Evaluation of different dosages of doxycycline during the adulticide treatment of heartworm (Dirofilaria immitis) in dogs

The endosymbiont bacteria Wolbachia plays an important role in the pathogenesis and inflammatory immune response to heartworm (Dirofilaria immitis) infection in dogs. Doxycycline is used to reduce Wolbachia from all life stages of heartworm to avoid large releases of the bacteria during the death of the worms. However, the dose and duration currently recommended have been extrapolated from the treatment of other rickettsial infections. Therefore, the aim was to study the dynamics of Wolbachia IgG antibodies in heartworm-infected dogs under adulticide treatment using different dosages of doxycycline. Forty-nine heartworm-infected dogs were recruited. On day 0 (diagnosis), monthly ivermectin (6 μg/kg) was prescribed, as well as daily doxycycline for 30 days, at 10 mg/kg/12 h (n = 13), 5 mg/kg/12 h (n = 19), and 10 mg/kg/24 h (n = 17). Dogs underwent adulticide treatment and blood samples were collected on days 0, 30, 90, and 120. All dogs had antibodies against recombinant Wolbachia surface protein (rWSP), confirming the important role of the bacteria in heartworm. No significant differences were found in anti-rWSP response by presence/absence of microfilariae, or by parasite burden on day 0. In all treated groups, the anti-rWSP antibody response was not significantly different between days 0 and 30 but was significantly lower between days 0 and 120 (p < 0.05). The results of the present study suggest that the administration of a lower dose than currently recommended is sufficient to achieve a significant reduction of Wolbachia in dogs infected by D. immitis.

Evaluation of serum biomarkers and proteinuria for the early detection of renal damage in dogs with heartworm (Dirofilaria immitis)

Glomerulonephropathy associated with Dirofilaria immitis (heartworm) is relatively frequent in infected dogs. Given the importance and the scarcity of studies focused on its prevalence and diagnosis, the objective was to determine the prevalence of proteinuria and functional indicators of glomerular filtration rate in dogs with heartworm disease and discuss its utility in the detection of renal impairment. Sera and urine from 47 infected dogs were analyzed in a reference laboratory. Urea, creatinine, plasma proteins and serum symmetric dimethylarginine (SDMA) were analyzed in sera, while the UPC ratio was performed in urine. Dogs were further evaluated for the presence/absence of microfilariae, pulmonary and systemic hypertension, and the parasite burden was assessed. The results showed that 19.1 % of dogs showed proteinuria (UPC > 0.5) and 17 % showed borderline proteinuria (UPC 0.2-0.5). Creatinine and SDMA were high (>1.8 mg/dl and ≥18 μg/dl, respectively) in 4.2 % of dogs. UPC ratio was significantly increased in dogs with high parasite burden and in dogs with microfilariemia (p < 0.05). Dogs with pulmonary hypertension showed higher increases in proteinuria as well, which was probably due to the chronicity of the infection. No significant differences were found in serum and urine values regarding systemic blood pressure. Despite the limitations of this study, proteinuria/borderline proteinuria was present in 36.2 % of dogs with heartworm disease, and this may be due to glomerular disease. Therefore, the detection of proteinuria, along with other renal biomarkers in the diagnostic protocols, could help identify kidney alterations or risk of renal damage in heartworm disease.

Variation of the adulticide protocol for the treatment of canine heartworm infection: Can it be shorter?

The treatment of canine heartworm has been modified over the years, adding improvements for greater efficacy, safeness and better prognosis. Currently, the recommended adulticidal protocol consists of the administration of three doses of melarsomine dihydrochloride, preceded by the administration of macrocyclic lactones over two to three months. The objective of this study was to evaluate a variation of the adulticide protocol of heartworm in 76 dogs infected by Dirofilaria immitis, which consists of the pre-administration of macrocyclic lactones (ivermectin) during a single month. On the day of diagnosis, presence of circulating microfilariae was determined and an echocardiography was performed to assess the parasite burden. Treatment began on day 0, with doxycycline for 30 days (10 mg/kg BID) and monthly ivermectin (6mcg/kg). On day 30, the first dose of melarsomine dihydrochloride was administered, followed by a second and third dose on days 60 and 61, respectively. On day 90, the dogs were examined and discharged. Six months after the last dose, all dogs were negative to the presence of antigens and amicrofilaremic. Also, 38.1% of animals were evaluated by echocardiography, showing absence of adult parasites. It is considered that the ineffectiveness of melarsomine against worms <4 months should be avoided by the previous administration of macrocyclic lactones for two to three months, killing larvae <2 months while older filariae are allowed to mature to be susceptible to melarsomine dihydrochloride. With this protocol, this gap would be covered for the 2nd and 3rd injections, when worms would be four months and older. In addition, there is evidence that melarsomine is effective against worms under four months and macrocyclic lactones have some efficacy against heartworms older than two months. This modification allows a faster elimination of heartworms and a better compliance from the owners of the infected dogs.