In Pursuit of a Stealth Pathogen: Laboratory Diagnosis of Bartonellosis

Hidden Burden of Bartonella quintana on the African Continent: Should the Bacterial Infection Be Considered a Neglected Tropical Disease?

Bartonella quintana is a louse-borne gram-negative bacillus that remains a poorly characterized cause of bacteremia, fever, and infective endocarditis. Due to the link with pediculosis, B quintana transmission is tied to poverty, conflict, overcrowding, and inadequate water access to maintain personal hygiene. Although these risk factors may be present globally, we argue that a substantial burden of undocumented B quintana infection occurs in Africa due to the high prevalence of these risk factors. Here, we describe the neglected burden of B quintana infection, endocarditis, and vector positivity in Africa and evaluate whether B quintana meets criteria to be considered a neglected tropical disease according to the World Health Organization.

Blood Supplementation Enhances Bartonella henselae Growth and Molecular Detection of Bacterial DNA in Liquid Culture

Bacteria of the genus Bartonella, a member of the Alphaproteobacteria, are fastidious, Gram-negative, aerobic bacilli that comprise numerous species, subspecies, and genotypes. Bartonella henselae, with a worldwide distribution, infects cats, dogs, horses, humans, and other mammals. Diagnostically, direct detection of Bartonella henselae in patient blood specimens by culture or molecular methods is required to confirm infection with this bacterium. Enrichment blood culture combined with quantitative PCR (qPCR) or ddPCR enhances the sensitivity of direct detection. The addition of sheep blood to liquid culture media increased the Bartonella henselae DNA concentration compared to controls, additionally improving PCR direct detection sensitivity. IMPORTANCE This study aims to improve diagnostic detection of Bartonella henselae. Patient samples are combined with enriched bacterial cultures aimed at growing Bartonella henselae for the best possible chance at detection. However, current Bartonella growth methods could be improved. The DNA extraction method used by most laboratories should also be optimized. Sheep blood was added to increase the growth of Bartonella henselae and multiple DNA extraction methods were to be compared to each other.

Comparison of molecular methods for Bartonella henselae detection in blood donors

The Bartonella genus consists of neglected pathogens associated with potentially transfusional-transmitted and fatal human diseases. We aimed to evaluate Bartonella sp. prevalence in 500 blood donors and compare the results with the data already published about these samples. We used molecular diagnostic methods to detect Bartonella sp.-DNA from blood and liquid culture samples: (A) conventional PCR for two gene regions, the ITS targeting the genus Bartonella and the specific gltA Bartonella henselae; (B) nested PCR for the ftsZ gene and (C) qualitative real-time PCR for the gltA gene, both B. henselae specific. We obtained 30/500 (6%) DNA detections from the blood samples; 77/500 (15.4%) DNA detections from liquid culture samples and five (1%) samples had DNA detection from both. In total, we detected B. henselae DNA from 102/500 (20.4%) donors. The samples used in this study had already been submitted for Bartonella sp.-DNA detection using only a conventional PCR in liquid culture. Sixteen samples (3.2%) were positive previously, and from these 16 samples, 13 were negative in the new investigation. We concluded that the use of liquid culture combined with different molecular tests increases the possibility of detecting Bartonella sp.-DNA, but the tests do not avoid false-negative results. More than a fifth of blood donors had at least one PCR that detected Bartonella sp.-DNA among the eight molecular reactions performed now (four reactions in whole blood and four in liquid culture). Seven percent had B. henselae-DNA detection for two or more distinct regions. Considering the results obtained previously, the DNA of Bartonella spp. was detected or the agent isolated in 23% of analyzed blood donors. The results establish that the low bacteremia and the fastidious characteristics of the bacterium are challenges to laboratory diagnosis and can make it difficult to confirm the infection in patients with bartonelloses.

Bartonella henselae Recombinant Pap31 for the Diagnosis of Canine and Human Bartonelloses

