Blood- and vector-borne bacteria (VBB) can cause severe pathology and even be lethal for dogs in many regions across the globe. Accurate characterization of all the bacterial pathogens infecting a canine host is critical, as coinfections are common and emerging and novel pathogens that may go undetected by traditional diagnostics frequently arise.

In 2016, the World Health Organization declared Sri Lanka as having successfully eliminated lymphatic filariasis as a public health concern. However, in recent decades, several infections with subperiodic filarial species suggestive of zoonotic infections have been recorded across the country. The arthropod-borne filarioids Dirofilaria repens, Brugia malayi, Brugia ceylonensis, and Acanthocheilonema reconditum are historically known to be endemic in dogs in Sri Lanka. Despite this, limited information on the prevalence, diversity, and predictors of filarial infections in dogs in the country has resulted in suboptimal control and prevention of these parasites, some of which are known to be zoonotic. To address this, whole blood and metadata were collected and analysed from 423 pet dogs across three geo-climatic zones within Sri Lanka. Blood samples were screened using the Modified Knott's Test (MKT) and PCR followed by Sanger sequencing. Multivariable logistic regression models were used to assess predictors for canine filarial infections. Dirofilaria sp. ‘hongkongensis’ (Dirofilaria sp. HK) and Brugia sp. Sri Lanka (SL) genotype were identified infecting dogs. The overall prevalence of filarial infection in pet dogs by PCR was 36.9% (95% CI 32.3–41.7%, n = 156), compared to 18.8% (95% CI 15.2–22.9%, n = 79) detected using the MKT. >80% of filarial-positive dogs were infected by Dirofilaria sp. HK, while the remaining dogs were infected by Brugia sp. SL genotype. Increasing age (p < 0.001) and residing in the low-country wet zone (p < 0.001), which includes regions that were endemic for human filariasis in Sri Lanka, were associated with filarial infections in dogs. No clear pathognomonic signs for filarial infection were identified, indicating that dogs act as reservoirs for these potentially zoonotic pathogens. Given the morphological similarity of Dirofilaria HK and Brugia sp. SL microfilariae with those of D. repens and B. malayi, respectively, it is likely that these species have been misidentified in the past. Prevention and control measures of these potentially zoonotic canine filarial infections are highly advocated to safeguard both canine and human health.

Vector-borne pathogens (VBPs) cause significant diseases in dogs in the tropics. In Sri Lanka, the scarce availability of previous studies on canine VBPs has hampered an accurate evaluation of their prevalence in pet dog populations. In this study, we collected demographic, clinical, and environmental data together with whole blood from 423 pet dogs from three geoclimatic zones in Sri Lanka. All blood samples were screened using a previously validated multiplex qPCR assay to detect the six most prevalent canine VBPs in tropical Asia. Multivariable logistic regression models were used to investigate environmental and host factors as predictors of VBP infections. Overall, 254 dogs (60.1%, 95% CI: 55.3–64.6%) were infected with one or more VBPs. Babesia gibsoni was the most prevalent VBP with 37.4% (95% CI: 32.7–42.2%) of dogs infected followed by Hepatozoon canis (21.04%, 95% CI: 17.25–25.24%), haemotropic mycoplasmas (10.2%, 95% CI: 7.5–13.4%), Babesia vogeli (5%, 95% CI: 3.2–7.5%), Ehrlichia canis (4.5%, 95% CI: 2.7–6.9%), and Anaplasma platys (3.8%, 95% CI: 2.12–6.1%). Predictors of VBP infections included tick infestation for H. canis ( ) and A. platys ( ), as well as age for B. gibsoni ( ) and H. canis ( ) infection. Local breed ( ), male dogs ( ) and flea infestation ( ) were significantly associated with haemotropic mycoplasma infections suggesting direct-blood exchange through fighting and fleas as a possible means of transmission for these pathogens. Clinical results suggest that B. gibsoni and E. canis caused clinically significant disease, especially in exotic breeds such as German shepherds and Rottweilers compared to the local breeds ( ). Measures such as educating pet dog owners on the importance of being vigilant on ectoparasite infestation of their pets, preventing pet dogs from interacting with stray or community dogs, and the compliant use of effective ectoparasiticides will be crucial for effective control of VBPs in pet dogs in Sri Lanka.

Canine vector-borne pathogens (CVBP) have a worldwide distribution and show a high prevalence in tropical countries such as Sri Lanka. Some CVBP are zoonotic, with dogs identified as reservoir hosts for human subcutaneous dirofilariasis and potentially for spotted fever rickettsioses and re-emergent brugian filariasis in Sri Lanka, making these pathogens emerging public health issues in the country. Veterinarians are crucial in monitoring, preventing, and controlling these pathogens in dogs. Therefore, it is imperative to understand veterinarians’ knowledge, attitude, and practices (KAP) regarding CVBP to mitigate their impact. A survey was designed and administered electronically to veterinarians residing and practising in Sri Lanka. Responses were evaluated using descriptive, univariable, and multivariable analyses to investigate associations between demographic factors, knowledge, attitude, and practices related to CVBP. Out of the 170 participating veterinarians, nearly 70% had moderate or high knowledge. However, the awareness of zoonotic pathogens, Brugia spp. (16%) and Rickettsia conorii (18%), was low, and a considerable number of veterinarians were unaware of the zoonotic nature of Dirofilaria repens. Based on multivariable analysis adjusting for experience and self-rated knowledge, new graduates had higher odds of knowledge compared to experienced veterinarians (OR 5.7, 95% CI 1.7–23, p = 0.028). Questions assessing the attitude towards CVBP indicated that most participating veterinarians comprehend and agree with their importance. Nearly all participants agreed that ectoparasite control is the best option to prevent CVBP infections (91%, 153/167) and that for effective treatment of CVBP, a definitive diagnosis is required (81%, 135/167). However, veterinarians recommended suboptimal treatments for some CVBP, like Babesia gibsoni. Better practices were associated with being a companion animal practitioner (OR 2.4, 95% CI 1.1–5.7, p = 0.032) and having a low to moderate canine caseload (OR 3.6, 95% CI 1.3–10.4, p = 0.038). Limited knowledge of zoonotic CVBP among veterinarians, along with suboptimal treatment, might contribute to dogs acting as reservoirs and high prevalence of these pathogens in Sri Lanka. Therefore, continued veterinary education is recommended to improve knowledge and practices, which in turn will help to improve the diagnosis, treatment, and control of these infections in Sri Lanka to ensure the well-being of dogs and humans.

