r

A Day in the Life Here We Go Again ...

Over the years I have seen similar cases too many times. The scenario begins when I receive a call from a farmer reporting several cows being off feed. During ~he visit, it is obvious a respiratory infection outbreak is spreading through the herd. Often, a quarter to half of the cattle show clinical signs. These animals cough, breath heavily, and have nasal discharge. Typically, they present with high fevers and very poor appetites (Figure 15-1).

The classic history reveals that a few animals were purchased recently and introduced to the herd. These new cattle do not show any clinical signs of disease. Additionally, the herd has not been recently vaccinated. The purchased animals are typically healthy, but with the stress of transport and a new environment they shed bacteria or viruses. However, they have adequate immunity because of prior exposure and therefore remain healthy. Unfortunately, the existing herd is not immune and the disease spreads rapidly.

In any herd with such problems, the economic costs can be quite staggering. Expenses include veterinarian examinations, treatment (medication costs can be very high for large animals), death loss, and a decrease in productivity as afflicted animals produce little milk or gain little weight.

Fortunately, not all of my work is treating the ani­mals after they are sick. Many producers understand the concept of disease prevention and ask for advice before purchasing cattle. For example, a large dairy that I service planned to purchase a group of 40 dairy cows. The dairyman, the seller, and I worked together on a plan . We recognized that there are always risks asso­ciated with purchasing cattle, but the right approach

1' -~,. I ' ,. . ·-. ~ ... ; ! pb -,-

FIGURE 15-1 Heifer suffering from pneumonia. This heifer has a thick nasal discharge and labored breathing.

~ E ~ Cl) en

"' en C: Cl) u r--

~ IQ)

\

FIGURE 15-2 An anesthetized dog with a large number of porcupine quills.

would help to minimize the risk. We screened the incoming cattle for several diseases and were able to somewhat isolate them for several weeks after arrival. Thankfully, all of the tests were clear and there was no evidence of disease problems.

Many kennels require visiting dogs to be current on all their vaccines, including kennel cough. The kennel cough vaccine is not one that I recommend for every animal. When many dogs are combined in a confined area such as a kennel, however, the risk increases for kennel cough , and this is why kennel owners require the use of the vaccine .

As I do my preparation for writing a chapter, my job often leads me to important information to include in the book. My practice is in a rural area and many of the pets have access to the outdoors. Unfortunately this puts the pets at risk of being struck by a car, bitten, or even shot. One day, I had two dogs that tangled with a porcupine. I had to anesthetize the dogs and carefully pull each quill (Figure 15-2). I can only imagine how painful it was for the poor dogs to have hundreds of quills in their mouths and skin.

I remember graduating from veterinary school. For the first time, I heard the word doctor in front of mffY

'do name. All the years of hard work had finally pal . · Actually, there was one more step. In addition to obtain; ing a doctorate, veterinarians must meet additiona licensing requirements before practicing medicine. .

1na· I had already passed the National Board Exarn d tion. The majority of states require a minimum st8ndar

--------------------- continues

~ . the Life continued

~ .. . test before permitting the veterinarian to

on th '_s ManY states have additional requ · enter ct1ce, irements

pra d the Nati onal Board Examination. When 1 110n . . d h gradu-oe, per1nsy1vanIa require t e successful compl t · ted, h • . . e 10n

a al cornpre ens1ve examInatIon for all new f

an or . veter-o . The candidate entered a room and sat b f . anans- . th 1. . e ore ,n terinanans on e 1cens1ng board. The cand'd f ur ve . 1 ate o Id be asked anything about veterinary medicine b

cOIJ y

thiS groUP• W

hile waiting for my turn to enter the examinar 1 . t . . 10n,

1·1<e I was being sen into an interrogation My . d

felt 1 • • • min

d with the thought of bright lights shining int

race . o my sweat beading on my forehead and the ·int

eyes, . • er-

tors prying answers from me. The entire pro roga . . . . cess was quite int1m1dat1ng. Over the fo~r years of veterinary

school, a tremendous amount of information was cov­

ered. 1 wondered what they were going to ask.

