PARASITIC AND INFECTIOUS DISEASES OF WHITE-TAILED DEER IN OKLAHOMA
A. Alan Kocan Ph.D. (Deceased)
College of Veterinary Medicine
Oklahoma State University
Stillwater, Oklahoma 74078
Internal and external parasite populations are a common part of the normal biology of most animals. Studies have shown that at least 137 species of parasites have been identified that infect deer of the genus Odocoileus. Studies undertaken by the O.S.U. College of veterinary Medicine and the Oklahoma Department of Wildlife Conservation have identified over 21 internal and 7 external parasites occurring on deer in Oklahoma.
Because some of the parasites that infect or infest deer are large enough to be seen by the unaided eye, hunters and biologists often encounter them during outdoor activities. The most common questions posed as a result of being able to see these parasites are 1) are the parasites transmittable to man and 2) do they impact on either the health of the individual deer or the herd in general.
Few, if any, parasites are directly transmittable from deer to humans. All potential parasites will be rendered harmless following thorough cooking. Most external parasites found on deer will not establish on humans and few if any parasites of deer are transmittable directly to domestic or pet animals.
Parasites and diseases can take a toll on both individual deer and on deer populations in general. An understanding of both the biology of the organisms involved
and the methods of transmission help to determine the significance of these types of infections in free-ranging animals. In general, wild species such as deer are of little consequence in either transmitting or maintaining parasites that infect domestic animals. In comparison, domestic animal parasites and/or infectious diseases often have devastating effects when transmitted to free-ranging deer. However, there are some instances, however, when natural parasites of deer can cause considerable pathogenesis in some domestic species and other introduced wild species. As we continue to see an expansion of both farmed wildlife and population growths in free ranging animals, we will continue to see increased instances where infectious and parasitic diseases become of increasing importance.
Transmission of parasites from deer to deer is often a natural phenomenon with the outcome being of little consequence to the infected animal. When conditions change and deer numbers increase beyond acceptable levels and when suitable habitat is either reduced or destroyed, parasites and other diseases can often have a dramatic impact on populations. As a result, monitoring deer numbers and habitat condition as well as ascertaining parasite and diseases surveillance becomes extremely important in maintaining adequate numbers of healthy deer.
The text is offered as a reference guide for parasites and infectious diseases that are known from deer in Oklahoma. Portions of the text were adapted from a publication by M. Shaw and A. Kocan, Parasites of white-tailed deer in Oklahoma, supported by Federal Aid in Wildlife Restoration projects to the Oklahoma Department of Wildlife Conservation.
PARASITES FOUND ON THE BODY SURFACE OF WHITE-TAILED DEER
Lepotena mazamae "deer ked"
These arthropods, often refereed to as "deer ticks" are actually wingless flies. The adult is about 1/8 of an inch long and they live in the hair of the animal. They are well adapted to this existence and feed on blood. They can live on the deer for up to 6 months. The blood feeding activity produces irritation and can result in hair loss and an anemia. Animals in poor condition with heavy infestations may experience difficulty in severe winters. Transmission from one animal to another is by direct contact. This species appears to be restricted to infesting only deer. The distribution in Oklahoma is state-wide.
There are several species of lice that have been reported from deer (Solenopotes binipilosus - sucking louse, Tricholipeurus lipeuroides and T. parallenus - chewing lice). Lice feed on skin and epithelial debris (biting lice) or feed on blood (sucking lice). Infestations are often heaviest in the winter months with severe infestations causing irritation and hair loss. Transmission is again by direct contact with other infested deer. Lice are vary host specific and these species are restricted to infesting only deer. The distribution in Oklahoma is state-wide.
Numerous species of ticks feed on deer at differing times of the year. In Oklahoma, the major problem is Amblyomma americanum, the lone-star tick (Lower picture). All three stages of this tick feed on deer with heavy infestations resulting in poor condition, hair loss, anemia, and local pathologic change at the point of attachment. Significant mortality in fawns has been reported as a direct or indirect result of heavy infestations. Other ticks commonly infesting deer include the black legged tick (Ixodes scapularis) (upper picture) and the winter tick (Dermacentor albipictus) (not shown). The distribution of the lone-star tick is expanding being the heaviest in the south and southeastern regions of the state. The distribution of I. scapularis and D. albipictus is also expanding and may be more uniformly state-wide.
