Zoonotic diseases

Zoonotic diseases are diseases that are transmitted to humans from animals.

It is not possible to provide a summary of all the zoonotic diseases and therefore this article will mainly focus on some of the most important zoonotic diseases transmissible between dog and man.

Echinococcosis or hydatid disease is caused by Echinococcus granulosus, a tapeworm that uses dogs and other carnivores as definitive or final hosts (a host in which the parasite develops to an adult or sexually mature stage) and humans and other herbivorous animals, especially sheep as intermediate hosts (a host in which a parasite goes through its developmental stages).  The adult tapeworm is extremely small and is only about 5mm long and has 3 to 7 segments or proglottids.  It is found in the intestine of the dog and other carnivores.  Gravid proglottids (matured last segments that resembles a flattened grain of rice containing several hundred of the eggs) brfeaks off and is voided in the dog's faeces.  The tiny eggs may cling to the hair coat at the base of the tail, and may be transferred to the dog's lips and muzzle when it licks itself.  the eggs also adhere to the paws of a dog.  Man becomes infected with the tiny eggs that are invisible to the naked eye are taken in by mouth.  In man, the ingestion of eggs result in the release of larvae which develop into bladderworms (hydatid cysts), which may contain several litres of fluid, in the liver, lungs, brain and other organs.  These cysts cause pressure in the various organs, resulting organ dysfunction.  Echinococcosis may be prevented by:

• Regular correct and effective deworming of dogs.
• Never feeding raw red offal of slaughter stock or game to dogs, as these may contain undetected cysts and transmit the tapeworm to dogs.
• Good personal hygiene - washing hands after playing with pets.

Rabies is a disease caused by a virus and is almost always fatal in any unvaccinated animal or man.  Man usually contracts rabies by being bitten by a rabid dog, mongoose, cat or other mammals.  The virus cannot penetrate unbroken skin, but may do so via cuts or bite wounds.  It may also enter the body through the mucous membranes of the eyes, mouth or nose.  The rabies virus causes progressive inflammation of the brain and spinal cord in man.  As a result the earliest signs of rabies in man include sever headaches, anxiety, slight muscle pain, fever and vomiting.  The voice may also change and paralysis of the swallowing muscles may result in difficulty in swallowing.  Fear of water (hydrophobia) may also develop.  Later the affected person may start secreting excessive saliva (hypersalivating), has fits, becomes paralysed and comatose and eventually dies.  There is virtually no prospect of recovery once symptoms appear.  Rabies may be prevented by regular vaccination of pets in accordance with legislation.

Larva migrans is a broad term for the conditions that can result when humans become infected with Toxocara species or Ancylostoma species.

Toxocara canis is a roundworm of dogs.  Man contracts the infection by taking in a hatched egg which has developed to the stage of an infectious larva via the mouth.  This may occur by indirect transfer via hands or the intact of larva-contaminated soil, faeces or food, as well as direct transfer be handling infested dogs.  The worm larvae migrate in the internal organs and tissues of man, causing a syndrome known as visceral larva migrans.  They cause tissue damage and elicit tissue reaction, but never develop into adult worms.  The symptoms in man are fairly non-specific and include fever, loss of appetite, muscular pains, coughing, asthma etc.

When the larvae of Ancylostomma caninum (dog hookworms) and Ancyclostomma braziliense (cat hookworms) come in contact with human skin and penetrate it, they elicity a local irritation and inflammatory reaction characterised by severe irritation, pain and itching of the red, swollen and blistered areas.  This syndrome is referred to as cutaneous larva migrans or sandworm.  The larvae meander around aimlessly with the skin until they eventually die after several weeks or even months.

Both visceral larva migrans and cutaneous larva migrans may be prevented by regular correct and effective deworming of pets as well as good personal hygiene.

Ringworm is caused by various fungi including Microsporum species, Trichophyton species and Epidermophyton species.  Man becomes infected by direct contact with the fungus on the living animal or contaminated material.  In man lesions are usually circular with a flaky centre, crusty formations along the outer edges, and a moist exudate surrounded by a red area of inflammation.  Lesions mostly occur on the arms, legs, face and scalp of humans.  Ringworm may be prevented in man by isolation and treatment of infected pets that are kept in close contact with people.

Sarcoptes scabeii var. canis is a mite that primarily affects dogs, but can also cause disease in cats and humans.  It is transmitted from dog to man via direct contact and result in skin lesions characterised by hair loss, thickening of the skin, formation of crusts and itching.  Sarcoptes may be prevented in man by isolation and treatment of infected pets that are kept in close contact with people.

Following the discussion of a few of the important zoonoses transmissible between dog and man, it should be clear that veterinary assistance with regards to correct, effective deworming and vaccination, as well as early and correct diagnoses of diseases are essential.

Go from Zoonotic Diseases to Veterinary Articles

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• Biliary
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• Tick Bite Fever
• Ticks
• Hot Spots
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