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Chapter Twelve Health and Disease
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Health and Disease A major function of the laboratory animal facility staff is to keep research animals healthy. Experimental studies cannot be properly completed using sick animals. Everything an animal technician does is designed to reduce the danger of disease at the animal facility. It is the purpose of this chapter to acquaint the new animal technician with the signs of disease and factors affecting the health of laboratory animals which are entrusted to his or her care.
Identifying Diseased Animals Observe each animal, checking for common signs of disease. Animals found dead must be promptly reported so valuable tissues & data can be obtained. Promptly note signs of sickness so persons responsible for diagnosis can notify investigator & treatment started. Brightly colored card placed on cage of animal w/ signs of disease, card indicates signs observed. Animal health technician to remove dead animals, observe sick animals, record info. in a log & inform veterinarian.
Identifying Diseased Animals II Veterinarian can advise PI of treatment or euthanasia. While cleaning cage, check for weight loss, diarrhea, hair coat problems & abnormalities. Experiments may cause animal to become sick. Report a sick animal when experiment may have made it sick; this information is helpful to investigator. If an animal seems in pain, even if expected due to research experiment, notify facility veterinarian immediately.
Signs of Disease Look for signs of illness. Signs vary by species. Change in behavior may be only indication of illness. Report observations. Learn terms to describe signs of disease. Learn systems affected to understand the disease.
Signs of Disease Alopecia - usually associated w/ skin disease, fighting, parasites or barbering Barbering is when one animal chews off patches of hair from another & is done by a dominant animal. Anemia - skin or mucous membranes are pale Gums may appear almost white, usually associated with blood loss or reduced numbers of erythrocytes. Anorexia - animal is not eating Often noted when animals not drinking due to inaccessible, broken or disconnected water valve. Animal ill or in pain may have decreased food intake. Bleeding - can be external or internal You may see fresh blood in cage but not on animal.
Signs of Disease II Change in behavior - animal that suddenly becomes aggressive, quiet or loses interest in surroundings is usually sick or in pain. Circling or head tilt - a rodent spins in a circle when held by the tail, or an animal walks in a circle or holds its head to one side. Often indicates an infection of the middle or inner ear. Constipation - no feces being passed because it is not being moved through the large bowel. can be caused by lack of feed or water, serious infections & a number of other disease problems Coughing - rapid, forced expelling of air through the mouth indicates a problem in throat or lungs.
Signs of Disease III Diarrhea - passage of watery or loosely-formed feces; often feces stain perineum or tail region Bowel infections or parasites can cause diarrhea. Discharge - secretion of a wet material from a body opening often associated with internal organ infection Dyspnea - difficult, labored or rapid breathing common sign of pneumonia Listlessness - lack of alertness in an animal, animal seems tired compared to others in cage Animals in pain also usually seem listless.
Signs of Disease IV Loss of weight - decrease of body weight often associated w/ anorexia due to a serious disease or can be caused by internal parasites Paralysis - inability to move all or part of body often due to nerve damage or a disease affecting central nervous system Prolapse - organ within body is forced externally most commonly rectal or vaginal often due to straining during defecation (bowel movement) or parturition (giving birth) Pruritus - constant or frequent scratching usually due to irritation of skin because of external parasites; skin often appears scaly or reddened
Signs of Disease V Rough hair coat - change from normal smooth, shiny hair to a ruffled and dull appearance can indicate many problems including vitamin deficiencies, external parasites, internal parasites & severe infections one of most reliable indications that animal is ill Sneezing - rapid, forced expelling of air through nose is usually a sign of nasal irritation Stunted - animals appear smaller than most animals of same age; can be due to genetic composition, infections, parasites or poor husbandry Tumor - abnormal growth
Signs of Disease VI Vomiting - passage of gastric contents from mouth, usually indicates animal has an irritation in stomach or throat Vomiting is common in cats/dogs & uncommon in rodents/ruminants. Essential that technicians recognize and report occurrence of these signs in any animal under their care. It will be easier to communicate clearly, both verbally and in writing, signs that you have seen if the above scientific terms are used.
Causes of Disease Concerned with diseases that cause noticeable illness, also with those that don’t make animal look sick. Such diseases are called sub-clinical. Difficult to detect changes can ruin an experiment by producing altered physiologic data in response to disease rather than to experiment. Disease = any alteration of normal anatomy or physiology of an animal. Disease causes will be classified as follows: environmental / nutritional / genetic / microbiologic / parasitic / unknown
Environmental Variations of temp, noise, humidity, lighting & contaminants which produce stress and alterations of animal’s physiology. Most animals are comfortable at about 70°F. Animal rooms kept too warm, cold or which frequently have temp variations are stressful. 30% to 70% relative humidity comfortable for people & animals under their care. Prolonged dry or wet environ- ments can contribute to disease.
