Control and preventation of disease outbreaks in shelters
Preventing and controlling disease outbreaks in shelters
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The Pet Doctor www.thepetdoctorinc.com
Identify common risk factors for outbreaks
Identify most common causes of outbreaks in small animal populations
Review basic tools for outbreak control
Provide overview of diagnostic approach to outbreaks of unknown cause
Risk factors for outbreaks of contagious disease in shelters include stress, over-crowding, mixing of species, poor sanitation, facility in poor repair, use of antibiotics when not indicated, lack of vaccination, concurrent disease
Common causes of outbreaks in dogs include: parvovirus, canine distemper, canine influenza, multifactorial respiratory disease and a variety of gastrointestinal afflictions (bacterial, viral and parasitic/protozoal)
Common causes of outbreaks in cats include: panleukopenia, calicivirus ringworm, multifactorial respiratory disease and a variety of gastrointestinal afflictions (bacterial, viral and parasitic/protozoal)
Control of outbreaks requires efficient diagnosis and isolation of diseased animals, identification and removal of at-risk animals, environmental decontamination, and protection of newly admitted animals
Documentation of outbreaks can be summarized as “what (case definition), how many (#affected/# at risk), who (animal risk factors), when (with respect to entry into facility) and where (source within community, exposure within facility)”. Assessment of this information is important to identify cause and determine success of control measures.
Overview of the Issue
With an increasing proportion of pets being obtained from multi-animal backgrounds, a growing number of people involved with foster care or animal rescue, and an increasingly mobile society, any veterinary practitioner or shelter may be faced with an outbreak either within the clinic or in a shelter or rescue foster home.
In past years, measures such as total depopulation have often been utilized in shelters to control outbreaks. Such measures are not viable when infectious disease invades a veterinary clinic or boarding facility, and are becoming increasingly unacceptable at shelters as well. Fortunately, with a well-thought out and systematic approach, most outbreaks can be controlled successfully with far less drastic measures.
Animal risk factors for outbreaks include:
Stress
Animals not vaccinated on intake (shelters) or prior to intake (boarding facilities)
External and internal parasites
Concurrent disease (such as upper respiratory infection)
History of predation or scavenging
Environmental risk factors for outbreaks include:
Overcrowding (and resultant lapses in cleaning, proper housing and care)
”Some in–some out” housing
Failure to isolate ill animals
Mixing of species
Antibiotic use
1. Efficient Diagnosis and Isolation of Diseased Animals
In order to be effective in halting an outbreak, rapid and sensitive diagnostic methods are needed so that affected animals can be recognized and appropriately isolated. If it takes days or weeks to get answers, disease may continue to spread while veterinarians await results. Unfortunately, quick and accurate tests are not always available. For example, canine parvovirus and feline panleukopenia can often be quickly diagnosed using a snap ELISA test. Canine distemper, on the other hand, often requires expensive and time consuming methods of diagnosis, especially in recently-vaccinated dogs when serology is not reliable.
When rapid diagnostic tests are not available, it is often necessary to proceed under the assumption of “worst case scenario” and treat all animals with suspicious clinical signs as if they are infected. In a shelter suffering an outbreak of distemper, for example, it may be necessary to treat all dogs with respiratory signs as potentially infected (and infectious), even though some of these dogs may only be suffering infection with more benign agents. A common and potentially dangerous belief is that mildly diseased animals do not pose a great risk to others. While this may be the case for some conditions, often the severity of disease manifestations in an individual animal reflects more on that individual’s immunocompetence rather than the severity of the infecting pathogen. Transmission of severe and even fatal disease by mildly infected animals is commonplace with some important diseases such as canine distemper and virulent systemic feline calicivirus.
