Viral Infections

Rabies: Rabies is a disease that is cause by the rabies virus, which is a small, bullet-shaped RNA virus. Rabies is usually transmitted from one mammal to another when an infected animal bites an uninfected one, as the rabies virus is capable of dividing rapidly within the salivary glands of an infected animal. The rabies virus cannot penetrate skin by itself and the deposition of infected saliva on an animal's skin does not always mean that the animal will contract the disease. Once the virus enters an animal's body, it is usually deposited within muscle tissues, where it will rapidly multiply. Rabies viruses normally replicate in muscle or subepithelial cells. After the virus has replicated extensively within the muscle tissue, it will begin to infect the neurons in the animal's muscles or skin. Rabies viruses can bind to the acetylcholine receptor of neurons. The virus will then travel through the sensory or motor nerves to the animal's central nervous system, and will most likely then infect the animal's spinal column. The virus will then end up in the animal's brain, where it will leave inclusion bodies, called Negri bodies, in the neurons.
Initial symptoms of the disease include anxiety, irritability, depression and sensitivity to light and sound. As the disease progresses, hydrophobia (fear of water) will develop, as the animal will experience difficulties swallowing. Paralysis then occurs, which will be followed by coma, and then death.
In urban settings, dogs were once the main rabies vector. Now, thanks to pet vaccination programs, rabies has become rare in domestic animals in developed countries. Wild animals, especially raccoons, foxes, skunks, jackals, mongooses, squirrels, coyotes, badgers and bats are now the main transmitters of rabies. In North America, raccoons are the largest reservoir for the disease, and 98% of all cases of rabies are found in raccoons, skunks, bats or foxes. Rabies is extremely rare in North American wolves today. In the last few decades, only a handful of wolves have died from rabies, and most have been in Alaska, where wolves are common. In 1976, rabies was suspected of causing a decline in wolf numbers in northwest Alaska, although only one wolf from the area was actually found to have rabies. In 1977, rabies destroyed one wolf pack on the Brooks Mountain Range in Alaska, although the disease did not spread to other packs. In 1990, a rabies outbreak among red and arctic foxes in Alaska spread to wolves and caused 3 confirmed and 5 suspected wolf deaths. The disease only affected four wolf packs. Theberge et al. (1994), reported that rabies was responsible for 21% of the mortality among 29 radio collared wolves that died in Algonquin park from 1987-1992, although the rabies-caused mortality occurred in three different packs during a nine month period. In 1992, the Center of Disease Control reported that there were no cases of rabies in wolves during that year.
In the Asiatic region of Russia, rabies has occurred in wolves occasionally during the past three decades. In Kazakhstan, 17 out of 54 wolves examined as part of a study that spanned from 1972-1978 were found to be carriers of the rabies virus, and in 1980, ten peasants were attacked by a rabid wolf in the Voronezh region of Russia. In 1991, 11 people were bitten by a rabid wolf near L'vov.
Rabies continues to be rare in North American and European wolves. However, that was not the case during the middle ages. Rabies is thought to account for many of the numerous attacks on humans by wolves that occurred during that time period, and it is thought to account for much of the strange wolf behavior that was reported. Rabies was also common in North American wolves during the 1800s and the early part of this century, as many settlers and Natives reported encountering rabid wolves.

Canine Distemper: Canine distemper is a contagious viral disease that affects the skin, eye membranes, intestinal tract and sometimes the brain of the animals it attacks. Initial symptoms include fever, loss of appetite and a discharge from the animal's eyes or nose. Diarrhea then follows, which will usually cause dehydration. Seizures may follow, and if the disease progresses that far, the animal will most likely die. It usually occurs in young puppies, and is more likely to kill puppies than adults.
Distemper has been reported in captive wolves since 1904, although it is rather rare in wild wolves. A few outbreaks have occurred however. Carbyn (1982) found that distemper killed three 5-8 month old wolf pups in Riding Mountain National Park, Manitoba, and concluded that distemper was the second largest known mortality factor among the wolves in the park. In 1978 and 1980, two wolves were found to have died from distemper in Alaska.
Other than the two cases described above, distemper is not a major source of mortality in wild wolves. Many wild wolves do carry the disease (for instance, 48% of 71 wolves tested seropositive for distemper in northern Minnesota from 1977-1984) although distemper is rarely fatal to wolves, particularly the adults. It is possible that pups die from the disease occasionally, as the disease usually strikes puppies that are from 3 - 9 weeks old. However, pup recruitment is usually high in North America so distemper most likely does not kill very many wild wolf pups.

