Neonatal brucellosis: rare and preventable.

Abstract

In industrialised countries, brucellosis prevention is now under strict veterinarian control and is close to being eradicated. In developing countries, however, it continues to be an important zoonosis in many regions such as Latin America, the Mediterranean basin, the Middle East and central Asia. Brucellosis is mostly caused by Brucella melitensis, B. abortus and B. suis. It is maintained in nature among a variety of mammals, feral and domesticated, for which the different Brucella species exhibit a relative host preference. Brucellae are highly infective (infective dose between 10 and 100 organisms), and humans acquire the disease by exposure to infected animals and their products, usually through the gastro-intestinal tract, by aerosol inhalation and through abraded skin. Human-to-human transmission is rare and has been reported after blood transfusion, bone marrow transplantation and by the transplacental route, as in the infants described in the two reports in this issue. In endemic areas, brucellosis is particularly common in children who acquire the disease by ingesting contaminated dairy products, especially unpasteurised milk and soft cheese derived from unvaccinated bovines, sheep and goats. Neonates become infected congenitally by the transplacental route in the course of a maternal bacteraemic episode, by exposure to blood, urine or genital secretions during delivery, and by breastfeeding; these are also the main routes of dissemination of brucellae among mammalian reservoirs. Accidental acquisition of the disease through blood and exchange transfusion in the neonatal period has also been rarely reported. In animals, invasion of the trophoblast by circulating organisms is a frequent event in the course of the disease, and usually causes septic abortions. This tendency has been attributed to the high concentration of erythritol, an essential growth factor for the bacterium, in placental tissues of susceptible ungulates. Deliveries and abortions of infected animals also play an important role in the dissemination of brucellae within herds through contamination of pastures by infected blood, lochia and genital secretions, and the organism can survive in the soil for several weeks. The issue of whether brucellosis can also cause abortion or premature delivery in humans is subject to controversy. Brucella species have been isolated from human fetal or placental tissue but it has been suggested that the disease causes fewer spontaneous abortions in humans than it does in animals because of the absence of erythritol in human tissues. However, a study by Khan et al. demonstrated an excess of 1st and 2nd-trimester spontaneous abortions among pregnant women with active infection and Elshamy & Ahmed showed that Saudi women with positive serological tests for brucellosis have a higher incidence of miscarriage and intrauterine fetal death than control women with negative serology. Obviously, the observed poor outcome of pregnancy might not necessarily be caused by an overwhelming fetal infection but might merely have resulted from the severity of the underlying maternal illness. After infecting the host, brucellae become sequestrated within macrophages. They evade host defences, avoiding the killing Annals of Tropical Paediatrics (2010) 30, 177–179