Tick-Borne Diseases in Dogs: Clinical Syndromes and Diagnostic Approaches

Canine tick-borne diseases represent a complex group of vector-borne infections that manifest with overlapping clinical syndromes, making accurate diagnosis essential for effective management. These diseases are caused by obligate intracellular bacteria, protozoan parasites, and viruses transmitted primarily through hard ticks (Ixodidae) and, less commonly, soft ticks (Argasidae) [1]. The clinical presentation often involves fever, thrombocytopenia, anemia, and multi-organ dysfunction, yet the specific etiologic agent determines the pathophysiologic trajectory and required therapeutic intervention [2, 3]. This article provides a comprehensive reference for veterinary clinicians and diagnostic pathologists, detailing the major tick-borne pathogens affecting dogs, their associated clinical syndromes, and the contemporary diagnostic modalities available.

Major Pathogens and Clinical Syndromes

Ehrlichiosis (Ehrlichia canis and Ehrlichia ewingii)

Canine monocytic ehrlichiosis, caused by Ehrlichia canis, is a globally distributed disease transmitted primarily by Rhipicephalus sanguineus (the brown dog tick) [4]. The pathogen infects monocytes and macrophages, leading to a triphasic clinical course: acute, subclinical, and chronic. Acute phase signs include fever, depression, lymphadenomegaly, and thrombocytopenia [4]. Chronic infection can result in pancytopenia, epistaxis, and secondary infections due to immune-mediated bone marrow suppression. Ehrlichia ewingii, in contrast, predominantly infects granulocytes and tends to cause a milder, non-febrile polyarthritis, though thrombocytopenia remains a consistent finding [3]. Coinfections with Anaplasma platys and Ehrlichia canis have been documented, particularly in tropical regions, and these coinfections often exacerbate the clinicopathologic abnormalities [5]. Biomarkers such as erythrocyte sedimentation rate, C-reactive protein, and interleukin-6 are elevated in naturally infected dogs and may serve as adjunctive inflammatory indicators [6].

Anaplasmosis (Anaplasma platys and Anaplasma phagocytophilum)

Anaplasma platys infects platelets, causing cyclic thrombocytopenia in dogs [5]. The clinical syndrome is often subclinical, but severe cases may present with petechiation, epistaxis, and prolonged bleeding times. Anaplasma phagocytophilum, the agent of granulocytic anaplasmosis, is less commonly reported in dogs but can cause acute febrile illness with lethargy, anorexia, and polyarthritis [7]. Both species are members of the family Anaplasmataceae and are transmitted by ixodid ticks [8, 7]. Diagnosis relies on detection of morulae within infected cells on blood smear or via molecular techniques.

Babesiosis (Babesia canis and Babesia gibsoni)

Canine babesiosis is a protozoal disease caused by large (e.g., Babesia canis) and small (e.g., Babesia gibsoni) piroplasms. Babesia canis infection produces hemolytic anemia, hemoglobinuria, fever, and splenomegaly, with severity influenced by the geographic strain and host immune status [9, 10]. In southeastern Romania, Babesia canis has been reported as a frequent cause of clinical disease in dogs with outdoor access [11]. The hallmark of babesiosis is hemolytic anemia, which may progress to systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS). Plasma biomarkers of SIRS and MODS, including eicosanoids and lipids, are significantly altered in infected dogs, reflecting the inflammatory response [12, 13]. Large Babesia species infections are often associated with more severe hematological alterations and higher mortality than infections with small species [9].

Hepatozoonosis (Hepatozoon canis)

Canine hepatozoonosis differs from other tick-borne diseases because transmission occurs not through tick saliva but through ingestion of an infected tick or tick parts containing oocysts [14]. Hepatozoon canis infects mononuclear cells and causes a chronic, debilitating syndrome characterized by fever, muscle atrophy, periosteal bone proliferation, and neutrophilic leukocytosis [14]. The disease is most common in the Mediterranean basin and tropical regions. Diagnosis is frequently made by detecting gamonts in blood smears or by histologic examination of skeletal muscle.

Rickettsiosis (Rickettsia species)

Rickettsia rickettsii, the agent of Rocky Mountain spotted fever, is a significant cause of systemic vasculitis in dogs, characterized by fever, edema of the face and extremities, and petechial hemorrhages [15]. Other spotted fever group rickettsiae, such as Rickettsia parkeri detected in Amblyomma maculatum ticks feeding on dogs in Mexico, may also cause febrile illness in dogs, though the clinical spectrum is less well defined [15]. Rickettsial infections often present acutely and require prompt anti-rickettsial therapy.

