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Cats: Effect on Human Health

SUMMARIES OF ARTICLES ABOUT CATS AND THEIR EFFECTS ON HUMAN HEALTH

We've given you two headlines, the first (in blue) being the original, and the second (in red) aims to be a more informative headline, so you can gain an idea of what the article is about more quickly. The source is also given in case you want to track down the original article.

See also:
Cat Health: Vaccination, infections and epidemiological studies
Cat Health: Digestive problems
Cat Health: Other health issues
Cats: General
Cats: Behaviour and training
Reviews of cat books, including books on health and behaviour

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Cat and mouse game

Effects of Toxoplasma gondii make mice easier prey for cats

source: New Scientist vol 211 no 2827, August 27 2011 p41

The effects of Toxoplasma gondii make mice easier prey for cats. Mice affected by T. gondii, a protozoan parasite, are often infected through cat faeces or raw meat. The parasite raises dopamine levels in the amygdala of the mouse, which becomes more reckless and is easier prey for cats. This permits the parasite to continue its lifecycle within the cat. Human males affected by T. gondii tend to be warier, less trusting, less likely to respect rules, more dogmatic and have slower reaction times than men who are not infected.
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Parasite slows reaction times of 'negative' people

Toxoplasma may affect host according to blood type


source: Debora MacKenzie
New Scientist vol 202 no 2711, June 6 2009 p11

Cats can spread Toxoplasma gondii, which can infect humans through contact with cat faeces or meat infected by cat faeces. The parasite's cycle starts in rodents. Infection makes rodents less cautious, so more vulnerable to cats. T. gondii was thought not to harm humans, except foetuses, but it appears to make humans more prone to traffic accidents, due to their reacting more slowly. New research by Jaroslav Flegr and team from Charles University, Prague, Czech Republic, has discovered that rhesus-negative humans infected with T. gondii are more likely to have slower reaction times than infected humans with Rh-positive blood. They also recorded accident rates for 3,890 military drivers over 18 months, and found that the Rh-negative drivers had a 2.5 times greater risk of accidents than non-infected Rh-negative drivers, and all drivers who were Rh-positive. More research is needed, according to Joanne Webster from University College, London.
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I ain't got the genes to be around cats

Cats can increase eczema risk in genetically predisposed children

source: New Scientist no 2662
June 28 2008 p21

Danish researcher, Hans Bisgard, and his team from Gentofte Hospital, Copenhagen, have studied eczema risks in 460 British and 358 Danish children. Children with a mutation that affects barriers to foreign substances entering the skin, were more likely to develop eczema, 45% compared with some 25% without this genetic susceptibility. However, this eczema  risk was even higher for children with the mutation who also shared their home with a cat; 14 of the 16 susceptible children in homes with cats developed eczema.
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Prevalence of Bartonella henselae in young, healthy cats in Sweden

Swedish study on prevalence of Bartonella henselae in cats

source: E. Olsson Engvall et al
Veterinary Record vol 152 no 12, March 22 2003
starts p366, 4 pages long

Bartonella henselae is a bacterium which can cause infections in cats and humans. It causes cat scratch disease in humans, which usually involves mild fever and regional lymphadenopathy, and patients usually recover spontaneously, though some people with immune system problems can have more serious conditions, such as bacteraemia and endocarditis. Cats are the reservoir for B henselae, and cat fleas pass the disease from one cat to another, and may even pass it on to humans. Stray cats are more likely to be infected than pet cats. This study examines the prevalence of Bartonella bacteraemia in health pet cats given access to outdoors.

The samples comprised 66 cats from southern Sweden and 25 from central Sweden. Most were one year old. Only one cat of those from central Sweden had fleas, while 23 cats from southern Sweden has fleas, or 35%. Two cats from southern Sweden tested positive for B henselae, and none from central Sweden. This is the first time that a Bartonella species has been isolated from cats in Sweden.

These results from Sweden indicate that Bartonella bacteraemia is less prevalent in Sweden than in France and Germany, where other studies have found higher rates, of 11% and 16% in France, and 13% in Germany. The reason for Sweden's lower rate may be that cat fleas are less common in central and northern Sweden.

