Growing up, fairytales such as Little Red Ridinghood and the Three Little Pigs taught me to perceive wolves as evil, vindictive creatures. During early childhood I remember studying carnivores at school and I always felt a strong sympathetic emotional consideration for prey species. I still do – I dislike pain in all its forms – but I certainly have a better understanding of the ecological world now. I have mentioned in an earlier post that it wasn’t until high school that I truly began to explore my passion for wildlife, and wolves as species. It was then that I began to learn about the struggles their species and others must experience just to survive. It is not an easy life, even when you take human interference out of the picture!
Internal and external (endo- and ectoparasites) are almost everywhere. And of course, naturally, different parasites plague wolf populations commonly if not constantly. The aim of a parasite is generally not to kill its main host but to allow the host to continue to survive whilst the parasite benefits. Wolves do tolerate a wide range of parasites without significant hardship, however parasitic infections can become seriously detrimental or even fatal especially when factors such as malnutrition or viral disease are also weakening the wolf.
Protozoan parasites are unicellular organisms in which metabolism and locomotion are carried out by organelles within the cell. Deaths have been reported in wolves from Isospora (which causes coccidiosis, a disease of the intestinal tract), Toxoplasma (causing toxoplasmosis, a zoonotic disease) and Babesia (causes babesiosis, a haemolytic disease where red blood cells are destroyed). Wolves have also been known to host Sarcocystis and Giardia. While Giardiasis is not uncommon in dogs, it has not been known to cause major suffering or morbidity in wolves.
Helminth parasites (commonly known as worms – yuck!) have three major groups that use wolves as definite hosts.
Trematodes – also known as ‘flukes’. These worms have flattened, one-piece bodies. They use suckers, hooks or clamps to attach themselves to internal organs, either inside the organ or outside its walls. Trematodes may use several intermediate hosts before establishing themselves inside a wolf’s body, including slugs or snails and a mammal species preyed on by the wolf. Common flukes found in wolves include Alaria (a lifestage of which develops in tadpoles and frogs which are then ingested by the wolf or small rodent) and Metorchis conjunctus (also known as ‘liver fluke’ – its larvae live in fish to be ingested by wolves). Most trematodes known to infect wolves inhabit the intestinal tract, liver or lungs.
Cestodes – ‘tapeworms’. Ungulates, small mammals and fish harbour tapeworm larvae – wolf prey species. Tapeworms range from a few millimetres in length to several meters long (for example Diphyllobothrium latum, whose intermediate host is a fish, can reach lengths of up to 20 metres! That makes me feel queasy). Their bodies consist of a head (usually with suckers or hooks for attachment) and a strobila (the bulk of the tapeworm’s body) which is made of a number of segments (proglottids). Each proglottid contains both male and female sexual organs, therefore eggs can be self-fertilised as well as cross-fertilised. Segments containing fertilised eggs break off either singly or in groups and are shed in the wolf’s faeces. The gravid segments then go on to break down in the environment, releasing the eggs. An intermediate host then ingests an egg, the egg hatches inside the host and the tapeworm embryo penetrates the intestinal wall of its host for further development. When a wolf eats the intermediate host, the larval tapeworm attaches to the intestinal wall and develops into an adult inside the wolf.
Tapeworms can cause serious problems depending on number and size of worms, and the susceptibility and sensitivity of the host. Ill effects include intestinal blockage (due to numerous, large strobila), generalised toxis or allergic reactions, mechanical irritation of the intestinal musocsa, nutrient deprivation of the host, secondary bacterial infection of the intestine and absorption of proteins and vitamins from the intestinal mucosa.
Larval infections of the intermediate host are more serious than adult infections of the definitive host. Larvae produce cysts in which to develop, and these can promote neoplastic symptoms that can eventually destroy the host’s liver, and germinal tissues of the liver cysts commonly metastasize to other organs. Deaths in humans due to such infections have been recorded; no drugs are effective in killing the larvae, and complete surgical removal of such cysts is extremely difficult as cells of any ruptured cysts simply spread the infection further.
An intermediate host weakened by a parasitic infection can be advantageous to hunting wolves, and many kills have been observed to be ridden with parasites. This also, of course, ensures a continuation of the tapeworm lifecycle.
Nematodes – roundworms. Roundworms are elongated, unsegmented, and vary greatly in size. They usually inhabit the intestine but can be found in other organs such as the heart or kidney. Life cycles also vary from simple (e.g. the shed eggs from one definitive host are ingested by another) to complex (involving more than one intermediate host). The larvae of some species penetrate the skin or mouth and migrate to the lungs, where they are coughed up and swallowed to become mature adult roundworms in the intestine. Sexes are usually separate and roundworms can be dimorphic.