Infestations with Demodex folliculorum are not common in deer but when they do occur, they usually result in considerable pathogenicity. This mite lives in the hair follicles and sebaceous glands of its host and varieties are reported from most animals. Excessive tissue growth occurs associated with the lesions. Lesions may become secondarily infected with bacteria, compounding the problem. In most instances, infestations with this mite are seen in either captive animals or isolated free-ranging individuals.
Psoroptes conniculi is reported from deer with infestations ranging from being confined to the ear canals to total body involvement. The entire life cycle of this mite involves infestations of the skin. Most reports are from captive individuals and many reflect exposure to other infested domestic animals.
PARASITES FOUND IN THE BLOOD OF DEER
This is a protozoan parasite that can be found free in the blood plasma of deer. The parasite consists of a single cell that is leaf-like in appearance. A free flagellum, which is used for locomotion, is attached to an undulating membrane. The parasite is not considered pathogenic to deer. Infection rates are generally low and culture procedures are often necessary to document its presence. Microscopic identification of the stained organism in blood films is necessary. The transmission of the parasite is probably via horseflies and its distribution in Oklahoma is nearly state wide.
Theileria cervi is another protozoan parasite found in the blood of deer. In this instance, the organism, referred to as a piroplasm, is found within circulating erythrocytes. The parasite is transmitted via the tick vector Amblyomma americanum. Transmission appears to be mainly from infected unfed adults that feed on newly born fawns in the spring. Once infected, the fawns develop a parasitemia sufficient to allow infection of other tick stages that feed on them, thus perpetuating the infection. Adult deer remain infected for life but usually have parasite infection levels of below 1%. The parasite is not pathogenic in healthy animals. Diagnosis is dependent on finding the piroplasms in stained blood films. Distribution in Oklahoma appears to be coincident with the distribution of the lone-star tick.
Babesia odocoilei is another protozoan parasite that is tick-transmitted. In this instance, just as in T. cervi. the piroplasms are found in circulating erythrocytes. The tick vector appears to be Ixodes scapularis. The infection does not appear to be pathogenic in healthy animals. Diagnosis is difficult and may require culture procedures as well as microscopic detection of the organisms in stained blood films. Distribution appease to be related to that of its tick vector..
PARASITES FOUND OUTSIDE OF THE DIGESTIVE TRACT OF DEER
Setaria yehi - abdominal cavity
Nematode parasites of this genus are found in the abdominal cavity of horses, cattle and other ungulates. S. yehi is found only in deer. It is white in color and measures from 1 1/2 to 3 1/2 inches in length. This parasite is often observed by hunters while field dressing deer. The exact life cycle is unknown but biting flies are probably involved in the transmission . Small embryos called microfilaria, circulate in the blood and serve as a source of infection for flies. The parasite is not consider pathogenic. The parasite appears to be state wide in distribution.
Wherdiksmansia cervipedis -subcutaneous tissue
This nematode is found in the subcutaneous tissue of deer, occurring most frequently in the fore and hind legs and the neck region. The male worm is about 2 inches in length while the female may reach 8 inches in length. The parasite appears as a thread-like object on the surface of the skinned animal. Like Setaria, the parasite is not considered pathogenic. It appears to be restricted in distribution to the southeastern region of Oklahoma.
Cephenemyia phobifer - nasal bot
Nasal bots are the larval stage of flies. Deer become infected when the adult fly that looks like a honey bee, deposits eggs on the nasal passages of the deer. The larvae that hatch migrate into the nasal passages and attach to the tissue by means of hooks located on their anterior end. They remain attached to the tissue until they are ready to pupate. At this time they migrate out of the nose or are sneezed out, falling onto the ground. After about one month of pupation, adult flies emerge and begin the cycle again. Although deer sometimes harbor large numbers of this parasite, it does not appear that much more than a mild irritation and discomfort is experienced by the infested animal. Larvae have been reported from locations other than the nasal passages of deer including the lungs, stomach, and esophagus. However, this is probably due to larval migration in animals that have been dead for an extended period of time. Based on a typical life cycle, the heaviest infestation are seen in the summer months. Distribution in Oklahoma appears limited to the south and southeastern part of the state.
