What is a zoonosis?

A zoonosis, or ‘zoonotic disease’, is an illness that can be passed between humans and animals.

The source of such an infection can come from a variety of agents, i.e. viruses, bacteria, external parasites (e.g. fleas), internal parasites (e.g. worms) and fungi. The method of transmission is equally diverse, ranging from skin contact to ingestion (swallowing something). Most are relatively easy to detect and treat; others can be life-threatening so there is no easy, one-stop answer to the question what a zoonosis entails and what it will mean, if we contract it.

Should we worry about zoonoses?

There are several diseases that can be transmitted from dogs to humans. Dogs can carry agents that make us ill and caution is advisable. Zoonosis often works both ways and we can infect dogs with a disease as well.

However, there is no cause for panic and taking some common-sense precautions will keep both us and our dogs free from cross contamination. These include public and personal hygiene such as washing our hands after we have touched the dogs and before eating. This will greatly reduce the risk of catching something contagious. Equally, if a dog is ill with something potentially infectious (e.g. diarrhoea), vulnerable people (children, the elderly, the sick) must be advised to be particularly vigilant and careful with regards to how they interact with the animal. That does not mean staying miles away from them, but just being aware of the risks and making absolutely sure that cleanliness is observed.

In contrast to how complex this all may look across a variety of species, it is safe to live with our animals, and that applies not only to our domestic pets but also to animals with which we come in contact working in industries, like farming, and visiting places, such as zoos. All that is often needed is a good regime of hand washing with soap and hot water.

The efficacy of such simple measures becomes obvious when looking at the fact that wherever in the world general and public health are taken seriously and are well-developed, zoonoses are rare indeed.

Sensible precautions

For the majority of zoonoses, effective treatments are available but that is not a reason to abandon common sense and basic hygienic principles.

As in all situations, being forewarned is forearmed and knowing about potential hazards is best but must not lead to panic. With any infection, there are those who are more at risk than others, because their immune system is compromised. Factors are: pregnancy, existing illness, old age, generally poor health, and treatment such as chemotherapy which reduces the capabilities of the body’s immune system. If in doubt, find out first before visiting a farm or petting zoo and never allow your dog to lick your face, your food, or any open wound.

Staying safe

The following is a short list of sensible precautions that will keep you and your pets safe:

•  Wash your hands after touching an animal, even your own dog or cat, and especially before preparing or eating food
• Normal soap and hot water are sufficient and anti-bacterial preparations are not normally necessary
• Wash hands immediately after any animal has licked them
• Make sure children wash their hands and stop small children and babies from putting their fingers in their mouths until you have washed their hands
• Always wash your hands after picking up dog poo, even if using a plastic bag
• If in a farm or factory environment, pay careful attention to and comply with any hygiene instructions
• Always wash your hands following a visit to the vet
• If you have vulnerable people in your party; infants, small children, the elderly, those who may be sick or with a compromised immune system, pay additional attention to their and your own personal hygiene

Which diseases are zoonotic?

Below is an alphabetical list of the main dog-related zoonoses:

