Molecular Diagnosis of Ehrlichia canis in Dogs and Ticks Rhipicephalus sanguineus (Acari: Ixodidae) in Yucatan, Mexico

Molecular Evidence of Ehrlichia canis (Rickettsiales: Anaplasmataceae) in Ticks (Ixodida: Ixodidae) Associated with Dogs (Carnivora: Canidae) from Nuevo Leon, Mexico

Background: Ehrlichia canis is transmitted by ticks causing Canine monocytic ehrlichiosis, which is considered one of the most critical tickborne pathogens. Materials and Methods: This study aimed to identify by PCR technique E. canis in ticks associated with dogs from urban and rural homes in Nuevo Leon, Mexico. The study was conducted at 13 localities in eight municipalities from 2012 to 2021. Results: A total of 1873 ticks of three species were captured: Amblyomma tenellum, Dermacentor variabilis, and Rhipicephalus sanguineus s.l. The overall infection rate of E. canis in ticks was 59.12% (149/252). Of the 15 sequences, three haplotypes were identified. Conclusion: The urban transmission cycle of canine ehrlichiosis is demonstrated, where the potential vector is the tick R. sanguineus s.l.

Morphological and molecular identification of the brown dog tick in Mexico

Ticks of the Rhipicephalus sanguineus complex are known as the brown dog ticks. This complex groups at least 12 species of ticks that are distributed worldwide. On the American continents, R. sanguineus sensu stricto (s.s.), is distributed in temperate areas, while Rhipicephalus sanguineus sensu lato (s.l.), also called "tropical lineage" is distributed in tropical regions. Previous analyses of brown dog ticks from Mexico have identified the so-called tropical lineage and the country generally has a climate more favorable for these ticks (> 20o C in average). In addition, some pathogens thought to be transmitted by this lineage (such as Ehrlichia canis, and Rickettsia rickettsii) are prevalent in Mexico. Herein we aim to contribute to the study of brown dog ticks by providing morphological identification and molecular analysis of mt 12S rDNA and 16S rDNA sequences from ticks collected from 12 states in Mexico. Our results indicate that the tropical lineage of R. sanguineus s.l., recently redescribed as R. linnaei is widely distributed in Mexico.

Molecular Detection and Characterization of Ehrlichia canis Isolates from Three Geographic Regions in Mexico: A Retrospective Study

Canine monocytic ehrlichiosis (CME) is the most common tick-borne disease affecting domestic dogs and other wild canids. It has a worldwide distribution and is associated with the presence of the brown dog tick. Few studies have been conducted in Mexico to identify and characterize Ehrlichia canis genetic variability. In the present study, 111 dogs of different sex, breed, and age from three geographic regions in Mexico were included. All of them had a previous history of tick infestation and/or the presence of one or more clinical signs compatible with CME. All dogs were tested by a commercial ELISA and nested PCR assay for the detection of E. canis. In addition, we analyzed the E. canis genetic diversity from the 16S rRNA gene sequences obtained in this study, along with 15 additional sequences described for E. canis in Mexico and obtained from GeneBank. Serological detection by commercial ELISA results showed overall infection rates of 85.58% (95/111), including 73.1% (30/41) in samples from Guerrero state; 75% (15/20) in Morelos; and 100% (50/50) in Chihuahua. On the other hand, molecular detection (nPCR assay) showed 31.5% (35/111) overall infection rate, with 41.4% (17/41) in Guerrero state; 55% (11/20) in Morelos; and 14% (7/50) in Chihuahua. We observed a high 16S rRNA gene sequence conservancy in most of the E. canis isolates in the three geographical areas from Mexico, including those analyzed in this research, suggesting a common geographic origin among isolates.

Epidemiological Study of the Occurrence of Typhus Group Rickettsia Natural Infection in Domiciliated Dogs from a Rural Community in South-Eastern Mexico

Simple Summary

Rickettsioses are relevant emergent and reemergent zoonoses in the Americas, including Mexico. Murine typhus caused by typhus group (TG) Rickettsia is prevalent in humans and their companion animals, such as dogs. This study found that 23.9% of the dogs (34/142) were infected by TG Rickettsia in Maxcanú, Yucatan (southeastern Mexico). Statistical analyses showed that reduced outdoor activities, age, sex and previous antiparasitic treatment are associated factors with less risk of TG Rickettsia infection in the sampled dogs. Monitoring and controlling these factors could help to restrict the enzootic transmission risk and prevent the potential zoonotic transmission.

