Expert recommendations on feline parasite control

Despite the increasing popularity of cats as pets, little attention is given to the importance of internal parasites as disease agents in cats and as potential zoonotic agents in people. Also, increasing evidence suggests that cats harbor common internal parasites more frequently than previously thought (Table 1).1-4

Dr. Byron L. Blagburn

The perception that cats are infrequently infected with internal parasites probably results from less frequent fecal examinations performed on cats and lower parasite burdens in adult cats. Lower parasite burdens necessitate the use of more sensitive fecal examination procedures, such as centrifugal fecal flotation.Use of other techniques, such as simple flotation, usually results in lower parasite recovery rates.Recent recommendations by the Centers for Disease Control and Prevention (CDC) and the Companion Animal Parasite Council (CAPC) strive to increase pet-owner compliance in parasite control and decrease the likelihood of human exposure to potentially zoonotic parasites. In this article, I will discuss some of the key internal parasites found in cats and summarize the expert CAPC recommendations for controlling them.

Key parasites

Cats can host numerous internal parasites, but heartworms, roundworms, and hookworms are among the more important.

Table 1. Prevalences of Selected Feline Internal Parasites Reported in Recent U.S. Surveys*

Serologic studies indicate that cats' exposure to heartworm infected mosquitoes is common in many regions of the United States.5 Although most infected cats are asymptomatic, it's impossible to predict when-and under what conditions-asymptomatic cats will develop clinical heartworm disease.

Table 2. Selected Broad-Spectrum Feline Internal Parasiticides

Symptomatic cats present with respiratory signs such as coughing or dyspnea, or intermittent vomiting not associated with eating. Respiratory signs are similar to those observed with feline asthma. A small percentage of cats exhibit acute respiratory distress and may die suddenly. This peracute presentation also mimics signs of feline asthma or cardiomyopathy involving dyspnea. Many of these cats are clinically normal before the acute heartworm-induced event. Some affected cats also exhibit weight loss or diarrhea without respiratory signs. Problems associated with the diagnosis and treatment of feline heartworm disease emphasize the need to prevent infection (Table 2), especially in high-prevalence areas.

Table 3. Important Characteristics of Toxocara cati

The importance of Toxocara cati infections is often overlooked or underestimated (Table 3).6

Surveys indicate that round-worms are the most common internal parasite in cats and, possibly, the most important (Table 1). Contrary to the beliefs of many, these surveys also indicate that cats may harbor roundworms throughout their lives, which can result in significant environmental contamination (Figures 1 & 2).

Figure 1. Anterior end ofToxocara cati. The prominent cu-ticular inflations (cervical alae) differentiate T. cati from Toxocara canis and Toxascaris leonina. Re-cent publications suggest that the zoonotic impor-tance of T. cati is underestimated.6

The high prevalence of roundworms in cats results from the multiple ways in which cats may become infected (e.g., embryonated eggs, paratenic hosts, such as rats and mice, and transmammary transmission) and the long life of embryonated eggs in the environment (Figure 3). Clinical signs of feline roundworm infections may include an enlarged abdomen, failure to thrive, vomiting, and diarrhea.

Toxocara cati may also cause diseases in people who accidentally ingest embryonated eggs from the environment. The diseases in people are known as larva migrans. Disease can result from larval migration in the liver, lungs, kidney, or brain (visceral larva migrans), or migration in the posterior chamber of the eye (ocular larva migrans), resulting in granulomatous retinitis. Ocular disease can result in retinal detachment, loss of vision, and, in severe cases, blindness. Research in laboratory animals indicates that ocular damage caused by T. cati may be as severe as the damage caused by T. canis.7 Because of the prevalence of T. cati infection in cats and the potential for T. cati infections in people, attention should be given to effective internal parasite control (Table 2).

Figure 2. Eggs of Toxocara cati and the smaller oocysts of Isospora (Cys-toisospora felis). Sandboxes and soil can contain large numbers of these common feline parasites.

The prevalence of hookworm (Ancylostoma tubaeforme) infections in cats is exceeded only by roundworms (Table 1). Cats acquire A. tubaeforme infections by skin penetration or ingestion of infective larvae, or from transport hosts such as rats and mice. Apparently, neither transplacental nor transmammary transmission of hookworms occurs in cats. Results of experimental infections suggest that hookworm infections in cats can cause weight loss and anemia.8 Interestingly, clinical disease and death have resulted from infection rates of only 100 worms.9 Given the potential for hookworm-induced disease in cats and the availability of effective products (Table 2), this parasite should be a target for feline internal parasite control.