Campylobacter	This bacterium is one of the most common causes of food poisoning. Humans and dogs can contract the disease, but we usually pick it up by eating contaminated and undercooked food. Our pets may get it from fouled water or food. However, although Campylobacter can be passed from animal to human and, in theory, from your dog to you, very few cases have ever been confirmed. The pathways described above are by far more common. Consequently, prevention by adhering to hygienic principles is the most important action you can take. Symptoms are non-specific, as is usual in these cases, and include for both humans and dogs: – Diarrhoea – Vomiting – General weakness / tiredness – Inappetence – Dehydration in prolonged cases – Abdominal pain   Treatment is first of all supportive, i.e. rest, plenty to drink (dehydration is the greatest risk in standard cases), easily digestible food. Only if the infection persists or if relapses occur, will a doctor or vet consider antibiotics and other measures. See also E. Coli and Salmonella
Cryptosporidium	This is a small organism (protozoon) that infects the gut and can be found in all mammals, including dogs, cats, cattle, and humans but also other animals, such as birds and snakes. Their distribution is transmitted by water and soil that have been contaminated by oocysts (an egg-like stage in the life cycle of the organism). The main symptoms are fever, watery diarrhoea, abdominal pain and weight loss. The disease is mainly found in young dogs. Although Cryptosporidia are divided into host-specific species (e.g. C. canis in dogs) and few studies have been undertaken with regards to their transmissible nature, it is quite certain that oocysts from dogs can infect humans, particularly since dogs can harbour more species than just C. canis. As in dogs, the infection in humans is mostly found in children and the symptoms are similar. In severe cases, especially in immune-compromised persons (e.g. HIV and other viral diseases), it can easily lead to acute dehydration and weight loss, possibly aggravating any existing health issues and leading to a serious combination of problems. Up to now no effective medical treatment has been found. In normally developing cases (both in humans and animals) the condition lasts for anything up to three or four weeks and developing immunity has been reported. The main defence therefore is good personal hygiene and proper hygienic preparation of food and drinking water.
E. coli	Escherichia Coli, to call it by its full name, is a bacterium that is ubiquitous in the environment, in food, and in the bowels of animals and people, but despite news reports, only a few strains induce illness. Of course, these health problems can be very serious, especially since those most at risk are children, puppies, older people and dogs, and those whose immune system is compromised. Illness can occur in bowels, lungs, urinary tract or other parts of the body. It is one of the most frequent causes of food poisoning. Prevention is the best approach and depends on good hygiene (generally, but particularly when handling, storing and preparing food) and awareness.   Symptoms in humans and dogs depend on the tissues affected and a sudden onset and rapid deterioration are characteristic. In the intestinal form (bowels), symptoms can include: – Diarrhoea (sometimes bloody) – Shivering – Stomach cramps – Inappetence – Vomiting – Dehydration. There is a urinary tract form that in dogs also causes skin ulcers. This type is much more serious and can lead to kidney failure. Treatment is equally dependent on the version in question. In cases of bowel infection, the general approach is supportive (rest, plenty of fluids, keeping warm, etc.). Antibiotics are discouraged in human medicine, whereas in dogs they are used as a first line of attack. In terms of zoonotic risks, dogs have been suggested to be a source of infection, but the extent to which this is the case is very uncertain. See also Campylobacter and Salmonella.
Fleas	Fleas can go onto humans, but their bite is usually harmless enough to not be treated. Signs are little red and itchy spots, foremost on legs or arms. As in dogs, the worst that can happen is an allergic reaction which causes inflammation of parts of the skin and is more a nuisance than something serious to worry about. Every household with dogs should have a scheduled programme of flea treatment. The argument ‘Oh, but my house is spotless’ is, sadly, not one fleas take note of. It is best to go to your vet or veterinary supplier for proper anti-flea products. You can ask for combi-preparations effective against other bugs, such as ticks or lice, as well.
Giardia	Giardia is a small organism (protozoon) that causes diarrhoea, often with abdominal pain, in both humans and dogs. Especially in recurring or persistent cases it is worthwhile looking for it, unless other causes have been clearly identified (e.g. pancreatitis). Dogs pick them up from the environment, usually from something they eat, or from standing water they drink when outside. In humans, poor levels of hygiene are usually implicated, picking up the infection from handling contaminated animals, food, objects or being in close contact with infected people. In the UK the rate of infection is low, although exact numbers are difficult to ascertain as there are carriers (humans and animals) that show no symptoms and, therefore, remain undetected. Estimates speak of about 8% of dogs in the UK having Giardia in their system at any one time and diagnosis is made through analysing stool samples.   Treatment consists of a wormer and any necessary secondary medication, e.g. antibiotics, depending on the presentation of the individual case.