A previous study had found cats with antibodies to B Elizabethae, with only 1% seropositive to B henselae. Swedish elite orienteers were found to have high B Elizabethae prevalences, but B henselae was found in tissues from those orienteers who had died. The reason for these results is not clear, and one possibility is that Bartonella may interact with intracellular bacteria, like species of Chalmydia. Further research is needed on Bartonella subtypes.
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Prevalence of bartonella species causing bacteraemia in domesticated and companion animals in the United Kingdom

Bartonella infections in cats could pose a threat to humans

source: R.J. Birtles et al
Veterinary Record Vol 151 no 8, August 24 2002
starts p155, 5 pages long

Bartonellae species are bacteria that can infect a range of mammals, including humans. The infections are not usually serious, though there have been reports of syndromes which include liver and heart problems, and uveitis. Of all domesticated animals, cats have most often been found to harbour bartonellae. Cats owned by human patients with bacillary angiomatosis were found to be harbouring B henelae, in one study reported in 1994. Dogs appear to be less affected by the infection, and a subspecies of B vinsonii, berkhoffii is the most common Bartonella species found in dogs.

In this UK study, samples were taken from 360 cats, and 211 dogs, as well as from cattle, horses, and a gorilla. The only animals found to be infected were 34 of the cats, or 9.4% of the total sample of cats, within the range of rates found in surveys in other countries, though the time of year (from October to February) may have affected the rate found. The species involved was B henselae in all 34 cases, though this could change with the pet passport scheme. Cats in the UK do appear to be an important reservoir for Bartonellae henselae. This finding has implications for human health, so more research is needed to be able to assess and control the risk.
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Forsaking sex allowed parasite to multiply

Toxoplasma gondii could spread more rapidly away from cats after changing reproduction methods

source: James Randerson
New Scientist no 2379 January 25 2003 p17

Toxoplasma gondii is a parasite with three main forms. Researcher, David Sibley, from Washington University, Missouri, has traced the development of these strains to 10,000 years ago, and his team has found that modern strains are more infectious than ancestral strains. Toxoplasma can only reproduce sexually in its main host, which is the cat. The ancestral strains could probably only be passed between cats and rats. Modern strains can be passed between intermediate hosts with no need for reproducing sexually. Modern strains are thought to have originated with the development of agriculture, when cats were also domesticated.
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All in the mind?

Possible effects of Toxoplasma gondii, which reproduces in cats, on humans

source: James Randerson
New Scientist no 2366, October 26 2002
starts p40, 4 pages long

Toxoplasma gondii is a parasite related to malaria that has usually been though of as harmless, though it has been linked to miscarriages and damages to foetal brains, and can endanger people who have problems with their immune systems. An estimated 30% to 60% of humans worldwide are infected. The parasite can infect all mammals, but can only reproduce sexually in cats. Eggs are spread through cat faeces, and can be effective for as long as 18 months, if the cat faeces are in damp soil. The infection can spread to rats and mice from the soil, and cats can become infected from eating the rodents. Pregnant women are advised not to handle cat litter trays. The parasite can be carried by sheep, cattle and pigs, so undercooked meat is another source of infection. Humans also need to wash hands after contact with soil, in case it is contaminated.

The parasite initially causes acute toxoplasmosis, usually involving a sore throat and headache, though eye damage can also occur. At this stage, the parasite is located in the blood. It then develops cysts in nerve tissue and muscle, and may lodge in the brain. This latent infection was thought not to be problematic unless the infected person developed immune system problems.

Infected rats have been found to be less fearful of novelty, and more active. Researchers from Charles University, Prague, Czech Republic, have investigated whether humans are affected in the same way. They found that men with latent infections tend to show greater independence and a greater inclination not to obey rules, though the reverse is true for infected women. Both women and men with latent infections also reacted 8% more slowly to prompts from computer monitors, and their performance worsened during the experiment, so their attention spans may also have been affected. The Prague team also tested 146 people involved in traffic accidents for which they had some responsibility, comparing them with controls. They found that the more accident-prone were more likely to be carriers, and that people with latent infections have a 2.7 fold greater likelihood of being involved in traffic accidents. The parasite may also be linked to schizophrenia, since schizophrenics have a greater likelihood of having latent toxoplasmosis, and are more likely to own cats. Drugs that help schizophrenics may also damage the parasite.

Vaccines have yet to be developed, so public health measures are important. Thorough cooking of meat, and improved hygiene in kitchens should help to lower infection rates.One study by researchers from Manchester University, England, found toxo DNA in 27 meat products of a total of 71, though it is not clear whether there were viable parasites.

