Since Crab Monkeys have a "close physiology ( with humans) , they can share infections". This is why they are the most common monkey used in lab work. Diseases that have affected humans because of these monkeys include B virus , plasmodium knowlesi, and Ebola. (3) Crab monkeys happen to be the animal that is closest to humans biologically. That makes it easy for I factions to jump from seminal to human. "Disease organisms, particularly virus, tend to live only in a small group of animal species to which they have adapted. In those species, the virus often does little or no damage. That is why exotic pets other than monkeys are much less likely to make their owners ill. But humans are primates of a sort - similar to monkeys - and many of the disease-causing organisms that belong in sub-human primates, can live in humans and go out of control. When they do, they can cause a much more severe disease than in the monkeys in which they belong" (2) .
Pigs are also closely related to humans but Pigs do not die from Ebola like humans and monkeys do. It has even been found that "people who receive transplanted pig organs are unlikely to contract incurable, infectious diseases." (4) .
As a study says "Pigs look to be the most promising source of these organs because the animals are close in size to humans and are easy to breed in large numbers." But this large scale breeding is also dangerous.