There is an old joke that circulates among veterinary students.
The gist of it is that physicians are single species doctors, while
veterinarians are multi-species doctors. While this statement arose out
of the friendly competition between medical students and veterinary
students for professional status, there are very real benefits of our
training in multi-species medicine.
What veterinarians do as second nature is to examine the animal within its herd and to examine the herd within its environment. In companion animal practice, the ’herd’ is the pet’s human family and the ‘environment’ is urban Seattle.
Veterinary care impacts the health of the pet, the health of human family members, and the health of the environment.
Intestinal parasite prevention
has recently been at the forefront of our discussion of zoonotic
diseases. The reason for concern is that roundworms, Toxocara, can be
transmitted to people. Human infection occurs via ingestion of eggs of
these parasites which are shed in feces of infected dogs and cats.
The
eggs that are shed in feces are not immediately infective to humans.
Parasite larvae contained within the eggs must spend several weeks in
the environment maturing to the infective stage. Once the larvae have
matured, ingestion of eggs (usually via ingestion of contaminated soil)
can result in human disease.
Toxocara larvae do not replicate
within human tissue. Instead, the infective larvae undergo what it
termed aberrant migration. These larvae migrate through body tissues
producing diseases called visceral larva migrans (VLM) and ocular larva
migrans (OLM).
When OLM occurs, larvae encyst in the eye causing inflammation
which can result in blindness.
Signs of VLM include fatigue, weight loss, fever, anorexia, headache,
and abdominal pain. In this country, most cases of human toxocariasis
occur in people under 20 years of age.
Most dogs and cats are infected with Toxocara before leaving their litters.
This is why puppies and kittens are dosed with worming medications
multiple times. Monthly de-worming of juvenile and adult dogs and cats
reduces the likelihood that the individual pet will become infected and
it also decreases the number of parasite eggs in the environment.
Decreasing
the parasite load in the environment decreases the likelihood of:
reinfection of treated animals, infection of previously uninfected
animals, and human infection.
Toxoplasma gondii is a protozoan parasite which can infect
all warm blooded animals.
Cats become infected by ingesting smaller mammals (mice, rats) or raw
meat containing tissue cysts. Kittens can also be infected via passage
of the parasite across the placenta and breast milk of the queen.
Most
cats have been infected with T.gondii by the time they are acquired by
their owners. Oocysts, the infective form of the parasite, are shed in
the feces of cats. After 1-5 days of exposure to air and moisture, the
oocyst becomes infective and can remain stable in the environment for
months.
After ingestion of oocysts, the parasite forms cysts
within the muscle tissues of the host. These tissue cysts can persist
for life. The robust immune response of a healthy host prevents
replication of the parasite and clinical disease does not occur.
Humans and cats experience clinical illness when reactivation of the parasite occurs due to immune suppression of the host.
Clinical
disease in cats can consist of anorexia, lethargy, fever, liver
disease, or central nervous system disease. Disease in immunosuppressed
humans results in heart disease, liver disease, or central nervous
system disease. Infection of a woman during pregnancy can result in
birth defects or spontaneous abortion.
Attention to routine hygiene measures including hand washing after gardening, washing fruits and vegetables, and fully cooking meats prevents human infection.
Because
oocysts shed in cat feces are not immediately infective, daily cleaning
of litter boxes reduces the potential for human exposure. Infection in
cats is minimized by keeping cats indoors and preventing predatory
behavior.
Leptospirosis
is a bacterial disease which can infect most mammals. The frequency of
disease varies in different geographic areas, and different animal
species manifest different susceptibilities to disease. Cows, pigs, and
numerous non-domestic animals such as rats, raccoons, and skunks, become
infected and shed the organism in their urine without experiencing
clinical illness.
Unlike dogs, cats seem to be fairly resistant
to infection. Exposure of dogs to contaminated water and soil is a more
common route of infection than direct contact with an infected animal.
The same is true of human infection.
Leptospires penetrate wet or
abraded skin or the mucous membranes of the mouth and nose. The
organisms replicate in many tissues (kidney ,liver, spleen ,central
nervous system); damage to these tissues is variable. Infective
organisms can be shed in urine even after active disease has resolved.
We
recommend annual vaccination of dogs against Leptospirosis. By
decreasing susceptibility to infection of our canine companions, we hope
to decrease environmental contamination and thereby decrease the
incidence of canine and human disease.
Finally, we highly recommended vaccination of all dogs and cats against Rabies.
Rabies is a viral disease which can infect all warm blooded animals.
The Rabies virus is shed in saliva of the infected animal. The organism
is introduced to the susceptible animal via bite or scratch wounds.
The
virus replicates in nervous tissue and travels along nerve axons to the
central nervous system. Early clinical signs of disease consist of
apprehension, anxiety, irritability and fever. As disease progresses,
weakness, incoordination, vicious behavior and seizures may occur. Signs
in infected people are similar to those in cats and dogs.
Once clinical signs occur, the disease is fatal.
Reducing
human infection has centered around the vaccination of domestic dogs.
Because dogs live in intimate contact with people,
dogs have been and continue to be a major source of human infection.
Elimination of feral and un-owned dogs has been attempted in many
locales and has not been effective in controlling human infection.
Similarly,
eliminating wildlife populations known to be infected with Rabies has
not been feasible due to logistics and expense. Vaccination of domestic
dogs continues to be the focus of Rabies control programs around the
world.
In King County, it is now a legal requirement to vaccinate cats as well as dogs.
The wildlife source of Rabies in this area is the bat. Due to their
predatory behavior, cats are more likely to come into contact with bats
than are dogs, hence the recommendation for vaccination of cats.
We hope that this information is useful to you –please ask us any questions that arise!
Dr. Ann Whereat earned her degree from the University of Pennsylvania. She also received a B.A. in Biology from Lawrence University in Appleton, Wisconsin.
She has a veterinary interest in internal medicine and the human-animal bond.
Outside
the office, Dr. Whereat has one pet – a Great Swiss Mountain dog – and
likes to spend time with her husband and three daughters.
Seattle Veterinary Associates
was founded in 1971 by Dr. Sanford Olson, Dr. Donald Canfield, and Dr.
Stephen Jones. In 1971, the original practice opened its doors at the
current location of Queen Anne Animal Clinic. Coupled with our
considerate expansion and the advancement of our medical capabilities at
all our hospitals, we are proud to be providing the highest quality
veterinary care to pets and their families. SVA is comprised of four
locations: Queen Anne Animal Clinic, Green Lake Animal Hospital, Ravenna
Animal Hospital, and Northwest Veterinary Hospital.