When I finally entered the room, the group was

quite nice. They welcomed me and told me to make

myself comfortable . The honest truth was that 1 was not going to be comfortable until I knew if I had

passed. My entire career had come down to the next

few questions. The first question concerned a condition called gas­

tric torsion in dogs. In this situation the dog' s stom­

ach twists, trapping gas inside. This is a life-threatening

problem, requiring surgical and medical treatment. I had

just been through the emergency service rotation, and

this disease and its treatment were fresh in my mind.

DISEASE PREVENTION

Objective

1 Name the Basic Components of Disease Prevention

Many factors contribute to an animal's resistance

~o disease, such as immunity and nutrition, which

te already been discussed in depth in previous

~-apters. A healthy animal remains resistant to most

iseases. The skin and mucous membranes serve to prevent i · • fl nvas1on of pathogens. The normal bactenal

rno~a plays a role in maintaining the health of an ani­

g/ · these bacteria secrete substances that inhibit the

rn~;th of other organisms. In addition, pathogens

adh compete for adhesion sites. The pathogen must

begi:~ to the animal's cells before an infection can

It is an b · · · · th norn,

1 ° v1ous conclusion that mamtauung e

an a ? bacterial flora helps to maintain the health of

ea~"nst_tnal. Stress, nutrition medications, and other dis-~ ~fl ' .

uence the normal bacteria. Humans can think

Chapter 15 u1sea::;t: r11::vc.""V "

At this point, I was feeling quite smug. Maybe this oral

exam was not so tough after all. The next question burned in my mind. I was asked

to discuss the causes and treatment of wool eating,

wet dewlap, and cannibalism in rabbits . My jaw dropped

and heart stopped. I' m sure the panel immediately

knew I was in trouble from the expression on my face .

Exotic animals were not a significant part of the core

ve~erlnary school curriculum. Plenty of opportunity

existed for studying this kind of information, but it was

elective , and up until that moment, I did not have a lot

of interest in the subject. I honestly could not remember hearing of these dis­

eases before that moment, and I surely did not know

any specifics. But one thing that veterinary school does

teach is how to use the knowledge that you do have.

After a few seconds of stuttering, I began to discuss

some very important principles in disease prevention. I

discussed in general terms proper nutrition , proper san­

itation, and minimizing stress. They asked me to explain

a few other points about the topics before moving to

the next question. (Fortunately, the remaining questions

related to familiar material and I was granted a license!)

As I left the room , I did not know if I had passed.

I just had to investigate the unfamiliar diseases. Even

though I had not learned about these specific diseases,

I had learned the important principles of disease pre­

vention. My answers, although more general than the

board may have wanted, were quite correct. In this

chapter, the discussion centers on important principles

in preventing infectious diseases.

of factors that produce stress (e.g., a major examination

pending). In animals, stress does not require conscious

th~ught. Stress_ is any factor considered a threat by the arumal. An arum.al under stress releases higher levels

of epinephrine and cortisol (see Chapter 10). In addi­

tion, stress increases the activity of the sympathetic

nervous system. A wide range of factors can contribute to stress.

Examples include overcrowding, competition for feed,

extremes of weather, rough handling, noise, and trans­

port (Figure 15-3). Environmental conditions also have

a significant impact on health risk. Wet conditions,

manure accumulation on hair coat, and poor air quality

(dust, smoke, and ammonia) can all increase the stress

and demands on an animal. Commingling animals

from multiple sources also adds to the stress as the ani­

mals establish their social hierarchy. Some factors that

are designed to help an animal can also contribute to

stress. Hospitalization and surgery both stress the at · _

mal. Following major surgery, an animal can be m~~e

susceptible to contagious diseases.

266 I Unit 3 Diseases

FIGURE 15-3 These individually tied cows have feed delivered directly to them. This feeding method greatly decreases competition.

