Chapter 9 - Human & Animal Health - PDF

# Chapter 9 - Human & Animal Health ## Lesson 1: Genetics & Disease ### Introduction Genetics is the study of how characteristics are passed from one generation to the next. Heredity is the transmission of characteristics from parent to offspring by means of genes in the chromosomes. Genes are ca...

# Chapter 9 - Human & Animal Health ## Lesson 1: Genetics & Disease ### Introduction Genetics is the study of how characteristics are passed from one generation to the next. Heredity is the transmission of characteristics from parent to offspring by means of genes in the chromosomes. Genes are carried on threads of living matter, called chromosomes. Alleles are alternative forms of the same gene (dominant versus recessive). Chromosomes and genes occur in pairs; one gene transmitted from the paternal parent and one gene from the maternal parent. ### Genotypes and Phenotypes - The genetic make-up for a single trait of an individual is called its **genotype**. - The pair of genes for a trait may be alike (**homozygous**), with either two dominant or two recessive alleles, or different (**heterozygous**), with different alleles. - **Genotypes** are not visible. - A particular trait that is observed (hair type and color, body type) in an individual is called its **phenotype**. - Individuals with similar phenotypes may have different genotypes. **Example:** Cattle have a gene that controls height. The gene is completely dominant and any animal with the dominant gene is normal in height. If a homozygous, normal cow (DD) is crossed with a homozygous, dwarf bull (dd) the offspring will all have a normal phenotype and a heterozygous genotype (Dd). ### Genetic Diseases Offspring with hereditary defects or diseases inherited two recessive alleles, one from each parent. Some of these abnormalities are more severe than others and are called **genetic diseases**, or **congenital defects**. Such abnormalities include severe structural changes and altered metabolism. Deafness, blindness, and hairlessness at birth are possibly genetic defects. Some of the structural deformities that result from genetic diseases are listed and defined below. | | Genetic Structural Deformities | |---|---| | Anal atresia | lack of opening from the rectum | | Scrotal hernia | rupture into the scrotum | | Cryptorchidism | failure of a testicle to descend into the scrotum | | Albinism | lack of pigment | | Hip dysplasia | deformed hip joints | | Cleft palate | opening in roof of mouth | | Over-shot jaw | upper jaw protruding over lower jaw | | Combined immuno-deficiency (CID) | absence of immune response | | Mulefoot | fusion of functional toes of calf | | Dwarfism | large abdomen, short legs, abnormal head | ### Genetic Resistance Some individuals within populations do not appear to be susceptible to disease agents, or have milder forms of the disease. Sometimes this susceptibility is explained by other risk factors, and sometimes it is explained by genetic influence. There are disease agents that attack one species, but do not affect other species. For example, the hog cholera virus does not infect other animal species. This phenomenon of species resistance is known as natural or innate immunity. Resistance to a disease can also exist within a species and is controlled by genetic inheritance. For example, some cattle lines are not susceptible to brucellosis while other lines are susceptible. This results from certain alleles providing protection to the cattle to prevent illness by that organism. Research in the fields of human and animal medicine study the genetic structure of cells to identify the presence or absence of genes or alleles that control susceptibility or resistance to a given disease. ## Lesson 2: The Battle Against Disease ### Introduction The spread of bacterial, viral, and fungal disease or parasites indicates that the primary agent has escaped from an infected host and traveled to a new host. The place where the agent lives or is maintained prior to transmission is known as the **reservoir**. ### Sources of Diseases and Parasites - The most common source of disease is contact with an infected animal. Disease agents may be found in manure, urine, blood, saliva, and fetal fluid; in aerosol droplets from the lungs; and in genital fluid - The environment is another source of disease - Contaminated vehicles and contaminated and infected vectors are other important sources of disease ### Direct Transmission of Diseases Direct disease transmission generally involves direct or close contact between the original host and the new host. Infections of different organ systems, including the skin, respiratory system, nervous system, circulatory system, musculoskeletal system, and reproductive system, may be directly transmitted to susceptible animals. ### Indirect Transmission of Diseases - When an infectious agent infects and develops in the vector, the vector serves as a **biological vector**. - If no development occurs in a vector, the transmission is **mechanical**. - **Fomites** (e.g., food, water, soil, air) that can transmit disease agents. - Contaminated vehicles and fomites can play a part in mechanical and/or biological transmission of disease. ## Lesson 3: Diseases Common to Humans & Animals ### Introduction A disease common to both humans and animals is known as a **zoonosis**. There are over 30 zoonoses that can be potential health risks to people who work with and around animals. These include various infectious diseases (bacterial, viral, and fungal) and parasitic infections. ### Bacterial Zoonoses There are bacterial and rickettsial caused zoonoses which will be discussed in this section. Each has its own characteristics and modes of transmission. ### Anthrax Anthrax is a bacterial disease which is found worldwide wherever livestock