Zoonotic Diseases in Dogs

A zoonotic disease (zoonosis) is a disease which can be passed between separate species. This can be done directly from one infected animal to another or through a vector such as a mosquito. Left untreated, these diseases may spread quickly and cause serious damage. It is extremely important that dog owners make themselves aware of zoonotic diseases, especially if they keep other animals on the premises (particularly livestock and poultry).

Zoonoses can be separated into five types of agent: Bacteria (Salmonella, MRSA, etc.), fungi (Ringworm, Thrush, etc.), parasites (roundworm, fleas, etc.), viruses (Rabies, Influenza, etc.) and prions (Bovine Spongiform Encephalopathy, Scrapie, etc.).

Most illnesses falling under the first four of the above agents are treatable to various extents. Prions, however, are untreatable and fatal diseases. Luckily, most prions are not zoonotic, and those which are zoonotic are not transmittable through a wide variety of species. There are currently no confirmed prions which affect dogs.

Rabies – a viral disease; perhaps one of the most well-known zoonotic diseases due to the unique symptoms, extremely high fatality rate and ability to infect any warm-blooded animal. This disease can have an incubation period of up to three or four months, depending on the location of the entry point of the virus. Once it hits the central nervous system, presenting symptoms, it is usually untreatable. Death most often occurs a few days later. Symptoms of rabies include: headache, fever, anxiety, pain, seizures, with mania occurring shortly before death. Most instances of rabies are caused by a bite from an infected animal, with an extremely high percentage of these instances occurring in Africa and Asia. Rabies has been eradicated in dozens countries, including the United Kingdom (with occasional exception; bats have very rarely been found with a similar virus), Ireland and Australia. In the United States of America, Raccoons (Southern states) and skunks (Midwestern states) are common reservoirs for rabies, although the main reservoirs for rabies are bats. Despite this, human rabies is quite rare in the USA. It is important to realise that even people living in areas where rabies has been eradicated should always be careful when travelling to and from an area with rabies.

The following map shows the countries announced to be free of rabies in 2010:


Rabies can be prevented by vaccinating people and pets who live in or travel to an area where rabies is common – it is especially important to vaccinate cats, dogs and ferrets. Even if places such as the UK, vaccines are recommended for people who handle bats regularly. The vaccine may present mild symptoms, such as temporary swelling of the injection site. In rare cases, flu-like symptoms may be present for one or two days afterwards. Severe reactions to the vaccine are extremely rare. People are strongly advised to avoid contact with wild animals in areas where rabies is common (particularly bats), and to report aggressive animals to the authorities. If somebody is bitten by an animal, it is recommended that they thoroughly clean the wound and seek medical advice as soon as possible to assess the injury and determine whether or not treatment for rabies is necessary.

Roundworm (Toxocariasis) – the intestinal parasite most commonly found in pet dogs and cats. They can grow up to seven inches in length, resembling a string of spaghetti, and may lay up to 200,000 eggs in one day. This is the parasite which is very often passed down to unborn puppies through the placenta, which is why worming is extremely important when you take on a new puppy. Dogs may also become infected by roundworms if they ingest eggs from soil, infected faecal matter or other infected animals (mice, for instance). These eggs hatch into larvae in the stomach, where they then pass through the circulatory system and into the lungs, entering he air sacs. This causes one of the tell-tale symptoms: coughing. Once they arrive in the lungs, they migrate upwards through the windpipe and are swallowed when they reach the oesophagus. When they reach the intestines, they mature and produce eggs. Most dogs acquire a resistance to roundworms when they reach six/twelve months old. Any infections of roundworms encyst in body tissues and fall dormant unless they are activated by pregnancy; this is how bitches pass roundworms onto their puppies. Although symptoms are often very mild in adult dogs, puppies may become extremely ill and death can occur if it is left untreated.

Giardiasis (caused by the parasite Giardia) – an intestinal parasite which can lead to symptoms such as: foul-smelling diarrhoea, vomiting, abdominal pain, appetite loss, blood in the urine or faeces and lethargy. Contaminated water is the most common route of transmission and can be passed from one host to another via the faecal-oral route. This parasite can affect a wide variety of species, including humans. This infection is usually fought off by the immune system, although veterinary care may be necessary to prevent dehydration and malnourishment.

Cryptosporidiosis (caused by the Cryptosporidium parasite) – infects the gastrointestinal system of the animal, with symptoms including: diarrhoea, vomiting, fever and abdominal pain. It is found throughout the world. The main cause of Cryptosporidiosis is drinking contaminated water. However, it can also pass directly from animal to animal via the faecal-oral route (ingestion of infected faecal matter) and may be present in the earth. Treatment aims to relieve symptoms and prevent dehydration until the body is able to fight off the illness. Other animals commonly susceptible to this disease are humans, cats, livestock, birds and reptiles.

Leptospirosis (caused by Leptospira) – most often carried by rodents such as rats and creates symptoms such as: lethargy, fever, joint stiffness and pain, vomiting, and loss of appetite. In severe cases, it may cause liver and kidney failure, as well as possible internal haemorrhaging. Due to the fever, dogs often develop polydipsia (increased drinking). Leptospira can be shed almost continuously from their hosts (commonly rats) and can be contracted by dogs when they inhale or ingest urine particles. It can also be contracted if the Leptospira come into contact with an open wound. Unlike many bacteria, Leptospirosis has not required resistance to antibiotics, so treatment for this illness is relatively easy. However, it is likely that the dog would need additional veterinary care to replace the fluids lost by vomiting. There is also a vaccine available, particularly recommended for dogs living in areas highly populated by rats.

