Eficacy of reduce doxycycline dosage on inflammatory and stress responses in dogs with heartworm disease

Abstract

nternational heartworm guidelines recommend doxycycline at 10 mg/kg BID for 28-30 days to eliminate Wolbachia pipientis, a key pro-inflammatory bacterium in heartworm disease. However, evidence suggests lower doses may be sufficient. This study evaluated the efficacy of different doxycycline doses in 78 heartworm-infected dogs, divided into two groups: Group A (n=43) received 10 mg/kg BID, while Group B (n=35) received 5 mg/kg BID for 28-30 days.ll Dogs also received ivermectin (6-12 ug/kg) on day 1. Blood samples were collected at baseline (day 0) and after treatment (day 30) to measure CRP and basal cortisol. Anti-rWSP antibodies were analyzed using a non-commercial ELISA.

At day 0, 59% of dogs had pathological cortisol levels (3.55+3.24 ug/dL), and 51.3% had elevated CRP (41.66+42.81 mg/L). By day 30, 52.6% still had high cortisol (3.39+2.22 ug/dL), while 21.8% had persistently elevated CRP (26.78+32.65 mg/L). CRP and cortisol significantly decreased in both groups (p<0.05), with no differences between treatments.

There were no statistically significant differences in anti-rWSP antibody response between days 0 and 30 in either group. High baseline CRP confirmed the strong inflammatory response in heartworm infection, while elevated cortisol suggested stress, consistent with previous reports in animals and humans infected by other parasites. The reduction in CRP aligned with prior findings, likely reflecting W. pipientis elimination and its associated inflammatory response. Similar CRP decreases in both groups suggested that 5 mg/kg BID may be as effective as 10 mg/kg BID in reducing W. pipientis.

On day 30, cortisol levels decreased in both groups, likely due to the significant reduction of W. pipientis. However, a high percentage of dogs still exhibited elevated cortisol levels, which may be attributed to the persistence of vascular damage caused by adult parasites. Additionally, external factors such as handling stress and shelter conditions should also be considered.