William C. Campbell

The in vivo and in vitro analysis of immunity to Trichinella spiralis in mice and rats.

Wistar-Furth strain male rats and CFW strain male mice were immunized against Trichinella spiralis using an antigenic fraction derived from a cell-free homogenate of mature muscle larvae. In rats, animals immunized with 250 mug of antigen harboured significantly fewer (135000) muscle larvae 30 days after oral challenge than controls (231000). Further 7-day-old adult worms derived from immunized rats shed 48% fewer (P less than 0.001) newborn larvae over a 24h period in vitro than adult worms from non-immunized animals. Mice were injected with either 10 or 100 mug of antigen. In comparison with non-immunized controls, mice immunized with 100 mug of antigen harboured significatnly fewer adult worms at days 7 and 9 after oral challenge infection, while female worms recovered from immune mice on days 6-10 after challenge shed fewer newborn larvae in vitro. Finally, mice immunized with 100 mjg of antigen harboured significantly fewer (10391) muscle larvae at 30 days after challenge than did controls (47750). Immunization of mice with 10 mug of antigen did not induce a statistically significant reduction in adult worms at either day 7 or 9 after challenge (P less than 0.5). However, adult female worms from mice receiving 10 mug of antigen still shed fewer larvae than did adults from control mice (P less than 0.05). Mice immunized with 10 mug of antigen harboured significantly fewer (13700) recoverable muscle larvae than did controls at 30 days after challenge (39000).

Use of Ivermectin in Dogs and Cats

This is a product for the prevention of heartworm disease in dogs. It is for use by, or on the order of, a licensed veterinarian, and consists of color-coded packages of white, hard tablets containing ivermectin in the amount of 65 μg (blue code, for dogs weighing up to 25 lb), 136 μg (green code, for dogs weighing 26 to 50 lb), or 272 μg (brown code, for dogs weighing 51 to 100 lb). When administered according to this schedule, the tablets provide a minimum ivermectin dosage of 6 μg/kg.

Epidemiology I Modes of Transmission

Trichinosis is a zoonosis, a disease of nonhuman animals transmissible to man. Because of the direct life cycle of Trichinella, and the parasite’s lack of host specificity and wide geographic distribution, there are many opportunities for interspecific transmission. As more of these transmission possibilities have been recognized, the epidemiological concept of trichinosis has been modified, and what had appeared to be a simple epidemiological pattern has tended to give way to a picture of considerable complexity (Kozar, 1962; Madsen, 1976; Steele and Schultz, 1978; Stoimenov and Gradinarski, 1981; Pawlowski, 1981). The situation has been aggravated in recent years by the discovery of regional variants of the parasite having greater or lesser infectivity for synanthropic animals (e.g., rats, mice, swine) as compared to their infectivity for feral animals. These interrelationships have been analyzed recently by Pawlowski (1981) and Dick (Chapter 2).

Use of Ivermectin in Horses

This is a paste, for oral use, containing 1.87% w/w ivermectin. In the United States, it is available in a prefilled syringe, calibrated so that each increment represents the amount of drug needed for 250 lb (114 kg) of body weight at the rate of 200 μg/kg. Each syringe contains enough paste to treat one mature horse. The syringe sold in international markets is calibrated to deliver the amount of drug needed for 100 kg (220 lb) of body weight at 200 μg/kg.

Trematode Infections of Man

A consideration of the chemotherapy of trematode infections of man will invariably be unevenly distributed with respect to the parasites involved. The great preponderance of attention must be devoted to the blood flukes or schistosomes, because of their great medical importance and because so much is known about their treatment. The remaining flukes, having various degrees of medical importance and having a lesser body of therapeutic lore, can be covered more briefly.

Insect Infestations of Man

The field of medical entomology properly includes many insects that attack man directly but that are not parasitic in the conventional sense. Some inject poisons; others, coming closer to a parasitic way of life, feed on man with various degrees of exclusivity but do not dwell for extended periods in or on his body. Prime examples of the latter are mosquitoes, bedbugs, and fleas. Reactions to such stinging or biting insects and the diseases they transmit may require treatment, and the premises they inhabit may require treatment, but infection of the human body is not involved. They are controlled by environmental measures rather than by chemotherapy, and so generate a need for pesticides and exterminators rather than drugs and physicians; they are not considered herein. By contrast, certain fly larvae are truly parasitic, causing infections that may require treatment; they are considered briefly, even though treatment is usually not chemical. The lice, although not so deeply embedded in host tissue, have a prolonged and intimate contact with man; measures for the clinical management of these insects, and a few others, are also considered. While this review is thus limited to insect-man associations that might reasonably be described as infection, the term infestation is generally used in deference to convention.

Synopsis of Morphology

A synopsis of the general morphology of Trichinella spiralis is presented herein. The material is designed to provide a concise source of information on the anatomical features referred to in the various chapters of this book. This summary is intended to complement those chapters and thus make possible a comprehensive understanding of the species.