Leishmania	Leishmania affecting dogs is a microorganism that is transmitted by sand-flies. While these organisms are more commonly associated with warmer, southern climes the disease has nevertheless gained relevance in the UK in recent years. Dog owners now travel more and farther with their pets using the Pet Travel Scheme, including to the Mediterranean, and dogs continue to be introduced to Britain as rescue animals from Eastern and Southern Europe where Leishmaniosis is endemic. The focus therefore remains on dogs visiting infested countries and protecting them from disease. Additionally, it is worth being aware of the possibility of introducing Leishmania unnoticed and unchecked to the UK, which is a progressively warming climate that will very probably create positive conditions for the sand fly and the infectious agent here in the future. In humans, three different forms can be found (although it must be stressed that the overwhelming majority of cases occurs in the tropics and subtropics): – Visceral (affecting several organs, mainly spleen, liver and bone marrow; it is the most serious form and fatal if left untreated). – Mucocutaneous (causing ulcers in nose, mouth and throat). – Cutaneous (the most common with skin ulcers). In dogs: – The cutaneous type seen expressed as skin lesions, small swellings that can break open, localised hair loss, scaling. – The visceral type means that several internal organs have been invaded. Although any organ can be affected, the agent predominantly attacks liver, spleen and/or kidneys. The symptoms are varied and diverse and can comprise: inappetence and weight loss, muscle atrophy, lethargy, oral ulcers, vomiting, dehydration despite increased drinking, staggering, swollen joints, stiffness. Treatment consists of prolonged regimes with antiprotozoal drugs and supportive measures. However, it is accepted that complete eradication is rare, and relapses can occur at any time. Also, reinfection in endemically infested environments can create the appearance of a failed therapy.
Leptospira	These are bacteria that cause Leptospirosis, which in humans is also known as Weil’s Disease. The organism favours wet conditions so the most common way of infection for dogs is from sources in the countryside, especially water courses, lakes, ponds, etc.  Dog owners should be aware that leptospirosis can be transmitted from dog to human, but this is very rare indeed. Like dogs, we are far more likely to catch it when bathing and enjoying ourselves outdoors. Another group at particular risk are farmers and anyone else in contact with livestock.   In both humans and dogs, the bacterium infects mainly kidneys and liver, but it readily spreads to other organ systems, such as the nervous system, lungs, spleen, blood vessels, uvea/retina, skeletal and heart muscles, pancreas and the genital tract. Because of its multi-organ character, the symptoms of Leptospirosis reflect the systems affected: – Fever sore muscles and, consequently, reluctance to move – Stiffness – Shivering – General weakness – Inappetence – Vomiting – Drinking and urinating more – Internal blood loss (blood in urine or faeces, petechial bleeding, etc.) For dogs, the first line of defence is vaccination. The recommended treatment in dogs consists of antibiotics (intravenously in the acute stage if necessary) and supportive action depending on the organ systems involved (e.g. blood pressure regulators, supplementary oxygen, IV fluids, nutritional support).
Mites	Mites are tiny parasites, usually under a millimetre long, that burrow into your dog’s skin and cause irritation and inflammation. They live in the fur and sometimes in the ears and can cause a range of skin conditions, from dry skin to hair loss.  A number of mites are considered to be zoonotic risks: Sarcoptic Mite Resulting in sarcoptic mange, aka scabies. It is highly contagious and is passed on by direct contact between animals, and animals and humans. It burrows into the skin and thereby causes intense irritation and itching. You might see areas of hair loss, red skin or crusts but these are made worse by the dog scratching and biting at the areas due to the intense itching. Diagnosis will be made by skin scraping and examination under a microscope. Treatment will consist of a topical anti-parasitic product, as well as any accompanying medication, e.g. antibiotics, depending on the nature and extent of any other problems. In humans, the infestation is largely self-limiting, due to not being the right host, once the source has been illuminated. However, there is also a specific human Sarcoptic mite. Cheyletiella In dogs it lives on the surface of the skin (also called ‘walking dandruff’) whereas, in humans, the female mite burrows into the skin. It causes itching and scaly skin (hence resembling dandruff); scratching often causes small-scale infection (pustules). A diagnosis is made by harvesting scales with sticky tape and examination under a microscope. Treatment consists of topical anti-parasitic preparations and any necessary accompanying therapy, especially antibiotics in case of infections. Harvest Mite Harvest mites are most active in the second half of summer. The larvae sit on taller grasses and other vegetation from which they readily transfer onto humans and dogs. They stay on the surface of the skin (in dogs often on feet and lower legs) and crawl around before they start to feed. Their bites cause eruption in the skin that itch, and this increases the risk of self-harm due to scratching and biting. Their life cycle makes the attack self-limiting, because the larvae will drop off again to develop into the adult stage but symptoms like itchiness, reddening, allergic reactions, etc. will probably persist. Diagnosis is similar to Cheyletiella – under the microscope after sampling with sticky tape. Treatment – the advice usually given is to bathe with warm soapy water to remove any remaining larvae. Any additional measure depends on the nature and extent of the secondary problem. Itchiness can be counteracted with appropriate creams. Any other effects, such as infection due to scratching, have to be assessed individually. For humans a visit to the pharmacy is often all that is needed. It is advisable to seek veterinary advice concerning your dog, as they might see the need to use anti-parasitic preparations to hasten recovery.
Pasteurellosis	Pasteurella is a bacterium that can be the source of infection in a wide variety of places in dogs, from ears through joints to even causing meningitis. It is an agent living on the skin, in the mouth and the bowels, normally causing no trouble at all. However, under the right circumstances, it can be the source of serious illnesses. The symptoms depend entirely on the organ affected. It is important to recognise that pasteurellosis is spread by biting, and licking open wounds, as this is also the way it is transmitted to humans. In humans the infections and the areas involved are just as varied. Examples are rhinitis (nose), pneumonia or abscesses in flesh after bites.   Treatment depends entirely on the individual type of illness.