are produced. It is caused by the bacteria Bacillus anthracis. Most commonly three clinical forms of human anthrax occur: **cutaneous**, **intestinal**, and **pulmonary**. ### Brucellosis Brucellosis is a fairly common disease found worldwide in domestic, semi-domestic, and wild animals. There are various species of Brucella organisms, each specific to its natural host or hosts. Humans can contract the disease by exposure to infected animals and ingestion of contaminated foods such as unpasteurized milk products. Humans can prevent infection by practicing proper hygiene when handling cattle, especially at calving time, and by consuming only pasteurized milk and milk products. ### Intestinal Campylobacteriosis Campylobacteriosis, more commonly known as vibriosis, it is one of the most common zoonoses. Humans are exposed to the organism in manure contaminated water, milk, meat, and garden vegetables. All animal species can carry C. jejuni organisms with or without signs of illness. ### Infectious Zoonoses | | | |---|---| | Anthrax (bacterial) | Brucellosis (bacterial) | | Campylobacteriosis (bacterial) | Cat Scratch Disease (bacterial) | | Chlamydiosis (bacterial) | Leptospirosis (bacterial) | | Listeriosis (bacterial) | Lyme disease (bacterial) | | Q Fever (bacterial) | Plague (bacterial) | | Salmonellosis (bacterial) | Staphylococcal (bacterial) | | Tuberculosis (bacterial) | Encephalitis (viral) | | Rabies (viral) | Ringworm (fungal) | | Histoplasmosis (fungal) | Toxoplasmosis (ptotozoal) | ### Cat Scratch Disease Cat Scratch Disease (CSD) is caused by the bacterium Bartonella henselae, which is inoculated into a human's skin when scratched by a cat or when a break in the skin is licked by a cat. Persons who have or have had CSD appear to be protected for life. ### Chlamydiosis Chlamydiosis, also known as parrot fever, is primarily a disease of birds in the parrot family, pigeons, sea-birds, ratites, and occasionally turkeys and waterfowl. The disease is caused by the bacteria Chlamydophila psittaci and is transmitted through the feces of infected birds. The disease in humans ranges from unapparent infection to mild, flu like symptoms to death. ### Erysipelas Erysipelas, caused by the bacteria Erysipelothrix rhusiopathiae, is primarily a disease of swine. However, many animals, such as poultry, ratities, and fishes can contract the disease. Humans, an accidental host, contract the disease through direct contact with sick or carrier animals, infected animal products, or contaminated objects. ### Leptospirosis Leptospirosis, caused by Leptospira species, is a worldwide zoonosis that affects a wide variety of domestic and wild animals as well as humans. It primarily affects small mammals, especially rodents. ### Listeriosis Listeriosis, caused by the bacterium Listeria monocytogenes, is found worldwide. It affects a large number of animals, both domestic and wild, including birds and fishes. Humans are also susceptible and are infected primarily through contaminated food although other routes of infection may occur. ### Lyme Disease Lyme disease, caused by the organism Borrelia burgdorferi, is a zoonotic disease transmitted by certain species of ticks. The clinical signs seen in dogs, cats, horses, and cattle include fever, lethargy, arthritis and/or swollen joints, and stiffness. ### Q Fever Q fever, caused by the bacterial organism Coxiella burnetii, can infect most domestic animals worldwide. ### Plague Plague is a flea transmitted bacterial disease of rodents. Yersinia pestis, the bacteria that causes plague, is transmitted to humans by infected fleas or through direct contact with infected animals. ### Rocky Mountain Spotted Fever Rocky Mountain Spotted Fever (RMSF) is a tick transmitted rickettsial disease primarily of the United States, but also in Canada, Mexico, and parts of Central and South America. It is caused by the organism Rickettsia rickettsii that infects small mammals, especially rodents ### Salmonellosis There are more than 2000 serovars of Salmonella worldwide that can be transmitted to humans, most of which are pathogenic. ### Staphylococcal and Streptococcal Infections Both streptococci and staphylococci are bacteria found closely associated with humans, animals, and the environment. The main Streptococcus implicated as a human disease agent is Streptococcus pyogenes, causing "strep throat" in humans. Staphylococcal infections are primarily associated with Staphylococcus aureus, however, S. epidermidis, S, hyicus, and S. intermedius are important in some animal infections. ### Tuberculosis The cause of tuberculosis, commonly called TB, is the bacteria Mycobacterium that is found worldwide. There are several Mycobacterium species that affect mammals, birds, and humans. ### Viral Zoonoses There are infectious viral diseases that are considered to be important zoonoses. ### Encephalitis Encephalitis, also known as sleeping sickness, can be caused by any of these mosquito-borne viruses. Human cases of encephalitis range in severity from subclinical to severe encephalitis and even death. ### Herpesvirus Herpes B, caused by Herpesvirus simiae virus, affects non-human primates worldwide. The disease infects the brain and spinal cord (encephalomyeli- tis) in humans and is usually fatal. ### Hantavirus Hantavirus is disease in the southwestern United States. A variety of rodents serve as reservoirs for the disease, although the rodents do not appear to suffer from the disease or illness. Hantavirus produces flu-like symptoms in humans including fever, muscle pain, headache, and cough that are followed by rapidly developing respiratory failure and death. ### Rabies Rabies, also known as hydrophobia, is caused by a virus (rhabdovirus) primarily transmitted in saliva through a bite from an infected animal. The virus may also be transmitted