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.
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.