All Pets Veterinary Clinic
The importance of parasites and parasite control may or may not be obvious to many
people. Parasites can cause a variety of problems in animals ranging from mild to severe.
In some instances, parasites can even cause death. In addition to the illness that they
cause, parasites can transmit other diseases to the animals that they infect. For
example, ticks can transmit Lyme disease or Erlichia. However, one of the biggest
concerns of parasitism in animals is the potential for spread to humans. Many of the
parasites that infect animals can cause disease or illness in people as well.
The types of parasites can be divided into two main categories--external or ectoparasites
and internal or endoparasites. The remainder of this article will discuss the common
types of parasites that affect cats and dogs, the signs that they can cause, the methods
for diagnosis, and the drugs that are used to treat them.
The ectoparasites, or parasites that live on the dog or cat, are probably the most
common and most recognized of all parasites. Parasites within this category include
fleas, ticks, mites, and lice.
Fleas are probably the most common parasite of dogs and cats. In this area, fleas
have been increasing and they can be a year-round problem. Favorable weather conditions,
including warmer than average winters are probably to blame. Fleas typically cause one
or more of the 4 following problems: 1) mild to severe itching, scratching, biting, and
chewing, 2) flea saliva hypersensitivity or allergy and resulting skin problems, 3) the
transmission of tapeworms, and 4) anemia and possible death (most often in very young or
small animals). Fleas can be detected by direct examination of the animal. The presence
of adult fleas or flea dirt, or small black specks of dried flea feces, on the animal is
confirmatory. The presence of a flea allergy can be detected by a blood test.
Ticks, like fleas, have also been a big problem in this area. Over the last several
years, the tick season seems to have lengthened. This is presumably due to favorable
environmental conditions, mainly mild winters. Ticks can cause signs that range from
mild local irritation to severe anemia. In addition, ticks can transmit many other
diseases to animals and humans. These diseases include Lyme Disease, Rocky Mountain
Spotted Fever, and Erlichia, among others. Ticks can be detected by direct examination
of the animal.
Mites and lice are less commonly seen in dogs and cats than fleas and ticks but do occur.
The three main types of mites include sarcoptic mange, demodectic mange, and chyletiella.
Signs of mites and lice may or may not include itching, hair loss, dandruff or crusty
lesions, bleeding or oozing skin, etc. Some types of mites are transmissible to people.
However, animal lice IS NOT transmissible to people. Lice are species specific. This
means that dog lice lives only on dogs and human lice lives only on humans. (Thus, you
cannot blame the dog for giving your kids head lice!) Mites and lice can be detected
through skin scrapings and direct examination of the animal.
The endoparasites, or parasites that live within the dog or cat, are often less obvious
to owners but typically cause more severe disease than ectoparasites. The most common
parasites within this category include heartworms, roundworms, hookworms, whipworms, and
tapeworms. Other parasites that are not common within this area of the country include
liver flukes, kidney worms, and lung worms.
Heartworms are one of the most important endoparasites in this area. The number of
animals that we find with heartworms has been increasing over the past several years.
Heartworms are transmitted to dogs and cats through the bite of an infected mosquito.
Adult heartworms primarily live in the major blood vessels of the heart and lungs.
Immature heartworms circulate throughout the blood vessels in the rest of the body.
The signs of heartworm infection can be vague. It is not uncommon for an animal infected
with adult heartworms to exhibit no signs of illness until late in the course of disease.
Signs of heartworm can include coughing, difficulty breathing, panting, exercise
intolerance, decreased activity level, and sudden death. Heartworms can be easily
detected through a blood test.
Roundworms, hookworms, and whipworms are among the most common internal parasites.
These parasites live within the gastrointestinal (GI) tract of animals and can cause
diarrhea, anemia, loss of body condition, etc. Transmission of these parasites from
animal to animal can occur in several ways. The main means of transmission for all of
three of these parasites is fecal-oral contact. The eggs from the parasites are passed
within feces and gain entry into the next animal when the eggs are ingested. In addition,
some of these parasites, mainly roundworms, can be passed from mother to offspring (puppy
or kitten) through the milk or across the placenta. These parasites can be easily
detected through a fecal float.
Tapeworms are another example of a gastrointestinal (GI) parasite. Tapeworms can also
cause diarrhea, weight loss/poor body condition, etc. Tapeworms can be passed in two
main ways. First, fleas can carry and transmit tapeworms to the animals that they infect.
Second, tapeworms can be carried and transmitted by rodents and rabbits. Dogs and cats
that hunt and eat these animals tend to pick up tapeworms fairly readily. The fecal
float techniques used to detect roundworms, hookworms, and whipworms will often not
detect tapeworms. Diagnosis is often made by direct observation of tapeworm segments
in freshly passed feces or on the animal.
Over the years, the number and types of parasite treatments for small animals have
grown tremendously. There are two main approaches to parasite treatment--preventative
treatments and curative treatments. Preventative treatments are given on a regular
interval in an effort to keep animals from getting a large burden of parasites.
Curative treatments are given only in response to the positive identification of
parasites. As with most things, prevention is easier and better than treating a
problem once it is present. Many of the newer anti-parasite medications aim at preventing
a wide variety of parasites while many of the curative treatments only kill one or two
types of parasites. A complete discussion of all of the available parasite medications
is beyond the limitations of this article, thus only the newest, preventative, prescription
products will be discussed. These include Advantage, Frontline, Revolution, Heartgard,
Interceptor, Program, Sentinel, and Proheart.
Advantage and Frontline are monthly topicals that kill ectoparasites. Advantage
will kill adult fleas and flea larva and Frontline will kill adult fleas and ticks. A
new version of Frontline, called Frontline Plus, will soon be available. This product
will kill adult fleas, larva, and eggs.
Revolution is a monthly topical that will kill adult fleas, eggs, ear mites,
roundworms and hookworms in cats and adult fleas, eggs, ticks, ear mites, and sarcoptic
mange in dogs.
Program is an oral monthly that will kill flea eggs only. Program is also
available in a long lasting injectable form.
Heartgard, Interceptor, and Sentinel are oral monthly tablets that will kill a
variety of parasites. Heartgard will kill immature heartworms, roundworms, and hookworms.
Interceptor will kill immature heartworms, roundworms, hookworms, and whipworms. Sentinel
is the combination of Interceptor and Program and thus will kill immature heartworms,
roundworms, hookworms, whipworms, and flea eggs.
Proheart is the newest heartworm medication availalble for use in dogs. It is
an injection that is given twice a year. Proheart will kill immature heartworms and
The information provided is for educational purposes only and is not
intended to take the place of your regular veterinarian. Please do not hesitate
to contact your regular veterinarian if you have questions regarding your pet.
Karen Blakeley, DVM, MPH
14 December 2002