The increase of cortisol in response to stress has specific benefits. Cortisol helps to increase carbohy­drate metabolism and shifts glucose to the brain. The cortisol also minimizes inflammation in damaged tis­sue. As a side effect, the elevated cortisol suppresses the immune system, increases the risk of diabetes, and weakens muscle tissue. These signs are quite evident in hyperadrenocorticism (Cushing's disease), where cortisol levels remain chronically elevated.

Nutritional problems can also be considered a stress, or may have a direct effect on diminishing the immune response. Many vitamins and minerals (such as vitamin E and selenium) are crucial in maintai.ni.ng a healthy immune system. All the antioxidants, oxid~­tion-inhibiting vitamins and minerals, play a role m the animal's immune system. Other deficiencies may weaken the defense of the animal in more general ways. For example, a protein and energy de~ciency may weaken the skin and mucous membranes, mcreas­ing the likelihood that pathogens will invade_-

Sudden changes in diet are also an important stressor in animals. A major effect of diet changes is the decline in the normal bacterial flora in the intestinal tract. This greatly increases the risk of pathogen inva­sion and consequential disease. Medications, primarily antibiotics, pose the same threat to the a~imal's ~e~e~se system. When treating a bacterial infection, an~b10tics also cause a decline in the normal flora-a particularly high risk if the pathogen has resistance to that antibi­otic. This is another key reason why antibiotics should be used only in situations in which they are actually required. . , Some factors that increase the animals stress also contribute to increasing exposure to pathogens. O~er-

d. g was mentioned as a stressor. Overcrowding crow m f · dd' increases the competition for feed and co~ ort, ma . I-tion to increasing the contact between arumals, which

ilids in the spread of _conta~ious diseases. The hi density of ilnimals typically increases fecal and u _gh . . t I rtne conh1miniltion tn the _env1ronmen ~s w~ I. _Hurnidi is often higher in confined areas, which aids 10 the S\J;

l·v"I of pathogens outside the body. Pathogens that · v u ' . . I I h 1 . are sprcild through the air phys1ca y ave ess distance travel when contactin? another susceptible individ~~

Ventilation describes the exchange of air fr within a building to the outside. ~s animals extiZ: they add moisture, heat, and pote~hal pathogens to th~ • Ammonia and hydrogen sulfide are also rel""'r-d air. h b 'Id . E --from the urine and feces in t e u1 mg. xcess of these

toxic gases can cause irri~ation to the mucous mein. branes and lower the respiratory defense mechanisms increasing the risk of a pa!hogen's ~vasion of th~ respiratory tract. Most orgarusms req~ire some degree of moisture to survive, so exhaled m01~~e contributes to the success of pathogens. The activity of animals in a barn also creates airborne dust particles. These particles can help to carry p_athogens and damage the protective ability of the respiratory ~act.

To help prevent disease, fresh_ai~ from the outside needs to be brought into the bwldmg and the stale air exhausted. This helps to lower the moisture, heat, ammonia, and pathogen load in the air. Some facili­ties are built to allow for natural airflow to make this exchange (Figure 15-4). Other build~g~ rely on fans to move the air efficiently. Tunnel ventilation has become quite popular (Figure 15-5). In tunnel ventilation, the fans are placed at one end of the barn, and all the air inlets are on the opposite end. With the fans running, the air is brought into the barn over a broad area and an even flow of air is swept over the animals. In warm weather, enough air is exchanged to produce a breeze of 3 to 5 miles per hour.

In cold weather, less air can be exchanged. In these conditions, enough body heat must be maintained to

FIGURE 15-4 A free stall barn with comfortable cows. Note the high open side walls and the large number of fans.

RGURE 15-5 Barn equipped with tunnel ventilation.

nt freezing within the barn. Even in the coldest Preve . . ther at least four air exchanges per hour should wea / ' ccornplished. This means that the exhausted air be a . al f . h , ,hould be eqwv ent to_ o_ur times t e amount of air ~ontained within the building. Unfortunately, in many b ms there are areas that do not completely exchange a These areas can be regions where confined animals all' , are at a higher risk for disease. In the heat of the sum-mer, up to 30 air exchanges per hour may be needed to maintain appropriate conditions.