Rabies	Rabies is an extremely serious viral disease that attacks nerve tissue and is almost always fatal. The UK is officially rabies-free, apart from a virus that is thought to be related and carried by a small number of bats. A real risk only arises when travelling abroad with your dog. However, as this falls under the Pet Travel Scheme, your dog will be vaccinated anyway. The UK government issues a list of countries and their rabies risk levels. Unless planning to travel beyond mainland Europe with your dogs, there is very little to worry about, especially with the immunisation in place. The National Health Service (NHS) of the UK also provides information about the disease should one wish to read more about it. In areas known to have had cases of rabies: – Look out for warning signs put up by the government organisation in charge. – Keep your dog on a lead when walking in the countryside – Keep away from and ideally notify the authorities of any animals (especially wild ones) that behave strangely, e.g. having lost their natural fear of humans – Stay and keep your dog away from any dead animals you may find. Rabies is mainly transmitted by a bite or scratch which could come from an unknown dog so caution should be observed in approaching dogs you do not know when travelling. Should you think you and/or your dog have been hurt by an animal that could have shown signs of the disease immediately consult a doctor and/or veterinary surgeon.
Ringworm	Ringworm is a misnomer, because it is a fungal infection without any worms being involved. Its name derives from the usually red, ring-shaped appearance in humans encircling an area, with a combination of symptoms like itchiness, flaky skin, reddish colour and swelling. In dogs its manifestation is similar, although the shape is normally less defined. As well as itching and scales you might see broken hairs or hair loss, dry areas in the coat, and brittle claws, as they can equally be affected. It is always passed on by direct contact, either with an infected person, animal or object (e.g. rails on farms, towels, combs, etc.). It takes time but treatments are straight forward. In humans, as in dogs, ointments or creams are the first part of the treatment. Since it is a contact disease anything remotely under suspicion of carrying spores, e.g. bedding, clothes, brushes etc., will have to be decontaminated, and your veterinarian might recommend a systemic approach, i.e. medication for your dogs, depending on the spread of the infection and any obstacles to fighting it (e.g. long hair or a dense coat).
Salmonella	The Salmonella bacterium is often implicated in food poisoning but has further zoonotic significance. This is because it lives in dogs without causing symptoms most of the time, while still retaining the potential for being passed on. In humans it is a major factor in the field of food poisoning, and there is a small risk of catching it from your dog. The symptoms are mostly intestinal (i.e. diarrhoea and bowel inflammation with abdominal pain, tiredness, inappetence, dehydration etc.). Like other comparable infections (see Campylobacter and E. coli) most cases run their course and don’t require any treatment other than supportive measures. However, sometimes they do become more serious and intensive care is indicated, especially if there are complications involving other parts of the body. The use of antibiotics is usually discouraged, unless absolutely unavoidable, because they are unlikely to materially affect recovery and might even contribute to the globally increasing problem of drug resistance.
Worms	Roundworms Toxocara canis No parasite should be taken lightly but this roundworm is of global importance. If humans contract Toxocara it can have one of four outcomes: 1. The infection is so low that the body simply copes, and the person affected will never notice any symptoms 2. The ‘visceral’ form is when juvenile stages (larvae) of the worm migrate to organs, such as the liver. 3. The ‘ocular’ form is when the larvae migrate to the eye 4. A combination of 2.) and 3.) where both conditions are treatable but there is a risk of long-term organ damage and blindness. Spreading is via eggs in faeces. Children and elderly people are most at risk but, as stressed previously, simple common-sense hygienic measures are the main line of defence against an infection: – Wash hands after handling dog bedding or faeces – Teach children not to eat dirt and wash their hands – And especially as responsible dog owners: maintain a regular worming regime, do not let your dogs foul in areas where children might play, remove faeces and dispose of them conscientiously by bagging and binning them. If not disposed of effectively, poo bags will split over time which not only mean faeces remaining in the environment, but scientists also predict that abandoned plastic in the environment will take anything from decades to centuries to decompose.   Tapeworms Echinococcus granulosus is an infection, or echinococcosis, and in humans is rare but can have very serious consequences. As with Toxocara, the larvae can invade organs and can then trigger the formation of cysts. Treatment is difficult and may involve surgery.   Prevention is the same as for other similar parasites deworming of dogs good, sensible hygiene regime conscientious handling of our dogs in the environment Hookworms Ancylostoma In humans, adult forms of these worms live in the bowels. However, the species that have animals as their main host, including dogs, do not usually migrate that far, because humans are the wrong environment for them. In this case, infection is not by mouth but by larvae penetrating unprotected skin, e.g. when walking barefoot through contaminated grass. They then stay in the skin and cause inflammation but, in very rare cases, the dog-related hookworm can reach the bowels and cause an inflammatory reaction there.   Prevention is the same as for the other worms described here. The illness is treated with anti-parasitic drugs.

Read our A-Z of canine health problems.