© Ann Storey MSc.
This is a brief document dealing with those infections that may be caught from rats in the UK. The correct term for diseases caught from animals are zoonoses. Generally, they are rare, but it’s well to be informed so that medical attention can be obtained promptly where necessary. I have included wild ones because I am well aware that keeping pet rats sometimes brings you in contact with the other. On the whole, wild rats are more likely to carry these diseases than domestic ones but this does not mean that domestic rats are risk free.
Contact with wild rats is maybe not the first thing a rat owner considers, however, if you keep your rats in outbuildings, then it is likely at some point that you will have to deal with a wild rat. Certainly I have had my run ins with wild rats over the years.
Even if you keep your rats in the house does not mean that it will never happen, as wild rats frequently come into houses during the winter months, as some members have found to their cost.
Disease risk from wild rats is largely overstated. For instance wild mice carry most of the same diseases as rats plus a few more, such as a type of viral meningitis, Lymphocytic choriomeningitis virus (also carried by hamsters) for good measure, And if you really want the star performer you have the feral pigeon. However, many people seem pretty laid back about mice in their sheds and houses where they would be concerned about rats.
Much of the information repeated in popular books about diseases carried by rats is old or based on faulty science. More modern research (Webster and Macdonald 1995) (Battersby 2000), show a slightly different picture, with lower levels of disease carriage in both rural and urban rats than was originally supposed. This is not to say that wild rats are risk free. Like all animals rats can act as reservoirs for a wide range of pathogens, some of which can infect man. However, the most famous disease, bubonic plague, caused by Yersinia pestis, no longer occurs in the UK and there have been no cases contracted here since 1918. Murine typhus, another disease carried by rats and mice and transmitted by fleas is also not present in the UK. One disease, often wrongly associated with rats; Lassa fever, is in fact not carried by rats at all but by multimammate mice and is restricted to West Africa.
A list of the diseases associated with rats in the UK is as follows. This list and more information is available on the Government website.
https://www.gov.uk/government/publications/pet-rats-mice-hamsters-reducing-the-risk-of-infection/reducing-the-risk-of-human-infection-from-pet-rodentsThe major disease and the one that exercises most people's minds is Leptospirosis, sometimes known as Weil’s disease, although technically this applies only to the more extreme cases. The bacterium responsible, Leptospira interrogans, can be carried by almost any mammal and there are over 200 strains or serovars, of greater or lesser risk to man. The principle strains that are important in human disease in this country are
This disease does not make the animal carrier ill. Spread is by contact with infected urine, tissues, body secretions, water or other environments contaminated with urine, such as the top of cages, river banks etc. Leptospires enter the skin through cut or damaged skin and the mucous membranes including the eyes. In humans the disease causes a wide range of symptoms ranging from no symptoms at all, through a flu like illness with severe headache, chills, muscle pain, and vomiting. For many this is as far as it goes and these cases probably go undiagnosed. In some cases however there will be a return of the fever, with jaundice, red eyes, abdominal pain, diarrhoea and sometimes a rash. Some will develop meningitis, or kidney/liver failure. These more severe symptoms are called Weil's disease or Weil's Syndrome. Most people make a full recovery within three months but a few will die. Symptoms usually occur 7 to 14 days after contact but it can be as little as 3 days and as much as 1 month. Treatment is with antibiotics such as penicillin or doxycycline but is needs to be given early. There is no vaccination available in the UK. The problem is that it can go undiagnosed by the average GP even though it is a notifiable disease. If you develop symptoms and you think you have been in contact (this includes fishermen, windsurfers, cavers, miners etc) you should inform your GP. Some literature give the carriage rate as 75% of wild rats, however more recent information (Webster and Macdonald) puts it around 14% . It is not normally carried by domestic rats unless they have been in contact with infected wild ones. Some years ago, following my rat problems, I did have a few tested and all were negative. Obviously if your rats are infected then you or anyone handling your rats would be at risk. On average between 50 and 25 people per annum are confirmed with Leptospirosis of all strains in this country.
Also known as Haverhill fever. This is a rare human disease with only approximately three reported cases per year in the UK, and some of these have been contracted abroad. Outbreaks can follow the consumption of milk or water contaminated by infected rats, generally however the disease is contracted by contact with the saliva, nasal or eye secretions of an infected rat, usually via a bite, although not always. The bacterium lives in the mouth and throat of rats, both tame and wild and also a range of other small mammals such as weasels, ferrets and squirrels.