1n summary, proper ventilation helps to protect the animal in several ways. It maintains appropriate , temperature and humidity levels in the barn. It also minimizes the accumulation of irritating gases as well as lowers dust levels. Removing the already breathed air also physically removes infectious agents that h~ve '. become airborne through exhalation and coughing. Properly designed ventilation also minimizes dead . air space and drafts. Considerable emphasis is put into ventilation design in new construction. Modifying existing barns to provide proper air flow can be more difficult. , In general, older animals have a higher level of immunity than the very young. They have been exposed to more organisms and vaccines over th~ years.

Chapter 15 Disease Prevention \ 267

proper sanitation and providing clean, dry bedding are extremely important in reducing pathogen load. Phys­ically, these steps help to lower the number of organ­isms in the environment. In addition, they help to keep the animal's hair clean and dry. Hair has a very impor­tant role in insulating the animal and conserving body heat in cold weather. When the hair coat becomes wet and matted with feces, the animal loses higher levels of heat. In addition, prolonged exposure to moisture, urine, and feces increases the risk of developing skin disorders (such as wet dewlap in rabbits, an infection in the skin of the lower neck) .

VACCINES

Obiectlve

■ Describe the Types ot Vaccines Available and Their Roles in Disease Prevention

The previous details discussed are designed to mini­mize the exposure of the animal to pathogens and to limit any factors that decrease the animal's resistance to disease . Another component of disease prevention is to increase the animal's immunity with vaccination. Much has been discussed about vaccines in Chapter 11. Many factors are involved in determining a vaccination

· They also have a higher likelihood of being earners ~o_r · P_afuogens. Therefore when desigrun· g animal facih-tie · · · ' th

s, it 1S rrnportant for the airflow to move from e :~ungest to the oldest. In this way, the young animals

program. . . The goals of a vaccin~hon program va~y with the I\ & e not exposed to the pathogens that could be ex~aled 1

\ __ · d~rn the mature animals. It is ideal that young arumals B ~ot commingle with adults for the same reasons. aving separate areas of confinement is very helpful. Uri mmonia into the . ne and feces not only release a . . atr but also contribute pathogens. Estabhshing

t pe of animal and the disease. Most vaccines do not ~fer complete disease pro_tection. Properly vaccinat~d imals can still become ill when overwhelmed with an Th f . . posure to a pathogen. ere ore, vaccination pro-e:ams must be established with realistic goals in mind. ~uccessful vaccination requires that an effective vaccine

268 j Unit 3 Diseases

be given to an animal that is capable of responding well. In addition, the vaccine must be given long enough before exposure to allow immunity to develop. Consideration must be given as to which vac­cines should be included in the program. The risk of acquiring an infection is one important factor. Certain organisms have a specific geographic location. There­fore, vaccination is not considered in areas where the organism is not found. Other factors such as age, sex, and functional purpose of the animal must also be eval­uated. Some diseases may be common only in young animals, and some infections are associated with repro­ductive problems that require females to be vaccinated. Certain diseases are spread from bulls to cows during natural breeding. Artificial insemination and the use of semen from bulls free of these diseases prevent the need for vaccination against these organisms. The severity of the disease must also be evaluated in terms of medical and economic impact. A very mild and self-limiting disease usually does not require vaccination. Diseases such as distemper in dogs and panleukopenia in cats are so deadly that they are included in all vacci­nation programs for these species. In food-producing animals, a disease may be self-limiting, but if it attacks a large percentage of animals, it may still be a very costly disease, due to loss of production. This type of disease may be included in the vaccination program. Vaccines vary considerably in how effective they are at preventing disease. Some vaccines provide only a short-lived immunity. Others may decrease the inci­dence only slightly or may lessen the severity of the disease. The success must be evaluated against the cost of the vaccine. A costly vaccine that has only limited success may not be used. A vaccine may also have adverse effects (such as suppressed milk production in dairy cattle), which is another factor considered in establishing a program.

