猫からうつる病気：猫ひっかき病
Cat-Scratch Disease
日本大学 生物資源科学部 教授・丸山 総一

Soichi MARUYAMA, DVM, PhD, Professor,
College of Bioresource Sciences, Nihon University

Hello, everybody. I am Soichi Maruyama of Nihonas pets in Japan. This tells us that many people are pet

University. Today I am going to talk about cat-scratch

owners. Actually, I am one of these people as I am a dog

disease (CSD) as a representative example of diseases

owner. When we look at the figures for the number offrom cats.

pets being kept per pet-owning household, it turns outthat an average of 1.29 dogs and 1.7 cats are kept per

To begin, as Dr. Okabe introduced earlier, I will try tohousehold. So, from the data, it is clear that many of the

explain in simple terms about zoonoses, or zoonotic

households keep more than one animal as pet.

infections. As my slide shows, a zoonosis is an infectious
disease or an infection that can be transferred between

This is a dog that my family and I take care of. The way

human beings and other vertebrates under natural

we treat pets in Japan is different to the old days. In

conditions. Sometimes, zoonoses are spread fromtreating them as members of the family, we have muchhumans to other animals but, in many cases, they arecloser contact with our pets. In this picture, we hug andspread from animals to humans. As was introduced

stroke our dog every day and in general maintain a very

earlier, the technical term for diseases maintained inclose distance. But sometimes disease-causing agentsnature by humans and other animals is ‘zoonosis’.

carried by cats or dogs infect people accidentally. Givensuch circumstances, when we keep pets, we need toAmong the 1,709 pathogens that infect humans, almost

know more not only about the biology of the animals

half of them are zoonotic infections. Moreover, among

themselves, but also about the diseases they carry.

156 emerging infectious diseases listed as having

So today, I would like to talk to you about CSD as an

begun to spread since 1970 (a number which is now

example of a disease that is often transmitted from cats

a little higher), 73% have been found to be zoonotic

to humans.

infections. So, I think it is fair to say that we are
surrounded by a great many infectious diseases from

CSD was first reported over half a century ago in 1950

animals.

in France. The first case in Japan was reported three
years after that, in 1953. However, it took a long time

We share our living environment with a variety of

to isolate the disease-causing agent from the patients. It

animals. These include the livestock that provide thewas finally identified in 1992. So I think we can countmeat we eat every day. Also, in Japan in recent years,

CSD as an emerging infection.

wild animals have been intruding more frequently than
before into human residential areas. Cats and dogs are

Unfortunately we do not have precise data on how

extremely popular as pets, and there are also many

many people have contracted CSD. The number ofpeople who keep reptiles as pets.

cases is taken from an article according to which there
were approximately 22,000 cases in the United States

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According to the data in 2009, approximately

in 1992, and the number increased to approximately

12,320,000 dogs and 10,020,000 cats are being kept

40,000 cases by 1997. The status of CSD in other

りぶ・らぶ・あにまるず 神戸アニマルケア国際会議 2012

countries is totally unknown.

the fat cells under the skin.

This is a questionnaire survey that was given toThis picture shows an early lesion. Here is an injury thatJapanese physicians in order to try to ascertain what

was caused by a cat scratch. This picture also shows

types of zoonosis they had found among their patients.

where a claw mark on the arm has caused an injury

The respondents included internists and surgeons here

resembling that of an insect bite but which doesn’in Kobe. According to the results, the most commont heal. This picture shows a symptom developed by azoonosis found by physicians both in Fukuoka and in

student who is a graduate of my college. She comes

Kobe was CSD. They also reported high rates of otherfrom Kobe, and while she was taking an instructiondiseases, such as psittacosis, which will be discussed

course at a private veterinary clinic in Kobe during herlater today, but the research indicates that CSD is thesummer vacation, she was scratched by a tomcat thatmost common zoonosis in terms of the number of cases

had been brought to the clinic for spaying. According

discovered. However, there is no legal requirement

to the student, she developed the symptom shown here,

to report CSD infections in Japan, so there are

and then her lymph nodes became swollen. Soon after

unfortunately no national statistics.

the lesion occurs, such symptoms can appear. Later,
she developed a fever and her lymph nodes swelled

The agent of CSD is the bacterium, Bartonella henselae.

to the size of eggs, as shown in the slide. The lymph

The bacterium can propagate in artificial medium,

nodes close to the wound site caused by a scratch or

and Bartonella henselae is a very small bacterium

bite become swollen like this. After that, the woundthat can exist inside the red blood cells of cats. I will

becomes red if it is rubbed and I have heard that it can

explain later why bacteria in cats’ red blood cells

be very painful.

