Routine Examinations Veterinarians initiate preventive measures by taking a medical history of each animal, preferably first examining them when they are several weeks old. The condition of the animal is assessed and basic diagnostic tests for parasites and infectious diseases such as distemper are administered and evaluated. If animals test positive, appropriate treatment is begun. For both cats and dogs, a heartworm test is crucial. When a mosquito that has bitten an infected animal bites another dog or cat, these spaghetti-like parasites are injected as larvae into the skin, then migrate to the bloodstream. Adult heartworms can grow as long as fourteen inches inside host animals' hearts, impeding their circulation and potentially causing death. Mosquito control and regular doses of heartworm medicine help prevent the spread of heartworms. Cats are also tested for feline leukemia virus, a fatal, contagious disease. Horses are given a Coggins test to detect equine infectious anemia. A series of vaccinations prevent diseases from occurring in young animals and are given as immunity boosters in mature animals. Some diseases can be combated with combination injections which combine vaccines for distemper, hepatitis, leptospirosis, parvovirus, and parainfluenza. Rabies vaccinations are required by law in many countries to prevent the disease spreading between animals and fromanimals to people. Veterinarians recommend parasite control through flea and tick repellents, many of which can be applied topically to the skin or swallowed in a pill, as well as nutritional diets to prevent many diseases from occurring. Some veterinarians offer other preventive measures in the forms of tattoos and implanted microchips to prove ownership in case animals are stolen or lost.
Successes in Restoring Endangered Species Several species in the United States-the California condor, the black-footed ferret, whooping cranes, and a bird called the Guam rail-have been saved from extinction because of the 1973 Endangered Species Act. The road to extinction has also been reversed for the brown pelican, found in the southeastern states, the American alligator, which had been hunted almost to death in Florida, and the perigrine falcon in the eastern states. Other species, however, such as the dusky seaside sparrow and the Palos Verdes butterfly, have totally disappeared. The spotted owl, found in parts of the rain forest in Oregon and Washington, has attracted a good deal of attention because of efforts to save it. The case of the owl points to the most difficult questions raised by the act: Which comes first, the welfare of the plant or animal or the economic needs of people? Each pair of spotted owls needs six to ten square miles of forest more than 250 years old in which to hunt and breed. The owls also need large hollow trees for nesting, plus large open fields in which to search for mice and other small animals.Asuitable ecosystem that meets all these needs is found only in parts of twelve national forests in the region. At the same time, loggers in the areas need jobs. The two interests, the lumber industry and environmentalists, collide, and it is left to the courts to determine which interest will prevail or whether a compromise can be arranged. Outside the United States, the future of endangered species appears muchgrimmer. Scientists at IUCN think several hundred thousand species will disappear by the end of the second decade of the twenty-first century. Many of these species have never even been identified or named. The most endangered habitats in the world are the tropical rain forests, which have been reduced by half, nearly 3.5 million square miles, during the twentieth century. About 43,000 square miles is destroyed each year, mainly to provide farms and cattle ranches. The most threatened large animal species in these forests are the large cats, including tigers, jaguars, and leopards; fifteen of the twentyfive species of cats that live in the forests are on the most endangered list. One solution to forest destruction has been the creation of large wildlife refuges. Several African nations have created one or more of these, but there are limits to the amount of land available for conservation efforts. Another solution is the establishment of more wildlife zoos. Several zoos have successful programs for saving species on the very edge of extinction. However, capacity is limited, and the very small numbers of animals in a zoo's herd create problems of interbreeding and the handingdownof recessive genes. For many species, it is too late to do very much, so scientists and biologists divide populations into three groups: those that can survive without help, those that would die whatever help was provided, and those species that might survive with help and would certainly die without it. Environmentalists focus their efforts on the plants and animals that fall into the third category. Resources are limited, however, and much work needs to be done, or extinctions will take place at a pace as yet unseen in the history of living things.