Sarcocystus spp -
This is a protozoan parasite that has a complicated life cycle involving other animals. In the infected deer, sarcocysts appear in the muscle tissue as white spindles or rice-grain-like structures (Upper photograph is of histologic section through a typical sarcocyst). The cysts vary in size but are usually around 1/2 inch in length. The exact life cycle of all species of Sarcocystus infecting deer are not know. Proper and thorough cooking of meat renders the cysts harmless. Distribution in Oklahoma is state-wide.
Parelaphostrongylus tenuis - meningeal worm
This is another nematode parasite with a complicated life cycle. The adult worms live in the sinuses and blood supply of the tissue covering the brain of the deer (upper picture). The adult worms produce eggs that are carried via the blood to the lungs where they hatch. The larvae migrate up the trachea, cross over to the esophagus, and are passed out of the body with the feces. These larvae then penetrate one of several snails or slugs where further development of the parasite occurs. Other deer become infected when the ingest the infected mollusks. In white-tailed deer, the parasite causes little problems, inspire of its location of infection. When abnormal hosts such as elk, moose, llamas, goats, etc. ingest the infected snails, abnormal migrations of the parasite often occur, usually resulting in both neuralgic abnormalities and death. In Oklahoma , the parasite is restricted to the eastern and southeastern regions of the state. Reports have implicated the presence of this parasite with unsuccessful restocking efforts for elk in eastern regions. Additional reports have demonstrated that habitat manipulation may help reduce the infection levels in some susceptible species. Successful treatment is not available but the reduction of overlapping range appears to reduce accidental infections.
Diagnosis is by either visual observation of the adults in the meninges of infected deer or by detection of larvae in feces (lower picture). Careful examination of feces is essential since other similar larvae also occur in deer feces and larvae are not shed continuously or evenly. Treatment with some antihelminthics (Ivermictin) has been shown to reduce larval production for a short period but does not eliminate infections.
Dictyocaulus viviparus - lung worm
The adults of this nematode live in the lungs and bronchi of cattle, deer, elk and bison. The parasite is milk-white in color and measures 1 1/2 to 2 1/2 inches in length. Adults produce eggs that hatch in the lungs; the larvae migrate up the respiratory tract, cross over to the digestive tract and are eliminated with the feces. In the soil, the larvae develop to the infective stage. Ingestion of these larvae are the source of infection for other animals. Moderate to heavy infection levels often result in impaired respiratory function and may lead to death. Infections in deer appear to be associated with cross-contamination with infected domestic species. Reports in Oklahoma are rare and limited to the southwest region of the state.
Elaeophoria schneideri is another nematode parasite infecting deer. The adult worm occurs in the carotid arteries and related areas. Female worms produce microfilaria that are carried throughout the body via the blood where they concentrate in specific locations, especially the skin of the head. Horseflies become infected when they feed on this area and acquire the microfilaria while feeding. The parasite matures in the fly and is inoculated when the fly feed on a susceptible host. In white-tailed deer, the most common sign of infection is oral food impactions, tooth loss, and occasionally fractured jaw bones. Infections in other animals, such as elk, often result in damage to tissue as a result of restricted blood flow to areas distal to the worms. Diagnosis is by detecting adult worms in arteries of infected deer. Infections in Oklahoma are rare and limited in distribution to the eastern regions.
Monezia spp - tapeworms
Adult tapeworms are restricted to the small intestine of deer. This genus is white in color and can reach a length of 20 feet. Several species belonging to this genus are reported from sheep, goats, cattle, and other ruminants. Non-parasitic mites that live in the soil serve as intermediate hosts allowing the animal to become infected while grazing. Most infections are considered non-pathogenic. Larval stages of some other tapeworms also infect deer. The most frequently encountered larval stage is that of the canid tapeworm, Taenia hydatigena. The stage appears as a bladder-like larvae (cysticerci) that is usually attached to or in any of the visceral organs. Its presence is not considered pathogenic although its consumption would result in adult infection in canids.
