Diseases That Can Be Transmitted From Dog To Man

Diseases that are transmitted to man from other animal species or lower vertebrates are called zoonoses  (zoonosis being the singular form).  This article focuses mainly on the diseases that can be passed from dogs to man.

People tend to become alarmist at the mention of zoonoses but the only real danger is to the very young, the very old or to those who are immunosuppressed.  There is very little risk of zoonoses affecting healthy humans as long as proper hygiene precautions are carried out.  Preventative measures include careful washing of hands after animal handling, not allowing dogs to lick your face, washing animal bowls and utensils separately from human tableware, cutlery and cooking utensils, not allowing children to play where dogs might have defecated, washing animal bedding and animal areas frequently, vaccinating dogs and cats and treating them appropriately against parasites. 

Two of the zoonoses discussed are not present in the UK today but have been included to illustrate the importance of the UK’s strict Pet Passport regulations and to highlight the reasons why it would be unwise to lift these restrictions in the future.  These diseases are rabies that is spread through the bite of an infected animal and echinococcosis caused by infection with the larval/cystic stage of the tape worm Echinococcus  multilocularis. 

Parasitic infections present in the UK include Visceral Larval Migrans from Toxocara canis, giardiasis and scabies. 

Toxoplasmosis is related to cats but it is included here as many dog owners keep cats and there is a significant risk to women who are pregnant.

Ringworm, unlike its name would have you to believe, is caused by a fungal infection and can be contracted from many other species of animal including cats and horses. 

Salmonella spp. and Campylobacter spp. are bacteria that can cause severe gastric problems.

And finally a disease that is rare, largely due to regular vaccination of dogs, is leptospirosis (or Weill’s disease as the infection is known in humans) which is spread by microscopic organisms known as spirochaetes.  These organisms are transmitted in urine from infected animals such as rats and can be picked up when swimming in still waters such as lakes or rivers.  

For more details on these zoonoses continue to scroll down.



RABIES

RABIES is a viral infection of the Central Nervous System (CNS) and is transmitted in saliva through the bite of rabid animals.  Clinical signs usually appear within 4 weeks of contracting the virus, although incubation periods vary from 3 to 6 weeks in dogs and 2 to six weeks in cats. The clinical process of the disease is divided into three phases, the prodomal, furious ( excitative) and paralytic (dumb) phase. 

During the promodal phase that generally lasts about 3 days, friendly dogs may become more irritable and aggressive dogs more friendly.  They may bite or worry the site of infection, show increased nervousness, be slightly feverish and have a characteristic high pitched bark. 

In the furious phase that can last up to 7 days, affected dogs become restless, hyperactive and aggressive.  The facial expression may be fearful with the pupils of the eye dilated.  There may be a greater tendency to bite objects that are placed near the dog’s mouth.  This is the phase when the animal is most likely to attack and therefore spread disease.  Later in the phase the dog may lose muscular coordination, become disorientated and seizures may develop.

The paralytic or dumb phase occurs when the throat and jaw muscles become paralysed and there is increased salivation (foaming at the mouth) due to the inability to swallow.  At this point the animal is quiet and unable to eat or drink.  Death is due to respiratory failure following progressive paralysis of the muscles.

Currently animals under the Pet Passport Scheme have to be vaccinated against rabies and after three weeks they must have a blood test to assess their immunity to the disease.  In some cases dogs have had to been revaccinated because their antibodies against rabies have not reached the required level.  Following a positive blood test animals are not allowed to re-enter the UK for 6 months.  Should the current regulations be relaxed and the blood test for antibodies was no longer a requirement, there would be a risk of pets from this country becoming infected by rabid animals in other countries.  Rabies not only occurs in cats and dogs but also a variety of wild warm-blooded animals. 

Echinococcus multilocularis (echinococcosis)

Echinococcosis is the name given to human or animal infection with the larval/cystic stages of the tape worm of the Echinococcus or Taenia species.  A species of tapeworm known as Echinococcus multilocularis is prevalent in North America, Greenland, Scandanavia, the Middle East, India and Japan and recent studies on foxes have found it to be evident in many parts of France including the North West and Calais.

This parasite has little impact on the health of its hosts, predominantly the fox and wild canids although domestic dogs and sometimes cats are vulnerable, but if spread to humans through contact with infected faeces, it often proves to be fatal.  Cysts generally occur in the liver and their invasive nature stimulates malignant cancerous growth that spreads at such a rate that it is inoperable. 

