Biosecurity

George M. Barrington

Biosecurity involves efforts designed to prevent introduction and spread of disease within populations, herds, or groups of animals.¹ These efforts may be further divided into those directed at the prevention of entry of new diseases into a group (external biosecurity) and those directed at preventing spread of disease within a group (biocontainment or internal biosecurity).² Furthermore, biosecurity may be implemented at various levels, from the farm level to the regional or national level. To be effective, a minimum biosecurity plan should address (1) isolating new animals, (2) isolating animals returning to the herd, (3) regulation of animal, human and equipment movement, and (4) the design and implementation of cleaning and disinfection procedures directed at the reduction of pathogen loads. Although much of the following may be applicable to various animal systems, special camelid situations will be addressed, when appropriate.

General Principles

Clearly, our ability to control disease has been, and will continue to be, enhanced through technologic advances in vaccines, therapeutic agents, and diagnostic techniques. However, overdependence on these technologies may blur the importance of, and encourage indifference toward management components of disease control such as biosecurity.³ Management, including directed input from qualified veterinarians, should strive to incorporate the breadth of available tools including risk assessment, computerized record keeping, implementation of modern diagnostic technologies and the practice of optimal husbandry techniques, including biosecurity and biocontainment.⁴

Biosecurity practices should be prioritized to address those factors that pose the greatest risk of disease introduction. The most common means by which contagious diseases are introduced to a herd involves introduction of new animals or the return to the herd of animals that had been on other premises or locations. Obviously, introduction of animals displaying any clinical signs of disease must be avoided. Importantly, producers must be educated that mere exclusion of clinically ill animals is unlikely to prevent introduction of disease. Often, animals that appear clinically normal may be incubating disease or be subclinically affected. It is well documented that in a given population of animals, only a fraction of those infected typically exhibit clinical disease, the larger proportion being subclinically affected. Consequently, appropriate and effective efforts in biosecurity must focus on the entire population of animals, rather than simply concentrating on those that are clinically affected.

External Biosecurity

The basic tenets of external biosecurity include isolation of new animals, quarantine procedures, disease testing, preventive measures, and hygiene. As mentioned earlier, the most prevalent means of introducing disease into a group of animals is via addition of new animals into the herd. The concept of a “new animal” must include animals that have never resided on a farm as well as those returning after travel to offsite facilities (e.g., shows, fairs, breeding facilities).

Animals commingled at other facilities undergo an increased risk exposure and infection. Producers must be made aware that many pathogens do not necessarily require direct contact between animals for transmission to occur. Some pathogens are efficiently transmitted via air, water, fomites (e.g., equipment, tack), pests (e.g., flies, rodents), or personnel. Some pathogens can survive in soil or organic material for weeks or even months.⁵

To lessen the risk of disease introduction, producers must be knowledgeable about health status of a new animal’s herd of origin. This obviously requires communication between parties long before any animal movement. Ideally, purchasers should be familiar with both current and past health status of the seller’s herd. Conditions of concern may include evidence of diarrhea, respiratory diseases, ill thrift, failure of passive transfer, abortion, and herd-based diseases. Buyers must also be knowledgeable about fundamental biosecurity practices of the seller’s herd. Specific areas should include information regarding animal movement, quarantine practices, disease testing practices, vaccination practices, deworming schedules, hygiene practices, and so on. Finally, prospective buyers should minimize the number of source-herds from which newly acquired animals are purchased.

During public sales, shows, and auctions, animals from different sources are brought into varying levels of proximity. Some animals may have travelled long distances, and on arrival, they must adapt to new environments, which can serve as an additional source of stress and potential immunosuppression. Environmental changes are numerous and include temperature and humidity, ventilation, lighting, bedding, water, feed, and personnel. Numerous risk factors for disease transmission include recrudescence of latent infections and increased shedding of organisms.

Newly purchased animals or those returning from events where commingling has occurred should be placed in quarantine for a minimum of 30 days. To be effective, quarantine facilities must be physically separate from the main herd, its handling facilities and housing. Although it is not practical to identify a single, defined distance for separating the quarantine facility from the main herd, it is safe to state that the farther it is, the better it is. Ideally, this would invoke a separation distance of several hundreds of yards, positioned downhill and downwind such that prevailing winds or surface drainage does not carry aerosols or contamination toward the main herd. Finally, quarantine facilities must be located such that access is not made too difficult or impractical for personnel attending to animals at the facility.

Effective quarantine practices utilize the concept of “all in—all out.” That is, when multiple animals are placed in an isolation facility concurrently, all animals leave the facility at the same time. If multiple animals are placed in a facility over time, the last animals to arrive dictate the time when all the others in quarantine will be allowed to leave.⁴ Animals in quarantine must be monitored on a daily basis. Basic parameters include gait, attitude, activity, appetite, water consumption, urination, and defecation. Potential signs of disease may include nasal or ocular discharge, changes in stool consistency, coughing, lameness, and so on. If body temperature is recorded, it should be consistently obtained during the same time of day. Animals showing unique changes in activity, behavior or signs of disease should be further separated from other quarantined animals and examined by a veterinarian.

Personnel attending to quarantined animals should wear protective clothing (e.g., coveralls) and boots that are devoted solely to the quarantine facility. Clothing and boots should be washable, and boots should be made of rubber or other impervious materials. All equipment and supplies used in a quarantine facility (e.g., halters, ropes, feeders, buckets) must be solely devoted to that facility and remain at the facility. Ideally, personnel working with quarantined animals should have minimal or no contact with the main herd. If dedicated personnel are not available, quarantined animals should be attended to only after animals in the main herd have been cared for.

Testing for specific diseases may be accomplished during the quarantine period. A period of 30 days is generally adequate for collecting and submitting samples as well as receiving and interpreting results. Preventive measures such as deworming and vaccinations may also be performed during the quarantine period.

Owners must be informed of the potential for disease transmission by visiting personnel. Ideally, visitor contact with herd animals should be minimized and appropriately controlled. Owners or herd managers should know the background of visitors, especially with regard to recent animal contact, including contact with camelids and other domestic and wild species. Visitors should be dressed in clean clothing and be provided with coveralls and boots. Protective clothing should be collected at the end of the visit, and all personnel should have access to a hand washing area. Uncontrolled access to a herd by the general public should be prevented.

Exporting camelids to breeding farms is a common practice within the industry. Producers must be aware that animals returning from these farms are essentially equivalent to newly imported animals. Commingling of animals from varying backgrounds and different ages at these facilities carries an extremely high risk for both exposure to and recrudescence of infectious diseases.

Owners must also be made aware that other animal species may function as mechanical or biologic vectors of infectious agents. Domestic pets and vermin (insects, rodents, birds) are of particular importance, especially if present in high numbers.

An often overlooked vector that presents a significant disease transmission risk is the common house fly Musca domestica.⁶ These insects have physical characteristics (mouth parts, hairs, sticky foot pads) and activities (defecation, vomiting) that greatly enhance their ability to transmit large numbers of pathogens. Under the right conditions, flies may harbor certain pathogens (e.g., Cryptosporidium parvum) for several weeks.⁷Numerous methods have been described for controlling flies during different points in their life cycle, including the use of various chemical agents. In addition to chemical means, control must also include removal of feces and wet organic debris, since fly larvae require appropriate substrates and levels of humidity.

Rodents are also a source of disease transmission. In other livestock industries (dairy, beef, and poultry), mice have been implicated in the transmission of salmonellosis.8–11 Mice are also significant reservoirs of Cryptosporidium. Importantly, significant numbers of rodents may be present long before signs of their presence (feces) become noticeable.