Infections with Bartonella bacilliformis result in Carrion's disease in humans. In the first phase of infection, the pathogen causes a hemolytic fever ("Oroya fever") with case-fatality rates as high as ~90% in untreated patients, followed by a chronical phase resulting in angiogenic skin lesions ("verruga peruana"). Bartonella bacilliformis is endemic to South American Andean valleys and is transmitted via sand flies (Lutzomyia spp.). Humans are the only known reservoir for this old disease and therefore no animal infection model is available. In the present review, we provide the current knowledge on B. bacilliformis and its pathogenicity factors, vectors, possible unknown reservoirs, established and potential infection models and immunological aspects of the disease.

Background Bartonella bacilliformis is the aetiological agent of Carrión's disease, a biphasic and highly lethal illness formerly restricted to the South American Andes that is now spreading to adjacent areas. Reliable serodiagnostic approaches and vaccines are urgently needed. In this study, we aimed to identify immunodominant proteins of B bacilliformis and to establish novel and reliable serodiagnostic tools. MethodsWe used a reverse vaccinology approach in combination with an analysis of heterologous genomic expression libraries to identify immunodominant proteins, on the basis of the genome sequences of B bacilliformis strains KC583 and KC584. Antigens were screened with serum samples collected from Peruvian patients with B bacilliformis infections and from German healthy blood donors without history of travel to South America. We further analysed immunoreactive proteins of B bacilliformis with immunoblotting and line blots. We used selected target proteins to develop a diagnostic ELISA. To assess the performance of this ELISA, we did receiver operating characteristic analyses to assess the area under the curve, cutoff values, sensitivities, and specificities with 95% CIs. FindingsWe used serum samples obtained between Dec 23, 1990, and May 5, 2018, from 26 Peruvian patients with B bacilliformis infections and serum samples taken between Aug 28 and Aug 31, 2020, from 96 healthy German blood donors. 21 potentially immunodominant proteins were identified and recombinantly expressed, and their reactivity was assessed with immunoblotting and line blots. Of these 21 antigens, 14 were found to be immunoreactive. By using serum samples of Peruvian patients with Carrión's disease and of healthy German blood donors, we identified three antigens (porin B, autotransporter E, and hypothetical protein B) as suitable immunodominant antigens, and we applied them in a diagnostic ELISA using two different antigen combinations (porin B plus autotransporter E and porin B plus autotransporter E plus hypothetical protein B). For the combination of porin B and autotransporter E, with optical density measured at 450 nm (OD 450 ) cutoff value of 0•29, sensitivity was 80•8% (95% CI 60•7-93•5) and specificity was 94•8% (88•3-98•3) for all Peruvian patient samples. For a combination of porin B, autotransporter E, and hypothetical protein B, with an OD 450 cutoff of 0•34, sensitivity was 76•9% (56•4-91•0) and specificity was 93•8% (86•9-97•7) for all Peruvian patient samples. Interpretation This novel ELISA could represent a useful serodiagnostic tool for future epidemiological studies of B bacilliformis in endemic areas. Additionally, the immunodominant antigens we have identified could provide a first basis for future vaccine development to prevent the highly lethal Carrión's disease. Funding DRUID (Novel Drug Targets against Poverty-Related and Neglected Tropical Infectious Diseases) Initiative and Robert Koch Institute.

The current problem of increasing antibiotic resistance and the resurgence of numerous infections indicate the need for novel vaccination strategies more than ever. In vaccine development, the search for and the selection of adequate vaccine antigens is the first important step. In recent years, bacterial outer membrane proteins have become of major interest, as they are the main proteins interacting with the extracellular environment. Trimeric autotransporter adhesins (TAAs) are important virulence factors in many Gram-negative bacteria, are localised on the bacterial surface, and mediate the first adherence to host cells in the course of infection. One example is the Neisseria adhesin A (NadA), which is currently used as a subunit in a licensed vaccine against Neisseria meningitidis. Other TAAs that seem promising vaccine candidates are the Acinetobacter trimeric autotransporter (Ata), the Haemophilus influenzae adhesin (Hia), and TAAs of the genus Bartonella. Here, we review the suitability of various TAAs as vaccine candidates.

Bartonella bacilliformis is the biological agent of Carrion’s disease, a vector-borne, life-threatening human bartonellosis restricted to South America. Here, we report the complete genome sequence of B. bacilliformis KC584 (ATCC 35686). Although it is commonly used as a reference strain, to date, its complete genome has not been published.