2. Identification and Removal of Exposed/At-risk Animals
Animals which are not yet symptomatic but may be incubating disease must be identified and isolated for a suitable quarantine period (or euthanized in shelters if no quarantine facility exists or can be devised). Quarantine can be costly and labor intensive, and euthanasia is obviously a last resort; therefore it is important to distinguish those animals genuinely at risk for infection. In order to assess risk level, the veterinarian or shelter needs to know the method of disease spread, risk factors for infection such as age or breed, and the extent to which vaccinated animals are reliably protected.
Assessing Exposure
For conditions that are spread via aerosol transmission, it may be necessary to consider all animals within a facility potentially exposed. This is the case for canine respiratory infections, such as distemper and canine influenza. Contrary to common assumption, feline respiratory infections are generally not spread via aerosol transmission; provided stringent cleaning control is in place, feline respiratory disease does not tend to spread more than 5 feet via droplet infection. “Hair-borne” disease such as ringworm or perhaps some strains of feline calicivirus can certainly drift readily through a facility or spread on contaminated clothing if care is not taken to prevent this.
Assessing Risk
Even when animals are exposed to a pathogen, it is not uncommon for some to escape infection, depending on the animal’s risk factors and immune status. The two most important factors are age and vaccination status. For example, cats which are fully vaccinated against feline panleukopenia at the time of exposure are very unlikely to get sick and need not be quarantined. This assumption can be made regarding dogs which are vaccinated parvovirus and canine distemper as well. On the other hand, vaccine protection against respiratory infections tend to be mediocre at best, and all exposed animals should be assumed to be at risk regardless of vaccine status.
Use of Serology for Risk Assessment
For diseases in which serologic status correlates well with protection, serological testing may be valuable in identifying animals which are NOT at risk for infection and therefore need not be quarantined or euthanized. Diseases for which this is the case include feline panleukopenia, canine parvovirus and canine distemper. Only serological tests utilizing viral neutralization or hemagglutination inhibition or validated by same should be used. Positive titers at the time (or within a few days) of exposure in asymptomatic animals correlate well with protection; negative titers do not necessarily mean the animal is susceptible. In-house serological tests are available in some cases, and this may be a highly cost effective method of assessing risk.
Length of Quarantine
The quarantine period must be equal to or longer than the longest probable incubation period of disease. Again, this is easier achieved with some diseases than others; a two week quarantine period for canine influenza or parvovirus is sufficient, while the incubation for some strains of canine distemper can be four weeks or even longer. Recommended quarantine periods for common shelter infections can be found at http://www.sheltermedicine.com/portal/is_infectious_diseases.shtml – top3.
3. Decontamination of the Environment
In some cases minimal cleaning with almost any disinfectant will suffice to render a contaminated environment safe again. For example, canine distemper and canine influenza do not last long in the environment. Clean-up for these conditions is not a major challenge, and outbreaks are unlikely to be resolved through improved cleaning efforts (although of course such efforts are never contraindicated). However, several of the infectious agents associated with outbreaks in cats and dogs are extremely durable and resistant to all but a handful of disinfectants. This includes the un-enveloped viruses (canine parvovirus, feline panleukopenia and calicivirus), ringworm (Microsporum canis) and assorted GI pathogens such as coccidia and whipworm. Once a clinic, home or shelter is contaminated with one of these pathogens, careful mechanical cleaning followed by effective disinfection is imperative before naïve animals can be re-introduced.
An often over-looked source of ongoing contamination is subclinically affected or carrier animals, (those that are chronically infected but show no signs of disease). Feline respiratory infections are notorious for establishing carrier states, and this can be an issue in resolving a feline calicivirus outbreak. Subtle or subclinical infection may also be an issue in diarrheal or ringworm outbreaks; it may be necessary in diarrheal outbreaks to prophylactically treat all exposed animals, and in ringworm outbreaks to culture and treat accordingly regardless of visible lesions.
Basic steps for environmental decontamination following any outbreak:
1. Identify and treat/isolate carrier or subclinically affected animals, as described above.
2. Mechanically clean the environment as well as possible. Irrigate outdoor areas such as lawns and gravel yards. Steam clean carpeting and furniture. Clear surfaces of clutter, wash with detergent, disinfect and rinse to the extent possible. Allow all areas to DRY thoroughly between cleaning, and maximize exposure to sunlight. Often environments can be rendered safe through careful mechanical cleaning, even following contamination with highly durable agents such as parvo.
