Transmission through Birth

T. cruzi can travel through the placenta, birth canal, and maternal milk. Infected mothers pass Chagas’ disease to their children, but in lesser percentages than might be expected. Some unknown immunologic process often protects the infant (Calvo et al. 1978:80). In general, the incidence of congenital T. cruzi transmission is under 10 percent, although this rate is much higher in endemic areas such as Bolivia (Mufioz and Acevedo 1994). In Punata, Bolivia, the mortality rate for children infected congenitally was 47 percent (SOH/CCH 1994). Rates of congenital transmission have increased over the years (Azogue, La Fuente, and Darras 1985:176).[19]

In Bolivia, congenital transmission rates were 7 percent in La Paz and 43 percent in Cochabamba (Brénière et al. 1983). Antibodies were detected in the serum of the mother and in the umbilical cord, with the concentration and quality of the antibodies similar. In Santa Cruz, Bolivia, 329 newborn babies were examined from 1979 to 1980; T. cruzi was found in twenty‑five cases (Azogue, La Fuente, and Darras 1985:176‑80).[20]Some 51 percent of the mothers and 13 percent of the infants tested positive for Chagas’ disease. Twenty‑one (80 percent) of the infected infants weighed less than 2,500 grams (5.5 pounds). It is not clear whether nutrition is an independent or dependent variable; that is, whether the immune system of nutritionally healthy babies resists Chagas’ disease or whether babies infected with Chagas’ disease lose weight. Also, not one case was found before the sixth month of gestation. Although the mother is infected from conception, transmission of T. cruzi from her to the fetus takes time.[21]

The delayed infection of fetuses raises the possibility of treating infected mothers during pregnancy to reduce transmission of the disease to the fetus. The high toxicity levels of nifurtimox and benznidazole used pose serious threats to unborn infants. Moreover, congenitally infected fetuses have been delivered from mothers both positive and negative for parasitemia, and infants have been born uninfected from pregnant women with acute infections and positive parasitemia. Intrauterine T. cruzi infection can cause abortions and premature births (WHO 1991:5).

Mechanisms of transmission of the disease from mother to fetus have not been determined. Possibilities include through the extra‑embryonic membranes by diffusion of the parasites, or through progressive migration of the parasite throughout the stroma of the umbilical cord towards the blood vessels, provoking fetal infection by way of the blood (Azogue, La Fuente, and Darras 1985:180).[22]

The chances of getting Chagas’ disease from contaminated blood in Bolivia are higher (14 to 18 percent) than they are of contracting the disease by being born from a Bolivian mother infected with T. cruzi (5 to 10 percent). Even though these percentages vary greatly and are in part guess‑estimates, the figures are perplexing in that rates of infected blood and infected mothers are roughly the samefrom 40 to 50 percent. One explanation for the lower rates of congenitally transmitted disease is that it is difficult to diagnose, especially in endemic areas, unless the tests are conducted at birth, since the possibility also exists of infection, or reinfection, by the vector (Mufioz and Acevedo 1994). Secondly, parasites are difficult to detect in the placenta, and, even if they are present, they may not infect the fetus (Thiermann et al. 1985; Muñoz 1990).

Significantly, Chagas’ disease in newborns correlates highly with low weight: in one study, 13 percent of babies weighing less than 2,500 grams (5.5 pounds) were infected with Chagas’ disease in Bolivia (Azogue, La Fuente, and Darras 1985:176‑80). Prenatal and postnatal nutrition helps babies resist T. cruzi.