Abstract

The aim is to describe the Typhus group (TG) Rickettsia infection in dogs and to identify factors associated with this infection. We collected blood samples and gathered exposure and clinical data of 142 dogs from a rural community of Yucatan. The Rickettsia group was determined by semi-nested PCR. Generalized linear models with binomial error distribution were used to model the associated factors from the dog sample for risk ratio (RR) estimation. Thirty-four dogs (23.9%) showed molecular evidence of TG Rickettsia DNA. The multivariate model showed that mixed-breed dogs (RR = 0.06) and dogs that had received antiparasitic treatment (RR = 0.049) had a lower risk of getting infected, taking as reference the purebred group and the non-treated dogs, respectively. Looking at variable interactions, adult dogs without outdoor activities had a lower infection risk than puppies (RR = 0.26). Among dogs with antiparasitic treatment, females had a higher infection risk than male dogs (RR = 26.2). The results showed enzootic TG Rickettsia circulation in dogs of a rural community. The factors outdoor activities, age and previous antiparasitic treatment, as well as the clinical variables signs of hemorrhages and epistaxis, were associated with a less chance of natural infection in the studied dogs. Prevention and control of the enzootic transmission risk of TG Rickettsia should help to reduce the potential zoonotic transmission of this pathogen.

Ticks (Acari: Ixodidae) and Associated Pathoge Collected From Domestic Animals and Vegetation in Stann Creek District, Southeastern Belize, Central America

Data on the prevalence and distribution of ticks and tick-borne diseases in Belize are lacking. Ticks (n = 564) collected from dogs, horses, and vegetation in two villages in Stann Creek District in southeastern Belize in 2018, were molecularly identified and screened for tick-borne nonviral human pathogens. The identity of 417 ticks was molecularly confirmed by DNA barcoding as Rhipicephalus sanguineus (Latreille) (66.43%), Amblyomma ovale Koch (15.59%), Dermacentor nitens Neumann (11.51%), Amblyomma sp. ADB0528 (3.6%), and the remainder being small records (2.87%) of Amblyomma coelebs Neumann, Amblyomma imitator Kohls, Amblyomma tapirellum Dunn, Amblyomma auricularium Conil, and Amblyomma maculatum Koch. Individual tick extracts were screened for the presence of Rickettsia spp., Babesia spp., Babesia microti, Borrelia spp., Ehrlichia spp., and Anaplasma spp. using available conventional polymerase chain reaction (PCR) assays. Rickettsia parkeri strain Atlantic Rainforest was identified in five specimens of A. ovale, and one other unidentified tick, all collected from dogs. Another unidentified tick-also collected from a dog-tested positive for an undefined but previously detected Ehrlichia sp. With the exception of D. nitens, all eight other tick species identified in this study were collected on dogs, suggesting that dogs could be usefully employed as sentinel animals for tick surveillance in Belize.

Possible Association between Selected Tick-Borne Pathogen Prevalence and Rhipicephalus sanguineus sensu lato Infestation in Dogs from Juarez City (Chihuahua), Northwest Mexico–US Border

Tick-borne bacterial pathogens (TBBPs) show a worldwide distribution and represent a great impact on public health. The brown dog tick (Rhipicephalus sanguineus) is a vector of several pathogens that affect dogs and sometimes humans as well. In addition, TBBPs represent a diagnostic challenge and imply financial resources and medical treatment for long periods of time. In the present study, R. sanguineus s. l. was identified as the main tick species naturally parasitizing dogs that inhabit. Juárez City, Chihuahua, in the Paso del Norte region, Mexico–US Border, representing 99.8% of the cases. Additionally, an end-point PCR was performed to search for whether pathogens in R. sanguineus s. l. can transmit in DNA extracted from ticks and dog blood samples. This is the first molecular detection of Rickettsia rickettsi infecting domestic dogs in Mexico; however, other pathogens were also identified, such as Ehrlichia canis and Anaplasma platys in both ticks and dog blood samples, while Anaplasma phagocytophilum was identified only in dog blood samples. Moreover, co-detection in tick pools and co-infection in the analyzed dog blood samples could be found. Similarly, this research showed that dogs were found mostly parasitized by adult female ticks, increasing the possibility of transmission of E. canis.

