have a more practical design. Alligators and crocodiles can be raised in captivity with "open cycle" or "closed cycle" methods. Open cycle refers to programs that are concerned with the health of the wild population and are using captive rearing as a means to supplement the wild populations. Closed-cycle operations are primarily concerned with harvest. In closed cycle operations, adult females are kept in captivity, and the eggs they lay are collected, incubated artificially, hatched, and the juveniles are grown to a certain size and harvested. Closed cycle operations provide no incentive for conservation and are often unsuccessful because the cost of starting and managing the operation often outweighs the profits gained from products. Although the cost of operating an open cycle operation is comparable to closed cycle, the goal of an open cycle operation is the overall health of the species, rather than economic profit. Captive breeding and ranching operations provide more incentive to protect natural populations and are important contributors to the success of crocodilian populations. Concerns Animal welfare Welfare concerns include the threat of crocodilian diseases such as caiman pox, adenoviral Hepatitis, mycoplasmosis, and chlamydiosis. Crocodiles suffer from stress in confined spaces such as farms, leading to disease outbreaks. Most crocodilians keep a body temperature within 28 and 33 degrees Celsius. On farms, body temperatures can reach 36 degrees Celsius, which affects the animals' immune system, and puts them at risk of various illnesses. Another concern is for the cleanliness of the water in enclosures. Pests Many alligator farms in the United States have experienced property damage from Sus scrofa (feral swine). Disease Between 2001 and 2003, West Nile virus (WNV) infected and caused deaths resulting in economic loss in American alligators in Georgia, Florida, Louisiana, and Idaho. The disease is transmitted by mosquitoes. WNV has been found in Mexico at a crocodile farm in Ciudad del Carmen. The skin, most notably the underside, of alligators and crocodiles is of commercial value, so diseases of the skin need to be treated properly and effectively. Crocodilian diseases vary between species. Salmonellosis is common on some farms, and is acquired from infected food; it may also be spread by poor hygiene practices. Chlamydia, (specifically Chlamydophila psittaci) can persist for years if not treated, for example with tetracycline. Crocodilians may acquire mycobacteria from infected meat. Illnesses affecting crocodilians include crocodile pox, which is caused by Parapoxvirus, affecting hatchlings and juveniles.