In companion animals, vaccination programs are established with the goal of preventing the disease in every animal vaccinated. The emotional attachment to pets makes the individual animal of extreme signifi­cance. The vaccines are given at frequent intervals in young pets with the goal of developing immunity as the maternal antibodies decline. Even the most thor­ough program may not prevent every case. Experts in organizations such as the American Animal Hospital Association and the American Associ­ation of Feline Practitioners have developed guidelines to help practitioners in making vaccination decisions. Certain organisms are considered so important that they are recommended to be included in all vaccina­tion programs. These core vaccines include distemper, adenovirus, parvovirus, and rabies for all dogs. In cats the vaccines for panleukopenia, herpes virus, calicivi­rus and rabies are also considered core. Decisions on no~core vaccines are then made based on particular

risk factors for the individual pet. For example, al vaccine may be recommended for a hunting dog .Ylt\e endemic area but not include_d in a program for a~ at\ in a large city in a nonendenuc area. 0g In the farm setting, vaccination programs h establish herd immunity. These vaccination progr e\p are designed to decrease the number of suscep:s animals in an attempt to prevent a herd outb le . reak Ideally, every ~al w~uld de':'elop complete inunu~ nity. However, it is qmte possible for an individ 1. · 1 d' U h d . · tial to develop c imca is~ase. er lmffiuruty is estab. lished, the disease . will not spr~~d throughout the remainder of the arumals. In addition, even if dise occurs in a vaccinated animal, the severity may ~e much less and recovery much quicker when compare~ to an unvaccinated animal.

Herd immunity is maximized when all the at-risk animals are vaccinated. The vaccination programs are established to minimize the potential losses experi­enced with an outbreak of clinical disease. Producers also attempt to keep the cost of the program as low as possible. Therefore, only animals with a reason­able threat of exposure are vaccinated, and they are vaccinated only as often as is necessary to maintain immunity. Timing of vaccinations is also critical to the suc­cess of a program. Vaccinations need to be adminis­tered early enough that an immune response can be mounted prior to exposure to the disease. Vaccinating a dog for kennel cough after it has arrived at a kennel would not be protective. Likewise, vaccinating cattle in the presence of a pneumonia outbreak will not prevent clinical disease in cattle already incubating the disease. Vaccines may also be scheduled to maximize protec­tion at particular times of the year or production cycle. In some facilities, pneumonia may be more likely in the winter when the cattle are housed, rather than when grazing on an open pasture. Vaccinating these animals in the fall allows for an appropriate immune response to be mounted prior to the high-risk time. Certain vac­cines may also be used to improve colostrum quality. In this case, timing the vaccination a month or two prior to the end of gestation can maximize the benefit of the vaccine.

In review, immunity may be active or passiv:· Passive immunity is acquired with the transfer of anti­bodies. This may occur with the -ingestion of colostrum by a newborn. A well-vaccinated mother generally has better-quality colostrum. The higher quality of colostrum improves the amount of antibody absorbed by the newborn. The volume and how quickly after birth the colostrum is delivered directly influence the passive transfer. . Certain vaccines also provide passive immunity by supplying antibodies. The immunity is only te~­porary, and therefore the timing of the vaccination 15

:f cal. An example is tetanus antitoxin, which may be ell

1 · I · I. h' I . k

d 11. ustered at a time w 1en an arnma 1s at 1g 1 ns . a IT1 . h. may include a horse with a deep puncture wound

T 15

1 animal that is being castrated. If the animal was or at . . . • t vaccinated previously for tetanus, these antitoxins

110 e the distinct advantage of delivering immediate hav

un111unity. for an animal to develop active immunity, a vac-

. 1e must be administered that allows the animal to c~oduce its own antibodies. Natural infections also Preate an active immunity. Natural infections often c rovide the strongest and longest lasting immunity. ~accines must provide enough antigens to stimulate tl1e inunw1e system. The two major types are killed (commonly virus or bacteria) and modified live vac­cmes (typically virus). In a killed vaccine, enough antigens are provided for the immune stimulation. The organism within the vaccine is completely inactivated.

