Experimental Toxocara canis Infections in Chickens and Pigeons

Abstract

Studies were made to determine whether chickens and pigeons could serve as paratenic hosts of Toxocara canis. It was found that both types of hosts harbored living infective-stage larvae for at least 142 days after inoculation. At this time, of the number of larvae inoculated, it was possible to recover approximately 30% from chickens and 18% from pigeons. Human infections with larvae of Toxocara canis are known to occur throughout the United States and in Mexico, Europe, Australia, the Philippines, and South Africa (Beaver, 1962). In the majority of cases, the infected individual is a 1to 3-year-old child who acquired the infection by ingesting infective eggs in contaminated soil (Beaver et al., 1952). In some cases, however, especially those in which the eye is invaded, the infected individual is an older child or young adult (Beaver, 1962). Although in such instances the invading larvae possibly have persisted elsewhere in the body since early childhood, it is also possible that they were acquired by eating raw or poorly cooked parts of infected meat animals. T. canis larvae persist for months or years in a wide range of mammalian laboratory hosts (Beaver, 1962), and it is presumed that they are transferred from animal to animal through paratenic hosts in nature (Sprent, 1954). It has been suspected that the eosinophilia observed in persons eating raw liver for the control of pernicious anemia was caused by infection with nematode larvae, possibly Toxocara, harbored in the liver (Beaver, 1956). Done et al. (1960) found that in the experimentally infected pig, many infective-stage Received for publication 21 August 1963. * Supported by grants EF-, EPD-14573, and AI04919 from the National Institutes of Health, U. S. Public Health Service. t Present address: Department of Veterinary Parasitology, Agricultural and Mechanical College of Texas, College Station. larvae of T. canis could be recovered from the liver, brain, lungs, and muscles more than 2 months after inoculation. In a similar study on T. canis in sheep and lambs, Schaeffler (1960) recovered the larvae from liver, muscle, and other tissues 3 months after inoculation. Studies on poultry have been brief and inconclusive. Sprent (1956) recovered six larvae of T. cati from the carcass of an experimentally infected chick at 10 days but none could be found in others at 15, 20, or 25 days. Beaver (1956) found that larvae of T. canis persisted for at least 3 months in the liver of chickens and pigeons. The present study was undertaken to get further information on the persistence and distribution of T. canis larvae in the tissues of chickens and pigeons. MATERIALS AND METHODS T. canis eggs obtained by sedimentation of feces from naturally infected dogs were incubated in 1% formalin at room temperature for 4 to 6 weeks before use. Estimated numbers of infective eggs were injected by pipette directly into the crop of young chickens and pigeons. Recovery of larvae was accomplished by two procedures: by one, the tissues were ground in saline with a Waring blendor and digested in 1% pepsin (pH 1.5) in saline (0.83%) at 37 C for 3 to 4 hr; suitable aliquots were then washed and concentrated by centrifugation in saline and the sediment was examined microscopically for larvae. By the other, tissues were chopped and finely minced with scissors and scalpel, placed in a Baermann apparatus in which the suspending medium was pepsin digest fluid, allowed to stand at 37 C for 3 to 4 hr, after which the sediment was collected and examined in the usual manner. This method, though