Why Parasite Control is Important for All Cats
World Small Animal Veterinary Association World Congress Proceedings, 2011
Michael R. Lappin, DVM, PhD, DACVIM
Director, Center for Companion Animal Studies, Colorado State University, Fort Collins, CO, USA

Parasitic diseases are extremely common in cats. Overall, the most common are those that involve the gastrointestinal system and the skin. Some parasites like Dirofilaria immitis can result in significant clinical illness, including death, in infected cats. Many internal parasites and ectoparasites also cause illness in people and so are zoonotic. Ancylostoma tubaeforme (cutaneous larva migrans) and Toxocara cati (visceral and ocular larva migrans) are classic examples. Infections with these nematodes are extremely common in many parts of the USA and the organisms are shed by both healthy and ill cats as well as both kittens and adults. For example, in one of my studies of cats in north-central Colorado, which is a hot, dry state in the summer and a cold state in the winter, 3.8% of adult cats were shedding T. cati into the human environment. Human exposure to roundworms is still very common. For example, sera collected between 1988 and 1994 from 30,930 people ≥ 6 years of age in the United States had an age adjusted Toxocara seroprevalence rate of 13.9%.

Some ectoparasites, like Ctenocephalides felis, also serve as vectors for other infectious agents that can result in clinical illness in the cat and for some agents, the owner. For example, many C. felis are infected by Mycoplasma haemofelis, 'Candidatus M. haemominutum,' and 'Candidatus M. turicensis,' common causes of hemolytic anemia in cats (previously called Haemobartonella felis; now collectively known as hemoplasmas). Bartonella henselae, the most common cause of cat scratch disease in people, is found in C. felis feces on the skin of infected cats and fleas are responsible for transmission of B. henselae between cats. Flea-associated illnesses are important in almost all of the USA.

Parasitic diseases occur in both indoors and outdoors cats. For example, mosquitoes capable of transmitting D. immitis commonly enter the household. Transport hosts like flies, cockroaches, and rodents are known to harbor T. cati and other feline parasitic diseases. Transport hosts are commonly found within the home. In some households, while the cats are exclusively indoors, the pet dogs go indoors and outdoors and can bring shared parasites like C. felis into the house, resulting in an infestation of the cats. Based on these examples, it is my personal opinion that parasite control for the most common agents should be maintained year round in most cats of most states, regardless of housing status. This opinion was shared by my co-panelists on the American Association of Feline Practitioners Feline Zoonoses Guidelines (www.aafponline.org) and the Bartonella Panel Report.

In my opinion, the following are the most important points supporting use of feline parasite control products:

 Because T. cati occurs in all of the USA and shed by adult cats as well as kittens, strategic deworming is recommended for most cats.

 Because C. felis-associated illnesses are common in cats in most of the USA, flea control is recommended for most cats.

 While D. immitis infection varies widely within the USA and around the world, dirofilariasis can be a fatal disease. In addition, heartworm associated respiratory disease may be a common cause of bronchitis. Because current preventatives are almost 100% safe, I believe heartworm prevention is indicated for most cats living in endemic areas.

 Transport hosts or vectors for many common feline parasites can enter the home and so parasite control is for indoor cats as well as those that are allowed outdoors.

There are multiple safe and effective products available to achieve these goals. Each clinician should determine the most appropriate product or products to be used based on geographical location and the individual cat and its owner. However, products that achieve more than one goal like selamectin are easiest for the owner.

The following websites give great information concerning feline infectious and parasitic diseases:






Feline bartonellosis is one of the most important emerging feline parasitic diseases. Cats have proven by culture or DNA amplification to be infected by Bartonella henselae, B. clarridgeiae, B. koehlerae, B. quintana and B. bovis. Cats are the main reservoir hosts for B. henselae and B. clarridgeiae and are likely to be the reservoir for B. koehlerae. Bartonella henselae is the most common cause of Cat Scratch Disease as well as bacillary angiomatosis, and peliosis hepatis, common disorders in humans with AIDS. Please see the proceedings of Dr. Breitschwerdt for a discussion of the human health risks. These proceedings will emphasize Bartonella associated illnesses in cats.

