In this final part of our series on zoonotic infections, we’re going to look at rarer or emerging zoonoses – those where the zoonotic risk is perhaps less well known.
Toxoplasma is a protozoa (a tiny single-celled organism) carried by many cats, and in fact, many humans too. It is transmitted from cats to people in infected faeces. In the vast majority of cats and people, there will be no symptoms. However, Toxoplasma can be very dangerous in people with weak immune systems, such as people with AIDS, and children. A very horrible form of the disease infects unborn children via their mother’s placenta. This is why pregnant women are often told to avoid contact with cats, cat faeces, and areas where cats frequently defaecate.
In adults, significant Toxoplasma infections can cause eye and brain problems, and even mild infections may affect behaviour by increasing risk-taking behaviour! In children and unborn babies, the disease leads to serious developmental abnormalities of the eyes, and problems with coordination, hearing, movement and other senses, and is a well-known cause of stillbirths. There are treatments for Toxoplasma, but for children infected at birth, it can be too late to prevent abnormalities. Prevention is key, by following the advice mentioned above. Cats can be tested for the protozoa, but this is not a fool-proof solution for pregnant women.
Influenza, or flu, are a group of viruses that almost everyone has had at some point. We all know that ‘coughs and sneezes spread diseases’. But did you also know that animals can get flu too? In animals, the virus causes many of the same symptoms as in humans. Most strains of flu only infect one species (pig to pig, chicken to chicken, or human to human, for example) and just cause the mild symptoms we all know about. These are the flu strains we catch every year, which do little more than make us miserable and miss a few days of work (so not all bad!). The reason they usually aren’t dangerous is because they are so common, and we all carry some resistance to their worst effects – simply put, we are used to human flu viruses and our bodies know how to fight them off effectively.
However, there has been a lot of fear in the news lately of flu strains that might become zoonotic and jump from animals to humans. Flu viruses rapidly mutate and through random mutation, animal flu can start to infect humans. You may have heard of ‘bird flu’ and ‘swine flu’, two flu viruses which we worried would do exactly that. Because humans have never been infected with these strains of flu before, they cause much more severe symptoms, such as vomiting, diarrhoea, organ failure, secondary bacterial infections, and death. Unlike common flu, young healthy people are often severely affected.
These kinds of flu outbreaks can spread globally as a pandemic, and present a huge global threat. Previous pandemics, such as the 1918 Spanish flu, have killed millions of people. Thankfully, we have so far controlled any strains that have jumped to humans, but it may only be a matter of time before one is too infectious to control. On a day to day basis, you don’t need to worry about catching flu from your animals, but do be aware that there is always that tiny risk.
Our final disease, MRSA, needs no introduction. Brought up in the news all the time as a deadly ‘superbug’, methicillin-resistant Staphylococcus aureus is a bacteria that medical facilities worldwide are struggling to deal with. MRSA is resistant to many common antibiotics, meaning a person infected with MRSA may struggle to receive effective treatment. Symptoms of MRSA include skin problems, fever, septicaemia, infected wounds, pneumonia and sometimes even death if a suitable antibiotic is not found.
So why are we mentioning MRSA in this article? Well, MRSA is one of the most important ‘anthroponoses’, or reverse zoonoses, to be aware of. An anthroponosis is a disease which is transmitted from humans to animals – the opposite of a zoonosis. Many human diseases are anthroponoses to primates, due to their similar biology, but there are also anthroponoses that affect our pets as well, of which MRSA is one.
We can pass MRSA to our pets, which causes the same symptoms in them as it does in people. This can mean that pets may face a greater risk when visiting the vets for surgery in future. Vets will always ensure the greatest sterility possible, but the risk is always present. Animals infected with MRSA will also struggle to be treated with antibiotics, like people infected with MRSA, and there is a worry that MRSA will become as big a problem in veterinary practices, as it is in human hospitals.
So to answer the heading of this series: Yes! People can catch diseases from animals, and in fact, animals can catch diseases from people too! There are a great many zoonoses and reverse zoonoses out there, far too many to talk about here. We have instead discussed the most common, relevant and topical diseases to us as pet owners. Note that many of the prevention strategies are the same – vaccination, washing hands, having good hygiene, etc. – so it is not impossible to prevent these diseases. Just be aware of the potential risks owning a pet can have, and take the necessary precautions to ensure you both have healthy lives together!