VISCERAL LARVA MIGRANS (toxocariasis)

Visceral Larval Migrans is a condition in humans caused by Toxocara canis, a round worm that is common in the UK.

For more information on Toxocara canis click here



GIARDIASIS

Giardia lamblia are microscopic parasites known as protozoa and can be the cause of acute or chronic diarrhoea in dogs, man and other animals.  An infected dog can act as a reservoir of infection for humans if careful hygiene is not applied.  Cysts of Giardia are excreted in the faeces and therefore diagnosis can be made from faecal samples.  The infection is treated with an appropriate antibiotic such as metronidazole.  Routine hygiene and the use of disinfectants such as bleach and Lysol on suitable surfaces are affective against the cysts and will reduce the risk of transmission.

SCABIES



A mite known as Sarcoptes scabiei  is the cause of mange in dogs and other domestic animals but the same disease in man is generally referred to as Scabies.

The fertilized female mite burrows under the skin and lays its eggs within the tunnels.  The eggs hatch within 2 to 5 days and the six legged larvae crawl out onto the surface of the skin.  The larvae then burrow again into the skin to create small pockets where they will undergo moults from larva to nymph and from nymph to adult.  The male mites will then look for females and so the life cycle continues unless treated. 

Infection with this mite causes severe itching.  Visibly the skin becomes red and spotty followed by scabs and alopecia.  The intense itchiness is often the cause of self trauma.  Early infection tends to occur on areas such as the ears muzzle, face and elbows but heavy infestations may occur all over the body.  Dogs that are infected are highly contagious to other domestic animals and it is essential that they are treated as soon as possible. 

Humans have their own strain of Sarcoptes which is equally as unpleasant; however infection that comes from an animal origin is much less severe.  Mites that infect animals will not burrow in human skin and do not multiply therefore the symptoms in humans are comparatively mild in the form of a red itchy rash and will disappear in a few weeks. 

TOXOPLAMOSIS

Toxoplasma gondii  is a protozoan parasite that is transmitted by domestic cats.  Although infection with this parasite is relatively common in humans, disease arising from the infection is rare.  However human infection is very serious if a woman is pregnant as there is a risk that it may produce serious congenital defects in the developing foetus or may cause abortion or stillbirth.   In immunosuppressed individuals such as AIDS and cancer patients, T. gondii can cause severe disease that may be fatal.

In order to prevent infection, litter boxes should be changed twice a day and pregnant woman and those in high risk categories should avoid contact.  The eggs of the parasite that appear in the cats faeces are resistant to most household disinfectants therefore boiling water should be used where contamination is suspected.

RINGWORM

Ringworm, unlike its name suggests, is caused by species of dermatophytes that are closely related to fungi.  The typical circular lesions that are the result of infection give rise to its common name.  These lesions commonly appear as bald patch with redness and scaling. Diagnosis is confirmed with an ultraviolet lamp known as a Wood’s lamp.  When UV is shone on an infected hair or claw it will fluoresce.   Ringworm is treated with a fungistatic antibiotic.

SALMONELLOSIS

Salmonellae are bacteria that thrive in the intestinal tract of both warm blooded and cold blooded animals.  In order to cause disease they need to colonise in certain tracts of the digestive system.  Under normal circumstances the normal flora of the intestine will keep the Salmonella spp.at bay and therefore the animal remains free from disease.  While most infections are subclinical, clinical signs include diarrhoea and vomiting and a low grade fever.  As infection is usually transmitted by the faecal oral route it is essential that hands are washed thoroughly after handling animals.  Salmonella can be transmitted by all domestic animals including reptiles. 

CAMPYLOBACTERIOSIS

Campylobacter spp. are bacteria that can also cause acute enteric disease with different degrees of severity and can be transmitted from domestic animals especially dogs to humans. Symptoms include diarrhoea (sometimes bloody), abdominal pain, and vomiting.  Again these bacteria are commonly passed by the faecal oral route and therefore careful hygiene is essential. 

LEPTOSPIROSIS


Leptospirosis in animals is caused by microscopic organisms called spirochaetes.  The disease when it occurs in man is known as Weill’s disease.  Transmission occurs through contact with urine from carrier animals either directly or in water.  Many species of animals wild and domestic can be carriers but it is commonly associated with rats.  Symptoms of infection in humans include fever and headache. Meningitis, haemolytic anaemia and jaundice may be a feature.  The occurrence of infection is extremely rare however it is wise to have dogs vaccinated against leptospirosis particularly if they enjoy swimming.