The organisms are transmitted between cats by Ctenocephalides felis and so prevalence is greatest in cats from regions where fleas are common. In areas with heavy flea infestation, bacteremia rates can be > 50% and seroprevalence rates can be > 90%. Most cats with serological evidence of exposure to a Bartonella spp., a Bartonella spp. cultured from blood, or microbial DNA amplified from blood by PCR assay are clinically normal. However, Bartonella spp. infection of cats has also been associated directly or indirectly with a variety of clinical manifestations like fever, lethargy, lymphadenopathy, uveitis, hyperglobulinemia, endocarditis, myocarditis, gingivitis, and neurological diseases. How often cats become ill from Bartonella spp. infections is unknown and more information is needed.

Blood culture, PCR assay on blood, and serologic testing can be used to assess individual cats for Bartonella infection. Bacteremia can be intermittent and false-negative culture or PCR results can occur. While serologic testing can be used to determine whether an individual cat has been exposed, both seropositive and seronegative cats can be bacteremic, limiting the diagnostic utility of serologic testing. In our laboratory, we offer a combination of Bartonella spp. serology and PCR which I believe gives the best combined positive predictive values.

If the results of Bartonella tests are negative in a clinically ill cat, the organism is not likely the cause of the clinical syndrome unless the infection was peracute and serological testing was used as the diagnostic test. If the results of Bartonella tests are positive, the agent remains on the differential list, but other causes of the clinical syndrome must also be excluded.

In experimental studies, administration of doxycycline, tetracycline, erythromycin, amoxicillin-clavulanate, or enrofloxacin can limit bacteremia but does not cure infection in all cats. To date, use of antibiotics in healthy cats has not been shown to lessen the risk of cat scratch disease. Thus in the United States, treatment is generally recommended for clinically ill cats. If clinical bartonellosis is suspected, the AAFP Panel Report recommends doxycycline at 10 mg/kg, PO, daily for 7 days as the initial therapeutic trial. In the United States, I have my doxycycline prescriptions formulated into a flavored suspension to avoid esophageal strictures. If a positive response is achieved, continue treatment for 2 weeks past clinical resolution of disease or for a minimum of 28 days. If a poor response is achieved by day 7 or doxycycline is not tolerated and I still believe bartonellosis is a valid differential diagnosis, I consider fluoroquinolones as second choices. Bartonella henselae rapidly becomes resistant to azithromycin in vitro and so should not be used for feline bartonellosis. In my experience, Bartonella spp. positive cats that have failed to respond after administration of 2 different drugs with presumed anti-Bartonella activity generally have another cause of the clinical syndrome. There is no clinical utility in rechecking Bartonella serological test results in cats.

Bartonella henselae survives in flea feces for days after being passed by infected C. felis. We recently showed that the administration of imidocloprid to cats monthly could block transmission of B. henselae which is the most important prevention technique.


1.  Biswas S, Maggi RG, Papich MG, Keil D, Breitschwerdt EB. Comparative activity of pradofloxacin, enrofloxacin, and azithromycin against Bartonella henselae isolates collected from cats and a human. J Clin Microbiol 2010;48:617–618.

2.  Bradbury CA, Lappin MR. Evaluation of topical application of 10% imidacloprid-1% moxidectin to prevent Bartonella henselae transmission from cat fleas. J Am Vet Med Assoc 2010;236:869–873.

3.  Brunt J, Guptill L, Kordick DL, Kudrak S, Lappin MR. Association of Feline Practitioners 2006 Panel report on diagnosis, treatment, and prevention of Bartonella spp. infections. J Feline Med Surg 2006;8:213–226.

4.  Centers for Disease Control and Prevention (CDC). Outbreak of cutaneous larva migrans at a children's camp - Miami, Florida, 2006. MMWR Morb Mortal Wkly Rep 2007;56:1285–1287.

5.  Lappin MR, Breitschwerdt E, Brewer M, Hawley J, Hegarty B. Prevalence of Bartonella species DNA in the blood of cats with and without fever. J Feline Med Surg 2009;11:141–148.

6.  Won KY, Kruszon-Moran D, Schantz PM, Jones JL. National seroprevalence and risk factors for zoonotic Toxocara spp. infection. Am J Trop Med Hyg 2008 Oct;79(4):552–557.


Speaker Information
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Michael R. Lappin, DVM, PhD, DACVIM
College of Veterinary Medicine and Biomedical Sciences
Colorado State University
Fort Collins, CO, USA

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