Symptoms generally occur within ten days of having a bite that healed normally. They include a rash (sometimes petechial like meningococcal meningitis), chills and fever, headache and muscle pain. The rash is usually more pronounced on the extremities and is then often followed by swollen joints. Untreated cases may develop infection of the heart (bacterial endocarditis) and abscesses, with a fatality of 10 - 7 %. Treatment is with Penicillin or doxycycline.
A second type of rat bite fever is caused by the bacterium Spirillum minus. Now this is not in the list of diseases caused by rats on the HPA website mostly because it has not been reported in the UK. Despite this I am pretty sure at least one member of the NFRS has caught it. However, no blood was taken and the person concerned got better with antibiotic treatment.
Like Streptobacillus moniliformis, Spirillum minus is a normal inhabitant of the mouth of the rat and is the common form of the disease in the far East. The symptoms differ from the previous infection in that there is no joint involvement and the rash forms purple or reddish patches. Also the original bite wound reopens when the symptoms appear. The incubation period is 1 to 3 weeks. Untreated, the case fatality is about 10%.
Hantaviruses are a group of viruses that can be carried and transmitted by rodents. Infection with certain strains of hantavirus can cause haemorrhagic fever with renal syndrome in Europe. Hantaviruses have been found in both pet and wild rodents in the UK.
Each hantavirus is specific to a different rodent host. Once infected, the rodent will be infectious for prolonged periods although the exact period is not known. Transmission of virus to people usually occurs through the inhalation of particles contaminated with the virus, such as dust from faeces, contaminated bedding, or splashes of urine. The virus is also present in rodent saliva, so a bite is also a means of transmission to people.
In people, infection with these viruses can cause a disease characterised by fever, headache, gastrointestinal symptoms and kidney problems. The more severe forms of disease can result in bleeding from internal organs and the skin. The incubation period is generally 2 to 4 weeks (range 2 days to 8 weeks). As for many infections, it is likely that most infections with hantaviruses are mild or cause no clinical disease at all.
There are several different types, all of which are transmitted by a particular species of rodent. Hantaan virus with Field or wood mice, Puumala with bank voles and Seoul virus with rats. In one study in Newcastle, 35 % of the cats were found to be carrying antibodies to Seoul virus and there much serological evidence of human infection where cases have gone undiagnosed. After all, when was the last time you had a blood test to confirm that the bad dose of flu you had was really flu? Seoul virus was responsible for an outbreak among lab workers in 1977 and there have been sporadic cases ever since. One study of rat fanciers carried out by the Health protection agency in 2014 in which the NFRS took part showed 32.9% of rat fanciers showed that they had a past infection with Hantavirus.
Due to how common this is in rat fanciers any fancier who gets a positive test for hantavirus antibodies following on from a possible diagnosis, must have a further test to confirm the diagnosis three or four weeks later. If the infection was indeed hantavirus, then the second test will show a higher level of antibodies. The NFRS is currently developing guidelines to protect the health of others for fanciers who have had a recent confirmed diagnosis of Hantavirus.
Rats can be tested for viral particles using a PCR test of fresh faeces and for antibodies using a blood spot collected on a blotting paper disc.
This is not on the Government website but I have included it because it is not uncommon.
Staph aureus is a bacterium that normally lives on the skin and up the nose of a wide range of animals, especially mammals. 30%-40% of humans carry it all the time. Most of the time it doesn't cause any particular problem but it can cause a wide range of infections ranging from a spot to death.
Rats can get a skin infection caused by this bacterium. It usually appears first as a irregularity in the coat. If you examine the skin underneath, it is usually flaky, with or without some superficial scabbing. Often, even with treatment, that patch of fur will drop out, although it does grow again. You may develop a small sore blister. This may be as far as it goes but it can develop into a circular patch up to the size of a 50p. This is very sore and full of yellowish pus. Treatment with Fucidin cream or chlorhexidine normally successful although the infection is usually self limiting.
For the following diseases, rats are not the most important source of the infection, although you may often see some of them quoted.
Salmonella is an important cause of food borne illness in humans but rats are not an important cause, if they are responsible at all, which I doubt. There are no cases of human infection linked to rats recorded in the last 25 years and the two studies carried out on rats found no rats carrying Salmonella. Infact, Salmonella is a serious infection for rats and is often fatal for them. In the first half of the 20th Century, strains of Salmonella, sometimes called Danysz virus and even sold by Rentokil, were used for rat control. Its use was condemned by the WHO because its use was associated with outbreaks in the human population. It is likely that the cause of rats transmitting Salmonella to humans was all down to the use of this rodenticide. Following infection with Salmonella, rats can carry it for a few months, just as we do
This intestinal parasite infects a wide range of animals including man and farm livestock. One strain (type 1) appears to be a human parasite only. Another, type 2, can cause infection in many species. Wild Rats are quite commonly found to carry this organism. It is not known if pet rats in the UK carry this parasite but it has been reported as causing disease in laboratory rats and in commercial breeder establishments. Symptoms in rats are failure to thrive, staring coat, watery diarrhoea and dehydration. Rats usually get better in 10 days or so and it is commoner in weaners. Symptoms in humans include fever, stomach cramps and diarrhoea lasting several days or weeks. There is no treatment and it can be very dangerous for AIDS sufferers.
