Veterinary entomology is the study of insects and insect-related problems that affect domestic animals, particularly livestock and cattle, and companion animals, especially dogs and cats. Veterinary entomology also investigates insect associated problems that affect wildlife and captive animals. Earlier in this module, we discussed how arthropod biting behavior can cause illness by causing animals to suffer from appetite loss and weakness due to stress. In addition to the suffering of the animal, this can also result in economically important losses in products quantity and quality. The treatment costs and reduced yield can result in severe economic burden to the producer. Feeding by some species of mites can cause persistent inflammation of the skin of their animal hosts. As mites burrow into and feed in hair follicles or skin tissue, they cause severe itching and skin lesions. Long-term infestations of certain mite species can cause crusty formations on the skin, and hair loss from excessive scratching in response to mite activity. This disease is known as mange. Mange is a common and highly contagious skin disease in animals which spreads by contact. Livestock afflicted with mange must be quarantined to prevent further dissemination of the mites to other members of the herd. Treatments can be costly, especially if the disease is widespread. Another unfortunate aspect of mange is that the disease can potentially be passed to humans depending on the species of mite. Although a dermal infection of mites may sound distressing, infestations by species which do not normally use human hosts typically results only in mild symptoms, which resolve themselves without significant intervention. Aside from causing disease directly through host feeding, some biting arthropods also transmit disease causing organisms, which include filarial nematodes, viruses, and bacteria that can weaken or kill the animal hosts. Let's first look at an example of an arthropod transmitted filarial disease, the dog heartworm. Dog heartworm is a disease transmitted by the bite of an infected mosquito that affects, you guessed it, canines. The mosquito acquires microscopic nematode larvae as it feeds on an infected dog. The worms are then transmitted to another host when the mosquito feeds again. As the nematode larvae mature, they become larger and begin to accumulate in the heart, lungs, and blood vessels. Large numbers of worms within a dog can cause blockages within the circulatory system which can lead to exhaustion, abnormal lung functions, and eventually death. Treatment for an established dog heartworm infection can cost between 400 and 1000 US dollars. Although preventative medications are available, the treatment kills the worms within the dogs, but the dogs remain vulnerable, because the bodies of dead worms can still cause blockages or inflammation until they are removed by the immune system. Unfortunately, dogs do not develop immunity against the heartworm after infection. Recurring infections are possible, and the use of preventative medications are recommended by veterinary agencies. On rare occasions, these nematodes can infect humans. Humans are dead end hosts for these parasites. Meaning that the parasite cannot continue the disease cycle or be transmitted from an infected human. It rarely causes problems in infected humans, although lesions created by heart worms can look like more serious conditions in X-rays such as cancer, which can lead to invasive biopsies. The most important arthropod-borne diseases in animals are the ones that cause substantial economic losses in the livestock industry. We will look at two examples in this lesson, the viral disease, Bluetongue along with Nagana, which is caused by a parasitic protozoan. Bluetongue disease is caused by RNA viruses called the Bluetongue viruses, which are transmitted by biting midges from the genus Culicoides. It affects domestic and wild ruminants such as cattle, goats, buffalo, deer, and elk. However, sheep are most severely affected and often develop swelling and cyanation of the tongue, hence the name Bluetongue disease. The virus can cause lesions, internal hemorrhaging, and fluid buildup in the lungs. Many infected animals die from respiratory problems. Additionally, wool growth is disrupted in sheep that survive infection. Infection in pregnant females can result in underweight or deformed young, as well as stillbirths and miscarriages. These deaths along with weight loss and other impacts cause substantial economic loss to livestock owners. Mandatory testing and vaccination for the disease costs the industry millions of dollars annually in Europe alone. The use of vaccines and changes to farming practices such as keeping animals indoors during times of high major activity from dusk until dawn, can be used to reduce infection rates. Nagana or animal trypanosomiasis is caused by several species of Trypanosoma parasites transmitted by tsetse flies. Some breeds of cattle from affected regions are tolerant to the disease and research efforts have led to increased use of trypanotolerant cattle which can be reared for food even in areas with large tsetse fly populations. The disease causing organism infects the red blood cells of cattle and causes fever, weakness, and lethargy. This in turn leads to weight loss and anemia, and infected animals can die from secondary infections. Due to the high mortality Nagana causes in livestock, this disease is considered a major barrier to commercial animal production across much of Africa. Locals living in regions where the disease is endemic lack a steady source of animal protein for human consumption. Infected and weakened animals are also unusable as working animals in agriculture. As local officials struggle to manage this disease, livestock production in affected regions remains stagnated. Research efforts have led to the use of trypanotolerant cattle, which can be reared for food even in areas with large tsetse fly populations. With this, we have come to the end of our discussion on examples of insect-borne human and animal diseases. In the next video, we will switch gears slightly and focus on examples of plant diseases that are vectored by insects.