Severe Fever with Thrombocytopenia Syndrome (SFTS) Virus

SFTS virus (Bandavirus dabieense) is an emerging tick-borne virus that causes severe illness in dogs and humans [16, 2]. The virus is transmitted by Rhipicephalus sanguineus and other tick species, and dogs can act as sentinel hosts [17, 18]. Clinical signs in naturally infected dogs include acute febrile illness, profound thrombocytopenia, leukopenia, and elevated liver enzymes [2]. Multisystem involvement and multiorgan failure have been reported in fatal cases, with unusual cutaneous manifestations sometimes observed [17]. The virus has been detected in multiple body systems and excreted in urine, indicating potential for environmental contamination [19]. Companion animals in endemic regions of Korea and Thailand have shown seroprevalence and active infection, underscoring the one health importance of this pathogen [20, 21]. In Thailand, molecular evidence has linked dog-associated ticks to fatal human SFTSV infections, confirming the zoonotic potential [16, 22].

Other and Coinfections

Dogs may present with coinfections involving multiple tick-borne pathogens, complicating the clinical picture. For example, simultaneous infection with Ehrlichia canis, Anaplasma platys, and Nocardia otitidiscaviarum has been described, leading to pleural effusion and severe systemic illness [5]. In some cases, tick toxicosis caused by the bite of Ornithodoros brasiliensis can mimic infectious disease through the action of toxins in tick saliva, producing acute paralysis and hematological abnormalities [1]. Additionally, emerging pathogens such as Candidatus Neoehrlichia mikurensis have been detected in canids and may contribute to unexplained febrile syndromes [7].

Diagnostic Approaches

The clinical overlap among tick-borne diseases necessitates a systematic diagnostic approach that integrates signalment, geographic exposure history, physical examination findings, and a sequence of laboratory tests. Table 1 summarizes the key diagnostic features of the major pathogens.

Table 1. Summary of major canine tick-borne pathogens and associated clinical and diagnostic features

Hematology and Blood Smear Examination

Complete blood count (CBC) with manual examination of stained blood smears remains a fundamental first step. An automated impedance analyzer can detect abnormalities in platelet count, hemoglobin concentration, and white blood cell differential, but manual smear examination is essential for identifying morulae (e.g., Ehrlichia canis in monocytes, Anaplasma platys in platelets, Anaplasma phagocytophilum in neutrophils) and intra-erythrocytic piroplasms (Babesia spp.) [5, 9]. Thrombocytopenia is a nearly universal finding across acute tick-borne infections, whereas anemia distinguishes babesiosis from most rickettsial diseases [6, 9]. In chronic ehrlichiosis, pancytopenia may be observed [4].

Acute Phase Protein and Biomarker Analysis

Serum markers of inflammation can provide supportive evidence. Dogs infected with Ehrlichia canis exhibit elevated C-reactive protein and interleukin-6 concentrations, which correlate with disease severity [6]. In babesiosis, eicosanoid profiles and serum lipids shift, reflecting arachidonic acid metabolism activation [13]. The quantification of these biomarkers can aid in monitoring response to therapy and in distinguishing between acute and chronic disease.

Serologic Methods

Detection of antibodies by indirect immunofluorescence assay (IFA) or enzyme-linked immunosorbent assay (ELISA) is widely used for pathogens such as Ehrlichia canis, Anaplasma spp., and Rickettsia rickettsii [20, 18, 15]. Seroconversion requires 7–14 days post-infection, limiting the utility of serology for acute diagnosis. In SFTS virus infection, Ig M and Ig G antibody detection can confirm exposure, especially in serosurveillance studies [20, 21]. A positive serologic result in a dog with compatible clinical signs is highly suggestive of active or recent infection.

Molecular Diagnostics

Nucleic acid amplification tests (NAATs) offer high sensitivity and specificity for the direct detection of pathogen DNA or RNA. Conventional polymerase chain reaction (PCR) and quantitative real-time PCR are available for Ehrlichia spp., Anaplasma spp., Babesia spp., Hepatozoon spp., Rickettsia spp., and SFTS virus [2, 19, 3, 10]. Real-time PCR assays can be multiplexed to detect multiple targets in a single reaction. A novel syndromic molecular assay utilizing barcoded magnetic bead technology has been developed that can simultaneously detect Ehrlichia canis, Anaplasma platys, Babesia vogeli, and other pathogens, providing a rapid, high-throughput screening tool for endemic regions [23]. For SFTS virus, reverse transcription PCR (RT-PCR) targeting the L, M, or S segments is the gold standard for confirming acute infection, and viral RNA can be detected in blood, urine, and tissues [16, 17, 19].

