*TICKS AND TICK-TRANSMITTED DISEASES IN OKLAHOMA
TEXT AND PHOTOS BY A. ALAN KOCAN. Ph.D., PROFESSOR (Deceased)
DEPARTMENTOF VETERINARY PARASTIOLOGY, MICROBIOLOGY, AND PUBLIC HEALTH
COLLEGE OF VETERINARY MEDICINE
OKLAHOMA STATE UNIVERSITY, STILLWATER, OKLAHOMA 74078
Ticks are of medical importance because they can be an annoyance, they can cause harm due to their blood feeding activities and because they can transmit many pathogenic organisms. Many diseases of importance to both human and veterinary medicine are transmitted by ticks. Included in these are:
Tick-transmitted diseases of humans.
Colorado tick fever
Ehrlichiosis (HME & HGE)
Rocky Mountain spotted fever
Tick -transmitted diseases of animals.
Anaplasmosis : cattle and sheep, deer.
Babesiosis: dogs, cattle, horses, deer.
Ehrlichiosis: dogs, deer.
Haemobartonellosis: dogs and cats
Rocky Mountain spotted fever: dogs
Lyme disease: dogs, cattle, horses, small mammals
Theileriosis: white-tailed deer
Hepatozoonosis: dogs, cats and small mammals.
Recent changes in both demographics and living preferences have influenced the number of both animal and human tick transmitted diseases. Increased human populations in rural areas has resulted in both reducing the number of some hosts that ticks might normally feed upon or conversely, increased the number of a particular hosts that ticks feed on. Changes in both hunting and trapping laws and social changes related to many wild animals products have also influenced the numbers and diversity of many animal species. As a result, these changes have placed both humans and their pets in more direct contact with wild animals and the ticks that feed on them. Because of these changes, parasite life cycles that have been established between wild animals and ticks may now be able to include pet animals and humans as well. Often, when parasitic organism are transmitted to new or different hosts, diseases may be either non apparent or more pronounced. Although pet animals such as dogs and cats can become infected with many of the same tick-transmitted organisms as humans and are often heavily infested with ticks, rarely do these animals play a role in either increasing the likelihood of human infections nor are they the source of infected ticks that might feed on humans.
Most common ticks can be identified microscopically to the generic level by examining the mouthparts. The mouthparts consists of a spined hypostome surrounded by a pair of palps. The area where the mouthparts are attached to the cephalothorax (the base of the mouthparts) is called the basis capituli.
There are two families of ticks. The Ixodidae or hard ticks and the Argasidae or soft ticks.
Ixodidae - Hard Ticks are characterized by having a visible scutum or shield that covers all or part of the dorsal surface and mouthparts that originate on the anterior margin.
Argasidae or soft ticks are characterized by lacking a scutum and having mouthparts that originate on the ventral surface.
The life cycle of all ticks include four stages (egg-larvae-nymph-adult) . In the majority of species, the ticks drops off the host animal between stages (exceptions are one host ticks that remain on the same animal through all stages). The larvae (seed ticks) hatch from the eggs and attach to vegetation in order to come into contact with passing animals. Larvae posses three pairs of legs. Attraction to the host is due to heat and carbon dioxide concentrations. Once on the new host, they attach and feed on blood. Nymphs and adults employ the same method of host seeking. Mating of adults takes place on the host while attached and feeding. Egg laying by the female tick occurs after detachment. Both nymphal and adult ticks posses four pairs of legs.
Ticks can transmit pathologic agents to a host by several means. In some cases, they can transmit organisms from one host to another by simple mechanical transfer. This usually occurs when ticks move from one host to another and their mouth parts are contaminated with blood-containing organisms. Ticks can also transmit organisms biologically. These methods require that the infectious organism goes through some sort of development or maturation within the tick. After this occurs, the organisms can be transferred either transstadially (between stages) or transovarially (from female to offspring via the egg). Transstadial transmission usually occurs in three-host ticks when one immature stage acquires the infectious agent while feeding and then maintains the infection through the next molt and transfers it to a new host the next time that it feeds. Transovarial transmission occurs when the female tick acquires the infection while feeding and transfers the agent to the developing ova. In this case, the newly hatched larvae are infected without having to take a blood meal. This is most common in one host ticks. Some ticks employ all of the above methods of transmission while others utilize only one.
Heavy tick infestations are often responsible for considerable morbidity and mortality in both domestic and wild species.
Male and female hard ticks can be separated by the presence of a complete scutum covering the entire dorsal surface of the male (below, bottom row) and a partial scutum on the female (below top row).
The ticks that will be covered in this section are those that are most commonly recovered from both humans and domestic animals in Oklahoma. Numerous additional genera and species of ticks also occur but have both feeding preferences and distributions that tend to confine them to wild species of animals or different geographic regions of the country.
Hard ticks common to Oklahoma.
Ixodes scapularis (dammini) - Black-legged tick (3 host).