3. Use disinfectants with broad spectrum. If you know what pathogen you are dealing with, use a disinfectant proven effective by independent studies. For un-enveloped viruses, this includes sodium hypochlorite (5% household bleach diluted at 1:32) and potassium peroxymonosulfate (e.g., Trifectant®). For ringworm, only sodium hypochlorite diluted at 1:10 has proven reasonably effective. If dealing with an unknown pathogen, consider using an additional disinfectant to that normally utilized: if you usually use a quaternary ammonium disinfectant, follow with bleach, or vice versa (check to ensure compatibility, or rinse thoroughly between disinfectants).
4. Scope out possible fomites/overlooked contaminated areas. Often a tremendous effort is expended cleaning animal areas, but key locations are over-looked. Especially important are animal transport vehicles, carriers, exam surfaces and equipment. In one shelter, an outbreak was apparently sustained for several months by a contaminated “rabies pole”; in another, contamination was detected in the siphon hose used to dispense disinfectant! It may be necessary to discard scratched plastic items such as carriers, beds and litter pans if these can not be successfully cleaned/disinfected.
5. Tincture of time? It is a common practice to empty a cage or facility for some time following a disease outbreak. While this may be helpful for relatively fragile pathogens such as canine influenza or distemper, it is not always necessary if careful mechanical cleaning and disinfection has been accomplished. In some cases, it may even lead to a false sense of security–a couple of weeks is insufficient to eliminate durable agents such as parvovirus or ringworm. In these cases, the only real benefit of holding areas closed is to allow multiple cleaning cycles to take place; this process can be accelerated by cleaning and drying repeatedly at shorter intervals if a shelter, clinic or boarding kennel is eager to re-open an area.
4. Protection of Newly Admitted Animals
If an effective vaccine is available, aggressive vaccination programs should be instituted to protect naïve animals from disease. In the face of an outbreak, modified live vaccines are generally preferred to killed. It may be appropriate to vaccinate starting at an earlier age (4-6 weeks versus traditional 8-9 weeks), at more frequent intervals (every 2 weeks in puppies and kittens < 16 weeks old), and in the face of mild illness or injury. In the case of a few infectious conditions, prophylactic treatment may be used in animals that must be exposed to a contaminated environment. For example, cats being admitted to a ringworm-contaminated facility may benefit from a single dip with lime-sulfur, or kittens and puppies may benefit from prophylactic treatment for coccidia when housed in a chronically contaminated environment.
5. Documentation and Communication
Cases or possible cases, test results, time and spatial pattern of spread should be recorded as described below. This will assist greatly in arriving at a diagnosis, developing a plan for control, and assessing success of said plan. In addition, every multi-animal facility needs a planned procedure to communicate with staff, clients/adopters, volunteers, and other stakeholders within the community in the event of a serious outbreak. For outbreaks at boarding facilities and shelters, it may be necessary to contact clients/adopters from the days preceding recognition of the outbreak; keeping easily retrieved records available is therefore crucial. Being pro-active about putting out accurate information can forestall undue alarm and facilitate rapid recognition and control should the infection spread beyond a single facility.
Identification and Documentation of Outbreaks
Our job would be relatively easy if the cause of an outbreak was always readily apparent. Of course, life is not always that simple, and veterinarians are often faced with outbreaks of unknown–and potentially multifactorial–origins. Although ideally we would discover the cause of each outbreak, it is often necessary to implement management practices prior to reaching a definitive diagnosis. An outbreak investigation/management plan needs to define the magnitude of the problem; identify risk factors for infection; determine whether animals were infected by exposure within the community or contracted disease within the facility; and whether control measures are adequately preventing further spread of disease. It is important to remember that toxic or other causes can closely mimic rapid spread of an infectious condition–don’t be too quick to rule out non-infectious problems such as spoiled food, caustic disinfectants, intentional poisoning, even stinging insects. Questions to be asked in an outbreak can be categorized as “what, how many, who, when and where”. Although presented here in numerical order, in reality these tasks often occur simultaneously.