HELMINTH PARASITES (WORMS) FOUND IN THE DIGESTIVE TRACT OF DEER
Gongylonema pulchrum -esophagus
This nematode parasite is worldwide in distribution. Although it is primarily a parasite of ruminants, it has been reported from many other animals including man. The parasite is found in the lining of the esophagus where it is embedded in the tissue in a zigzag pattern. The female parasite may reach 6 inches in length producing visible tunnels. The life cycle involves eggs that are released in the deer feces being eaten by various arthropods including dung beetles and cockroaches. In these arthropods, they develop into infective larvae and the life cycle is completed when deer ingest the infected beetles. Although not considered to be a pathogenic organism, heavy infections result in notable inflammation of the esophagus. The distribution of this parasite in Oklahoma appears to be state-wide.
Gongylonema verrucosum - rumen
This species of nematode occurs under the lining of the rumen. It is reported from a variety of animals including sheep, goats, cattle, and deer. The adults are reddish in color and smaller in size than G. pulchrum. Heavy infection levels often result in a mild inflammatory response which is not considered to be of significance. Distribution in Oklahoma is state-wide.
The following nematode parasites are found in the abomasum , small intestine, large intestine or cecum of white-tailed deer. Their presence is generally not considered of significance as these are normal parasites of this host. Heavy numbers can result in morbidity and occasionally mortalities. Identification and enumeration of these parasites, especially those found in the abomasum, are often used by biologists to help determine the general health statues of deer herds.
Consult a text book on veterinary parasitology for keys for identification as well as procedures for both isolation of parasites and enumeration procedures.
Trichostrongylus axei abomasum
Hemonchus contortus - abomasum
Apteragia odocoilei abomasum
Ostertagia dikmansi - abomasum
Ostertagia mossi - abomasum
Cooperia spp- small intestine
Capillaria bovis small intestine
Monezia spp tape worm - small intestine
Oesophagostomum venulosum - large intestine
Eucyathostomum webbi - large intestine
Trichuris sp - cecum
VIRAL DISEASES OF DEER
Hemorrhagic disease in deer can be caused by either epizootic hemorrhagic disease virus (EHDV) or bluetongue virus (BTV). There are two types of EHD virus and 5 types of BTV in the US. Clinical signs of infection vary greatly ranging from being non-apparent to depression, fever, respiratory distress, and death. Most deer show lameness, inappetence and reduced activity. Three forms of the disease have been reported. The peracute, acute and chronic forms. The peracute form is characterized by swelling of the head, neck, and tongue. The acute form is characterized by the above with the addition of hemorrhages and congestion of the heart, rumen and intestines. Necrosis may also occur on the tongue and dental pads as well as other areas of the body. The chronic form of the disease is characterized by lameness resulting from sluffing of the hoof walls and ulceration of this area (upper picture).
Domestic animals such as cattle are also susceptible to EHD virus although they are typically symptomatic carriers. BTV also infects a variety of domestic ruminants. with some, like sheep, developing severe disease after infection.
Both viruses are transmitted to susceptible hosts by biting midges (Culicoides spp). The disease usually occurs in late summer and ends with the first killing freeze.
Diagnosis is often based on presumptive determinations, serologic results, viral isolation or observation of chronic lameness in deer. Vary often, sick and /or dead deer may go undetected.
Hemorrhagic disease has proven to be of considerable importance in many deer herds in the southeastern U.S. In Oklahoma, serologic reactivity and virus confirmation has been documented, but major die offs are not known to have occurred.
Cutanious fibromas are usually caused by a virus and are harmless tumors that occur on the skin of white-tailed deer. The tumors may be small and localized or numerous and extensive. In all cases, they are not harmful to either the deer, to humans, or to other livestock.
Bovine viral diarrhea
This is a viral disease of domestic cattle and perhaps sheep. It does not appear that exposure to the virus results in infection in deer or that deer play any role in the spread of the virus.