There appears to be more concern about this issue in the US than in the UK, and meat is being analysed by US Agriculture department officials. There are too few studies for major policy changes, but there is a need for funding for more research.
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Modified moggies

US company plans to develop cats that do not cause allergic reactions in humans

source: Kurt Kleiner
New Scientist July 7 2001 p12

Transgenic Pets of Syracuse is a New York company that aims to produce cats for people who are usually allergic to felines. The owners of Transgenic pets are a husband and wife, both cat lovers who suffer from allergies to cats. The company aims to create transgenic cats within three years. The long-term plan is to sell the cats for some 1,000 US dollars each. Both sexes are to be neutered prior to the sale. The company has a contract with Connecticut University researcher into cloning, Xiangzhong 'Jerry' Yang. Yang plans to remove a gene for Fel d 1, a protein secreted by cats which causes most cases of cat allergies in humans. He aims to alter skin cells, using gene targeting so the copy of this gene they hold is faulty, then fuse altered cells with cat egg cells. The company is seeking to raise funds for the project. People for the Ethical Treatment of Animals spokesman, Troy Seidle, is concerned that not enough is known about what this gene does, so cats could suffer.
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Purrfect pets

Cats help children to resist asthma

Source: Kurt Kleiner
New Scientist no 2282, March 17 2001 p12

Cats can provide children with protection against developing asthma, though the reason why is in dispute. One view is that too much cleanliness can prevent the Th1 cells in the immune system from developing properly, while children in contact with cats have their Th1 system strengthened. Th2 cells are linked to allergies, and it is thought that they may overreact if the Th1 system is not strong enough.

Researchers from Virginia University, Charlottesville, US, have examined the way that 226 children from the US react to cat allergens. Some 20% of the children exhibited an immune response, while not being allergic to cat dandruff. The immune systems of these children produced IgG4, an antibody of a different type to IgE, linked to allergies. Both IgG4 and IgE form part of Th2 systems. Thomas Platts-Mills, who headed the Virginia University team, argues that the IgE response is somehow suppressed by IgG4, a possibility that he sees as running counter to the cleanliness hypothesis. The modified Th2 system appears to be providing protection, rather than the Th1 system. However, immunologist Graham Rook, from University College, London, England, sees the cleanliness hypothesis as still valid. He sees a possibility that the clue to understanding allergies lies in a system regulating both TH1 and Th2 systems.
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If a black cat crosses your path then an allergy may soon follow

Dark-haired cats more likely to cause allergies in humans

source: Roger Dobson
Independent May 1 2000 p1

Allergy specialists have discovered that owners of dark-haired cats have a six-fold possibility of suffering an allergy compared to owners of light-coloured cats. Owners with and without allergies were questioned on whether their cats were permitted to go into their bedrooms, and on the colour and gender of their cats. Gender and being allowed into the bedroom do not appear to be linked to allergies, whereas there does appear to be a link between colour and allergies, perhaps due to the composition or thickness of cat hairs.
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Poxvirus infection in the domestic cat: clinical, histopathological, virological and epidemiological studies

Poxvirus in European cats, and risks to humans

source: N. Nowotny et al
The European Journal of Companion Animal Practice vol 7 no 1 April 1997
starts p19, 8 pages long

Two cases of poxvirus were found in Austrian cats, and humans who had been in contact with the cats were also tested. The humans were free of infection, and this included a child who had not received smallpox vaccination.
Cats can catch poxvirus from hunting rodents, and 200 serum samples of cats were also tested for orthopoxvirus antibodies in this study, with a 4% positive result, though all the cats were clinically healthy. No sample tested positive for parapoxvirus. Meanwhile two further cats were found to have poxvirus.
Poxvirus was first reported in domestic cats in the UK in 1978, with 150 cases subsequently reported in Europe, most of them in the UK. Humans have been infected, with one fatality, involving a man whose immune system was already compromised. Symptoms in cats and humans are localised lesions, which spread if untreated. Cats do not usually die from the disease, though they may suffer complications due to additional infections, like pneumonia. Glucocorticoids are not recommended as a treatment, since they are immunosuppressive.
Orthopoxvirus has accounted for all recorded cases, except for one case of parapoxvirus in the UK. There are around 50 million cats in Europe, and only eight cases of humans being infected have been recorded, so the risk to humans appears slim. Vets should still warn owners that there are risks, especially to people with deficient immune systems.
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Cat Health: Vaccination, infections and epidemiological studies
Cat Health: Digestive problems
Cat Health: Other health issues
Cats: General
Cats: Behaviour and training
Reviews of cat books, including books on health and behaviour