis, Anaplasma phagocytophilum, and Borrelia burgdorferi infect unprotected animals without propensity. The purpose of this study was to determine the prevalence of these parasite species in three different landscape settings (sandbanks, plains and mountains) along a 60-km line. During a 6-month period, blood samples were collected from dogs (>12months old) living in the different settings. Prevalence of D. immitis was determined by modified Knott test and ELISA. Prevalence of E. canis, A. phagocytophilum, and B. burgdorferi was determined by ELISA, and Leishmania spp. by ELISA, indirect immunofluorescence, and immunocromatographic assays. D. immitis was most prevalent in the sandbank (68.9%) as well as Leishmania spp. (34.5%), and tick-transmitted agents, A. phagocytophilum and E. canis in the plains (61.7%). B. burgdorferi was not detected. Depending on the resources for arthropods present in regions, dogs are likely to be exposed to different arthropod-borne parasites and should receive preventives tailored to the risk of infection in the region in which the dog resides.

Chemoprophylaxis of Dirofilaria immitis (Leidy 1856) infection at a high challenge environment

BACKGROUND

The frequency of canine heartworm infection in the state of Rio de Janeiro, Brazil was high before chemoprophylactic treatment was available, with one of the highest rates of infection (52.5 %) found among dogs living on the eastern shore of the state. Following the launch of a chemoprophylactic product, the rate of infection gradually decreased, and new infections were rarely reported. After 2005, outbreaks reported at the eastern shore as well as for new infections in other areas of high infection frequency were considered to possibly be related to reduced efficacy of macrocyclic lactones. Therefore, this study aimed to evaluate the efficacy of topical heartworm preventatives from different drug families at the high challenge area of the state of Rio de Janeiro.

METHODS

A total of 46 dogs, including animals negative for Dirofilaria immitis microfilariae and antigen (Snap 4 Dx, IDEXX Laboratories, USA) at the initial screening were randomly allocated to two monthly treatment groups. Dogs in one group received topical moxidectin + imidacloprid and dogs in the other group received topical selamectin for eight consecutive months. Blood samples were obtained for microfilariae and antigen detection until the eleventh month after the first treatment. Dogs becoming microfilaremic or antigenemic on or before day 180 were considered to be infected prior to the first dose and were excluded from the study.

RESULTS

A total of 29 dogs completed the study, including 14 treated with moxidectin + imidacloprid and 15 treated with selamectin. No dogs treated with moxidectin + imidacloprid (0/14) became infected during the treatment period, whereas four dogs of the selamectin group (4/15) became infected.

CONCLUSION

Topical moxidectin + imidacloprid is 100 % effective in preventing D. immitis infections in dogs living in a high challenge natural environment.