Canine Parvovirus: Canine parvovirus (CPV-2) is a rather new infectious disease that first appeared in 1976 in Europe and was recognized as a disease in dogs in 1978. It is a viral disease that attacks the animal's intestines and causes diarrhea, vomiting, and, consequently, dehydration. Its origins are unknown, but it may have arose from a mutation of feline panleukopenia virus (FPV) or the mink enteritis virus, as it is quite similar to those two viruses.
CPV-2 was common in dogs by 1980 and first appeared in wild wolves in 1978-1979. From 1979 on, the disease began to increase its prevalence in wolves. In the early 1980's, it was found that 26% of Minnesota's wolves had been exposed to CPV-2, and in 1980, 9 out of 18 Alaskan wolves tested seropositive for the disease. CPV-2 may have been responsible for a decline in wolf numbers in Isle Royale National Park from 1980-1982. The decline occurred at the same time that a CPV-2 outbreak occurred among domestic dogs in the area. During the late 1980s, several wolves on the island had positive titers to CPV-2, although it is unknown as to whether or not the disease was responsible for the decline in wolf numbers.
CPV-2 strikes captive wolf packs far more often than it does wild wolves. In 1983, CPV-2 killed 11 out of 12 pups and yearlings in a captive wolf pack in Minnesota. CPV-2 has also killed wild red wolves (Canis rufus) - four red wolf pups died recently in the Great Smoky Mountains National Park of parvovirus.

Infectious Canine Hepatitis: This disease was first discovered in free-ranging wolves in 1974, and tests done on wolves in northern Canada and Alaska suggest that the disease can be quite common among wolves. In 1982, it was found that 100% of the wolves in the Tanana flats and Nelchina basins of Alaska had been exposed to the virus and in 1987, a study done in northwest Alaska found that only 40% of the wolves in the area had been exposed to the virus. There is no relation between the occurrence of the disease in domestic dogs and in any nearby wild wolves. It is not known if ICH is a significant cause of mortality in wild wolves.

Oral Papillomatosis: This virus infects the mouth and lips of canines and can cause swelling and infection of the lips. It can also cause small tumours to form in the animals mouth and on its lips. Symptoms can be quite mild or very severe. This disease does not kill wild wolves directly, although it has been known to kill coyotes indirectly. In coyotes, it can alter the feeding behavior of the animal and may lead to multiple secondary infections. Some coyotes who contract the disease recover from it and become immune to it.

Parasites

Wolves are susceptible to a variety of internal and external parasites. These include at least 24 species of nematodes (roundworms), 21 species of cestodes (tapeworms), nine species of trematodes (flukes), heartworms, and three species of acanthocephalia (spiny-headed worms). Wolves are also susceptible to being infested by fleas, ticks or mites. Below is a list of the most common or serious wolf parasites.

Heartworm: Mosquitoes are the major vector of dog heartworm, Dirofilaris immitis. Once the worms end up in a canine, they will mature and grow on the right side of the animal's heart and on its pulmonary arteries. Initial symptoms include detectable heart murmurs and pulse deficits. As the problem progresses, the animal's heart may become enlarged and if the the infection becomes severe (up to 200 worms have been found in some animals), blood flow will be blocked. Heart failure may result from a major infection.
Heartworm is thought to be one of the major causes of the red wolf decline that occurred in the southeastern United States during this century. Heartworm has been found in in free ranging wolves in Minnesota, and it has also occurred in captive wolf populations in the southern United States. It has not been reported in Canada or Alaska, as the mosquitoes that carry it prefer warmer climates.
There are medications that can be administered to dogs and captive wolves that can prevent the disease, and it is recommended that all dogs and captive wolves living in areas where heartworm occurs be on the preventative medication.

Hookworms: Two species of hookworms (which are a variety of nematode) occur in free ranging wolves, Ancylostoma caninum and Uncinaria stenocaphala. A. caninum is a large blood-sucking worm that attaches itself to and abrades its host's (which could be a gray wolf, red wolf, dog or coyote) intestinal wall. In dogs, symptoms include diarrhea, emaciation, anaemia, and, in severe cases, death. It has been known to kill coyotes and red wolves, but has not been reported to severely infect gray wolves, although it could pose a threat to them where it occurs in other canids. U. stenocaphala occurs in gray wolves, but its pathogenicity in them has not been studied.

Liver Flukes: The liver fluke, Metorchis conjunctus, is a trematode that infects the gall bladder and bile duct of a number of fish-eating mammals, as fluke larvae develop in the fish before they mature in a mammal. This parasite has been found in wolves in Alberta and Saskatchewan, and most of the cases involved wolves that were known to have been eating fish. Symptoms that were present in the infected wolves included swellings throughout the liver and dilated bile ducts. Two cases resulted in extensive damage to the pancreas. It is not known whether this parasite causes any mortality in wolves.

