First molecularly-confirmed canine rickettsiosis in Southern Philippines (Cebu): A case report

Canine rickettsiosis has previously been reported only in the northern Philippines. The present report documents the first case of canine rickettsiosis in the southern Philippines, confirmed by in-clinic and standard polymerase chain reaction (PCR). It aims to highlight the importance of PCR and accurate diagnosis, which affect the course of treatment for tick-borne diseases, including canine rickettsiosis.

A 3-year-old 4-kg male Shih Tzu was presented for hospitalization to an animal clinic in Cebu, Philippines. Presenting clinical signs included vomiting, lethargy, inappetence, and jaundice. About 14 months prior, the dog was diagnosed with canine babesiosis and canine ehrlichiosis from another clinic and was tested using commercial serological kits. Point-of-care initial serological tests were positive for Ehrlichia, Babesia, and Leptospira spp., leading to a preliminary diagnosis of multiple vector-borne diseases. Treatment was initiated with doxycycline, along with clindamycin and penicillin-based medications targeting the assumed pathogens. Additional treatments were mainly symptomatic. On day 12, in-clinic PCR testing procedures were performed. The sample was further tested using standard PCR. The PCR results revealed negative detection for Ehrlichia, Babesia, Leptospira, Mycoplasma, and Hepatozoon spp. but positive for Rickettsia sp. Standard PCR also showed positive results for Rickettsia sp. Because of the new PCR results, the prescribed treatment was modified before the patient was discharged.

This case demonstrated the challenges of serological detection, where cross-reactivity, persistent antibodies, and possible vaccine-induced antibodies complicated the initial diagnosis. It shows that a positive serological test indicates exposure but not necessarily active infection. The case also illustrates that, while doxycycline provides a broad safety net for common vector-borne diseases, unnecessary antimicrobials may be administered if confirmatory PCR is not performed. Further studies should clarify the epidemiological status of this pathogen in the southern Philippines.