Initial development and preliminary evaluation of a multiplex bead assay to detect antibodies to Ehrlichia canis, Anaplasma platys, and Ehrlichia chaffeensis outer membrane peptides in naturally infected dogs from Grenada, West Indies

Recent Advances in the Immunologic Method Applied to Tick-Borne Diseases in Brazil

Zoonotic-origin infectious diseases are one of the major concerns of human and veterinary health systems. Ticks, as vectors of several zoonotic diseases, are ranked second only to mosquitoes as vectors. Many ticks’ transmitted infections are still endemic in the Americas, Europe, and Africa and represent approximately 17% of their infectious diseases population. Although our scientific capacity to identify and diagnose diseases is increasing, it remains a challenge in the case of tick-borne conditions. For example, in 2017, 160 cases of the Brazilian Spotted Fever (BSF, a tick-borne illness) were confirmed, alarming the notifiable diseases information system. Conversely, Brazilian borreliosis and ehrlichiosis do not require notification. Still, an increasing number of cases in humans and dogs have been reported in southeast and northeastern Brazil. Immunological methods applied to human and dog tick-borne diseases (TBD) show low sensitivity and specificity, cross-reactions, and false IgM positivity. Thus, the diagnosis and management of TBD are hampered by the personal tools and indirect markers used. Therefore, specific and rapid methods urgently need to be developed to diagnose the various types of tick-borne bacterial diseases. This review presents a brief historical perspective on the evolution of serological assays and recent advances in diagnostic tests for TBD (ehrlichiosis, BSF, and borreliosis) in humans and dogs, mainly applied in Brazil. Additionally, this review covers the emerging technologies available in diagnosing TBD, including biosensors, and discusses their potential for future use as gold standards in diagnosing these diseases.

Epidemiology, Diagnosis, and Control of Canine Infectious Cyclic Thrombocytopenia and Granulocytic Anaplasmosis: Emerging Diseases of Veterinary and Public Health Significance

This review highlights the diagnostic methods used, the control strategies adopted, and the global epidemiological status of canine cyclic thrombocytopenia and granulocytic anaplasmosis at the animal–human interface. Canine anaplasmosis is an important worldwide disease, mainly caused by Anaplasma platys and A. phagocytophilum with zoonotic implications. A. platys chiefly infects platelets in canids, while A. phagocytophilum is the most common zoonotic pathogen infecting neutrophils of various vertebrate hosts. Diagnosis is based on the identification of clinical signs, the recognition of intracellular inclusions observed by microscopic observation of stained blood smear, and/or methods detecting antibodies or nucleic acids, although DNA sequencing is usually required to confirm the pathogenic strain. Serological cross-reactivity is the main problem in serodiagnosis. Prevalence varies from area to area depending on tick exposure. Tetracyclines are significant drugs for human and animal anaplasmosis. No universal vaccine is yet available that protects against diverse geographic strains. The control of canine anaplasmosis therefore relies on the detection of vectors/reservoirs, control of tick vectors, and prevention of iatrogenic/mechanical transmission. The control strategies for human anaplasmosis include reducing high-risk tick contact activities (such as gardening and hiking), careful blood transfusion, by passing immunosuppression, recognizing, and control of reservoirs/vectors.

Ticks and Tick-Borne Diseases in Central America and the Caribbean: A One Health Perspective

Ticks have complex life cycles which involve blood-feeding stages found on wild and domestic animals, with humans as accidental hosts. At each blood-feeding stage, ticks can transmit and/or acquire pathogens from their hosts. Therefore, the circulation of tick-borne pathogens (TBPs), especially the zoonotic ones, should be studied in a multi-layered manner, including all components of the chain of infections, following the 'One Health' tenets. The implementation of such an approach requires coordination among major stakeholders (such as veterinarians, physicians, acarologists, and researchers) for the identification of exposure and infection risks and application of effective prevention measures. In this review, we summarize our current knowledge on the epidemiology of tick-borne diseases in Central America and the Caribbean and the challenges associated with the implementation of 'One Health' surveillance and control programs in the region.

Molecular detection and characterization of Anaplasma platys and Ehrlichia canis in dogs from the Caribbean

Anaplasma platys is a tick-transmitted rickettsial pathogen, which is known to be the etiologic agent for cyclic thrombocytopenia in its primary canine host. Infections with this pathogen are also reported in cats, cattle and people. Similarly, Ehrlichia canis is another tick-borne rickettsial pathogen responsible for canine monocytic ehrlichiosis and is also reported to cause infections in people. We describe infections in dogs with these two pathogens on the Caribbean island of Grenada, West Indies by detection using molecular methods. We utilized a 16S rRNA gene-based PCR assay to detect both Ehrlichia and Anaplasma species by screening 155 canine blood samples from asymptomatic dogs. We found 18.7 % of the dogs to be positive for A. platys and 16.8 % for E. canis. Samples that tested positive for A. platys were further assessed by sequence analysis targeting 16S rRNA, 23S rRNA, citrate synthase (gltA) and heat shock protein (groEL) genes. Phylogenetic analysis revealed high correlation of A. platys 16S rRNA and gltA gene sequences with the geographic origins, while 23S rRNA and groEL gene sequences clustered independent of the geographic origins. This study represents an important step in defining the widespread distribution of active rickettsial infections in Caribbean dogs with no apparent clinical signs, thus posing a high risk for canine health and to a lesser extent to humans, as most dogs in the Caribbean are free-roaming.