Detection of Ehrlichia spp. in ticks collected from stray dogs in Central and Southeastern Iran

Ehrlichia is an etiologic agent of ehrlichiosis in humans and some animals. Rhipicephalus sanguineus is the main vector of the Ehrlichia canis and dogs, red foxes and yellow jackals are reservoirs of the bacterium. This tick has a worldwide distribution and is regarded as one of the commonest species of ticks in Iran. This research aimed to detect Ehrlichia spp. in R. sanguineus isolated from stray dogs in Central and Southeast Iran (Isfahan and Zabol), by using polymerase chain reaction (PCR) and to evaluate the prevalence of the microorganism in these two areas. Tick samples were collected from stray dogs in Isfahan and Zabol between April and June of 2018. The DNA extraction was performed with commercial kits. PCR was done to determine the 336 bp fragment related to Ehrlichia spp. Overall, 15.21% of pools in both areas were positive for Ehrlichia, 21.42% and 10% of pools were from Isfahan and Zabol respectively. The results confirmed the presence of Ehrlichia spp. in R. sanguineus in stray dogs revealing that dogs and their ticks may have a significant role in the epidemiology of the disease.

Current status of resistance to ivermectin in Rhipicephalus sanguineus sensu stricto infesting dogs in three provinces in Argentina

Intensive use of macrocyclic lactones for parasite control exerts strong selective pressure for arthropods such as ticks to become resistant to them. Rhipicephalus sanguineus sensu stricto is a tick and disease vector of significant public health and veterinary importance worldwide. We assessed the toxicological response to the macrocyclic lactone ivermectin (IVM) in R. sanguineus s.s. infesting dogs in Argentina. Samples of nine tick populations were obtained by inspecting dogs at veterinary clinics, hospitals, or rural areas in the provinces of San Luis, Rio Negro, and Buenos Aires. Pet owners were interviewed to gather data on the history of dog treatment with ectoparasiticides. The larval immersion test was used to assess the toxicological response of R. sanguineus s.s. to IVM. Dose-response mortality regressions, lethal concentrations (LC), and slope were calculated by probit analysis. The lowest LC concentrations were used to designate the reference susceptible population because a laboratory reference strain of R. sanguineus s.s. does not exist in Argentina. Compared with the most susceptible tick population in this study, six populations (66.66%) were classified as resistant to IVM. A clear interpopulation variation in the level of IVM resistance was present (resistance ratios at LC_50% ranged from 1.0 to 18.33 and at LC_99% ranged from 1.0 to 8.96). In San Luis Province, all tick populations were classified as resistant. The highest level of IVM resistance (resistance ratio at LC_50%:18.83 and LC_99%:8.96) was found in a population of R. sanguineus s.s. from a rural area in the province of Buenos Aires. It is concluded that populations of R. sanguineus s.s. from dogs in three provinces of Argentina were resistant to IVM. Clear interpopulation variation in the level of IVM resistance was present.

Historical Spatial Distribution of Zoonotic Diseases in Domestic, Synanthropic, and Wild Animals in the Mexican Territory of the Yucatan Peninsula

