Molecular discrimination and genetic diversity of three common tick-borne pathogens in dogs in Thailand

Visual Detection of Canine Monocytic Ehrlichiosis Using Polymerase Chain Reaction-Based Lateral Flow Biosensors

A conventional PCR (cPCR) remains an effective molecular technique for the diagnosis of canine monocytic ehrlichiosis. However, agarose gel electrophoresis requires additional time after thermal cycling. In the present study, we developed a PCR-based lateral flow biosensor (PCR-LFB) to detect Ehrlichia canis (E. canis). Lateral flow strips allow for the simple and rapid detection of PCR products and provide an alternative to gel electrophoresis. The sensitivity, specificity, and detection limit of PCR-LFB were compared to those of TaqMan probe-based real-time PCRs (qPCRs). The PCR-LFB was performed with 5' 6-FITC and biotin-labeled primers specific to E. canis, targeting the dsb gene. The detection limit of the PCR-LFB assay was 10-6 for the target DNA sequence in a 10-fold dilution of the recombinant plasmid, which is 10 times lower than that of qPCR. Among the confirmed qPCR results in the 30 dog samples, false-positive results were not detected by the PCR-LFB. Compared to qPCR, the sensitivity and specificity of PCR-LFB were 63.6% (95% CI; 42.9-80.2%) and 100% (95% CI; 67.5-100%), respectively. The Kappa value of the PCR-LFB is in moderate agreement with the qPCR (κ = 0.483). Perfect agreement (κ = 1) was observed between cPCR and PCR-LFB. Lower cost and shorter time consumption were demonstrated using PCR-LFB.

Molecular occurrence and genetic diversity of Ehrlichia canis in naturally infected dogs from Thailand

Canine monocytic ehrlichiosis is cause by Ehrlichia canis resulting in hematologic disorders and severe clinical signs. The aim of this study was to scrutinize the molecular detection and genetic diversity of E. canis based on the trp36 gene in dogs from Thailand's northern and central regions. A total of 120 dogs blood samples were amplified for trp36 gene of E. canis using the polymerase chain reaction (PCR). Forty-seven out of 120 dog blood samples (39.16%, 47/120) were positive for E. canis the trp36 DNA with 790 bp of PCR amplicon size. The factor significantly associated with E. canis infection is animal housing status (p < 0.05). Sequence and phylogenetic analysis showed that E. canis trp36 gene of Thailand isolates was clustered into 1st clade with similarity ranging from 95.65 to 100% together with the US genogroup. The 14 haplotypes of the trp36 gene shown in TCS network exhibited that haplotype #1-4 was found in Thailand. The entropy analysis of the trp36 gene illustrated 751 polymorphic sites and 271 entropy peaks of nucleic and amino acid sequences, respectively. Hence, these findings are crucial for better understanding the epidemiology of Ehrlichia infection and could be helpful for implementing control measures in Thailand.

Molecular Survey and Genetic Characteristics of Vector-Borne Pathogens in Domestic Dogs from Four Regions of China

Canine vector-borne diseases are widely distributed around the world. They are transmitted by arthropods, and many seriously threaten the health of animals and humans. In China, our knowledge of Ehrlichia, Hepatozoon, and Mycoplasma species circulating in dogs is still poorly understood. Therefore, the aim of this study was to understand the prevalence and genetic characteristics of canine Ehrlichia spp., Hepatozoon spp., and Mycoplasma spp. in Chongqing (southwest), Fujian (southeast), Shandong (southeast), and Hubei (central) Provinces of China. Blood samples from healthy pet dogs were processed to detect Ehrlichia, Hepatozoon, and Mycoplasma DNA with PCR. Haplotype and phylogenetic analyses were performed on 18S rRNA sequences. Among 306 dogs, no Ehrlichia spp. or Mycoplasma spp. were detected, whereas one Hepatozoon sp. was detected in 10 (3.27%) of the animals. Only Hepatozoon canis was identified and was endemic to Chongqing (2.46%) and Hubei (8.77%). A haplotype analysis identified eight haplotypes among the H. canis isolates. A phylogenetic analysis showed that the H. canis isolates in this study clustered into four clades, together with isolates from different countries and hosts, forming a large group that was clearly separate from other Hepatozoon species. These findings provided new information on the epidemiological characteristics of canine vector-borne diseases in China and will be helpful in the development of efficient measures to safeguard the health and well-being of companion animals and their owners.