Development of a Multiplex PCR and Magnetic DNA Capture Assay for Detecting Six Species Pathogens of the Genera Anaplasma and Ehrlichia in Canine, Bovine, Caprine and Ovine Blood Samples from Grenada, West Indies

Infections with tick-borne pathogens belonging to Anaplasma/Ehrlichia in various vertebrate hosts are a persistent problem resulting in nonspecific clinical signs during early infection. Diagnosis of single and multi-infections with these pathogens, causing diseases in companion/agricultural animals and people, remains a challenge. Traditional methods of diagnosis, such as microscopy and serology, have low sensitivity and specificity. Polymerase chain reaction (PCR) assays are widely used to detect early-phase infections, since these have high sensitivity and specificity. We report the development and validation of an assay involving PCR followed by magnetic capture method using species-specific oligonucleotides to detect six Anaplasma/Ehrlichia species pathogens in canine, bovine, caprine, and ovine blood samples. Overall, the assay application to 455 samples detected 30.1% (137/455) positives for one or more out of six screened pathogens. Single-pathogen infections were observed in 94.9% (130/137) of the positive samples, while co-infections were detected in 5.1% (7/137). Anaplasma marginale infection in cattle had the highest detection rate (34.4%), followed by canines positive for Anaplasma platys (16.4%) and Ehrlichia canis (13.9%). The assay aided in documenting the first molecular evidence for A. marginale in cattle and small ruminants and Ehrlichia chaffeensis and Ehrlichia ewingii in dogs in the Caribbean island of Grenada.

Demonstrating the presence of Ehrlichia canis DNA from different tissues of dogs with suspected subclinical ehrlichiosis

Background

Nowadays, Ehrlichia canis receives increasing attention because of its great morbidity and mortality in animals. Dogs in the subclinical and chronic phases can be asymptomatic, and serological tests show cross-reactivity and fail to differentiate between current and past infections. Moreover, there could be low parasitaemia, and E. canis might be found only in target organs, hence causing results to be negative by polymerase chain reaction (PCR) on blood samples.

Methods

We evaluated by PCR the prevalence of E. canis in blood, liver, spleen, lymph node and bone marrow samples of 59 recently euthanised dogs that had ticks but were clinically healthy.

Results

In total, 52.55% of the blood PCRs for E. canis were negative, yet 61.30% yielded positive results from tissue biopsies and were as follows: 63.15% from bone marrow; 52.63% from liver; 47.36% from spleen; and 15.78% from lymph node. In addition, 33% had infection in three tissues (spleen, liver and bone marrow).

Conclusions

Our results show the prevalence of E. canis from tissues of dogs that were negative by blood PCR. Ehrlichia canis DNA in tissue was 30% lower in dogs that tested negative in PCR of blood samples compared to those that were positive. However, it must be taken into account that some dogs with negative results were positive for E. canis in other tissues.

Ectoparasites of brown rats (Rattus norvegicus) in Grenada, West Indies

Background and Aim:

Arthropod ectoparasites (mites, lice, ticks, and fleas) on common house rats or brown rats (Rattus norvegicus) are known to transmit zoonotic pathogens and diminish rat health. To the best of our knowledge, there is no published information regarding the prevalence of ectoparasites on R. norvegicus in Grenada. This study aimed to determine the prevalence and types of ectoparasites present on brown rats from Grenada.

Materials and Methods:

One hundred sixty-eight rats were collected live from the parishes of St. George and St. David, Grenada, from May to July 2017. Following euthanasia, external parasites were collected using fine combs, thumb forceps, and paper tape. Tape samples and free specimens were placed in containers with 70% ethanol. External parasites were evaluated using dissection microscopy.

Results:

Over 2000 ectoparasites were collected from 149 of the 168 trapped rats (88.7%). Ectoparasites identified included mesostigmatid mites (found on 84.6% of infested rats), fur mites in the families Atopomelidae and Listrophoridae (67.1%), Polyplax spp. lice (6.7%), fleas (3.4%), an unidentified larval tick (0.7%), and a mite in the family Myobiidae (0.7%). Infestation rates were higher in St. David Parish (86/89; 96.6%) than in St. George Parish (63/79; 79.7%) (p=0.001). When comparing sex and age, males had a marginal increase in infestation rate (83/89; 93.3%) compared to females (66/79; 83.5%) (p=0.054), and adults had an infestation rate of 90.7% (97/107) compared to juvenile rats who had a 66.7% (14/21) infestation rate.

Conclusion:

Brown rats in Grenada are heavily infested with ectoparasites, including known vectors of pathogens. Future studies will examine the prevalence of zoonotic pathogens in these arthropods.