The neonatal period

Pneumocystis was first described by Chagas in 1909 in guinea pigs, small primate species, and a 4-month-old malnourished infant who had died in the area of Brazil where Chagas first discovered a trypanosome that was infecting railroad workers [1,2]. In the early 1950s, it was found by Vanek and Jirovec that the interstitial plasma cell pneumonia that had been reported in sporadic outbreaks in Europe for nearly 20 years was due to Pneumocystis [3-5]. These outbreaks involved mostly infants who had a predisposing condition, such as malnourishment. Endemic interstitial plasma cell pneumonia was the primary cause of death in European orphanages between 1950 and 1960, with a mortality rate between 10 and 60% [5,6]. This was thought to be a “European” disease until 1955, when cases showed up in children in the United States [7,8]. In 1964, an outbreak of Pneumocystis pneumonia was reported in an orphanage in Shiraz, Iran [9]. Sixty two children suffering from marasmus died from interstitial plasma cell pneumonia caused by pneumocystosis over a 7-year period, most being under the age of 1 year [6]. With the start of the AIDS epidemic in the early 1980s, the incidence of PcP in children once again became a problem. Significant efforts have been made to understand the underlying immunodeficiency diseases that predispose young children to PcP. However, more recently, there have been reports that Pneumocystis has been found in the nasopharyngeal aspirates of immunocompetent children suggesting that children may be a natural reservoir for these organisms [10,11]. Animal models of PcP have become important in determining the immunological basis for the success of the organisms in infecting infants and are discussed in detail in this chapter.