Zoonotic diseases in cats can be easily avoided with proper prevention, care

Zoonotic diseases in cats can be easily avoided with proper prevention, care

May 01, 2003

Table 1: Selected broad-spectrum anthelmintics for use in cats
Estimates indicate there are approximately 73 million owned cats in the United States with 30 percent of American households having at least one. Cats are host to a variety of parasites, including several that are zoonotic. Unfortunately, many owners are not aware of these diseases and the simple steps that can be taken to avoid them. This article focuses on the common zoonotic parasites of cats and their importance to the health of the cat and the owner.

Hookworms Hookworms in cats are represented by two species – Ancylostoma tubaeforme and Ancylostoma braziliense. Their prevalence among cats in the United States is virtually unknown. However, we do know their geographic distribution differs within the country. Ancylostoma braziliense is limited to tropical and subtropical regions of the southeastern United States while A. tubaeforme is more generally distributed. The host range for these two parasites also differs in that A. tubaeforme is primarily found in cats while A. braziliense can infect both cats and dogs.

Photo 1: Unembryonated hookworm egg. This could be either Ancylostoma tubaeforme or Ancylostoma braziliense.
The life cycle of these two parasites is similar and may be direct or indirect with a paratenic host. Adult parasites live in the anterior portion of the small intestine. Life expectancy of A. tubaeforme has been reported to be 18 months to two years while that for A. braziliense is shorter lasting four to eight months. A single adult female A. braziliense can produce 200 to 6,000 eggs per day although the number declines as the worm ages. Eggs of both species are passed with the feces of the host (Photo 1). First-stage larvae develop within the egg, hatch, and molt to become second-stage larvae which subsequently molt to become infective third-stage larvae (L3). Development to the infective L3 can occur in as little as one week. Cats can then be infected by one of several routes. Larvae may penetrate the skin and enter the circulatory system where they are carried to the lungs. Larvae then enter the alveoli, migrate up the trachea and are swallowed, maturing to the adult stage in the gastrointestinal tract. The prepatent period is 13-27 days.

Cats can also become infected by ingesting infective L3 or rodent paratenic hosts. Under these circumstances, the larvae penetrate the wall of the stomach or proximal small intestine but do not undergo extraintestinal migration prior to returning to the gut lumen to mature.

Clinical presentation for these two hookworms differ. The main clinical signs associated with A. tubaeforme infections are weight loss and a regenerative anemia, which goes along with the fact hookworms are blood-feeding parasites. Death can also occur if the rate of larval acquisition is high. Conversely, A. braziliense is less pathogenic with very little hemorrhage at the sites where adults attach. Clinical disease is usually not encounterd.

Photo 2: Cutaneous larval migrans.
Several products are available for the treatment of hookworm infections in cats (Table 1). Preventing infections by reducing predation by cats is desirable, but often difficult to achieve because of the strong instinctive nature of this behavior. Periodic anthelmintic treatment is the most effective means of control in adult cats.

While A. tubaeforme is more important to the health of the cat, A. braziliense is more important as a cause of cutaneous larval migrans (CLM) in humans. On contact with unprotected skin, L3 penetrate the epidermis. However, the larvae cannot penetrate the basement membrane and are, therefore, confined to the lower epidermis where they migrate aimlessly. As they migrate, the larvae release proteolytic enzymes which leads to an intense inflammatory reaction. Within one to two weeks, the characteristic reddened, serpiginous, and intensely pruritic skin eruptions are visible (Photo 2). Because the inflammatory reaction is not directed against the larvae themselves, the skin eruption tends to be located some distance from where the larvae actually are. Even though CLM is self-limiting, the intense pruritis usually necessitates some treatment to lower the risk of secondary bacterial infections.

Roundworms Roundworms in cats are also represented by two species - Toxascaris leonina and Toxocara cati. Toxascaris leonina is not associated with clinical signs in cats and is rarely zoonotic. Conversely, T. cati is not only zoonotic but is also considered to be the most common and the most important intestinal nematode parasite of cats. Adult T. cati live in the small intestine of the host, producing eggs that are passed with the feces (Photo 3). They are extremely prolific, producing as many as 24,000 eggs per day.

Photo 3: Unembryonated egg of Toxocara cati.
The life cycle of T. cati is direct or indirect with a paratenic host. Once eggs are passed in the feces, larval development and production of infective L3 occurs. This takes place entirely within the egg and can be complete in three to four weeks. Eggs are extremely resistant to adverse environmental conditions and can remain viable in the soil for months to years. Cats can then be infected by one of several routes including ingestion of larvated eggs. Once eaten, the egg hatches and the larvae undergo a hepatic-pulmonary migration prior to returning to the small intestine and maturing. The prepatent period for this route is about two months.

Cats can also be infected through ingestion of rodent paratenic hosts or by transmammary transmission. Larvae acquired by either of these routes do not migrate beyond the intestinal wall and the prepatent period for these infections is about three weeks. Of the three possible routes of infection, transmammary transmission is considered by many to be the most important although ingestion of paratenic hosts may be a primary means by which infections are maintained in cats that are allowed to hunt.