Bartonella spp. comprise a genus of Gram-negative alphaproteobacteria that are slow growing, fastidious, and facultative intracellular pathogens with zoonotic potential. Immunofluorescent antibody assays (IFAs), Western blot (WB), and enzyme-linked immunosorbent assays (ELISAs), the frequently used modalities for the serological diagnosis of canine and human Bartonelloses, generate numerous false negative results. Therefore, the development of a reliable serodiagnostic assay for Bartonelloses is of clinical and epidemiological importance. Pap31, a heme binding surface protein of B. henselae, is associated with bacterial adhesion and related to bacterial colonization. To our knowledge, B. henselae Pap31 and its fragments (N-terminal (NTD), middle (MD), and C-terminal (CTD) domains) have not been investigated for the serodiagnosis of canine and human Bartonelloses. In this study, we evaluate the diagnostic utility of B. henselae recombinant whole Pap31 (rPap31) and Pap31 fragments by ELISA using sera from 70 dogs (36 Bartonella spp. IFA-positive (naturally infected), and 34 Bartonella spp. IFA- and PCR-negative (control dogs)) and 36 humans (18 Bartonella spp. IFA-positive (naturally infected) and 18 controls)). In the dogs, the area under the curve (AUC) score of recombinant whole Pap31 was 0.714 with a sensitivity of 42% and specificity of 94% at an OD cutoff value of 0.8955. Among the evaluated recombinant Pap31 proteins for the diagnosis of canine Bartonelloses, rPap31-NTD yielded the highest AUC score of 0.792 (95% CI 0.688–0.895) with a sensitivity of 44% and specificity of 100% at a cutoff value of 1.198. In concordance with this finding, rPap31-NTD also had the highest AUC score of 0.747 (95% CI 0.581–0.913) among the Pap31 recombinant proteins for the diagnosis of human Bartonelloses, with 39% sensitivity and 94% specificity at a cutoff value of 1.366. Recombinant whole Pap31 (rPap31) resulted in 72% sensitivity and 61% specificity at a cutoff value of 0.215 for human Bartonelloses. Due to either low sensitivity or questionable specificity, our findings indicate that recombinant Pap31 and the selected fragments may not be appropriate diagnostic targets in detecting anti-Bartonella antibodies in Bartonella-infected dogs and humans. The findings from this study can be used to further assess the antigenicity and immunogenicity of B. henselae Pap31 as a diagnostic target.

Development of a Multiplex Droplet Digital PCR Assay for the Detection of Babesia, Bartonella, and Borrelia Species

We describe the development, optimization, and validation of a multiplex droplet digital PCR (ddPCR) assay for the simultaneous detection of Babesia, Bartonella, and Borrelia spp. DNA from several sample matrices, including clinical blood samples from animals and humans, vectors, in-vitro infected human and animal cell lines, and tissues obtained from animal models (infected with Bartonella and/or B. burgdorferi). The multiplex ddPCR assay was able to detect 31 Bartonella, 13 Borrelia, and 24 Babesia species, including Theileria equi, T. cervi, and Cytauxzoon felis. No amplification of Treponema or Leptospira spp. was observed. Sensitivity of 0.2-5 genome equivalent DNA copies per microliter was achieved for different members of the Bartonella and Borrelia genus, depending on the species or matrix type (water or spiked blood DNA) tested. The ddPCR assay facilitated the simultaneous detection of co-infections with two and three vector-borne pathogens comprising four different genera (Babesia, Bartonella, Borrelia, and Theileria) from clinical and other sample sources.

Development and validation of a droplet digital PCR assay for the detection and quantification of Bartonella species within human clinical samples

This report describes the development, optimization, and validation of a ddPCR assay for the detection of Bartonella spp. DNA within several sample matrices, including clinical blood samples from patients with or without documented Bartonella spp. bacteremia. The Bartonella spp. ddPCR assay was developed based upon previously published TaqMan-based qPCR assays that can amplify DNA of over 25 Bartonella spp. Host DNA (housekeeping gene) amplification serves as a reference target to facilitate quantification. The efficiency, sensitivity, and specificity of the Bartonella spp. ddPCR assay was assessed by direct comparison with the current qPCR methods used by the Intracellular Pathogens Research Laboratory (North Carolina State University, North Carolina, USA), and Galaxy Diagnostics (Research Triangle Park, North Carolina, USA). Bartonella spp. ddPCR assay parameters were successfully optimized to detect Bartonella concentrations equivalent to 0.5 bacterial genome copies per microliter of blood (0.001 pg/ul of bacterial DNA). The number of droplets detected (resolution) for each concentration was consistent across each of four assessed time points. The Bartonella spp. ddPCR assay detected 16 species/strains including B. henselae; B. quintana; B. vinsonii subsp. berkhoffii (genotypes I, II, III and IV); B. vinsonii subsp. vinsonii; B. melophagi; B. volans; B. monaki; B. alsatica; B. bovis; B. elizabethae; B. clarridgeiae; and B. koehlerae. Bartonella DNA was detected in only one previously negative patient sample (119/120 negative; 99% specificity). The ddPCR sensitivity (53/112) was significantly better than qPCR (6/112) when testing patient blood and enrichment blood culture samples. The development of commercial ddPCR systems with integrated technologies has significantly streamlined the DNA detection process, making it more efficient and standardized for clinical diagnostic testing. The assay described in this work is the first step toward the development of a multiplex ddPCR assay (i.e., using the QX One from Bio-Rad) for the simultaneous detection and absolute quantification of multiple vector-borne pathogens (such as Babesia, Bartonella and Borrelia) within clinical samples.

Vector-borne and zoonotic diseases of dogs in North-west New South Wales and the Northern Territory, Australia

Background

Vector-borne diseases of dogs in Australian Aboriginal communities are relatively unexplored. These dogs represent a unique group with variable ecto- and endo-parasitic burdens, nutritional stresses and a general lack of veterinary intervention. We investigated haemoprotozoal and bacterial pathogen prevalences in relation to erythrocyte and platelet numbers in dogs from North-West New South Wales (N-W NSW) and the Northern Territory (NT; Central Australia).