Avian Influenza (H5N1 being of the most concern, also known as Bird Flu) – a highly contagious illness originating from birds, with symptoms including: coughing, fever, respiratory problems and diarrhoea. The disease is primarily transmitted via close contact with infected poultry and their faeces. H5N1 and H1N1 are two of the very few strains of Avian Influenza which have become zoonotic to humans. Cats may also become infected by the H5N1 strain. Although not a great deal of research has been conducted into the relation between Avian Influenza and dogs, dogs in Thailand tested positive for the antibodies caused by H5N1.

Lyme disease (bacterial disease carried by vectors, i.e. ticks) – there are three known species of bacteria which cause Lyme disease, all born by ‘hard ticks’ of the Ixodes genus. It produces symptoms such as rashes (common symptom), fever, fatigue, chronic or recurrent lameness due to the swelling of joints, appetite loss and depression. In severe cases, kidney damage can occur; if left untreated, this may lead to kidney failure. Although very rare, the heart and nervous system may also be affected. Due to the severity of this disease, dogs should be checked for ticks regularly by their owners, particularly if they live in an area with a high tick population. Any ticks found should be removed immediately. Lyme disease also affects humans.

Ringworm – a fungal infection of the skin with leaves scaly, hairless, circular lesions. The fungi feed on hair and dead skin, causing the tell-tale bald patches, particularly on the head, paws and tail of dogs. The lesions may be inflamed and sore, causing discomfort. Ringworm can be transmitted by direct contact between dogs and other animals, including humans, so it is important to consult a vet if you see the above symptoms. Diagnosis of ringworm usually includes the use of an ultra violet lamp, although skin scrapes can also be done to detect it. Without treatment, ringworm will usually clear up of in a couple of months. However, during this time, it can be very uncomfortable and will most likely infect other animals. Anti-fungal creams and shampoos can be prescribed to treat ringworm. Surfaces should be cleaned thoroughly with a diluted bleach solution to insure that the fungal spores do not remain in carpets and furniture, as well as pet bedding. Vacuuming regularly afterwards should remove any spores left. Often, adult animals have immunity to ringworm. However, young animals may not, so it is important to talk to your veterinarian regarding preventative care.

Salmonellosis (caused by the Salmonella bacteria) – an infection of the digestive tract, most commonly caused by ingesting highly contaminated food, such as spoiled or improperly cooked meat and dairy products. Depending on how severe the infection is, the following symptoms may appear: lethargy, weight loss, diarrhoea, vomiting, fever, dehydration, miscarriage (in the case of pregnant animals). Very young and very old animals are more vulnerable to catching Salmonellosis due to weakened or underdeveloped immune systems. Owners should also be aware that the use of antibiotics to combat an infection in a dog may cause imbalance to the healthy bacteria in the dog’s digestive tract, putting them at a higher risk of Salmonellosis. In dogs, this illness is generally diagnosed by vets by taking faecal and urine samples. A prescription may be given to fight off the bacteria, as well as rehydration treatment and replacing electrolytes which may have been lost through vomiting and diarrhoea. Care should also be taken to wash hands before and after the handling of any reptiles and amphibians, as they frequently carry Salmonella in their skin.

MRSA (Methicillin Resistant Staphylococcus Aureus) – a bacterial infection most commonly found in humans, dogs and cats. Staphylococcus Aureus is a very common bacterium found on the skin which usually causes no problems to the host. However, this ‘super bacteria’ has developed a resistance to commonly used antibiotics such as Methicillin, giving it its name. In healthy people and animals, it is often carried on the skin and mucous membranes (nasal passages) without presenting symptoms. If these bacteria come into contact with an open wound, the injured person or animal is likely to become infected. Animals with weakened or underdeveloped immune systems are at a higher risk of becoming infected by MRSA, so it is important to maintain good standards of hygiene. Early symptoms may include minor skin conditions such as rashes, as well as infected injuries. In humans, pneumonia may also develop. If an MRSA infection is suspected, medical advice should be sought immediately.

Pasteurellosis (caused by the Pasteurella bacteria) – an infection usually situated in the upper respiratory tract, commonly found in poultry and livestock. The disease is usually transmitted through a bite from an infected animal or the bacteria coming into contact with a pre-existing wound. The most common symptom of Pasteurellosis is inflammation and infection of a wound, which may lead to abscesses and possibly cellulitis. If it then infects the respiratory tract, pneumonia may develop, as well as abscesses of the lungs. Antibiotics are used to treat this disease. Dog owners should use caution if they keep poultry, particularly with puppies, whose immune systems may not be fully developed. All poultry enclosures should be cleaned regularly.

The following zoonotic diseases can be vaccinated against:

• Leptospirosis
  

• Lyme disease
  

• Rabies
  

Remember to speak to your vet for information about vaccines available to your dog. By law in some areas, owners may be required to vaccinate against certain diseases such as rabies, so it is important to check your country/state's laws. If you have insurance, make sure you check all of the fine print; some insurance companies won't pay for your dog's treatment if he has not been fully vaccinated.

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