zoonoses and communicable diseases common to ... - PAHO/WHO

STREPTOCOCCOSIS 261In Germany, Denmark, the US, Great Britain, and Iceland, important epidemicshave had their origin in the consumption of raw milk or ice cream made with milkfrom cows with udders infected by S. pyogenes. These epidemics were due to infectionin the cows’ udders contracted from infected milkers. Between 1920 and 1944,103 such epidemics of septic sore throat and 105 of scarlet fever were recorded inthe US due to consumption of raw milk from cows with infected udders. In otherinstances, the milk was contaminated directly (without the udders’ being infected bypeople with septic sore throat or localized infections). In several epidemic outbreaks,the milk became contaminated after pasteurization.According to the WHO Expert Committee on Streptococcal and StaphylococcalInfections (1968), contamination of milk products has caused small outbreaks ofstreptococcal respiratory disease, but these are increasingly less frequent.Pasteurization has been the most important factor in the reduction of streptococcaloutbreaks resulting from milk. In Third World countries, much milk is still consumedraw, and even in developed countries, outbreaks are produced by productsmade with raw milk.Special attention has been given to neonatal sepsis caused by group B streptococci(S. agalactiae). Research has shown that S. agalactiae colonizes a high percentageof women (7% to 30% or more) in different locations, such as the intestinal tract, thecervicovaginal region, and the upper respiratory tract. The agent is possibly transferredfrom the rectal region to the vaginal canal, since most of the bacteria are intestinal.Infants can become contaminated in utero or during childbirth. Only a smallpercentage of neonates (approximately 1%) become infected and fall ill; in most, theagent colonizes the skin and the mucosa without affecting their health. The principalvictims of the infection, especially in the case of the early-onset syndrome, arepremature infants, low birthweight babies, and those born after a difficult labor. Theprincipal reservoir of group B streptococci causing neonatal disease is clearly themother. The S. agalactiae serotypes isolated from mothers and sick newborns arealways the same. Although S. agalactiae is an agent of bovine mastitis and has alsobeen isolated from other animal species, there is no evidence that the infection istransmitted from animals to man. In general, human and animal strains differ insome biochemical, metabolic, and serologic properties. It has been experimentallyshown that human strains of S. agalactiae can produce mastitis in bovines (Pattersonand el Batool Hafeez, 1976). However, some studies have suggested that a percentageof human infections may have derived from a bovine source (Van den Heeverand Erasmus, 1980; Berglez, 1981) or that there is reciprocal transmission betweenhumans and bovines. Nonetheless, research findings seem to indicate that if suchtransmission occurs, its importance is probably limited.The outbreak of disease caused by S. zooepidemicus (group C) in New Mexico(USA) (see the section on the disease in man) clearly indicates that raw milk andunpasteurized milk products can be the source of infection for man. The epidemiologicalinvestigation of this outbreak sampled milk from cows on the establishmentwhere the cheese was made as well as samples of the cheese itself. S. zooepidemicuswas isolated from many of the samples. In Europe, there have also been cases of S.zooepidemicus infection caused by ingestion of raw milk. A case of pneumonia causedby S. zooepidemicus in a woman who cared for a sick horse has been described (Roseet al., 1980). The cases of disease caused by S. zooepidemicus that occurred in HongKong were attributed to the consumption of cooked or raw pork (Yuen et al., 1990).