through inhalation (rare), ingestion, or direct contact with an infected animal. ### Fungal Zoonoses The fungal zoonoses will be grouped into three sections: ringworm, sporotrichosis, and systemic fungal infections. ### Dermatophytosis Various species of fungi are responsible for ringworm infections. These fungi are referred to as dermatophytes and the disease they cause, commonly known as ringworm and athlete's foot, is known as dermatophytosis. Ringworm is considered to be one of the most infectious diseases around the world. It most frequently affects owners, especially children, of infected cats and dogs. ### Sporotrichosis Sporotrichosis, caused by the saprophytic fungus Sporothrix schenckii, is a fungal disease that has a parasitic tissue phase that can infect humans and animals. Fungicides are the best method for controlling sporotrichosis. ### Systemic Mycoses Four fungal agents may cause systemic disease in both humans and animals. In humans and animals, infection with histoplasmosis, blastomycosis, or coccidioidomycosis starts with flu-like symptoms. ### Parasitic Zoonoses There are several parasitic diseases common to both humans and animals that are considered to be prevalent zoonoses. ### Cutaneous Larval Migrans The larvae of the species of Ancylostoma and Uncinaria, known as hookworms in dogs and cats, may infect humans. ### Dirofilariasis In North America, Dirofilaria immitis is the common blood parasite responsible for heartworm disease in dogs, and sometimes cats. In dogs, the adult heart-worms reside in the right ventricle and pulmonary arteries where they produce their offspring, microfilariae, that circulate in the bloodstream. ### Visceral Larval Migrans The larvae of intestinal roundworms of dogs and cats, Toxocara canis and T. cati, can infect humans. ### Toxoplasmosis Toxoplasmosis is a disease caused by the protozoan Toxoplasma gondii. The protozoan is a parasite which inhabits the intestinal tract of infected cats. Most human infections are subclinical. ## Lesson 4: Food & Animal Diseases ### Introduction Diseases of food-producing animals affect the abundant, safe, wholesome food supply of meat, dairy products, and eggs. The effects are either lowered production or increased condemnation of food animal products. ### Abundant Food Production Food-producing animals that are free of diseases are capable of high productivity in producing meat, milk, and eggs. When an animal production unit, whether it is a pen of feeder calves, pigs, or lambs; a flock of broilers or hens; a barn of dairy cows; or a pasture of beef cows, becomes infected with a disease, production and efficiency may decrease. ### Safe, Wholesome Food Supply When food-producing animals are free of disease, they produce a source of food that is safe and wholesome for the consumer. Diseased animals are usually treated with drugs and chemicals to cure them. ### References - Schwabe, C. W. (1984) Veterinary medicine and human health (3rd ed.). Baltimore MD: Williams and Wilkins. ## Lesson 5: Economic Losses ### Introduction Economic losses associated with problems in human and animal health may be obvious and easily documented or hidden and difficult to measure. Obvious economic losses occur due to the effects of deaths, clinical diseases, disabilities, and condemnations of food animals by health inspectors at or before slaughter. ### Obvious Economic Losses When an animal dies or aborts an offspring the value of the loss is realized. When an animal is sick, diseased, or injured, the costs of treatments are realized as a loss. ### Hidden Economic Losses Performance and production data are routinely collected and evaluated to identify hidden economic losses. These losses are not accepted as normal, but causes and contributing factors are diagnosed and corrections implemented. ### References - Atwell, J. K. (1984). Yearbook of agriculture: Animal health livestock and pets. Washington DC: US Government Printing Office. - Schwabe, C. W. (1984). Veterinary medicine and human health (3rd ed.). Baltimore MD: Williams & Wilkins. ## Lesson 6: Animal Assisted Therapy ### The Human - Animal Bond Today we are faced with greater opportunities for understanding interactions between animals and humans than ever before. The bond between humans and animals has been recognized throughout history and in every society and culture, and is a popular subject for researchers and educators. Animals continue to serve humans in many aspects of daily life by providing companionship, serving as guide animals for blind and disabled individuals, in national security and police work, and in many other areas. ### The Benefits of Pets and Companion Animals Research shows that the benefits people receive from interacting with animals are social, psychological, and physiological. Pets are enjoyed by all age groups and societies. ### Animals and the Disabled For the average person a pet offers comfort and friendship, but for those individuals who are physically disabled animals can provide much more than companionship ### Animals and the Elderly As people grow older, companion animals become increasingly important. When elderly people live alone because family members and friends have died or moved away, or when they choose to live in nursing homes, the closeness and touching of a pet animal are helpful in relieving loneliness and sadness. ### References - Arkow, P. (Ed.) (1987). The loving bond: Companion animals in the helping professions. Saratoga, CA: R & E Publishers. - Connor, K., & Miller, J. (2000). Animal-assisted therapy: An in-depth look, Dimensions of Critical Care Nursing, 19(3), 20-25. - Yates, J. (1988) Project pup...pets uplifting people. [Abstracts and Presentations] People, animals, and the environment: Exploring our independence. Orlando, FL: Delta Society Seventh Annual Conference.