The Mexican territory of the Yucatan Peninsula has a tropical climate and harbors a wide variety of domestic, synanthropic, and wild animals, as well as disease vectors. To determine the distribution of recorded zoonotic diseases in the Yucatan Peninsula, scientific publications referring to these diseases in animals and containing geographic coordinates of disease occurrence, were studied. The epidemiological bulletins of the national government were also consulted to obtain information on zoonotic diseases reported in humans in the territory. The territory harbors a wide variety of tropical zoonotic pathogens, including Trypanosoma cruzi, Leptospira interrogans, Toxoplasma gondii, Leishmania mexicana, Dirofilaria immitis, and Rickettsia felis. A variety of domestic, synanthropic, and wild animals act as hosts or reservoirs in the transmission cycle of the zoonotic diseases in the Yucatan Peninsula, and some spillover into human populations has also been recorded. There are still zoonotic diseases that have rarely or never been reported in humans, but it is not clear whether this is because these diseases in humans are not common, there is a lack of viable transmission cycle or there is a lack of appropriate diagnosis. It is necessary to continue monitoring vectors, animal hosts, and humans to identify risk factors for zoonotic diseases in the Yucatan Peninsula.

Ticks infesting dogs and cats in North America: Biology, geographic distribution, and pathogen transmission

A diverse array of ixodid and argasid ticks infest dogs and cats in North America, resulting in skin lesions, blood loss, and disease. The ticks most commonly found on pets in this region are hard ticks of the genera Amblyomma, Dermacentor, Ixodes, and Rhipicephalus, as well as the more recently established Haemaphysalis longicornis. Soft tick genera, especially Otobius and Ornithodoros, are also reported from pets in some regions. In this review, we provide a summary of the complex and diverse life histories, distinct morphologies, and questing and feeding behaviors of the more common ticks of dogs and cats in North America with a focus on recent changes in geographic distribution. We also review pathogens of dogs and cats associated with the different tick species, some of which can cause serious, potentially fatal disease, and describe the zoonotic risk posed by ticks of pets. Understanding the natural history of ticks and the maintenance cycles responsible for providing an ongoing source of tick-borne infections is critical to effectively combatting the challenges ticks pose to the health of pets and people.

Molecular detection of Bartonella, Ehrlichia and Mycoplasma in feral dogs of El Pedregal de San Angel Ecological Reserve in Mexico City

Free-ranging and feral dogs represent a group of unattended companion animals. They impact wild animal populations by predating native species, displacing predators and introducing exotic pathogens. The aim of this work was to describe the molecular occurrence of Rickettsia, Ehrlichia, Anaplasma, Mycoplasma and Bartonella in feral dogs. The study was carried out in the last relict of a protected area in Mexico City. Blood clots samples from 19 dogs were obtained and analyzed for detection of specific fragments of the 16S-rRNA gene for Anaplasma, Ehrlichia and Mycoplasma and citrate synthase (gltA) for Bartonella and Rickettsia. Our results showed that DNA from three bacteria species (Bartonella vinsonii subsp. berkhoffii, Ehrlichia canis and Mycoplasma haemocanis) was present with frequencies ranging from 5.3 to 15.8%. This is the first record of B. vinsonii subsp. berkhoffii and M. haemocanis in dogs from México, and also the first finding of Ehrlichia canis in Mexico City. It is important to perform surveillance of feral dog populations in order to identify the impact of these pathogens on wild animal populations and Public Health in order to establish prevention and protection programs.

Ehrlichia canis in dogs of Mexico: Prevalence, incidence, co-infection and factors associated

Rickettsial infections in dogs of Mexico were investigated. A total of 246 dogs were blood sampled and initially screened to detect Ehrlichia canis, E. chaffeensis, E. ewingii, Anaplasma phagocytophilum and Rickettsia rickettsii by a quantitative real-time PCR (qPCR) assay. Sixty-five dogs were monitored and sampled twice 7-8 months apart. Using the qPCR, 72 positive dogs to E. canis were detected (prevalence of 29.26%). These dogs were also tested by nested PCR to detect the same pathogens. None of the studied dogs were positive to E. chaffeensis, E. ewingii, R. rickettsii nor A. phagocytophilum by both PCR assays. The cumulative incidence of E. canis infection was 38.46%. Sequencing analysis of the nested PCR products revealed 100% and 98.1% identity of E. canis and R. parkeri, respectively. We found a dog co-infected with E. canis and R. parkeri.