can be transmitted to humans through cat bites andscratches. These bacteria require several weeks toThis next picture shows lymph nodes in the inguinal

form a colony. A colony in this sense means that thearea hugely swollen. This is a CT image, and you canbacteria have propagated in an artificial medium tosee how the nodes have swollen. Next, looking at thisthe point where they form a clump large enough to bepatient’s feet, you will notice a lot of fleabites. Thisvisible. Usually, in the case of coliform bacteria suchis because the patient was bitten many times by theas E. coli or Salmonella, a colony can be grown in an

fleas infesting his pet kitten. He was bitten and thenartificial medium within a single day. But in the case of

scratched himself many times. Then, the inguinal lymph

Bartonella, the agent of CSD, the process takes several

nodes became swollen. When he went for a medical

weeks. This bacterium will not grow into colonies

examination he was found to have been infected with

unless we cultivate it for a very long period of time.

CSD. This is an example of a flea-borne CSD case andthe case is uncommon.

As for the symptoms, when an immunologically healthy
individual is infected with CSD-causing bacteria, aHere is a case in which neuroretinitis has developed.

papule will appear at the site of infection resembling

If a person touches the fur of a cat with CSD-causing

an insect bite, (I will show you a picture of this later),bacteria and then rubs his or her eye with the sameor else the patient will develop a fever. Next, they

hand, the bacteria can transfer to the eye. Neuroretinitis

will develop a general malaise, and then the nearby

or conjunctivitis may then develop.

lymph nodes will become swollen. Many CSD-infectedindividuals exhibit these symptoms, but between 5

When immunosuppressed individuals are infected

and 10% of them also go on to develop additionalwith Bartonella henselae, they can develop bacillary

symptoms such as an eye symptom known as Parinaud’angiomatosis, a condition that may resemble Kaposi’s oculoglandular syndrome, encephalitis, and/ors sarcoma, on the skin. In this picture, you can see aerythema nodosum (EN), which is an inflammation oflesion that has developed on a finger. Such lesions can

2nd Live Love Animals International Conference on Animal Care in Kobe 201233

mimic a granuloma. They may also develop, not onlywith the dog without being discouraged. From this, iton the skin, but within the liver or spleen where they

seems natural that boys would have a higher frequency

can produce serious symptoms. Occasionally, otherof being scratched or bitten by cats. In the case of adult

symptoms such as a lung abscess or endocarditis canwomen, when the family has a cat, it is often the motheralso appear.

or elder sister who takes care of the animal, meaningthat women tend to have a higher frequency of close

As you might expect from the name of this disease,contact with cats.

cats are the main source of CSD infections. When we
performed examinations on 63 CSD patients, we found

When we checked the age distribution from thethat the infections were cat-related in 58 cases(92.1%),.

antibody prevalence rate, we examined 25 maleCases involving kittens were particularly common.

patients and 23 female patients clinically diagnosed as

As was mentioned earlier, there are rare examples inhaving CSD, regardless of whether or not antibodies

which dogs are also carriers of the infectious agent.

were present. The results showed that an greaternumber of women were carrying antibodies to theActually, these results were taken from researchdisease. I have found similar results when I observeon antibody prevalence rates. In this research, we

students at my own college. As may be expected, when

examined for the presence of antibodies in the blood,cats are present, the female students get closest towhich provides an indication of whether or not anthem, stroking them or patting them on the head andindividual has been infected with a given disease insaying “how cute!” From this, we can say that women

the past. Firstly, we roughly divided the subjects into

generally have a higher ratio of involvement with cats

those who had been in contact with cats and thosethan men do.

who had not. As a result, we ascertained that 17.4%of the subjects who had been in contact with cats had

This slide shows the causes of CSD. All of these cases

antibodies to Bartonella henselae while, among those

involved cats. Looking at the data, as you might expect,

who had no contact, 7.9% had antibodies. Among those

we find that 44.8% of the patients developed their CSD

who were unsure whether or not they had had contact,

symptoms as a result of being scratched. Surprisingly,

the corresponding ratio was 4.8%. From this, we canonly a few of them developed their symptoms due tosay that having contact with cats is an important factor.

bite wounds. Interestingly, 41.4% developed symptoms
after merely touching a cat and only 5.2% developed

On this occasion, we checked the age distribution of

their symptoms due to fleabites. These cases all

patients with CSD and discovered that among children

involved cats so we can say that bites, scratches or

up to nine years old, the majority of such patients areother close contact with cats are among the causes ofboys, while among teenagers and adults up to their

CSD development.