Figure 3. Embryonated egg of Toxocara cati. Ingestion of these eggs from sandboxes and contaminated soil can cause visceral and ocular larva migrans in people.

Recommendations for parasite control in cats

Recommendations for successful feline parasite control should be based on the biology and behavior of feline parasites, control of primary parasitic disease in cats, prevention of zoonotic disease in people, and the likelihood of pet owner compliance. Several organizations have established guidelines for controlling feline parasites and other zoonotic agents, including the CDC Guidelines for Veterinarians: Prevention of Zoonotic Transmission of Ascarids and Hookworms of Dogs and Cats; the American Association of Feline Practitioners 2003 Report on Feline Zoonoses; and the CAPC Guidelines for Controlling Internal and External Parasites in U.S. Dogs and Cats. All are similar in their recommendations.

Table 4. Summary of CAPC Guidelines for Managing Feline Internal and External Parasites

The CAPC is an independent council of U.S. veterinary, governmental, and association leaders brought together to create guidelines for optimal control of internal and external parasites. The CAPC recommendations address all facets of feline parasite control and are in agreement with the recommendations provided by the other organizations (Table 4). The CAPC guidelines are based on the concept that awareness of heartworms and other parasites, such as fleas, can increase compliant use of available broad-spectrum agents. Consequently, the CAPC recommends administering year-round heartworm prevention products with additional broadspectrum activity against roundworms, hookworms, or other parasites (Table 4). This strategy, combined with early aggressive control of feline roundworms and hookworms in 3- to 9-week-old kittens, can eliminate the risk of heartworm, roundworm, and hookworm disease in cats and larva migrans in people.

Table 5. CAPC Feline Heartworm Testing Recommendations

The CAPC guidelines also contain recommendations for heartworm testing in cats at risk of heartworm infection (Table 5). Testing recommendations are based on the clinical presentation of the cat as well as test performance and selection. Testing recommendations should be helpful because of the difficulty of diagnosing feline heartworm infections and because heartworms can cause unpredictable clinical signs. Complete and abbreviated versions of the CAPC guidelines and other information regarding canine and feline parasites and zoonoses can be obtained by accessing the CAPC Web site (www.capcvet.org).

CAPC Feline Heartworm Testing Recommendations*

References

1. Eiland, C.

et al

.: Prevalences of

Dirofilariaimmitis

,

Toxocara cati

,

Ancylostomatubaeforme

, and other endo- and ectoparasites in random source cats from East Central Alabama.

Proc. AAVP and ASP

, AAVP,ASP, Philadephia, Pa., 2004 (in press).

2. Carleton, R. et al.: Prevalence of Dirofilaria immitis and gastrointestinal helminthes in cats euthanized at animal control agencies in northwest Georgia. Vet. Parasitol. 1190:319-326; 2004.

3. Nolan, T.J.; Smith, G.: Time series analysis of the prevalence of endoparasitic infections in cats and dogs presented to a veterinary teaching hospital. Vet. Parasitol. 59: 87-96; 1995.

4. Spain, C.V. et al.: Prevalence of enteric zoonotic agents in cats less than 1 year old in Central New York State. J. Vet. Intern.Med.15:33-38; 2001.

5. Miller, M.W. et al.: Prevalence of exposure to Dirofilaria immitis in cats in multiple Changes in blood values and worm burden in relation to single infections of varying sizes. Z. Parasitenkunde 64 (2):149-155; 1981.9. Rhode, K.: Vergleichende undersuchungen uber die hakenwurmer des hunde un der kataze un betrachtungen uber ihre phylogenie. Z. Tropenmed. Parasitol. 10:402-426; 1959. areas of the United States. Proc. American Heartworm Society symposium, American Heartworm Society, Batavia, Ill., 1998; pp161-166.

6. Fisher, M.: Toxocara cati: An underestimated zoonotic agent. Trends Parasitol. 19: 167-170; 2003.

7. Akao, N. et al.: Ocular larva migrans caused by Toxocara cati in Mongolian gerbils and a comparison of ophthalmologic findings with those produced by T. canis. J. Parasitol.86 (5):1133-1135; 2000.

8. Onwuliri, C.O. et al.: Experimental Ancylostoma tubaeforme infection of cats:

Dr. Byron L. Blagburn is professor of parasitology in the Department of Pathobiology at Auburn University's College of Veterinary Medicine. He received his master of science degree in parasitology from Andrews University and his doctor of philosophy degree in parasitology from the University of Illinois. Dr. Blagburn is the recipient of numerous grants, and he received the Beecham Award for ResearchExcellence in 1987.