Prevalence of Ehrlichia canis (Rickettsiales: Ehrlichieae) DNA in Tissues From Rhipicephalus sanguineus (Acari: Ixodidae) Ticks in Areas Endemic for Canine Monocytic Ehrlichiosis in Brazil

Canine monocytic ehrlichiosis (CME) is a disease caused by the obligate intracellular bacterium Ehrlichia canis. Tropical lineages of Rhipicephalus sanguineus ticks play an essential role in the transmission of this pathogen. The aim of the present study was to evaluate the prevalence of E. canis DNA in tissue from R. sanguineus ticks in areas endemic for CME in Brazil and quantify levels of E. canis DNA in dissected tissues from these samples. A total of 720 ticks were collected from 72 dogs (36 dogs from the city Araçatuba in São Paulo state and 36 from Campo Grande in the state of Mato Grosso do Sul). Ticks were dissected to collect the guts, ovaries and salivary gland. A quantitative polymerase chain reaction (qPCR) targeting the disulphide bond formation (dsb) protein gene was performed to quantify the level of E. canis infection. The E. canis dsb-qPCR assay was positive for 31.9, 10, and 15.2% of the gut, ovary, and salivary glands, respectively. The average gut, ovary, and salivary gland bacterial load estimated by qPCR was 1.21 × 103, 2.60 × 103, and 4.92 × 103 gene copies/µl, respectively. This is the first report of E. canis DNA in ovaries of R. sanguineus ticks parasitizing dogs in these CME-endemic areas. These observations raise the possibility of E. canis trans-ovarial transmission.

A review on the occurrence of companion vector-borne diseases in pet animals in Latin America

Companion vector-borne diseases (CVBDs) are an important threat for pet life, but may also have an impact on human health, due to their often zoonotic character. The importance and awareness of CVBDs continuously increased during the last years. However, information on their occurrence is often limited in several parts of the world, which are often especially affected. Latin America (LATAM), a region with large biodiversity, is one of these regions, where information on CVBDs for pet owners, veterinarians, medical doctors and health workers is often obsolete, limited or non-existent. In the present review, a comprehensive literature search for CVBDs in companion animals (dogs and cats) was performed for several countries in Central America (Belize, Caribbean Islands, Costa Rica, Cuba, Dominican Republic, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, Puerto Rico) as well as in South America (Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, French Guiana, Guyana (British Guyana), Paraguay, Peru, Suriname, Uruguay, Venezuela) regarding the occurrence of the following parasitic and bacterial diseases: babesiosis, heartworm disease, subcutaneous dirofilariosis, hepatozoonosis, leishmaniosis, trypanosomosis, anaplasmosis, bartonellosis, borreliosis, ehrlichiosis, mycoplasmosis and rickettsiosis. An overview on the specific diseases, followed by a short summary on their occurrence per country is given. Additionally, a tabular listing on positive or non-reported occurrence is presented. None of the countries is completely free from CVBDs. The data presented in the review confirm a wide distribution of the CVBDs in focus in LATAM. This wide occurrence and the fact that most of the CVBDs can have a quite severe clinical outcome and their diagnostic as well as therapeutic options in the region are often difficult to access and to afford, demands a strong call for the prevention of pathogen transmission by the use of ectoparasiticidal and anti-feeding products as well as by performing behavioural changes.

First report of amitraz and cypermethrin resistance in Rhipicephalus sanguineus sensu lato infesting dogs in Mexico

Engorged female Rhipicephalus sanguineus sensu lato (Ixodida: Ixodidae) were collected from dogs in the state of Yucatán, Mexico. Fourteen tick populations were collected from dogs at seven veterinary clinics, four residential homes and three cattle farms. The larval immersion test was used in the progeny of collected adult females to test susceptibility to amitraz and cypermethrin. Dose-mortality regressions, 50% lethal concentrations (LC₅₀ ), confidence intervals and slope were estimated by probit analysis. For amitraz, 12 tick populations (85.7%) were classified as resistant and low inter-population variation in the phenotypic level of resistance was evident [resistance ratios (RRs) at LC₅₀ : 1.0-13.0]. For cypermethrin, 12 tick populations (85.7%) were classified as resistant and substantial inter-population variation in the phenotypic level of resistance was evident (RRs at LC₅₀ : 1.0-104.0). Thus, amitraz resistance in R. sanguineus s.l. is common, but generally occurs at low levels; however, alarmingly high levels of cypermethrin resistance are present in R. sanguineus s.l. populations in dogs in Yucatán, Mexico. The intensive use of both acaricides to control ectoparasites on dogs is likely to lead to more serious resistance problems that may cause high levels of control failure in the future.