forties, the majority are female. However, this does
not necessarily mean that there is any difference inThis graph shows how CSD develops on a month-by-

sensitivity to the infection between males and females.

month basis. The number of patients increases up to

It may simply reflect the frequency and intensity witha peak in September and October. Surprisingly, fromwhich people come into contact with cats. For example,

February until around April, May and June there areyoung boys who live with a cat at home may be more

fewer cases. I think this may be related in some way to

inclined than young girls to grab their pet suddenly,

the flea-hatching season. Possibly, when the hot season

which scares the cat and may lead it to scratch or bite

arrives, more fleas hatch and jump onto cats. Thisin response. In my own home, my children often playcauses the number of CSD-infected cats to increase, andwith the dog, and since the animal ranks the children

this in turn is linked to the increase in month-by-monthat the bottom of the social hierarchy, they often get

CSD development.

barked at or bitten. Still, the children continue to play34

りぶ・らぶ・あにまるず 神戸アニマルケア国際会議 2012

This is the mode of transmission of CSD. Consider

However, the carrier ratios increased as we moved tothat this cat has the bacteria Bartonella henselae in its

regions further south. This is the result of a survey byblood. A flea sucks blood from this cat, and later jumps

veterinarians in Sanda City, Hyogo. Here, the carrier

onto another cat, where it again sucks blood and also

ratio was very low. As a tendency, the carrier ratios

deposits feces. The bacteria in the blood are mixed in

become progressively higher in regions further south.

with the feces, which sticks to the cat’s skin or fur. We

Also, cats in urban areas tend to have unexpectedly

know from watching cats that they groom themselves

high carrier ratios.

frequently. While the second cat is grooming, it takes
bacteria into its mouth as well as onto its claws. If thisThis is because in the more southern parts of Japan,

cat later bites or scratches a person, the bacteria cancats are infested with fleas all year round. Also, in

infect that person. Alternatively, when a person hugs aurban areas, since the density of cats is high, free-

cat that has CSD bacteria on the surface of its body, theroaming cats have more opportunities to meet otherbacteria can infect the person by passing through ancats, making it more likely they will pick up fleas orexisting small wound, etc.

become infected with bacteria in the course of fights
with infected animals, etc.

Cats are a reservoir of CSD infection. On this occasion,
we researched the percentage of cats that actually host

We have also made a comparative study of different

CSD bacteria. We also made separate tabulations formethods of keeping cats and their rates of flea

the percentages of infected male and female cats, andinfestation. Compared with cats that are kept indoors,

we found little difference between them. In our survey,

those that is kept outside have almost double the ratio

the CSD carrier ratio was 7.7% for male cats and 7.1%

of flea infestation. When we examined the prevalence

for female cats. Moreover, the age-classified CSD carrierof CSD bacteria antibodies, we again found that theratio rose progressively from the age of less than one

ratio of animals testing positive for antibodies is about

year and peaked at between two and three years old.

double in the case of cats that are kept outside.

For cats over three years old, the carrier ratio declined
significantly to 3.4%. Accordingly, we can say that a

In other words, cats that are kept outside and arehigh percentage of cats from kittens up to three years

infested with fleas also have a very high CSD bacteriaof age carry CSD bacteria.

carrier ratio. These animals form an important reservoirof CSD infection.

Next, what is the CSD situation among newborn kittens?
As was mentioned in the earlier keynote speech, areNow, when a cat is infected with CSD bacteria, whatthese bacteria transmitted from mothers to theirkind of symptoms do they display? Actually, catskittens? In order to research that issue, we conductedshow very few if any symptoms at all. Cats that carry

tests on the blood of newborn kittens. However, wethe bacteria develop relapsing bacteremia, which

did not find even any positive result among the 88means that bacteria are present in the blood only

animals we examined. From this result, we ascertainedintermittently. They appear for perhaps a year or more,that vertical transmission does not happen, or in otherthen disappear for a time, and then appear again,

words, CSD bacteria are not passed from mothers toand so on. This data shows the results of research

their kittens.

conducted at my laboratory. The red sections indicate
where CSD bacteria are present in the blood. If weThis time, we researched the regionally classified CSD

follow the same cat over a period of time, you can see

bacteria carrier ratios among cats in regions throughout

the bacteria appear here and again here, disappear

Japan from north to south, from Hokkaido to Okinawa.

here, and reappear here. You can see from this that

Our results show that in the northern region, no

the bacteria repeatedly appear and disappear from thebacteria were detected at all in Hokkaido and Miyagi.

cat’s body. This is why even infected cats hardly ever

2nd Live Love Animals International Conference on Animal Care in Kobe 201235

show clinical symptoms, and it also helps explain why

carrying Bartonella henselae, which are sources of

it is difficult to discover whether an individual cat is a

infection. However, antibiotics such as erythromycin

carrier of CSD bacteria or not.

or doxycycline, etc., can be effective when given to
an immunocompromised person or an AIDS patient. I

As I said before, in recent years there have been

suppose that if you visit a physician for CSD you areoccasional cases of CSD involving dogs. The British

likely to be prescribed an antibiotic almost all the time.

