Serum Biomarkers are Associated with Asymptomatic Infections in Carrion’s Disease

A study performed in northern Peru and led by ISGlobal, an institution supported by “la Caixa” Foundation, sheds light on the immune response to infections by Bartonella bacilliformis, the causal agent of Carrion’s disease. The results, published in Plos Neglected Tropical Diseases, help explain the chronicity of asymptomatic infections and identify potential biomarkers for their detection.  

Carrion’s disease (CD) is a tropical neglected disease transmitted by sandflies and endemic to Ecuador, Colombia and most particularly Peru. An estimated 1.7 million people in South America live at risk of contracting the disease. It is characterized by two distinct phases: the Oroya fever and the Peruvian wart. However, there is a high percentage of asymptomatic carriers that can contribute to disease transmission but that are difficult to detect due to the lack of sensitive diagnosis tests. Indeed, very little is known on the immune responses to Bartonella baciliformis, the bacterium that causes the disease.    

In this study, performed in collaboration with the Health Faculty of the Peruvian University of Applied Sciences and the Peruvian Institute of Nutritional Research, the researchers analysed serum samples of 144 healthy individuals from five villages in northern Peru. Four of the villages experienced a CD outbreak in 2012 and the other one is in a traditionally endemic area. They measured 30 cytokines, chemokines and growth factors (three types of proteins involved in cell to cell communication), as well the presence of the bacteria (by molecular methods) and of bacteria-specific antibodies.  They identified several proinflammatory markers that were inversely correlated with detectable bacteria, while the immune-suppressive cytokine IL-10 and angiogenic chemokines (that promote the formation of blood vessels and are involved in bartonellosis-related wart formation) were positively associated with infection.  

These results suggest that infection by B. bacilliformis causes suppression of the immune system due in part to overproduction of IL-10. “This immune suppression likely contributes to the chronicity of asymptomatic infections and favours persistence of the bacterium and its transmission to the vector” explains Gemma Moncunill, study coordinator. Furthermore, the angiogenic factors identified in this study could be possible candidate biomarkers of chronic and asymptomatic infections, although further studies need to evaluate the sensitivity of these and other markers.   

Reference:

Pons MJ, Gomes C, Aguilar R, et al. Immunosuppressive and angiogenic cytokine profile associated with Bartonella bacilliformis infection in post-outbreak and endemic areas of Carrion's disease in Peru. PLoS Negl Trop Dis. 2017 Jun 19;11(6):e0005684.