The survival of pathogens in the environment is highly correlated to weather patterns. In hot weather, feces quickly dry out, killing most pathogens that were contained within them. In cooler weather, fecal pats are a more favorable environment for pathogens as the pats remain moist for a much longer period of time. To evaluate and confirm this phenomenon, we measured the ambient temperature and the temperature within fecal pats in two different environments- sun and shade, for a year. Based on the temperature fluctuation of the fecal pats, we were able to determine that Cryptosporidium parvum oocysts are inactivated in a matter of hours when the temperature of a fecal pat reaches 104 degrees Fahrenheit. The internal temperature of a fecal pat reaches this threshold when the ambient temperature is 78 degrees Fahrenheit. As ambient temperature decreases, C. parvum survival increases, taking up to 73 days to die when the fecal pat temperature is 50 degrees.
The Research: Effect of Daily Temperature Fluctuation during the Cool Season on the Infectivity of Cryptosporidium parvum. More>>
The Questions: At lower ambient temperatures on California rangelands, what happens to Cryptosporidium oocysts in cattle fecal pats? What is the peak temperature in fecal pats in winter? Do these temperatures kill oocysts? How long do oocysts survive?
What We Did: First, we measured air and the internal temperature of ~2 ½ pound cattle fecal pats at 11 different rangeland cattle and dairy operations around California using a temperature data logger. Temperature data was recorded every 15 minutes and downloaded every 2 months, at which time the logger was placed in a fresh fecal pat. Once the temperature data was obtained, we selected 3 typical daily temperature profiles and programmed a thermocycler in the lab to mimic these conditions. We exposed C. parvum oocysts to thermal cycles with peak temperatures of 59°F, 77°F, and 95°F for 1-5 days and inoculated lab mice with the heat-treated oocyst solution to determine if the oocysts were infective.
What We Found: Fecal pat temperatures in Decemnber through March fluctuated from a low of ~40°F up to 95°F. To achieve a 90% reduction in the number of infective oocysts, it took 5 days af the 95°F (peak) thermal regime, 29 days at 77°F, and 72 days at 59°F.
What it Means: During winter, Cryptosporidium oocysts can survive in fecal pats for several days. The cooler but above-freezing temperatures typical in California’s rangeland systems dramatically extend oocyst survival during the season when there are peak runoff conditions. Repeated cycles of daily warming and cooling contribute to the inactivation of oocysts, but the process is lengthier when daily ambient temperatures are low. In a previous article (link), we found that when peak fecal temperatures reach 104°F, oocysts die within 24 hours. During the cool season, runoff conditions are common and rainfall can flush oocysts from cattle fecal pats, potentially transporting them to surface waters.