Ehrlichia canis: Molecular characterization and genetic diversity based on the p28 and trp36 genes

Ehrlichia canis is a common tick-borne intracellular pathogen causing canine monocytic ehrlichiosis (CME) in dogs worldwide. The aims of this study were to investigate the genetic diversity and antigenicity of E. canis based on the p28 and trp36 genes in dogs in Thailand. The E. canis p28 and trp36 genes were amplified by the polymerase chain reaction (PCR) and cloned for sequencing and bioinformatic analyses. 36% (44/120) of dog blood samples were positive for E. canis DNA consisting of p28 (31%, 14/44) and trp36 (69%, 30/44) genes with 792 and 882 bp of PCR products size, respectively. The E. canis TRP36 from all Thailand sequences exhibited encoded nine amino acids (TEDSVSAPA) with 11 copies of tandem repeats along the sequences. The phylogenetic trees of E. canis, using the p28 and trp36 genes, exhibited that the Thailand isolates fell into two clades and one clade with similarity ranging from 55.95 to 100% and 100%, respectively. The results of diversity analysis revealed 10 and 20 haplotypes of the p28 and trp 36 genes, respectively. The entropy analysis of the p28 and trp36 nucleic acid sequences showed 442 and 1321 high entropy peaks respectively, whereas those of the P28 and TRP36 amino acid sequences showed 477 and 388 high entropy peaks, respectively. For B-cell epitopes analysis, the conserved amino acid of P28 and TRP36 sequences has been also demonstrated. Therefore, the results could be utilized to improve the understanding of phylogenetic relationship, genetic diversity and antigenicity of E. canis Thailand isolates.

Multiple blood pathogen infections in apparently healthy sheltered dogs in southern Thailand

In developing countries such as Thailand, free-ranging dogs are frequently involved in road accidents and contribute to the cost of public healthcare. Shelters play a vital role in communities because they help to control the population of unwanted and free-ranging dogs. This study aimed to investigate blood pathogen infection in sheltered dogs, as it is one of the factors contributing to animal welfare. Blood samples were randomly collected from 141 dogs from the largest shelter (approximately 400–500 dogs in total) in southern Thailand. Blood pathogens were detected using both PCR and light microscopy. Four blood pathogens were identified: Anaplasma platys, Ehrlichia canis, Babesia canis vogeli, and Hepatozoon canis. No trypanosomes were detected. The incidence of blood parasite infection was 56.7% (80/141) by PCR, and 28.4% (40/141) by microscopy. E. canis was the most prevalent pathogen, accounting for 46.1% (65/141) of the cases, while multiple infections accounted for 22% (31/141) of the cases. A triple infection with E. canis, A. platys, and B. canis vogeli was observed in 5.7% (8/141) of the cases. Although PCR is far more sensitive than microscopy, it appears to have equivalent specificity. In conclusion, this study reported a high occurrence of blood pathogen infections in clinically healthy sheltered dogs. Many of them were infected with multiple pathogens and may have been infected before entering the shelter. These findings suggest that a blood test is necessary to screen dogs prior to their admission to the shelter to prevent disease transmission and enhance animal welfare.

Prevalence of Ehrlichia-, Babesia-, and Hepatozoon-infected brown dog ticks in Khon Kaen Province, Northeast Thailand

Background and Aim:

The brown dog tick, Rhipicephalus sanguineus sensu lato, is the most common tick found on domestic dogs in Southeast Asia, including Thailand. Canine tick-borne pathogens are a public health concern worldwide. Tick-borne diseases are diagnosed by identifying pathogens based on the morphological or molecular analyses of dog blood samples. However, the collection of ticks, a non-invasive procedure, is easier than drawing blood. This study aimed to demonstrate the usefulness of collecting brown dog ticks for the diagnosis of tick-borne diseases and for estimating the prevalence of tick-borne pathogens among companion dogs in Khon Kaen, Northeast Thailand.

Materials and Methods:

Seventy brown dog ticks from 70 companion dogs in Khon Kaen Province, Thailand, were evaluated for molecular evidence of tick-borne pathogens, including Babesia spp., Ehrlichia canis, and Hepatozoon canis. Ticks were collected from dogs at a private animal hospital based on the presence of at least one of the three inclusion criteria: fever, anorexia, or lethargy. Molecular diagnosis was performed using conventional polymerase chain reaction for the detection of pathogens.