Medical Association’s journal ‘The Lancet’ published

But in the case of CSD, such drugs have almost noa report by a Japanese researcher from Yamaguchi

effect. We have to wait for the infection to clear up by

University about bartonellosis transmission from dogs,

itself.

and our own group has also come across such a case.
Lastly, I would like to talk a little about CSD prevention
A c c o r d i n g l y, w e i nve s t i g a t e d h o w m a ny d o g smeasures. The first thing you can do is to choose

are actually carriers of CSD bacteria. We tookgentle-natured cats as your pets. This can be rather

blood samples from dogs with the cooperation ofdifficult, but in situations where you have a choice of

the Veterinary Association of Kobe City and themany individual animals, if you choose a cat that isgovernment of Saitama City. In Kobe, our examination

too energetic, you will have a bigger chance of beingof blood samples from 206 dogs did not reveal thescratched by that cat when it grows up. So pleasepresence of any CSD bacteria at all. However, DNAbe sure to consult with the cat breeder or provider

from this bacterium was detected in a blood sample inregarding that point, and choose a gentle animal.

one case. In Saitama, we found ten cases in which dogs
were carrying CSD bacteria and three cases in which

Next, clip the cat’s claws periodically. As a cat’s claws

dogs carried both Bartonella henselae and Bartonella

lengthen, they grow into a hook shape. So if theyclarridgeiae. From this result, we can surmise that dogs

penetrate into the skin they can cut deeply. Also, if you

do not carry CSD bacteria permanently, but they may

are scratched, thoroughly apply an antiseptic agent todo so intermittently.

the wound. The antiseptic you keep at home is OK for
this purpose. But even if the injury is minor, be sure to

The method of diagnosing whether or not a cat isclean it thoroughly. And if the wound is deep, you mustcarrying CSD bacteria or not is to take a blood sample,

visit a physician for treatment.

examine the blood serum using the fluorescentantibody method, and ascertain whether the result is

Avoid excessive contact with cats such as kissing andpositive or not. This bright one is positive. The most

sleeping together. Also, and this is a very basic thing,important thing when bitten or scratched by a cat is tobut always wash your hands after touching a cat. And

check whether there is an injury. To isolate the bacteria

gargle your throat. It is quite difficult to carry out theseis not impossible, but is very difficult because, as I said

instructions. I doubt whether even I could follow themearlier, the bacteria takes several weeks to grow into

all the time, but at least I wouldn’t let my dog sleep

a colony. Also, physicians already use antibiotics foron my bed. Also, as I mentioned earlier, if your handtreatment of patients, which makes it rather difficult tobecomes contaminated with CSD bacteria and then you

isolate the bacteria. Another diagnostic method is thetouch your eye, you might develop conjunctivitis or

PCR method, which provides a way of detecting DNA

neuroretinitis, so please wash your hands thoroughly.

from a blood or lymph node samples.
The transmission of CSD from cat to cat often

36

How do we treat patients who are infected with CSD?

involves fleas. In rare cases, fleas are also involved

In many cases, antibiotics are used. But in general,in transmitting CSD to people. So be sure to conduct

antibiotics have very little effect when used onflea countermeasures properly. Nowadays there are a

CSD in immunologically healthy people or for catsvariety of flea expellants available, such as insecticide-

りぶ・らぶ・あにまるず 神戸アニマルケア国際会議 2012

impregnated cat collars, liquid medicines and injections,so make use of these to get rid of fleas completely.
Also, immune suppressed people should avoid keeping
animals. This is not only because of the risk of CSD but
because, generally speaking, such people’s physicalresistance tends to be weak so they can be easily
infected even by mild disease-causing agents. Suchindividuals can guard against getting diseases byrefraining from keeping animals.
Even so, as Dr. Okabe mentioned at the beginning,
I think that the positive effects of keeping pets athome are highly significant. Pets can help refresh
our spirits and they provide children with emotional
education. However, the animals themselves don’t
understand that kind of thing. So it is important to gain
an understanding of how to handle animals, including
the aspect of keeping them while also staying aware ofpotential diseases.
Finally, I would like to close my talk with the sentiment,“Let’s enjoy your life with pets with appropriatemanners.” Thank you very much for your attention.

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