Associated Factors to Seroprevalence of Ehrlichia spp. in Dogs of Quintana Roo, Mexico

The objective of this study was to determine the seroprevalence to Ehrlichia spp. in dogs from Xcalak, Quintana Roo, Mexico, and the associated factors. Serum samples were obtained from 118 dogs and used in an indirect immunofluorescent assay test for the detection of antibodies against Ehrlichia spp. A questionnaire was used to obtain information about possible variables associated with seroprevalence. These variables were analyzed through Chi² test and logistic regression. Dog seroprevalence of antibodies against Ehrlichia spp. was 64% (75/118). Fifty-two percent (61/118) of dogs had tick infestation which was identified as Rhipicephalus sanguineus sensu lato. Anemia was observed in 36% of dogs. Leucopenia (2.5%), thrombocytopenia (70%), and hemorrhage (14%) were also observed. Thirty-one percent (23/75) of dogs with anemia, 4% (3/75) of dogs with leucopenia, 80% (60/75) of dogs with thrombocytopenia, 17% (13/75) of dogs with hemorrhages, and 59% (44/75) of dogs with ticks were positive for Ehrlichia spp. antibodies. The factors associated with seroprevalence were age (1–3 and >3 years old, OR = 7.77 and OR = 15.39, resp.), tick infestation (OR = 3.13), and thrombocytopenia (OR = 3.36). In conclusion, seroprevalence of Ehrlichia spp. was high in the community of Xcalak and its associated factors were age, tick infestation, and thrombocytopenia.

Countrywide serological evaluation of canine prevalence for Anaplasma spp., Borrelia burgdorferi (sensu lato), Dirofilaria immitis and Ehrlichia canis in Mexico

BACKGROUND

Canine vector-borne diseases (CVBD) have become a major concern for canine and human public health. The aim of the study described here is to add epidemiological data regarding four pathogens responsible for CVBD, namely anaplasmosis, borreliosis, dirofilariosis and ehrlichiosis in a national survey conducted in Mexico.

METHODS

Seventy-four veterinary centres located in 21 federal Mexican states were asked to test dogs with clinical signs suspect for CVBD and healthy dogs, for detection of Dirofilaria immitis antigen and antibodies against Anaplasma spp., Borrelia burgdorferi (sensu lato) and Ehrlichia canis using the SNAP® 4DX® from IDEXX® Laboratories.

RESULTS

A total of 1706 dogs were tested, including 943 apparently healthy and 722 CVBD-suspect dogs. Infected dogs were 36.7 %. The highest percentages of infection with E. canis (51.0 %) and Anaplasma spp. (16.4 %) were obtained in the northwestern region, while D. immitis was most frequently found in the northeastern region of the country (8.9 %). Four dogs from the northwestern, northeastern, eastern and southeastern regions, respectively, were positive for B. burgdorferi (sensu lato). Northcentral regions showed lowest overall prevalence of infection (2.4 %). Co-infections were detected in 8.8 % of the dogs tested. Statistically significant lower positivity was found among dogs aged less than one year (23.2 %) and small-sized dogs (27.6 %), while higher prevalence of infection was found in dogs living outdoors (42.0 %), dogs with detectable tick infestation (43.3 %) and dogs that received treatment for tick-transmitted infections (58.8 %). Seropositivity was a risk factor for the presence of clinical signs as follows: Anaplasma spp. (OR = 2.63; 95 % CI: 1.88-3.67; P < 0.0001), D. immitis (OR = 2.52; 95 % CI: 1.61-3.95; P < 0.0001), E. canis (OR = 3.58; 95 % CI: 2.88-4.45; P < 0.0001), mixed infections (OR = 4.08; 95 % CI: 2.79-5.96; P < 0.0001), one or more agents (OR = 3.58; 95 % CI: 2.91-4.42; P < 0.0001).