With killed products, a primary vaccination initiates tlle immune response. A booster dose must be given in tliree to four weeks to stimulate the memory response. It is only after this second dose that effective levels of antibodies develop. Relative to modified live vaccines, tlle killed products provide a short immunity. Periodic boosters are then required to maintain immunity (which typically ranges from several months to a year).

Modified live virus vaccines (ML Vs) stimulate both antibody production and cell-mediated immunity. Ini­tially, ML Vs deliver a small amount of antigen. The virus then undergoes replication once injected into the animal. The amount of antigen then increases to a level adequate to stimulate the immune response. The virus has been modified so it can replicate-without causing clinical disease. In general, an ML V provides a higher level and longer-lasting immunity than do killed prod­ucts. Many ML Vs do not require a booster vaccination in the three- to four-week period, as the killed products do. The immunity may not be indefinite, however, and a booster is required every one to three years.

Numerous factors can lead to a failure of a vaccina­tion program. Modified live vaccines require very care­ful handling to ensure that the organism will replicate once injected. These products come as a dehydrated powder and a liquid to mix with it (Figure 15-6). Once rehydrated, the vaccine should be used imme­diately. The organism can be killed by extremes of temperature, direct sunlight, and exposure to many disinfectants. Proper storage at controlled refrigerated temperatures is essential. (These factors may also dam­age killed products.) If the organism does not replicate, not enough antigen will be present to stimulate an immune response.

With killed vaccines, failure to give a booster dose ~lso prevents acceptable levels of immunity .. ~e t~­tng of the booster is also important. Adm1rustenng the booster in less than two or more than eight weeks

Chapter 15 Disease Prevention 269

~ : ~ t~~·-.

, I -. ,

\ I .

I r FIGURE 15-6 Examples of vaccine selection ( clockwise from lower left): (1) Modified live vaccine. The freeze-dried powder must be reconstituted with liquid before usage. (2) An oral vaccine (bolus) used to provide . passive immunity to newborn calves. (3) A modified live vaccine admin­istered intranasally. The white nasal canula shown in front of the bottles is applied to the end of a syringe to administer the vaccine into the nasal passages. (4) A killed vaccine that is ready to be administered.

greatly decreases the level of immunity developed. It is essential to remember that immunity only develops following the vaccination with either type of product. Failure may occur if the animal is exposed before or shortly after the vaccination.

The animal must be able to respond to the vac­cine. Very young animals may have levels of mater­nal antibody that prevent the immune system from responding. The maternal antibodies quickly bind to the antigen and therefore prevent the need for the immune system to respond. Animals that are under stress or are ill may not be able to mount an effective response. Poor nutrition or certain medications also decrease the level of immunity.

Even a well-vaccinated animal with a good level of immunity can be overwhelmed if exposed to high lev­els of pathogens. In effect, poor management can defeat a good vaccination program. Any failure in manage­ment (such as poor sanitation, poor ventilation, or overcrowding) can result in the animal being exposed to such high numbers of pathogenic organisms that the immune system cannot defeat them.

CLINICAL PRACTICE

Objective

■ Link the Clinical Significance of the Academic Material Learned in This Chapter to Veterinary Practice

~ ,3

0 N

g

Kennel cough in dogs represents an excellent example of how vaccination programs are adapted. Several different viruses or the bacteria Bordetella bronchiseptica

270 I Unit 3 Diseases

may cause kennel cough . Dogs with kennel cough typ­ically present with a severe, dry hacking cough. Dogs that develop ke1mel cough generally respond to med­ication (cough suppressants and possibly antibiotics) and improve within one to two weeks.

