As a strict vegetarian, is it possible to contract deadly diseases from our food? Absolutely. Then why not eat animal products since it appears to some there is no escaping infectious disease through our food? This is a silly question when it is understood that much of the contamination originates in animals.
When bagged salads transmit e.coli, the bacteria originated in most cases from the intestines of cows. Although we know that deer and other animals can breed e.coli in their intestines also, as can man. Somehow bacteria and virus infect plants. It is even thought that prions can infect plants also. But, where are the infectious agents coming from? Animals via feces often. Soil and water are infected and then brought in contact with plants or their seeds and fruits.
Not long ago it was confirmed that one of my suspicions was true. There is a practice of using feces water in agriculture. Why would a farmer do such a thing? Why would one use manure in a garden? It is not strange at all since the practice goes back thousands of years. The Bible reveals that dung was used to fertilize trees. Jesus spoke in a parable regarding a fruitless tree "Let it alone this year also, till I shall dig about it and dung it; and if it bear fruit, well." This was to reveal God's patience with professing Christians that produce no good fruit. He labors long with us providing all He can to bring about conversion.
It was not dangerous at that time to place cow dung on the ground as a fertilizer. That was before the animals became diseased as they are today. Now, the dung is often full of dangerous bacteria, such as E.Coli, virus, such as Leukemia, and prions such as those that cause Mad Cow Disease. It is a very risky thing to place animal dung where it will come in contact with plants used for food. But, the practice is widespread. It saves a lot of money to take manure and spread it on the soil rather than to buy chemical fertilizers. There are farm operations that spread the manure through watering. A solution of the manure can be flood irrigated on the ground. Thus, bacteria, virus, and prions are spread over wide areas being used to produce food for human consumption. And equipment being used for food production is infected. Walking on the infected ground enables the disease infected soil to be transmitted to areas not irrigated by the infected water. And we wonder why a strict vegetarian can come down with diseases common to meat eaters.
Here is a very good article from a couple of years ago that gives a little information on the problem with infecting plants with animal diseases.
How Do Pathogens Get into Food?