CONCLUSIONS

Canine serological evidence supports that dogs from Mexico are at risk of acquiring Anaplasma spp., D. immitis and/or E. canis, while B. burgdorferi (sensu lato) transmission is minimal in the country. Practitioners play a fundamental role in the detection and control of these diseases to protect dogs and humans.

Molecular characterization of Ehrlichia canis infecting dogs, Buenos Aires

Canine monocytic ehrlichiosis (CME) is a worldwide potentially fatal tick-borne rickettsial disease of dogs caused by Ehrlichia canis and transmitted by Rhipicephalus sanguineus sensu lato. CME diagnosis includes indirect (serology) and direct (e.g. blood smears and PCR) methods. PCR is more sensitive and specific than direct microscopic examination and positive PCR results confirm infection, whereas positive serologic test results only confirm exposure. The aim of the present study was to perform a molecular characterization of E. canis from canine samples of the Metropolitan Area of Buenos Aires. We studied 223 blood samples of dogs submitted to our institute for CME diagnoses. The samples were initially screened for Anaplasmataceae family by PCR, resulting in 30 positive dogs (13.4%). Subsequently, positive DNAs were analyzed by nested PCR 16S rRNA specific for E. canis or Anaplasma platys, resulting in 15 (6.7%) and 16 (7.2%) positive dogs, respectively. For molecular characterization, samples positive for E. canis were subjected to amplification of a fragment of the dsb and p28 genes. The nucleotide sequences obtained for the dsb fragment resulted in 100% identity with others E. canis found in dogs from different regions of worldwide. The nucleotide sequences obtained for p28 gene resulted in 100% of identity with each other and closely with E. canis str. Jaboticabal (Brazil). Identity with others sequences of E. canis ranged from 76.9 to 79.7%. The occurrence of canine cases molecularly confirmed in Metropolitan Area of Buenos Aires highlights the need for more studies in order to understand epidemiological factors associated with CME, especially the disease transmission dynamic in South America given the existence of two lineages of R. sanguineus sensu lato with different vectorial capacity for transmission of E. canis.

Comparative Evaluation of the Vector Competence of Four South American Populations of the Rhipicephalus sanguineus Group for the Bacterium Ehrlichia canis, the Agent of Canine Monocytic Ehrlichiosis

This study compared the vector competence of four populations of Rhipicephalus sanguineus group ticks for the bacterium Ehrlichia canis, the agent of canine monocytic ehrlichiosis (CME). Ticks (larvae and nymphs) from the four populations—one from São Paulo state, southeastern Brazil (BSP), one from Rio Grande do Sul state, southern Brazil (BRS), one from Argentina (ARG), and one from Uruguay (URU)–were exposed to E. canis infection by feeding on dogs that were experimentally infected with E. canis. Engorged ticks (larvae and nymphs) were allowed to molt to nymphs and adults, respectively, which were tested by molecular analysis (E. canis-specific PCR assay) and used to infest naïve dogs. Through infestation of adult ticks on naïve dogs, after nymphal acquisition feeding on E. canis-infected dogs, only the BSP population was shown to be competent vectors of E. canis, i.e., only the dogs infested with BSP adult ticks developed clinical illness, seroconverted to E. canis, and yielded E. canis DNA by PCR. This result, demonstrated by two independent replications, is congruent with epidemiological data, since BSP ticks were derived from São Paulo state, Brazil, where CME is highly endemic. On the other hand, BRS, ARG, and URU ticks were derived from a geographical region (South America southern cone) where CME has never been properly documented. Molecular analysis of unfed adults at 30 days post molting support these transmission results, since none of the BRS, ARG, and URU ticks were PCR positive, whereas 1% of the BSP nymphs and 31.8% of the BSP adults contained E. canis DNA. We conclude that the absence or scarcity of cases of CME due to E. canis in the South America southern cone is a result of vector incompetence of the R. sanguineus group ticks that prevail on dogs in this part of South America.