WHY BE CONCERNED?

The risk of emerging, reemerging, foreign, and intentionally introduced animal disease is real, and many perceive this as a growing problem. The understanding of animal-human pathogen relationships relies on scientific information about various species and populations of animals. National regulatory statutes that provide disease protection between animals and humans must be current and must utilize up-to-date scientific data to protect human health and our food supply while not jeopardizing or overregulating any one animal.

In the United States, the U.S. Department of Agriculture (USDA), the Department of the Interior (DOI), and the Department of Homeland Security (DHS) are the federal agencies tasked with protecting the nation’s wildlife, livestock industries, companion animals, human population, and the food supply from disease. The need for regulations has become more acute with the advent of modern transportation systems that allow movement of animals from any part of the world in a matter of hours. Also, our animal and human populations, along with the U.S. food supply, will now and always need to be protected against the threat of intentionally introduced animal and human disease because bioterrorism will remain a threat.

In a late December 2003 news conference, then–Secretary of Agriculture Ann Veneman made the following statement while talking about a case of bovine spongiform encephalopathy that had been diagnosed Dec. 23, 2003, in a cow in the state of Washington: “The USDA has a primary goal of using science as the basis for decisions involving livestock health matters.”

It is not clear that all federal regulatory officials always use known science to draft regulations and apply them to risk situations. Zoo veterinarians ask only that camelids, which are classified as domestic animals, and other species of captive and free-ranging wild animals be treated fairly, using science-based consensus of understanding that may be incorporated into laws, regulations, policies, and programs. Current scientific information is the least that these populations of unique animals deserve.

CLASSIFICATION AND EVOLUTION

Camelids are not ruminants taxonomically, physiologically, or behaviorally.^7,8 Most importantly, from a veterinary standpoint, camelids and ruminants differ in susceptibility to infectious and parasitic diseases. The differences between camelids and ruminants should exclude camelids from being classified as ruminants. Nonetheless, camelids have been placed in various categories, such as “exotic animals,” “wild animals,” “other livestock species,” and “ruminants,” by state and federal regulators. Camelids have consistently been subjected to sudden, adverse regulations (some inappropriate) when an emerging disease of livestock appears on the scene.

The closing of the Canadian border to camelids when bovine spongiform encephalitis was diagnosed in a cow in Alberta, Canada, is a case in point. Camelids were classified as ruminants and subjected to all restrictions placed on ruminants. The fact that camelids have never been diagnosed with any of the transmissible spongiform encephalopathies anywhere in the world (and are not ruminants) was not given proper consideration.

When questioned about that action, the response was that ruminants are defined by an “encyclopedia” as animals that chew a cud, are cloven hoofed, and have three- or four-chambered stomachs. Regulators completely disregarded the scientific literature that clearly shows that foregut fermentation, complex multicompartmentalized stomachs, food regurgitation, and rechewing are not limited to “ruminants” but are found in species as diverse as kangaroos and nonhuman primates.¹³ In kangaroos, regurgitation and rechewing is referred to as merycism (Greek, “chewing the cud”). Foregut fermentation and multicompartmented stomachs are also seen in many species, including the hippopotamus, kangaroo, colobus monkey, and peccary.⁴

Modern paleontologic and taxonomic scientists clearly state that camelids belong in a separate suborder Tylopoda (Latin, “padded foot”) in the order Artiodactyla, which is distinct from the suborder Ruminantia^* (Box 46-1).

Camelid evolution began in North America 40 to 50 million years ago in the early Eocene epoch.^6,7 Separation of the Tylopoda and Ruminantia occurred early in the evolutionary process, when the progenitors of both groups were small goat-sized animals with simple stomachs.³³

Tylopods and ruminants continued to evolve by what is known as parallel evolution, which is the development of similarities in separate but related evolutionary lineages through the operation of similar selective factors acting on both lines^6,7,33 (Figure 46-1).

Fig 46-1 Diagram of parallel evolution of Camelidae and Ruminantia.

The Pleistocene epoch was characterized by a series of periods of extreme cold and glaciations in northern North America and Europe. The last glacial retreat occurred about 10,000 years ago, marking the beginning of the Recent epoch.

Asia and Alaska are now separated by the 90-km (56-mile)–wide Bering Strait. However, during the height of one of the early Pleistocene glacial periods, the sea level was lowered sufficiently to expose a wide land bridge. Plant and animal species moved back and forth across this bridge; the camel line of Camelidae migrated from North America into Asia, where the evolutionary process continued and domestication took place.

Progenitors of the South American camelids (SACs) (guanaco, vicu-a, llama, and alpaca) migrated to South America at the beginning of the Pleistocene epoch (∼3 million years ago), when an open land connection between North and South America developed.⁶ Evolution continued in South America, where llama and alpaca were domesticated.^9,10,35

DIFFERENCES BETWEEN CAMELIDS AND RUMINANTS

Anatomic and physiologic differences between camelids and ruminants abound (Table 46-1).

Table 46-1 Differences Between Camelids and Ruminants

* I, incisors; C, canines; PM, premolars; M, molars.

Susceptibility to infectious and parasitic agents is of greater concern. The USDA Animal and Plant Health Inspection Service (APHIS) has stated that camelids should be classified as ruminants because, “regardless of their taxonomic classification, camelids meet the definition of ruminants and are regulated as ruminants based on their susceptibility to ruminant diseases such as foot and mouth disease, tuberculosis (Mycobacterium bovis, M. tuberculosis, and M. avium), brucellosis, Johne’s disease, etc.”¹¹

It is true that there are diseases that camelids, cattle, sheep, and goats all acquire, but a careful appraisal of Tables 46-2 through 46-9 should dispel the myth that “llamas and alpacas are susceptible to all cattle and sheep diseases.”³⁴ In fact, they are quite resistant to many regulated ruminant diseases.

Table 46-2 Clinical Infectious Diseases of Camelids and Ruminants

Table 46-3 Infectious Disease Agents Producing Antibody Response, but Rare or No Clinical Disease in Camelids

Table 46-4 Programmed Diseases of Ruminants in United States Compared with Camelids and Other Species

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