Methods

Real-time PCR (qPCR) amplification of Anaplasma platys, Babesia vogeli, Mycoplasma haemocanis, Candidatus Mycoplasma haematoparvum and Bartonella spp., serological screening for Coxiella burnetii, and Bartonella spp. and haematological analyses were performed on dogs from the two cohorts (96 dogs in total). Brucella suis serology was determined additionally for the N-W NSW cohort.

Results

Anaplasma platys (n = 26 dogs), Babesia vogeli (n = 7), Candidatus Mycoplasma haematoparvum (n = 10 dogs), and Mycoplasma haemocanis (n = 14) were detected in the sample population (n = 96) using qPCR. There were significant associations between (i) A. platys and anaemia (OR 8.7, CI 2.4–31.7; P < 0.001), thrombocytopenia (OR 12.1, CI 3.4–43.2; P < 0.001) and breed (OR 16.1, CI 2.1–121.5; P = 0.007), and (ii) between B. vogeli and anaemia (OR 11.8, CI 2.3–61.6; P = 0.003). Neither protozoal nor bacterial DNA loads, estimated using qPCR, were positively correlated with anaemia or thrombocytopenia. Haemotropic mycoplasmas were not associated with any haematologic abnormality. Four dogs from the NT were seropositive for Coxiella burnetii, while no dogs were seropositive for Brucella suis or to a panel of Bartonella spp. antigens. Despite directed efforts, Bartonella DNA was not detected in blood from any of the cohorts studied. A sample of dogs from the NT recruited specifically for Bartonella α-proteobacteria growth medium enrichment blood culture were also Bartonella PCR negative.

Conclusions

Vector-borne pathogens occur in dogs free ranging near Aboriginal communities, with higher detection rates in NT than N-W NSW. The preponderant haematologic abnormalities were anaemia and thrombocytopenia, likely attributable to A. platys and B. vogeli infections, but also probably affected by nutritional, parasitic, lactational and environmental stressors. The absence of Bartonella spp. is of importance to the Australian setting, and work needs to be extended to tropical coastal communities where fleas are present as well as ticks. Dogs living in and around Aboriginal communities may provide valuable sentinel information on disease infection status of human public health significance.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1169-2) contains supplementary material, which is available to authorized users.

Bartonella spp. bacteremia in blood donors from Campinas, Brazil

Bartonella species are blood-borne, re-emerging organisms, capable of causing prolonged infection with diverse disease manifestations, from asymptomatic bacteremia to chronic debilitating disease and death. This pathogen can survive for over a month in stored blood. However, its prevalence among blood donors is unknown, and screening of blood supplies for this pathogen is not routinely performed. We investigated Bartonella spp. prevalence in 500 blood donors from Campinas, Brazil, based on a cross-sectional design. Blood samples were inoculated into an enrichment liquid growth medium and sub-inoculated onto blood agar. Liquid culture samples and Gram-negative isolates were tested using a genus specific ITS PCR with amplicons sequenced for species identification. Bartonella henselae and Bartonella quintana antibodies were assayed by indirect immunofluorescence. B. henselae was isolated from six donors (1.2%). Sixteen donors (3.2%) were Bartonella-PCR positive after culture in liquid or on solid media, with 15 donors infected with B. henselae and one donor infected with Bartonella clarridgeiae. Antibodies against B. henselae or B. quintana were found in 16% and 32% of 500 blood donors, respectively. Serology was not associated with infection, with only three of 16 Bartonella-infected subjects seropositive for B. henselae or B. quintana. Bartonella DNA was present in the bloodstream of approximately one out of 30 donors from a major blood bank in South America. Negative serology does not rule out Bartonella spp. infection in healthy subjects. Using a combination of liquid and solid cultures, PCR, and DNA sequencing, this study documents for the first time that Bartonella spp. bacteremia occurs in asymptomatic blood donors. Our findings support further evaluation of Bartonella spp. transmission which can occur through blood transfusions.

Bartonella is a genus of small bacteria with worldwide distribution, transmitted by blood-sucking insects, and is capable of causing disease in humans and animals. Some of the clinical presentations of Bartonella spp., such as cat scratch disease, trench fever, and bacillary angiomatosis are well documented; however, novel presentations have been described in the last two decades, ranging from cyclic flu-like syndrome to neurologic disease and life-threatening endocarditis. Asymptomatic human infection is possible and accidental blood transmission has been reported. Bacterium isolation is very difficult because they grow slowly and require special culture media and procedures. Serology testing poorly predicts active Bartonella infection, except in infection of cardiac valves. Therefore, diagnosis is generally challenging. However, when molecular detection techniques are coupled with special culture protocols, enhanced sensitivity and specificity can be achieved. We investigated Bartonella spp. infection prevalence in a large blood donor population and confirmed bacteremia in 1.2% of the subjects. Bloodstream infection was detected with at least three different molecular methods in 3.2% of donors. These results indicate that Bartonella is a genus of importance for transfusion medicine.