Noise, Overcrowding & Light Rabbits may jump and hurt themselves, rodents will not breed, & most animals show alterations in hormone levels at loud noises. If too many animals are in a cage or animals are in very small cages, they will be stressed. Animals become accustomed to specific lighting. Adjustment to a light/dark cycle is called circadian rhythm & determines when active & when asleep. Most animal rooms are set to provide 12 hours of light and 12 hours of dark. Breeding animals stop breeding by changes in light patterns.
Air Exchange, Contaminants & Nutrition Odors are evidence a room does not have enough air changes for number of animals. Poor air flow can be caused by major mechanical problems or as simple as dirty air vent filters. Contaminants can enter system by way of air, water, bedding, & especially feed. Nutritional causes of disease - deficiencies or excesses in quantity or quality of water, fats, carbohydrates, proteins, minerals & vitamins. »Levels of essential food components have been determined. »If fed proper quantity, needs will be met.
Genetic Natural mutations or experimental Transgenic & knockout animals have altered genes, frequently inherit disease problems. Some genetic differences affect susceptibility to diseases & reactions to drugs. Certain strains have high incidence of breast cancer. Spontaneous genetic mutations in research colonies rarely occur. An animal could develop genetic variation that may be a very important research model in our future understanding of disease or biology.
(Image) Nude Mice
Microbiologic Most microbes do not cause disease. Disease causing microbe = pathogenic organism. Pathogenic organisms enter animal through air, feed, water, or breaks in the skin. Microbes often cause cell damage, usually by release of toxic waste products. If signs are not obvious, they are sub-clinical, requiring special diagnostic laboratory tests to identify the disease. Even without obvious signs, disease will often affect experimental results. Go to web site;
Parasitic Parasites live on or in an animal & draw nourishment from host. Animals can be infested with protozoans, helminthes, lice, mites, fleas, etc. In most cases, they exist subclinically, & are often responsible for altered experimental data. Any sign that an animal might have parasites, such as diarrhea, vomiting, anemia or skin lesions, should be reported immediately.
Diseases of Unknown Cause Many degenerative diseases, cancers & process of aging itself develop without obvious infectious or environmental causes. Overlapping causes & effects Microorganisms may infect an animal w/ lowered resistance to infection due to environmental or nutritional problem. Injuries caused by improper restraint or handling Allergic responses to experimental immunization Experimentally induced tumors Try to learn as much as possible from other people, including veterinarian & investigator.
Transmission of Disease Living thing which carries disease = vector. Nonliving materials transmit a disease = fomites. If cats with contagious disease were removed from a cage & another cat placed into that uncleaned cage, 2nd cat could become infected. Infectious disease microbes can be transmitted via hands, air, bedding, cages, water, insects & a variety of other vectors & fomites.
Transmission of Diseases II Many noninfectious diseases inherited. Some animals have genes causing bleeding disorders. Others develop under certain environmental or nutritional conditions. Scurvy caused by inadequate amount of vitamin C. Genetic predisposition to noninfectious disease i.e., an allergy to penicillin SOPs designed to reduce disease transmission. Wash hands before leaving an animal room. Handle small rodents w/ sanitized forceps. Air should be fresh or filtered. Properly sanitize cages in water which is 180°F.
Transmission of Diseases III Remove animals found dead to reduce disease transmission. Separate sick animals in isolation, separate cages in separated rooms. Place newly received animals in quarantine. Determining the cause of disease in any animal found sick is referred to as diagnosis. Identification of a disease from its signs and symptoms involves a number of special tasks including culturing for microbes, blood cell evaluation and biochemistry of serum.
Transmission of Diseases IV Exam & dissection of a dead animal = necropsy. Sections of organs are removed so pathologist can examine tissues microscopically. The pathologist can often identify & associate certain tissue changes with a disease. Sick animals which have died must be sealed in waterproof bags, sent to pathology or investigator & eventually burned in an incinerator. To reduce chance of disease, technicians must maintain laboratory animal facilities “hospital clean.”
Monitoring Animals Cats & dogs are vaccinated, while monkeys are tested for tuberculosis at regular intervals. Rodent colonies tested through sentinel program. Sentinels are healthy animals placed in the animal room for the specific purpose of detecting any disease. They are left in the room for a period of 1–6 months. Adding dirty bedding from other cages increases chance of exposure to any disease present. Necropsy performed, blood samples checked for antibodies to rodent diseases & stool samples checked for parasites. If any diseases is found in sentinels, other animals in the room are assumed to be infected.
Additional Reading Harkness, J.E. and J.E. Wagner. The Biology and Medicine of Rabbits and Rodents, 4th Ed. Lea and Febiger, Philadelphia, PA Hrapkiewicz, Karen, Leticia Medina, and Donald D. Holmes. Clinical Laboratory Animal Medicine: An Introduction, 2nd Ed. Iowa State University Press, Ames, IA