Because the disease is generally self-limiting and the incidence of ke1mel cough is quite low in the average house pet, routine vaccination is not always required. Kennel cough is highly contagious and is able to be spread through the air or by direct contact. There­fore, dogs that are housed in close quarters with others are at a higher risk. This is especially true in a board­ing kennel, where dogs from multiple households are brought into close confinement. Because the risk is higher in these situations and the disease can spread so rapidly, vaccination for kennel cough is often required before boarding.

Biosecurity is a term used to describe practices that protect the health of the animals on a farm by prevent­ing the introduction of pathogens (Figure 15-7). Ideally, these practices prevent the introduction of disease into the herd. For example, horses are often screened for equine infectious anemia (EIA) prior to a show or pur­chase. EIA is a viral disease causing fever, an anemia from the breakdown of red blood cells, depression, and weight loss. Some horses die from EIA; others develop a chronic infection and become carriers of the virus. These horses may appear normal but when under stress may shed the virus. They can then be a source of infection for other animals on the farm. The testing of animals for infectious diseases before introducing them onto a new farm is an important biosecurity practice.

_ A11EH110H f :.· .~. :­~ --:,, •

~'. :;_.: !f;'· ]: 06 not enter !hose lacilitlei . . ~ . without permi~slon

· '.· ·,Y!.; For permlssio·n contact: · . :

·:-:.~ ~ fy5 f¥£ ~ S f/El..D(),4/' ~,

~ ,: l . . \ ~- : .Those with perm1s~1on: : . ~t ,: l J weiU ut~,,o~ub.lo booW or sunl11ZO ..,. • boots tMJloru enton.nw il , , : , · · :; 1. : ,~ Oo not touch youno y tock ;"' '

~ -\ -~ ~~- '.':''. -~'~'.~ ::~''.'. '.~:~· ........... .... :

FIGURE 15-7 This farm has Implemented biosecurity measures to limit the risk of disease entering the farm.

As discussed biosecurity begins at the farm 1.,.. . . . al ~v~ but it is also very important on region and nati , levels. For example,_ individ~al states develop sp::~ requirements for ammals bemg transported from oth states. National ?uideli_nes are in ~lace to prevent t~: importation of disease into the Umted States.

Bio-containment is the practice used to minintiz the spread of disease ~ it is in~oduced onto the fan: The previously menhoned dairy herd with the

O · break of respirat~ry infection e~ph~sizes the imp~:~ tance of biosecunty. The farm m this case had Pao biosecurity. The purchased cattle represented a re~ threat to the health of the existing herd. The purcha~d animals had not been screened for any infectious dis­eases, and the existing herd was not well vaccinated. By recognizing that the purchased cattle were a poten­tial threat to introduce infectious respiratory diseases the farmer should have vaccinated the herd. Even With proper vaccination, a small number of cases may have developed. The goal of the vaccination program is to establish herd immunity and minimize the spread of the disease.

Diseases can be introduced onto a farm by manv vectors. Visitors, trucks (feed, livestock), rodents, bir& and water supply are all potential sources for new dis~ eases. Even veterinarians represent visitors to a farm. Veterinarians take precautions by sanitizing boots and hands between farm visits.

The greatest risk of new disease is introducing new livestock. The newcomers have the greatest potential to introduce large enough numbers of pathogens in close contact to the existing animals. An excellent procedure for minimizing this risk is quarantine. Quarantine con­fines the animal in a location that prevents contact with the existing herd. A separate set of utensils (e.g., pitch­forks and feed buckets) should be used in the quaran­tine area. Proper sanitation in water troughs and feed troughs is also an important aspect of bio-containment.

The goal of quarantining is to ensure that the pur­chased animals are not incubating a disease. The new additions may appear perfectly healthy at the time of purchase but be in the earliest stage of infection. Separating the animals for two to four weeks helps to minimize this risk. Unfortunately, many farms do not have facilities to keep animals completely separated.

