Animals transmit a surprising number of diseases to humans

BY BEN WEST

The precise origin of the Covid-19 virus has not as yet been pinned down. However, most scientists agree that it crossed into humans from an animal species, most likely a bat.

Despite the recent spotlight the pandemic has shone on zoonotic diseases (diseases that can spread from animals to humans, or vice versa) many pet owners are unaware of the large number of serious diseases they can acquire from their animals. 

They can be caused by viruses, bacteria, fungi, protozoa or worms, or from insects or mites living in or on the animal. A huge number of diseases are caught from animals, and 75 per cent of all new emerging diseases come from them. 

The HIV virus, for example, entered the human race via a monkey. Bubonic plague originated from a bacterium infecting rats and can spread via fleas to humans. Other examples of zoonotic diseases include malaria, tuberculosis, rabies, ebola fever, yellow fever and typhoid fever.

Numerous zoonoses have achieved prominence in recent years. For example, in September 2009 an E. coli outbreak caused the closure of Godstone Farm in Surrey in September after 12 children were hospitalised following contact with animals. Eleven people were hospitalised following contact with animals at a Lancashire petting farm in 2014.

New variant Creutzfeldt–Jakob disease (nvCJD), which most scientists believe is transmitted from cattle with the neurodegenerative disease bovine spongiform encephalopathy (BSE), or mad-cow disease, has caused numerous deaths.

Avian influenza (‘bird ‘flu’), which is closely related to human influenza viruses, has been of much concern following the 1997 Hong Kong outbreak with 18 confirmed human cases and six deaths. 

Another pandemic was caused by a strain of influenza referred to as swine ‘flu (because similar strains are known to circulate in pigs). However, swine flu is not generally classed as a zoonotic infection, as cases of this particular infection were being transmitted through human to human, rather than animal to human, contact.

Dogs, cats and other mammals 

Being almost always fatal, rabies, of course, is the disease humans fear most from our four-legged friends. The UK has long been perceived as a rabies-free island but the threat is always there. Cases are occasionally imported, usually the result of a dog bite abroad. In December 2008, for example, a person died from the disease in the UK, having imported it from South Africa.

Yet dogs, cats and other mammals can be host to and carrier of a whole array of other diseases including the fungal skin infection, ringworm, and parasitic roundworms, which can end up in the human intestines and cause infection and disease. The dog roundworm (Toxocara canis) and cat roundworm (Toxocara cati) cause toxocariasis infection in humans when the eggs are accidentally ingested, which can result in a host of symptoms including fever, headache, coughing, abdominal pain and, occasionally, pneumonia.

Dogs, cats and other animals can also pass on to their owners a kind of tapeworm that causes potentially fatal echinococcosis, or hydatid disease. Transmission is typically from eggs found in faeces of dogs and ingested, usually by children. Larvae develop gradually, forming fluid-filled, often large cysts in various organs, especially the liver. Another zoonotic parasitic infection is cryptosporidiosis, which can cause abdominal pain, diarrhoea and ‘flu-like symptoms.

Your pet could be harbouring the bacterium campylobacter, which, when transmitted to humans via its faeces, causes food poisoning. Another, streptococcus suis, can cause meningitis. 

Persistent streptococcal infections in cats can cause tonsilitis and pharyngitis in their owners. The bacterium staphylococcus pseudintermedius is implicated in cases of food poisoning and skin and ear infections. 

Many dogs become infected with the bacterium helicobacter canis, which can affect humans, and indeed about one per cent of cases of human gastritis come from this. 

We are supposedly never more than a few feet from a rat, and these generally reviled creatures are often implicated in human cases of leptospirosis, or Weil’s disease, although other species can also be responsible for its spread. Man contracts it through skin abrasions and mucosa (lining) of the eyes, mouth and nose after exposure through water contaminated by urine from infected animals, such as from swimming in contaminated waters.

Cowpox, which most commonly manifests itself as painful skin lesions in human cases, got its name from dairymaids contracting the disease from touching the udders of infected cows, although today the source of infection for the tiny handful of cases seen in the UK is usually the domestic cat. 

Cats and dogs are often responsible for the spread of parasitic disease toxoplasmosis. While a healthy adult may experience no more than a mild ‘flu-like illness, people with a suppressed immune system or can become seriously ill with complications like encephalitis (inflammation of the brain) and neurological diseases. It can also be passed from a pregnant woman to her foetus and cause abortions and congenital defects.

Reptiles 

Owners of pet reptiles – such as tortoises, terrapins, snakes and lizards – should be wary of the bacterium salmonella. Whilst other animals can transmit it, it is estimated that nine out of ten reptiles carry the disease. They seldom show any visible symptoms of illness and the bacterium is shed intermittently.

Many cases caused by reptiles go unreported. The death in 2000 of a three-week-old baby girl after contracting the disease from her family’s pet lizard prompted the UK’s chief medical officer to issue a warning about the dangers of keeping reptiles.

In March 2008 a five-month-old girl ended up in intensive care and narrowly escaped death after contracting salmonella that developed into septicaemia from a pet snake given to her elder brother. Diagnosis took four days since she was too young to eat raw or undercooked meat. She ended up in intensive care and was given intravenous antibiotics as the salmonella developed into septicaemia.

Birds

Birds kept in the home, like macaws, budgerigars and cockatiels, can transfer a disease called psittacosis, sometimes known as parrot fever, to their owners. The disease is spread by breathing in bacteria present in the infected bird’s droppings, eye or nose  secretions. Found in more than 130 species of birds, in humans it can cause fevers, coughs, conjunctivitis, pneumonia and, occasionally, death.

Precautions

* Wash your hands thoroughly with soap and water after handling your pet

* Do not eat, drink or smoke while handling your pet

* Always supervise children to ensure that they do not put your pet, or objects that it has been in contact with, near their mouths

* Keep your pet out of areas where food is prepared and eaten

* Do not use kitchen sinks to bathe your pet or to wash their cage or equipment. If you use a bathroom sink or bathtub, it should be cleaned thoroughly with disinfectant afterwards

* Dispose of waste water, droppings and urine from your pet down the toilet instead of a sink or bathtub – in particular pregnant women and immuo-compromised people should avoid handling waste from pets.

* If you or other family members become ill with symptoms such as fever, vomiting, abdominal pain and diarrhoea, consult your doctor and inform the doctor that you keep a pet

* Cover childrens’ garden sandboxes so that wild animals and pets cannot foul them