1. What is causing the observed condition? Confirmation of diagnosis and definition of suspect and confirmed cases. In a suspected outbreak of serious disease, diagnosis should be confirmed in at least one or two cases by the accepted gold standard. If no single reliable method of diagnosis is available, multiple criteria should be used for disease confirmation. For instance, in a case of suspected panleukopenia, diagnosis could be confirmed by a combination of symptoms, ELISA test results, CBC results and necropsy findings. If none of the usual culprits are identified, it may be necessary to submit appropriate clinical and environmental samples for laboratory analysis; if animals die or are euthanized, full necropsy can be very helpful in establishing a cause. Once diagnosis has been confirmed, a written case definition should be established describing what constitutes a suspect or confirmed case. For instance, a suspect case may have symptoms consistent with the disease, while a confirmed case may have one or more positive lab tests in addition to symptoms.
2. How many animals are affected? Document the number of suspect and confirmed cases, and the method of diagnosis for each. It is also important to document the number of animals exposed. Comparing the number affected to the number exposed can help establish cause. For example, a disease such as canine influenza–for which little to no pre-existing immunity exists in most areas–is likely to affect the majority of the exposed population. If only a small percentage of exposed animals become ill, this makes canine influenza a much less likely rule-out.
3. Who is affected? Characteristics of affected animals, including age, breed, sex, and vaccination status. This helps determine which animals are at high risk, and may suggest which animals can be spared should rigorous quarantine or depopulation measures become necessary. Identifying risk factors also helps establish cause: for example, disease in well-vaccinated adult animals is very unlikely to be caused by parvovirus, panleukopenia or canine distemper, diseases for which vaccine resistance is rare.
4. When did disease develop? How many days since entry into facility? Speed of onset may give a hint as to cause; for example, feline calicivirus often develops following an incubation period of just a few days, where-as incubation for other feline respiratory pathogens is more commonly closer to a week. If signs developed in fewer days than the typical incubation period for the disease, the animal probably contracted the disease in the community and entered the facility already infected. Strict quarantine/cohort admission of incoming animals is indicated in the case of a community-wide outbreak. If signs developed after the typical incubation period, the animal almost certainly contracted the disease within the facility. Re-examination of sanitation, cleaning and other disease control procedures is indicated in this case.
5. How many days since control measures were established? This question is asked to determine whether initial control measure have been effective. Presumably, control measures are instituted immediately upon recognition of the first case of disease ( the index case). Additional cases may develop in animals exposed to the index case prior to establishment of control measures, even if those measures halted subsequent spread. If infection is due to exposure to the index case, signs would be expected to develop within the incubation period for the disease. However, if cases develop after this time has elapsed, and/or in animals that could not have been exposed directly or indirectly to the index case, control has not been effective and stricter measures are required.
6. Where did animal come from in the community/where was it housed in the shelter? Plotting location of affected animals may be helpful in tracking spread of the disease within the shelter or, if the disease is suspected to originate outside the shelter, affected areas of the community.
Summary
High density populations such as shelters, boarding kennels and even some veterinary clinics are at risk for outbreaks caused by known and unknown pathogens. Ideally, such outbreaks will be prevented by eliminating risk factors such as overcrowding, stress, lack of vaccination, mixing of species, and over-use of antibiotics. When the worst happens and an outbreak occurs, however, we still have many tools available for control: efficient diagnosis and isolation of diseased animals; identification and removal of at-risk animals; effective environmental decontamination; protection of newly admitted animals through vaccination and prophylactic treatment; and careful documentation and communication can all greatly mitigate the damage caused by an outbreak of even the worst disease.