Many farms eliminate the need for quarantining by practicing an all-in all-out system. All the animals leave the farm, the barn is cleaned and sanitized, and then the next group of animals is brought onto the farm. Ideally, all of these animals come from one source, minimizing the threat of animals becoming exposed to new pathogens.

Some farms are not able to practice an all-in all-out system and on others the animals may have to come from multiple sources. The risk of a disease outbreak is highest in the first days to weeks after the animal~

arri,•e on the farm. This is a result of the stress of trans-ort and the exposure to new pathogens from the other

~nin1als. Metaphylaxis describes the prophylactic use of antibiotics in these times of high risk. For example, calves arriving at a stocker operation may be given a tong-acting antibiotic injection at the time of arrival. The goal is to minimize the number of cases, limit the severity of cases that do develop, and increase the overall weight gain of the animals arriving. Numerous studies have shown improvements in average daily gain, dry matter . intakes, and f~ed conversion ratios with metaphylaxis. Metaphylax1s does not replace a proper vaccination program but merely works in con­cert with it.

Vaccination programs are developed to maximize protection of the animal. However, consideration must be given to the cost of the vaccine and the potential for side effects. In farm animals the cost of the vaccine is balanced against the potential for loss if the disease occurs. The effectiveness of the vaccine must also be considered.

Any vaccine has the potential to cause side effects. Soreness and swelling at the site of injection are very common. Many animals also develop mild fevers, leth­argy, and poor appetites. In general, these side effects are short lived and disappear without treatment. Some vaccines may increase the risk of abortion in pregnant animals. The most serious side effect is anaphylaxis.

SUMMARY Disease prevention begins with sound biosecurity practices such as maintaining a sanitary environment. Employing a comprehensive vaccination program tailored for each client's needs also helps prevent

REVIEW QUESTIONS 1. Define the following terms:

antioxidant ventilation tunnel ventilation wet dewlap biosecurity equine infectious anemia bio-containment quarantine metaphylaxis fibrosarcoma

2, True or False: All vaccinations offer complete pro­tection from the intended disease.

Chapter 15 Disease Prevention I 271

This allergic reaction may be so severe that it is life threatening. Prompt treatment with epinephrine is essential to reverse the allergic response.

In companion animals, vaccination programs gen­erally begin with a series of vaccines in the young. Recommendations vary significantly, but vaccination often begins in dogs and cats at six to eight weeks of age. Booster vaccinations are given at three- to four­week intervals until there is confidence that maternal antibodies have declined to a level that allows the pet to respond (recommendations vary from 12 to 18 weeks of age). The long-held standard is that the pets are then given yearly booster vaccinations to maintain a high level of immunity.

It has been discovered that certain vaccines may increase the risk of developing a cancerous tumor of connective tissue (fibrosarcoma) in cats. There is also evidence that certain immune-mediated diseases may be increased as a result of frequent vaccination. This discovery has raised significant controversy relating to vaccination recommendations. New protocols based on disease exposure are being developed and tested in which vaccines are not repeated as frequently. In addi­tion, testing may be done to measure antibody levels to see if vaccination protection is still present. With the development of new vaccine technology and an under­standing of the science of immunology, strategies for properly vaccinating animals will continue to evolve.

the spread of disease. Ultimately, disease prevention proves cost effective for both the large-scale producer and the pet owner alike.

3. A_ dose must be given a month or so after ad­ministration of a killed vaccine to elicit a memory response.

4. Which have higher immunity levels, young or older animals?

5. How long should a new animal be quarantined when brought home?

6. Name a common side effect of vaccination.

7. Does stress in animals require conscious thought?

8. Does a vaccine exist for distemper in dogs?

9. Can a vaccine affect milk production?

272 I Unit 3 Diseases

10. Should a modified live vaccine be refrigerated?

11. How does allowing an animal's hair coat to

become wet and matted contribute to disease

conditions?

12. Describe the cough in kennel cough.

13. Name two types of immunity.

14. List at least two factors used in developing a va . . ca.

nation program.

15. List the symptoms of equine infectious anemia.