Education, training and information are the key to ensure that pet and animal owners as well as people who have contact with animals are safe and healthy. There is no reason to fear animals or avoid them to protect oneself from zoonoses, and this book, the result of collaboration between experts in human and veterinary medicine, presents the message very clearly; continue to enjoy the close relationships you have with companion and other animals, the pleasure of watching and where possible interacting with wildlife, fishing, working with animals and eating whatever your favourite food may be, drinking milk, as long as you are aware of any possible risks and take the appropriate hygienic precautions in terms of their health and your to avoid infection.
A zoonosis is any disease or infection naturally transmissible from vertebrate animals to humans and vice-versa. Humans are often an incidental host that acquires disease through close contact with an infected animal that may or may not be symptomatic. More than 200 zoonoses of various types are recognised worldwide. Zoonoses can be caused by a range of disease-causing agents such as viruses, bacteria and many more; of 1,415 disease-causing agents known to infect humans, 61% were zoonotic (a disease that normally exist in animals but can infect humans). Statistical data indicate that 15% or more of the human population will pick up a zoonotic infection at some stage of their lives.
The human acquires the zoonotic infections by direct contact, inhalation (breathing in), ingestion by mouth, fomite transmission (contact with an inanimate object), and by insect transmission. Some people are more at risk of getting infected with these zoonotic diseases than others e.g. elderly people (over 65 years), children under the age of five years, pregnant women, anyone with a weakened immune system. Zoonoses also undermine the health, productivity and reproductively of livestock on which humans rely for their food (meat, milk, eggs), fibre (wool, hair, feathers) as well as labour and transport. The annual worldwide monetary losses due to tuberculosis, brucellosis and rabies in cattle amount to several billion rand and South Africa is not exempt from this loss. Zoonoses may thus, in the long run, add to the problem of human malnutrition, particularly in children. Similarly, millions of people throughout the world will have to receive post-exposure treatment for rabies. Zoonoses are of particular importance as occupational disease contracted by a person in the course of his or her occupation. Zoonotic water- and foodborne diseases as well as food poisoning are significant and widespread public health threat. Millions of man hours may be lost, and this has financial implications and brings about stress. The relationship or bond between people and animals is presently receiving worldwide attention because of the mutual overwhelming benefits that such a dynamic relationship has for both parties. Contributions of emotional, social and physical benefits by pets (especially dogs) and other animals to humans are indispensable. It is, however, imperative that the health status of such pets and animals is beyond doubt to ensure that contact does not lead to contraction of a harmful zoonotic infections. Zoonoses can be prevented and controlled through the necessary knowledge and information.
INTRODUCTION TO ANIMAL DISEASES THAT AFFECT HUMANS (ZOONOSES)
Zoonoses are of particular importance as disease contracted by a person in the course of his or her occupation, e.g. anthrax, brucellosis, Crimean-Congo haemorrhagic fever, Ebola virus disease, erysipeloid, psittacosis, Q-fever, rabies, Rift Valley fever and ringworm, among others.
THE HUMAN-ANIMAL RELATIONSHIP
The relationship or bond between people and animals is presently receiving worldwide attention because of the mutual benefits that such a dynamic relationship has for both parties.
PART 1: ZOONOSES CAUSED BY WORMS (HELMINTHS)
CUTANEOUS LARVA MIGRANS (CLM) OR SANDWORM
Dogs and cats (and sometimes cattle) harbouring hookworms in their intestines create the danger of people contracting sandworm. The condition develops when larvae penetrate the skin and migrate aimlessly, thereby causing an inflammatory reaction. (Ancylostoma caninum*)
ECHINOCOCCOSIS OR HYDATID DISEASE
Echinococcosis and hydatidosis are forms of a parasitic disease. The former involves the dog as the definitive host and the latter the sheep as the most common intermediate host. A person is an incidentally infested intermediate host. Echinococcus granulosis*
TAPEWORMS AND CYSTICERCOSIS IN HUMANS AND PORK AND BEEF ‘MEASLES’
Tapeworms constitute a health hazard to humans. For the stock farmer, they have important financial implications as they cause cattle and pigs to yield ‘measly’ meat, which is unfit for human consumption.
Trichinosis is a disease that occurs in people when the larvae of a specific type of roundworm penetrate the muscle fibres. The infestation may be contracted by eating the raw or partially cooked meat of pigs and various wild animals. The parasite completes its life cycle in all vertebrate animals that consume meat. Trichinella spiralis*
VISCERAL LARVA MIGRANS (VLM) OR TOXOCARIASIS
Roundworms that occur in the intestinal tract of the dogs and cats and spend part of their cycle in a non-animal environment (the soil), cause visceral larva migrans in humans when the larvae are taken in by mouth.