This is one of the fungi responsible for ringworm, rats typically get Trichophyton mentagraphytes. It causes a skin infection in rats involving hair loss and flaking skin. Ringworm is quite infectious and it can be transmitted to the owners. Ringworm in humans tends to appear on the skin as an itchy red rash, roughly circular in shape, usually with a clear centre. It is easily treated in rats and humans. Humans also catch it from other mammals and humans.
Pasteurella spp are a group of bacteria that usually infect humans via dog and cat bites, although there have been a few cases of rat scratches infected with this organism. It is a common cause of respiratory and genital tract infection in rats, and it is surprising that it doesn't infect rat bites, especially because the majority of cat and dog bites become infected with it, and rats carry it in the mouth and pharynx.
One of these species, Yersinia pestis has already been discussed. Other species carried by rats are Y. enterocolitica, which is normally caught from infected milk and water, and Y. pseudotuberculosis. Both of these in humans cause enteritis and a condition called mesenteric adenitis, which can be confused with appendicitis. However, it is not known how commonly rats are implicated, although approx 10% of wild rats do carry it. It does not appear to cause disease in rats.
This is a worldwide but common, mild tapeworm infection. Human infections with the same tapeworm that infects rats, Hymenolepis diminuta, are uncommon and mostly contracted in the Indian subcontinent. This tapeworm is small for a tape worm, only being about 60cm long.
This is caused by a bacterium, Coxiella burnetti, and its name stands for Query fever. This is because the symptoms, severity and duration of the infection is very variable. Symptoms may include fever, chills, headache, weakness, chest pain, cough, hepatitis, pericarditis, endocarditis etc. Most people survive even without treatment unless the heart valves are affected.
A wide range of farm livestock, rodents and cats are carriers and the infection is mostly passed on when the animal gives birth, as it is present in large numbers in the birth fluids. The organism survives in the dust and is normally transmitted by breathing in the infected particles, or direct contact with an infected animal. Since 1990, no laboratory reports have been received in the UK linking Q fever with rats, although rats may have been present at the time, there were other, more likely sources present as well.
Rats and cats both have a role in the life cycle of this parasite, Toxoplasma gondii. Rats become infected via infected cat faeces. The organism then takes up residence in the rat's brain and alters its behaviour, to the extent that it loses its fear and starts to come out during the day. It is then more likely to be eaten by another cat, and so it goes on. When humans become infected with Toxoplasma, it is usually from cat faeces and we are taking the place of the rat. in the lifecycle. Toxoplasma does cause brain lesions in humans (as well as elsewhere) but it is usually of concern only in unborn babies and people who are immunosuppressed.
There have been no reports of Toxoplasma contracted from rats since 1990.
There are a number of other diseases reported worldwide where rats can be considered as a possible cause of transmission, including tularaemia, rabies (one reported outbreak in the Far East), Trichinella, Hepatitis E, Listeria and Turkmenia rodent pox. However these conditions are either rare or unknown in the UK or rats are not recognised as a common cause.
Sendai virus, which rats quite often get, is more serious in mice than rats.
For rabbit breeders the most likely problem is Encephalitozoan cuniculi, which can be carried by rats (who don't appear to suffer symptoms) but can cause a range of symptoms in rabbits including runting of litters. Rats do suffer from coccidian parasites and Pasteurella, but these appear to be different strains than infect rabbits or cavies.
To recap, the chances of catching anything from a pet rat is low, although I would advise that you take care if your rat has any skin infections or diarrhoea. Don't let your rat lick your mouth (!) and always keep an eye on any symptoms you get following a bite.
Wild rats are more problematic and you should always make sure that they are kept away from your pet ones, even if this means using baits or traps.
Zoonoses that may be acquired from rats. Health Protection Agency
Parasites of Wild Brown Rats on UK farms. Webster and Macdonald. Parasitology (1995) 111, 247-255.
Parasite prevalence amongst Urban wild rats. Battersby (2000) Phd Thesis University of Surrey.