BVD - Bovine Viral Diarrhea - is a disease that is primarily found in cattle.  Unfortunately it has now been verified that it can occur in llamas and alpacas as well.

BVD is a major cause of lost revenue in cattle - it can cause abortions, ill health, and if females are exposed to this disease during a certain stage of gestation, then the offspring will be a chronic carrier of the disease - literally a "Typhoid Mary" for BVD. 

Since this is a fairly common disease in cattle, you are increasing your risk of getting it into your llama and alpaca herd if you have cattle near your animals.

One alpaca breeder in eastern Canada, who is also a medical doctor, was able to isolate the problem when it occurred on her farm.  The source of the infection was traced to an animal that had been brought in from an alpaca farm in Alberta. 

Here are some links to her website, and a link to the Alpaca Research Foundation