PART 2: ZOONOSES CAUSED BY BACTERIA, CHLAMYDIA AND RICKETTSIA
Animals with anthrax constitute a serious danger to humans. Because of this, the disease is controlled by the state and accordingly strict rules exist concerning the immunisation of livestock, post-mortem examinations and the destruction of infected cadavers.
BRUCELLOSIS (UNDULANT OR MALTA FEVER)
Brucellosis is a highly infectious bacterial disease of cattle, goats, sheep, pigs, dogs and game that also occurs in humans. Stockmen, veterinarians, abattoir personal, hunters and all who handle livestock run the risk of contracting brucellosis. In addition, the public at large also face the hazard of brucellosis in as much as the consumption of raw infected milk and milk products may result in the disease. (Brucella abortus*)
ERYSIPELOID AND ERYSIPELAS
The same bacteria responsible for the so-called ‘diamond skin disease’ in pigs are capable of causing disease in people, who may contract the infection handling contaminated fish.
PSITTACOSIS OR PARROT FEVER
No vaccine has, as yet, been developed that efficiently prevents the transmission to humans of psittacosis, an infectious disease of birds.
PLAGUE AND BUNONIC PLAGUE
Plague is primarily a disease of rodents such as mice and rats. It is a cyclozoonosis and is transmitted by fleas to other animals and people. It may be fatal in humans. Control of rodents and fleas constitutes an important measure in combatting plague.
Raw milk constitutes one of the more important sources of Q-fever infection in humans. Although the prevalence of the disease in humans appears to have dropped in recent years, the efficient pasteurisation of milk for consumption and the production of processed dairy products remain absolutely essential. Coxiella burnetii*
Unpasteurised bovine milk and milk products infected with Mycobacteruim bovisbacteria* are the main sources of infection that cause bovine tuberculosis in humans. Buffalo milk which is infected with bacteria may also be a source of infection for humans.
PART 3: ZOONOSES CAUSED BY VIRUSES
CRIMEAN-CONGO HAEMORRHAGIC FEVER (CCHF)
Crimean-Congo haemorrhagic fever (CCHF) is caused by infection with a tickborne virus. Ticks of the genus Hyalomma (bont-legged tick) are the principal vectors. This zoonotic viral disease has caused severe viral haemorrhagic fever outbreaks, and is one of the deadly haemorrhagic fevers. Hyalomma*
EBOLA VIRUS DISEASE (EVD)
The virus is transmitted to people from some wild animal species and spreads in the human population through human-to-human transmissions. This disease is a direct zoonosis. The first Ebola virus disease (EVD) outbreaks occurred in remote villages in Central Africa, near tropical rainforests. Pteropodidae*
Rabies is a fatal disease transmitted from animals to man. This virus causes acute inflammation (encephalitis) of the brain in humans and warm-blooded animals after infection. It is characteristic of the disease that affected animals show distinct behavioural deviations.
RIFT VALLEY FEVER (RVF)
Rift Valley fever – a haemorrhagic virus disease of sheep and cattle transmitted by mosquitoes – constitutes a considerable health hazard for humans. RVF is a notifiable animal disease in South Africa in terms of the Animal Diseases Act, 1984 (Act No. 35 of 1984). Aëdes*
Zoonotic influenza must be distinguished from the well-known seasonal influenza (commonly called flu) that is a highly contagious respiratory disease common to humans and a limited number of lower animal species, mainly pigs, poultry, domestic, aquatic and wild birds, horses, dogs and wild aquatic mammals, such as seals and whales. CoAquatic*
PART 4: ZOONOSES CAUSED BY PROTOZOA
CRYPTOSPORIDIOSIS (or 'CRYPTO')
Cryptosporidiosis is a diarrhoeal disease caused by a microscopic enteric protozoan parasite, Cryptosporidium. Many species of the parasite affect the intestine of humans and animals and it is passed in the stool of the infected persons or animals. Cryptosporidiosis is a zoonotic water- and foodborne disease. Cryptosporidium (or 'Crypto')*
Giardiasis is a zoonotic parasitic disease caused by a flagellate protozoon that is present in the intestinal tract of many domestic and wild animal species, as well as humans, and causes a diarrhoeal disease. Giardia*
Toxoplasmosis is a worldwide problem and one of the more common zoonoses. Humans are particularly affected as a result of contact with soil contaminated with cat excrement. Unborn babies may also contract the disease. T. gondii * and Toxoplasma gondii*
PART 5: ZOONOSES CAUSED BY FUNGI
Ringworm is a skin disease seen particularly in children as a result of contact with infected pets. Various domestic and wild animals may be infected. In combatting this disease, it must be borne in mind that the spores of the responsible fungi may survive for long periods, even years, on contaminated surfaces under favourable circumstances.