Filarioid nematodes are harmful vector-borne pathogens that afflict humans and other animals, with numerous species transmissible from animals to humans, i.e., zoonotic. In the last decade, one zoonotic filarioid, previously named Dirofilaria sp. Hong Kong genotype has been increasingly found as a cause of disease in people traveling from South Asia and has recently been characterized as a novel species: Dirofilaria asiatica . Nonetheless, the epidemiology of this parasite in Asia remains poorly understood. Therefore, with the aid of a novel pan-filarioid nanopore-based metabarcoding assay, we aimed to elucidate the epidemiology of dirofilariosis in Cambodia. We tested 504 canine blood samples collected from five regions and used the cytochrome c oxidase ( cox1 ) gene sequences obtained to conduct phylogenetic analyzes. We found no evidence of the canine heartworm Dirofilaria immitis nor Dirofilaria repens in the country. Conversely, we detected D. asiatica and genetically characterized it from the eastern district of Tbong Khmum at a local prevalence of 4% (95% CI = 1.6%–9.8%), an area just ~100 km northeast of the country’s capital, Phnom Penh. We also detected Acanthocheilonema reconditum from 0.2% of dogs sampled (95% CI = 0%–1%). Phylogenetic and haplotype network analyzes of Cambodian D. asiatica sequences clustered with strong support to those found from canines and humans in Bhutan, Hong Kong, India, and Sri Lanka. This genetic characterization of D. asiatica in Cambodia highlights the need for further epidemiological research into human filariases in Cambodia, given the zoonotic nature of this parasite and that mass drug administration targeting filarioids is no longer conducted in the country. IMPORTANCE: Parasitic filarioid nematodes are transmitted by blood-sucking arthropods and can cause significant disease in animals and humans (i.e., zoonotic). One such zoonotic filarioid ( Dirofilaria asiatica ) that has recently been characterized has been found responsible for a growing number of cases of human filariases, particularly in individuals who live in or have traveled to South and Southeast Asia. D. asiatica predominantly infects dogs, and therefore, to better understand this parasite’s distribution, we tested 504 dogs from five regions of Cambodia using an advanced diagnostic approach. We found that the local prevalence of D. asiatica in dogs in the eastern district of Tbong Khmum was 4%. Given that mass drug administration programs to control human-infecting filarioid nematodes in Cambodia have stopped, this first detection of D. asiatica in Cambodia is alarming, given its potential to cause disease in vulnerable cohabiting people.

Lymphatic filariasis (LF) affects approximately 120 million people globally and is caused by Wuchereria bancrofti, Brugia malayi and Brugia timori. Sri Lanka was historically endemic for both bancroftian and brugian filariasis, with B. malayi presumed eliminated by the late 1960s. The country achieved validation of LF elimination as a public health problem in 2016. However, sporadic Brugia infections have been detected in microfilaria surveys from the mid-2000s onwards; the sub-periodic periodicity of which is suggestive of a zoonotic origin and warrants further research. Night blood survey (NBS) surveillance was conducted by the Anti-Filariasis Campaign, Ministry of Health, Sri Lanka, from 2019 to 2023. Brugia-positive human samples and archived canine samples were analysed using a next-generation sequencing metabarcoding platform targeting mitochondrial and nuclear loci. Bayesian and neighbour-joining phylogenetic analyses and minimum-spanning network approaches were used to characterise lineage relationships. Among 1,855,165 individuals screened, 52 were identified with Brugia-like microfilariae. Metabarcoding generated 1.2 million high-quality reads with both mitochondrial cox1 and ribosomal DNA markers confirming a single Brugia lineage circulating in humans, mainly in children. Sequences of the c ox1 gene showed 99.4–100 percent nucleotide identity to the Brugia Sri Lanka (SL) genotype previously detected in dogs in Sri Lanka and Tamil Nadu (India). rDNA sequences showed low similarity to B. malayi or Brugia pahangi, indicating that the parasite represents a distinct Brugia taxon lacking a reference rDNA sequence. The findings provide evidence that human brugian filariasis in Sri Lanka is caused by a previously unrecognised zoonotic Brugia species maintained in dogs. This has important clinical and public health implications given that human infections have occurred in children despite LF being declared eliminated as a public health problem. Crucially, the incorrect classification of circulating filarioid species may lead to inappropriate clinical and programmatic responses. For example, the newly identified canine reservoir of this Brugia genotype means that human-only mass drug administration might not be sufficient to interrupt this species’ transmission. These results underscore the need for integrated One Health surveillance to prevent re-establishment of LF and safeguard regional elimination goals. No specific funding was received for the present study. This study was supported by a consulting funding (PRJ_002971).