Neglected bacterial zoonoses

Abstract

Bacterial zoonoses comprise a group of diseases in humans or animals acquired by direct contact with or by oral consumption of contaminated animal materials, or via arthropod vectors. Among neglected infections, bacterial zoonoses are among the most neglected given emerging data on incidence and prevalence as causes of acute febrile illness, even in areas where recognized neglected tropical diseases occur frequently. Although many other bacterial infections could also be considered in this neglected category, five distinct infections stand out because they are globally distributed, are acute febrile diseases, have high rates of morbidity and case fatality, and are reported as commonly as malaria, typhoid or dengue virus infections in carefully designed studies in which broad-spectrum diagnoses are actively sought. This review will focus attention on leptospirosis, relapsing fever borreliosis and rickettsioses, including scrub typhus, murine typhus and spotted fever group rickettsiosis. Of greatest interest is the lack of distinguishing clinical features among these infections when in humans, which confounds diagnosis where laboratory confirmation is lacking, and in regions where clinical diagnosis is often attributed to one of several perceived more common threats. As diseases such as malaria come under improved control, the real impact of these common and under-recognized infections will become evident, as will the requirement for the strategies and allocation of resources for their control.

Keywords: Acute febrile illness; Borrelia; Leptospira; Orientia; Rickettsia; chiggers; fleas; relapsing fever; ticks; vector-borne bacteria.

Figure 1

Zoonoses reported to the CDC and published in Morbidity Mortality Weekly Reports between 1981 and 2012. Not all diseases were reportable over this interval, and some case definitions changed. No neglected infectious disease as cited by the CDC or WHO appears on this list. Aside from malaria that is most often imported, the most commonly reported zoonoses in the US over this interval were Lyme disease, spotted fever group rickettsioses, West Nile virus infection, Anaplasma phagocytophilum infection, and Ehrlichia chaffeensis infection.

Figure 2

The proportional contribution of various infectious disease fatalities as reported in the Global Burden of Diseases, Injuries, and Risk Factors Study 2010 [7]. (A) Pie chart demonstrating all infectious diseases examined by the study. B. Zoonoses occupy a minority of the reported deaths and disease burden, and include no bacterial zoonoses.