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Cats: Effect on Human Health
SUMMARIES OF ARTICLES ABOUT CATS AND THEIR EFFECTS ON
HUMAN HEALTH
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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