Results:

Of the 70 ticks collected from 70 sick dogs, 55 (78.57%) were positive for tick-borne pathogens. The most common infection was a single infection with H. canis (65.71%) followed by Babesia spp. (31.43%) and E. canis (30.00%). Coinfection was observed in 14 ticks (20.00%), and coinfection with Babesia spp. and E. canis was the most prevalent double infection (n = 6). The prevalence of coinfection was identical for H. canis mixed with Babesia spp. and H. canis mixed with E. canis (n = 4).

Conclusion:

The present study showed that tick-borne pathogens are highly prevalent among companion dogs in Khon Kaen Province. Therefore, we encourage an increase in tick control or the reduction and prevention of tick-borne diseases in this region. Furthermore, this study revealed that ticks are valuable samples for the molecular detection of tick-borne pathogens.

First study on molecular detection of three major canine tick-borne pathogens in subclinically infected dogs in Chiang Mai, Thailand

Background and Aim:

Canine tick-borne pathogens (CTBPs) are an important cause of morbidity in dogs in Thailand. This study aimed to evaluate the occurrence of three CTBPs in clinically normal, owned dogs to understand the risk for the general canine population. We also examined sex, age, tick infestation, and packed cell volume (PCV) of the animals in association with active infection of the CTBPs.

Materials and Methods:

A total of 139 dogs were included in the study. Blood samples were collected for thin blood smear, PCV and nested polymerase chain reaction (PCR) assay. Statistical analyses were performed to examine the association between individual factors and CTBP infection status determined by PCR. In addition, sensitivity, specificity, and Cohen’s kappa were calculated to assess the utility of routine blood smear.

Results:

The PCR results showed that 31 dogs (22.3%) were infected with at least one of the three pathogens. The occurrence rate for Ehrlichia canis, Anaplasma platys, and Hepatozoon canis was 2.2% (3/139), 18.7% (24/139), and 2.8% (4/139), respectively. There were two cases of coinfection with A. platys and E. canis. The univariate analyses did not yield any associations between recorded variables and the active infection. Microscopic examination showed good sensitivity and agreement only for H. canis (Sn: 75%, 95% confidence interval: 24.9-98.7, k=0.85).

Conclusion:

Our findings confirmed the endemicity of the CTBPs in owned canine population in the study site. In-depth epidemiological investigation would be warranted to elucidate environmental risk factors for CTBP infection.

Retrospective analysis of canine monocytic ehrlichiosis in Thailand with emphasis on hematological and ultrasonographic changes

Background and Aim: Canine monocytic ehrlichiosis (CME) is a tropical endemic tick-borne disease that causes fatality or chronic infection involving many organs in dogs. This study aimed to examine the prevalence, risk factors, and hematological and ultrasonographic changes in the liver, gallbladder, kidneys, and spleen following CME infection. Materials and Methods: This retrospective study used 30,269 samples collected from dogs at the hematology section of the pathology unit of a university veterinary hospital and 35 samples collected from dogs at the diagnostic imaging unit. CME was determined using the buffy coat smear method. Data were analyzed using descriptive statistics and odds ratios. Results: CCl4 The data revealed that the average yearly prevalence of CME was 1.32%. Risk factors contributing to CME infection were a tick on the body during physical examination, lack of ectoparasite control, and outdoor living. All 148 dogs with CME infection had low platelet counts. The percentages of CME-infected dogs with elevated serum alanine aminotransferase, alkaline phosphatase, and both enzymes above the normal range were 33.6%, 65.9%, and 29.8%, respectively. The rates for elevated serum levels of blood urea nitrogen, creatinine, and both compounds were 33.1%, 19.1%, and 17.3%, respectively. The most common ultrasonographic changes were liver abnormalities (hyperechogenicity or hypoechogenicity, hepatomegaly, and hypoechoic nodules), hyperechogenicity of the kidneys, and an enlarged spleen. These ultrasonographic changes were consistent with the hematology results, which showed a greater elevation of serum liver enzyme levels than renal enzymes. Conclusion: Ultrasonographic changes during CME infection and after treatment with doxycycline can help to monitor and identify persistent pathological changes in the target organs resulting from immune response to CME.