While most roundworm infections are benign, fatalities do occur – especially in adults harbouring large numbers of worms and in pups. Toxocara canis is a hookworm that is commonly found in wolf pups and has been known to cause death by pneumonia (caused by intestinal blockage leading to aspiration of vomitus). Pups can be infected in utero with this particular worm. The giant kidney worm, Dioctophyma renale, has been found in wolves. This parasite develops in the kidney after larvae are ingested, and they have been known to reach lengths of up to one metre with a diameter of one centimetre in wolves. The presence of D. renale in the kidney results in the complete destruction of functional tissue, leaving only a distended and thickened capsule. The ureter remains functional and allows passage of eggs into the urine. To compensate for the loss of one kidney, the other kidney hypertrophies (increases in volume). If both kidneys are parasitized, the infection is fatal.
The dog heartworm, Dirofilaria immitis, has been found in both captive and free-ranging gray wolves as well as in red wolves. Dogs can tolerate low levels of heartworm infection for many years without showing clinical signs, but large numbers of these worms can cause cardiac enlargement, chronic passive congestion and death. Dogs are especially susceptible to serious effects during periods of exertion.
Acanthocephalans – thorny-headed worms. This fourth group rarely infects wolves, however secondary bacterial infection can result in perforation of the gut.
Diagnosis – diagnosis of helminths requires a microscope unless shed segments can be seen with the naked eye in faeces. Heartworm infection can be diagnosed by microscopic examination of the blood or by serology tests. There are treatments available, but not all lifestages of all species of helminths have a treatment.
Examples of external parasites include fleas, ticks and lice. Generally most ectoparasites are simply an annoyance, but some can be fatal. Perhaps the most harmful wolf ectoparasite is the mange mite, Sarcoptes scabiei. These mites can be spread to new hosts by direct body contact. The life cycle of the sarcoptic mite includes egg, larva, nymph and adult. All active stages have the capability to burrow into the skin, but most burrows are made by fertilized females that lay their eggs in the burrow. Burrowing causes intense pruritis (severe itching of the skin), scab formation, hyperkeratosis (thickening of the skin) and seborrhoea especially on the head and neck. In advanced stages the whole body may be involved, causing emaciation, decreased mobility, staggering and death.
Obviously, this mange can be a serious threat to wolves. Widespread mange can result in high mortality rates, especially amongst pups, and can quickly cull a large percentage of a population – in fact, whole populations can be affected by this disease.
Lice can cause high morbidity in wolf packs, but probably not high mortality. A louse epizootic has been known to cause alopecia and seborrhoea, with up to 75% of wolves’ bodies involved. Self-inflicted trauma caused by the associated pruritis results in inflammation and infection.
Certain ticks can transmit a variety of diseases, some of which can be fatal to wolves.
Diagnosis – most ectoparasites can be seen with the unaided eye. Louse eggs may be seen attached to hair, and mites can be observed by microscopic examination of skin scrapings of affected sites. There are several treatments for a range of ectoparasites available that have mostly been designed for dogs or cattle, but may be used in wolves.
Rabies is an acute infectious disease of the central nervous system caused by a rhabdovirus that generally persists as a salivary gland infection of carnivores. Rabies is one of the oldest recorded infectious diseases, enzootic on every continent except Australia (here in New Zealand we are completely rabies-free). Wolves are not considered to be the primary vector of rabies except in the Mediterranean region and India – dogs are foxes are. Rabies is almost always transmitted by bite, but has also been demonstrated to spread via aerosol routes. The incubation period in wolves is 8-21 days, whereas in dogs that contracted it from rabid wolves experience an incubation period of 17-39 days. In humans it can be as short as 9-11 days following severe injury inflicted by a rabid wolf. No controlled studies on wolves have been conducted, and so signs in wolves are mostly anecdotal.
There are two forms of rabies: Dumb and Furious. Dumb rabies is characterised by early paralysis of the throat, loss of voice, excessive salivation, general paralysis and death. There is little inclination to bite from Dumb rabies. Furious rabies proceeds through three stages:
1) Prodromal period: the animal exhibits abnormal behaviour, modification of voice and increased salivation,
2) Excitement phase: the animal becomes severely agitated and attacks inanimate objects, wanders aimlessly, bites other animals,
3) Paralytic phase: voice is lost, the tongue protrudes from a paralyzed jaw, and further paralysis soon leads to death.
These signs do not necessarily apply to wild animals under all conditions. Most documented wolf attacks on humans have been attributed to rabies; the disease makes a wolf lose its ‘fear’ of humans. Rabies is easily spread because the disease encourages agitation in animals thus promoting them to roam long distances.
Clinical rabies in wolves is untreatable. There are rabies vaccinations available for dogs that may be useful in wolves.
This is a febrile (fever-causing) disease of carnivores caused by a parmyxovirus. It is a world-wide problem in domestic dogs, but reports in free-ranging wildlife are few.