Tapeworms: At least 21 different species of tapeworm have been known to infest wolves. Wolves usually contract tapeworm cysts from the prey animals they eat. Once the tapeworm cysts enter the wolf's body, they will attach themselves to the intestinal wall of the wolf and will feed off of the wolf's body fluids. The segments of the tapeworm (tapeworms are made up of a tiny, microscopic head and hundreds of body segments that are full of eggs) are usually expelled in the wolf's feces, and resemble tiny grains of rice. Symptoms of a severe tapeworm infestation include loss of appetite, weight loss, and mild diarrhea. Tapeworm infestations do not directly kill wolves, but a wolf suffering from a severe infestation may become weakened and unable to hunt effectively.
The two tapeworm genera that most often occur in wolves are Taenia and Echinococcus. Tapeworms are quite common in free ranging wolves, and it is thought that Echinococcus plays an important role in regulating wolf and moose populations. The mechanism goes as follows: As wolf density in an area increases, the sites that are being used extensively by the wolves will become contaminated by a large number of Echinococcus eggs. The presence of Echinococcus cysts present in moose populations using the areas frequented by wolves will then increase. Since the cysts usually occur within the pulmonary tissue of moose, animals with severe infections will become weak. Such moose will be more likely to be killed by wolves than healthy moose, so the presence of the parasite enhances the regulatory effect of wolf predation on moose.

Mange: Mange is cause by tiny mites that attach themselves to an animal's skin or fur. There are two main types of mange: sarcoptic and demodectic. In sarcoptic mange, the female mites will dig under the animals fur and lay eggs there, and the animal will become very itchy. Sarcoptic mange is probably the most significant ectoparasite of wolves, and is caused by the mite, Sarcoptes scabei. S. scabei is found throughout the world and can live on a variety of host species. In demodectic mange, the mites live in the pores on its host's skin and cause very little itching. Symptoms of mange include skin lesions, fur loss and crusting of the skin. The skin of animals with severe infections may become thickened and gray. Some animals with severe mange may also loose weight. Mange is spread when an animal carrying the parasites comes into direct contact with an uninfected animal, or when an uninfected animal rubs against a surface that an infected animal has directly contacted.
Mange is most likely an important regulating factor of wolf and coyote populations. Cases of mange in wolf populations increase when wolf densities increase, and the number of surviving pups in a wolf population decreases as the number of wolves with mange increases. Wolves with mange often freeze to death because of the hair loss that occurs with a severe infestation of mites.
Sarcoptic mange has been used in the past by wildlife "managers" to control wolf populations. In 1909, wolves that were caught and infected with sarcoptic mange were released into Montana, in hopes that the disease would spread to and infect and kill other wolves

Lice: The dog louse (Trichodectes canis) has been found in wolves throughout their North American range. It was most likely transmitted to wolves from dogs. Lice are transmitted when an infected individual comes into close or direct contact with an uninfected one. Wolves infested with lice may lose some of their guard hairs, and their underfur often becomes quite matted. Some wolves with severe infestations of lice may lose small patches of fur. Damage and and loss of hair is usually not the direct result of a louse infestation, but often occurs when the wolf attempts to remove the lice by biting or scratching. T. canis most likely does not significantly affect wolf populations, as adult wolves with lice are often noted to be in good condition.

Other Ectoparasites: Other ectoparasites that occur in gray wolves include fleas (Pulex simulans, Ctenocephalides canis), ticks (Amblyomma americanum, A. macuklatum, Dermacentor albipictus, D. variabilis, and Ixodes spp.) and the deer fly (Lipoptena cervi). These ectoparasites do not exert any control over wolf populations, and are less of a problem in northern regions than they are in warmer, southern regions.

Bacterial Infections

Leptospirosis: Leptospirosis is a disease that is caused by bacteria from the genus Leptospira, which includes over 170 known species. This disease is transmitted when an uninfected animal comes into contact with the urine of an infected animal. The disease is very rare in free-ranging wolves.

Brucellosis: This disease is caused by bacteria in the genus Brucella. This disease primarily affects ruminants and symptoms include orchitis, abortion or other reproductive problems.
Wolves in northern Alberta, Siberia and the Canadian arctic have tested seropositive for the disease. In south-central Alaska, !% of the wolves have been found to carry antibodies for the disease. The effects of brucellosis in wild wolves is largely unknown. Two pregnant wolves that were experimentally infected with Brucella suis gave birth to some dead pups, although whether that was the result of the brucellosis infection or not could not be proven.

Lyme Disease: Lyme disease is caused by the bacterium Borrelia burgdorferi, and can affect dogs, horses and humans. The disease was first discovered in New England in 1975, and has since been reported in at least 43 states and eastern Canada. Infection typically results from bites from infected Ixodes dammini ticks (deer ticks). White-tailed deer are the major hosts for the mature ticks, while small rodents (usually white-footed mice or eastern chipmunks) are the hosts for the immature ticks. These hosts can become infected with B. burgdorferi, but never show symptoms of the disease.
Wolves in Minnesota and Wisconsin have been found to be infected with the disease, but clinical Lyme disease has not yet been found in wild wolves. A wolf that was once experimentally infected with B.burgdrferi showed some symptoms of the disease, which suggests that wolves may be susceptible to it.

Fungal Infections

Blastomycosis: This disease is cause by the fungus Blastomyces dermatitidis, and is not contagious. It is rare in wild wolves, but has occurred in wolf populations in Minnesota and Wisconsin. It can be fatal to wolves.