Malignant Catarrhal fever
There are two forms of MCF virus. The endemic or sheep form and an exotic or African form. In either case, deer infected with the virus die suddenly and show few clinical signs. These results suggest that deer are not and would not be an important carrier of this virus.
Rabies is rare in deer and has not been recorded in Oklahoma. No human cases of rabies have been traced to deer.
OTHER INFECTIOUS DISEASES OF DEER
Leptrospirosis can be caused by any of over 189 known serovars of the spirochete Leptospira interogans. The organism infects a large variety of domestic and wild animals, including humans. Studies indicate that deer are routinely exposed to the organism but rarely suffer clinical signs of infection. Additionally, it does not appear the deer are of significance in either the maintenance or spread of the organism in Oklahoma.
Although white-tailed deer are known to be susceptible to the spirochete organism, Borrelia burgdorferi, they do not appear to suffer from clinical signs of infection. Results of experimental infections in deer indicate that although they are susceptible to infection with the Borrelia organism, they are probably insignificant in either the maintenance or spread of the organism in nature. The apparent primary vector, Ixodes scapularis, often feeds in large numbers, as adults, on deer in Oklahoma and deer probably serve as a primary host for this tick.
Anaplasma marginale is a rickettsial organism that is infective for a variety of bovine hosts. In adult, uninfected animals, Infection often results in a severe anemia, often leading to death while infection in young animals is usually asymptomatic. Although white -tailed deer are known to be susceptible to infection, the level and duration of infection indicate that deer are of no or minimal importance in either maintain of perpetuating the Anaplasma organism. Transmission can occur by tick and fly transmission and by mechanical transmission of contaminated infected blood.
Ehrlichia spp are rickettsial organisms that are tick-transmitted and capable of infecting a variety of hosts, including humans. Most species appear to be host-specific. Recent studies have documented a yet un-named Ehrlichia spp in white-tailed deer. The significance of this organism is not yet known. Recent reports have documented at least two species of Ehrlichia that infect humans, as well as the already established species infecting dogs, horses, etc.
Kocan, A., M. Shaw, K. Waldrup, and G. Kubat. 1982. Distribution of Parelaphostrongylus tenuis in white-tailed deer from Oklahoma. Journal of Wildlife Diseases 18: 457-460.
Whitneck, D., A. Castro, and A. Kocan. 1981. Experimental malignant catarrhal fever (African Form) in white-tailed deer. Journal of Wildlife Diseases 17: 443-452.
Ewing, S., J. Dawson, A. Kocan, R. Barker, C. Warner, R. Panciera, J. Fox, K. Kocan, and E. Blouin. 1995. Experimental transmission of Ehrlichia chaffeensis among white-tailed deer by Amblyomma americanum. Journal of Medical Entomology 32: 368-374.
Raskevitz, R., A. Kocan and J. Shaw. 1991. Gastropod availability and habitat utilization by wapiti and white-tailed deer sympatric on range enzootic for meningeal worm. Journal of Wildlife Diseases 27: 92-101.
Kocan, a. A. Castro, M. Shaw, and S. Rogers. 1987. Bluetongue and epizootic hemorrhagic disease in white-tailed deer from Oklahoma: serologic evaluation and virus isolation. Journal of Veterinary Research 48: 1048-1049.
Laird, S., A. Kocan, K. Kocan, S. Presley, and J. Hair. 1988. Susceptibility of Amblyomma americanum to natural and experimental infections with Theileria cervi. Journal of Wildlife Diseases 24: 679-683.
Waldrup, K. A. Kocan, T. Qureshi, D. Davis, D. Baggett, and G. Wager. 1989. Serologic prevalence and isolation of Babesia odocoilei among white-tailed deer in Texas and Oklahoma Journal of Wildlife Diseases 25: 194-201.
Waldrup, K., A. Kocan, R. Barker, and G. Wager. 1990. Transmission of Babesia odocoilei in white-tailed deer by Ixodes scapularis. Journal of Wildlife Diseases 26: 390-391.
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