Diagnostic Decision Workflow

The following flowchart illustrates a systematic approach to the diagnosis of tick-borne diseases in dogs.

flowchart TD
    A[Canine patient with fever, thrombocytopenia, or lameness] --> B[Tick exposure history?]
    B -- No --> C[Consider other infectious or immune-mediated diseases]
    B -- Yes --> D[Perform CBC & blood smear]
    D --> E{Morulae or piroplasms seen?}
    E -- Yes --> F[Targeted PCR or serology for suspected pathogen]
    E -- No --> G[Acute phase serology + broad-range PCR]
    G --> H{Positive result?}
    H -- Yes --> I[Treat based on identified pathogen]
    H -- No --> J[Repeat serology in 2-3 weeks if suspected recent infection]
    J --> K{Seroconversion?}
    K -- Yes --> I
    K -- No --> L["Consider less common agents: Hepatozoon, Neoehrlichia, SFTSV"]
    L --> M[Specialized PCR or RT-PCR for rare pathogens]
    M --> N{Positive?}
    N -- Yes --> I
    N -- No --> O[Alternative diagnosis]

The workflow emphasizes that even in the absence of visible pathogens on blood smear, broad molecular testing should be pursued in endemic areas to capture acute and low-burden infections.

Emerging Diagnostics and Surveillance

Metagenomic next-generation sequencing (mNGS) is being increasingly applied to veterinary diagnostics for the unbiased detection of tick-borne pathogens. Although yet to be fully commercialized for routine use, mNGS can identify coinfections and novel variants without the need for a priori selection of targets. For SFTS virus, genomic and phylogenetic characterization of viral strains circulating in companion animals provides data for vaccine development and risk assessment [20, 21]. Additionally, long-term shedding of SFTS virus in canine urine as detected by isolation and RT-PCR illustrates the importance of diagnostic monitoring in potentially infected animals to prevent zoonotic transmission [19].

Conclusion

Canine tick-borne diseases present a diagnostic challenge due to their overlapping clinical syndromes and the diversity of etiologic agents. A hierarchical diagnostic approach that begins with thorough clinical assessment and hematologic evaluation, proceeds through targeted serology and molecular testing, and incorporates emerging technologies such as syndromic bead-based assays and next-generation sequencing, is essential for accurate identification. Increasing awareness of emerging pathogens like SFTS virus, combined with rigorous one health surveillance, will improve both canine and human health outcomes in endemic regions [16, 21]. The integration of cost-effective, point-of-care molecular tests into routine practice is expected to further enhance the speed and accuracy of diagnosis.

Disclaimer: This article is for educational and informational purposes only. It is not intended to substitute for professional veterinary advice, diagnosis, treatment, or regulatory guidance. Always consult a licensed veterinarian or qualified specialist regarding animal health, disease diagnosis, and therapeutic decisions.

References

[1] Reck J, Soares JF, Termignoni C, et al. Tick toxicosis in a dog bitten by Ornithodoros brasiliensis. Vet Clin Pathol. 2011. URL: https://pubmed.ncbi.nlm.nih.gov/21827517/

[2] Byun HR, Ji SR, Hwang JY, et al. Clinical characteristics of two companion canines with severe fever with thrombocytopenia syndrome virus (Bandavirus dabieense) in Seoul, Republic of Korea. Vet Res Commun. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41505002/

[3] Qurollo BA, Buch J, Chandrashekar R, et al. Clinicopathological findings in 41 dogs (2008-2018) naturally infected with Ehrlichia ewingii. J Vet Intern Med. 2019. URL: https://pubmed.ncbi.nlm.nih.gov/30604457/

[4] Skotarczak B. Canine ehrlichiosis. Ann Agric Environ Med. 2003. URL: https://pubmed.ncbi.nlm.nih.gov/14677903/ ***

[5] Garcia Ribeiro M, da Silva CPC, Pchevuzinske LM, et al. Pleural effusion-related Nocardia otitidiscaviarum, Anaplasma platys and Ehrlichia canis coinfection in a dog. Braz J Microbiol. 2023. URL: https://pubmed.ncbi.nlm.nih.gov/37351788/

[6] Asawapattanakul T, Pintapagung T, Piratae S, et al. Erythrocyte sedimentation rate, C-reactive protein, and interleukin-6 as inflammatory biomarkers in dogs naturally infected with Ehrlichia canis. Vet World. 2021. URL: https://pubmed.ncbi.nlm.nih.gov/34840450/

[7] Hofmann-Lehmann R, Wagmann N, Meli ML, et al. Detection of 'Candidatus Neoehrlichia mikurensis' and other Anaplasmataceae and Rickettsiaceae in Canidae in Switzerland and Mediterranean countries. Schweiz Arch Tierheilkd. 2016. URL: https://pubmed.ncbi.nlm.nih.gov/27707682/

[8] Tsiodras S, Spanakis N, Spanakos G, et al. Fatal human anaplasmosis associated with macrophage activation syndrome in Greece and the Public Health response. J Infect Public Health. 2017. URL: https://pubmed.ncbi.nlm.nih.gov/28189511/