Canine distemper is spread by aerosol or direct contact, including from faeces and urine. Within days of exposure, signs of the disease appear. Signs include oral jaundice and ulceration, swollen feet, anorexia, ataxia (loss of control of body movements), dyspnoea (laboured breathing) and neurological abnormalities.
Despite evidence of being exposed to the virus, wolf populations have demonstrated resilience. However, there is no known cure in wild animals. Captive animals may be given supportive and symptomatic treatment such as antibiotics and intravenous fluids, but in many cases this is futile. Prevention through the use of vaccines approved for dogs may be effective in protecting wolves. Vaccination with a Modified Live Virus in a species other than the approved may result in reversion of the virus to virulent form and actually induce this disease (this has been seen in black-footed ferrets and lesser pandas).
Infectious Canine Hepatitis
Canine adenovirus-1 causes infection canine hepatitis, and transmission is usually through direct contact with contaminated respiratory tract discharge, saliva, urine, faeces or ectoparasites. In dogs, death can result in death within 12-24 hours of onset of clinical signs. This disease is enzootic in wolf populations. Supportive treatment with fluids and antibiotics may be helpful in some cases. There is a vaccine available that may provide lifelong immunity.
Other viruses observed in wolves include papillomatosis and canine coronavirus.
Brucellosis is a highly contagious, worldwide infection of both ungulates and carnivores. It is caused by Brucella bacteria – small, gram-negative, non-motile, non-spore-forming rods. Brucella suis type 4 infects wild caribou and domestic reindeer, and is of significance to wolves. Brucella abortus type 1 infects elk and bison in certain ranges of America and Canada. Wolves most likely become infected when they consume infected prey. A study has been done in wolves where pregnant females were infected with Brucella suis type 4 – no adults showed clinical signs but six of eight pups died shortly after birth, and the final two died 24 hours later.
I’m really not a fan of studies such as this where it is more than likely that participating animals will suffer adverse affects. In this study, the first pups to die had signs consistent with mother-induced trauma, but B. suis was cultured from different organs and blood from the pups, indicating while actual cause of death was trauma, the organism surely led to this outcome.
Organisms can infect the uterus and foetuses, and may lead to reproductive failure. They can be shed in the urine, saliva and milk.
Infected animals can be treated with certain antibiotics, but not all can be relied on to eliminate all infection.
This disease infects humans and animals, and is caused by the spirochete Borrelia burgdorferi. Principal vertebrate reservoirs are thought to be the white-tailed deer and white-footed mouse. The organisms is primarily spread through the bite of infected deer and ticks, and these reservoir hosts do not show clinical signs of the disease. Transplacental transmission and contact are other possible routes of infection.
Clinical Lyme disease has not been reported in wolves, but the disease can be debilitating in dogs – causing fever, lymphadenopathy, arthralgia (joint pain) and arthritis. Abortion and faetal mortality have also been reported in infected humans and horses.
Lyme disease can also be treated with antibiotics.
Another worldwide diease. Leptospirosis is caused by Leptospira spirochetes. Leptospirosis may cause morbidity and sometimes mortality in numerous species. In dogs, leptospirosis can cause fever, anorexia, vomiting, anaemia, haematuria, jaundice and death is severe liver or kidney damage occurs.
Transmission is usually by contact with infected urine or by feeding on infected prey. It can be treated with antibiotics. There are vaccines approved for dogs that have been given to wolf pups and adults with no adverse reactions, but effectiveness of these bacterins in wolves has not been demonstrated.
Other bacterial diseases include tylaremia (an acute febrile disease or wild lagomorphs and rodents), bovine tuberculosis (which can remain viable in the soil for many years), salmonella and listeriosis.
A chronic pyogranulomatous pulmonary disease casued by the dimorphic gungus Blastomyces dermatitidis. Blastomyces is thought to reside in the soil, but experiments have not been able to maintain the fungus for extended periods in soil. Transmission probably occurs by inhalation of spores. Incubation times may be up to three months in dogs. The lung is the primary focus of infection, but the organism can disseminate to other organs. General clinical signs o infection include weight loss, fever, anorexia, weakness, skin lesions, depression, dyspnoea, lameness, ocular and nasal discharge, chronic coughing, draining lymph nodes, swollen joints, blindness and enlarged testicles. Although the illness can last up to three years, most animals survive less than four months.
Also known as ringworm. The is a mycotic infection of the skin caused by Microsporum gypseum or other dermatophytes. It is not usually debilitating, but can cause intense inflammation of the skin, pruritis and hair loss. It can be transmitted from animals to humans, and is treatable.
For this and more information see:
Behavior, Ecology and Conservation
Edited by L. David Mech and Luigi Boitani