SYSTEMIC FUNGAL INFECTIONS OR MYCOSES (SM)
A variety of fungi is capable of infecting both animals and humans and usually there is a common source in the environment in which they live. Strictly speaking they are not zoonoses, although animals may be responsible for large-scale contamination of the environment. This again increases the possibility of human infection. Cryptococcus neoformans*
PART 6: ZOONOSES CAUSED BY MITES
SARCOPTIC MANGE OR SCABIES
Sarcoptic mange or scabies is a skin infestation of humans and animals caused by a very tiny mite (cannot be seen by the naked eye) known as Sarcoptes scabiei. The microscopic mite burrows into the upper layer (epidermis) of the skin where it lives for up to two months and lays eggs. The most common symptoms of scabies are intense itching (a reaction within the skin to the faeces of the mite) and a pimple-like skin rash. The mite usually is spread by direct skin contact.
PART 7: ZOONOTIC WATER- AND FOODBORNE DISEASES, FOOD POISONING (INTOXICATIONS) AND HISTAMINE FISH POISONING
The importance of food of animal origin, i.e. milk, meat, fish, eggs, marine and aquatic animals in the balanced nutrition of humans is universally recognised. In preceding chapters mention was made of the transmission of disease by ingestion. Zoonotic foodborne diseases are caused by consuming food or drinking water or milk contaminated by pathogenic (disease-causing) microorganisms such as bacteria and their toxins, viruses and parasites that have animal hosts. Samonella* and Campylobacter*
A few examples of the magnitude, extent, effect, and consequences of zoonotic diseases
This horrifying disease is deadly not only for animals but tens of thousands of humans each year. Each year, it causes more than 55 000 human deaths worldwide – nearly one death every 10 minutes. Dogs are the source (up to 99%) of the vast majority of human rabies deaths. Forty percent of people who are bitten by suspect rabid animals are children under 15 years of age. Every year, more than 15 million people worldwide receive a post-bite vaccination. This is estimated to prevent hundreds of thousands of rabies deaths annually. Rabies is present on all continents with the exception of Antarctica, but more than 95% of human deaths occur in Asia and Africa. All warm-blooded animals with fur may be carriers and transmit the virus.
Zoonotic water- and foodborne disease and foodborne poisoning (intoxication) occur worldwide
Every year millions of people get sick because of zoonotic foodborne diseases and food poisoning such as salmonellosis, enterotoxicosis, Escherichia coli food poisoning (Shiga toxin), campylobacteriosis and others that cause fever, diarrhoea, abdominal pain, malaise, nausea, headaches, chills and sometimes more serious effects. Salmonella and Campylobacter bacteria account for over 90% of all reported cases of bacteria-related cases of food poisoning worldwide. Campylobacter bacteria are a major cause of zoonotic foodborne diarrhoeal illness in humans and are the most common bacteria that cause gastroenteritis worldwide. Campylobacter is one of the four key global causes of diarrhoeal diseases. Diarrhoeal diseases are the most common illnesses resulting from unsafe food, with 550 million people falling ill yearly (including 220 million children under the age of five years).
Listeriosis or mononucleosis is caused by the bacterium Listeria monocytogenes
Cattle, sheep, goats and fish are commonly affected. Listeriosis in humans is predominantly a zoonotic foodborne disease. Most humans are resistant to infection, but individuals who are immunosuppressed, pregnant or taking antacids are at increased risk of acquiring infection. Infection in humans usually occurs after eating contaminated soft cheeses, vegetables, processed meats, unpasteurised milk products and raw milk. The bacterium is tolerant of low temperatures and survives refrigeration. The clinical disease in humans can be mild and ‘flu-like’ or more serious, causing abortion, diseases in neonates-infected prepartum, meningoencephalitis and death.
IMPORTANT MILKBORNE ZOONOTIC DISEASES
Listeriosis or mononucleosis is caused by the bacterium Listeria monocytogenes. Cattle, sheep, goats and fish are commonly affected. Listeriosis in humans is predominantly a zoonotic foodborne disease. Most humans are resistant to infection, but individuals who are immunosuppressed, pregnant or taking antacids are at increased risk of acquiring infection. Infection in humans usually occurs after eating contaminated soft cheeses, vegetables, processed meats, unpasteurised milk products and raw milk. The bacterium is tolerant of low temperatures and survives refrigeration. The clinical disease in humans can be mild and ‘flu-like’ or more serious, causing abortion, diseases in neonates-infected prepartum, meningoencephalitis and death. Brucella*