[9] Preena P, Sarangom SB, Ramesh Kumar KV, et al. Hematological alterations in large Babesia species infection in dogs of Kannur District of Kerala. J Parasit Dis. 2021. URL: https://pubmed.ncbi.nlm.nih.gov/34789994/

[10] René-Martellet M, Chêne J, Chabanne L, et al. Clinical signs, seasonal occurrence and causative agents of canine babesiosis in France: results of a multiregional study. Vet Parasitol. 2013. URL: https://pubmed.ncbi.nlm.nih.gov/23685063/

[11] Leica L, Mitrea IL, Ionita M. Clinical Occurrence of Canine Babesiosis in the Coastal Area of the Black Sea (Dobrogea) in Southeastern Romania and Associated Epidemiological Implications. J Parasitol. 2019. URL: https://pubmed.ncbi.nlm.nih.gov/31268412/

[12] Kuleš J, de Torre-Minguela C, Barić Rafaj R, et al. Plasma biomarkers of SIRS and MODS associated with canine babesiosis. Res Vet Sci. 2016. URL: https://pubmed.ncbi.nlm.nih.gov/27033937/

[13] Mrljak V, Kučer N, Kuleš J, et al. Serum concentrations of eicosanoids and lipids in dogs naturally infected with Babesia canis. Vet Parasitol. 2014. URL: https://pubmed.ncbi.nlm.nih.gov/24468427/

[14] Baneth G, Allen K. Hepatozoonosis of Dogs and Cats. Vet Clin North Am Small Anim Pract. 2022. URL: https://pubmed.ncbi.nlm.nih.gov/36336424/

[15] Torres-Chable OM, Jimenez-Delgadillo BG, Alvarado-Kantún YN, et al. Rickettsia parkeri (Rickettsiales: Rickettsiaceae) detected in Amblyomma maculatum ticks collected on dogs in Tabasco, Mexico. Exp Appl Acarol. 2020. URL: https://pubmed.ncbi.nlm.nih.gov/33025238/

[16] Khongwichit S, Lertsakulbunlue S, Pruetpongpun N, et al. Multisystem Detection and Molecular Evidence Linking Dog-Associated Ticks to Two Fatal Human SFTSV Infections in Thailand. Vector Borne Zoonotic Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42257705/

[17] Khongwichit S, Chuchaona W, Vichaiwattana P, et al. Fatal severe fever with thrombocytopenia syndrome associated with multiorgan failure and unusual cutaneous manifestations: evidence of Rhipicephalus sanguineus (Brown Dog Tick) transmission. Int J Infect Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42061499/

[18] Saba Villarroel PM, Chaiphongpachara T, Nurtop E, et al. Seroprevalence study in humans and molecular detection in Rhipicephalus sanguineus ticks of severe fever with thrombocytopenia syndrome virus in Thailand. Sci Rep. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/38862576/

[19] Saga Y, Yoshida T, Yoshida R, et al. Long-Term Detection and Isolation of Severe Fever with Thrombocytopenia Syndrome (SFTS) Virus in Dog Urine. Viruses. 2023. URL: https://pubmed.ncbi.nlm.nih.gov/38005905/

[20] Lee DY, Lee HJ, Choi HY, et al. Genomic and phylogenetic characterization of severe fever with thrombocytopenia syndrome virus in companion animals in Korea, 2023-2024. PLoS Negl Trop Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42241469/

[21] Sansilapin C, Tangwangvivat R, Hoffmann CS, et al. Severe fever with thrombocytopenia syndrome (SFTS) in Thailand: using a one health approach to respond to novel zoonosis and its implications in clinical practice. One Health Outlook. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/39350294/

[22] Oshima H, Okumura H, Maeda K, et al. A Patient with Severe Fever with Thrombocytopenia Syndrome (SFTS) Infected from a Sick Dog with SFTS Virus Infection. Jpn J Infect Dis. 2022. URL: https://pubmed.ncbi.nlm.nih.gov/35228501/

[23] Mohseni N, Chang M, Garcia K, et al. Development of a Syndromic Molecular Diagnostic Assay for Tick-Borne Pathogens Using Barcoded Magnetic Bead Technology. Microbiol Spectr. 2023. URL: https://pubmed.ncbi.nlm.nih.gov/37166314/

[24] Cisneros-Saldaña D, Osuna-Álvarez LE, Castillo-Bejarano JI, et al. First report of pediatric ehrlichiosis in Mexico. Bol Med Hosp Infant Mex. 2023. URL: https://pubmed.ncbi.nlm.nih.gov/37490688/

[25] Prince LK, Shah AA, Martinez LJ, et al. Ehrlichiosis: making the diagnosis in the acute setting. South Med J. 2007. URL: https://pubmed.ncbi.nlm.nih.gov/17713310/