This tick was once thought to be a separate species from I. dammini but recent studies have shown them to be synonymous. This is the most common vector for Lyme disease in North America. The adults are cool weather ticks, appearing in spring and fall but usually remaining on the host throughout the winter. Larvae and nymphs are abundant in the summer and feed on small mammals and lizards. The life cycle is typically 2 years. Members of this genus are involved in the transmission of tularemia, human and animal babesiosis, and tick paralysis. Adults can be identified by the presence of large mouthparts (longer than the basis capituli) and an anal grove that forms an arch anterior to the anus on the ventral side.
Dermacentor variabilis - American dog tick (3 host).
The adults of this tick are common on a variety of hosts but dogs appear to be the most common host. It is widely distributed over the eastern two-thirds of the United States. Adult tick activity begins in mid-April and peaks by June, declining until September. In southern states, all stages may be found on the host throughout the year. It is a common vector for Rocky Mountain Spotted fever, anaplasmosis, feline cytauxzoonosis and tick paralysis in the eastern United States. The genus Dermacentor is similar in appearance to members of the genus Rhipecephalus. Dermacentor ticks can be recognized by he short mouth parts and a non-flared basis capituli.
Dermacentor albipictus- Winter tick. (1 host).
This tick is common on most large mammals including domestic and wild species throughout the cooler months of the year. It is responsible for "ghost moose" in northern states due to heavy infestations and the resulting hair loss. It is also often responsible for outbreaks of "winter anaplasmosis".
Rhipicephalus sanguineus - Brown dog tick (3 host).
This is an extremely common tick of dogs found throughout the world. Although common on dogs, it can be found feeding on other mammals but rarely humans. Adult activity is from spring until autumn. When off the host, the adult ticks have a tendency to crawl upward and are often found in roofs and cracks of dwellings. It is one of the most common ticks involved in infestations of houses. This tick is involved in the transmission of canine babesiosis, haemobartonellosis, canine ehrlichiosis and tick paralysis.
Amblyomma americanum - Lone star tick (3 host).
This is an extremely common tick in most southeastern states. It is primarily a problem as a pest but it is involved in the transmission of canine ehrlichiosis, tularemia, Q fever and cervid theileriosis. Adult females are easily recognized by having long mouth parts and a white spot on the dorsal scutum.
Ambylomma maculatum - Gulf Coast tick. (3 host). Once thought to be restricted to the area around the Gulf coast, this tick is now common in many southeastern states.
Common soft ticks
Otobius megnini - Spinose ear tick ( 1 host, adults free living).
This is a common tick in most warm areas the world. Larvae and nymphs invade the ears of its hosts. Host are numerous including horses, cattle, rabbits and occasionally man. Individual ticks may remain in the ears of the host for up to one year.
Argus persicus - fowl tick (3 hosts).
This is a widely distributed tick throughout the world. The nymphal an adult stages are active at night while hiding in trees, under houses, etc. during the day. Ticks may travel long distances to find their hosts. Large numbers of ticks may parasitize fowl at night, removing large amounts of blood. During the day, birds will show little sign of parasitism but a striking anemia. This ticks can be involved in the transmission of avian borreliosis and paralysis.
Ornithodoros hermsi. Relapsing fever tick (3 host). This is a common tick of wild animals. It is also thought to be the primary vector for human relapsing fever.
DISEASES TRANSMITTED BY TICKS TO HUMANS
Rocky Mountain spotted fever.
Rocky Mountain spotted fever is the most frequently reported tick-transmitted rickettsial disease in the U.S. Rickettsia rickettsii is the causative agent in the western hemisphere although other distinct strains exist throughout the world. Most cases in humans occur where Dermacentor spp ticks occur with the primary vectors being D. variabilis in the eastern states and D. andersoni in the western states.
Ticks are both reservoir hosts and vectors for R. rickettsii. Transmission to the tick can occur both transovarially and transstadially. Many small rodents serve as amplifying hosts being capable of developing high rickettsemias, thus serving as a source of infection for larval and nymphal ticks.
Most human cases occur between mid-April and mid-September with June and July being the highest months. Mortalities are highest in children and people over 30 years of age. Clinical signs in infected people are variable and often mimic upper respiratory infections. Most commonly, fever, chills, headache, and abdominal pain are reported. A rash may develop later, often beginning on the soles of the feet and palms of the hands. Although common, the rash may only develop in 50% to 80% of infected people. Neuralgic signs may also occur but are most common late in the course of infection.
Diagnosis is usually accomplished by both determining a history of exposure and by serologic means. The detection of antibody often takes 1 to 3 weeks and early cases will not show positive serologic results. Treatment with tetracycline (22 mg/kg, q 8 h, po) or chloramphenicol (15 to 20 mg/kg, q 8 h, po) is effective. Early diagnosis and treatment are essential in preventing complications, including death. Supportive care may be necessary in longer turn cases.
Avoiding tick exposure and proper and early detection of tick infection and tick removal all aid in reducing the chances of infection.
Lyme disease or borreliosis.
Lyme disease is the most frequently reported tick-transmitted disease of humans in the U.S. It is caused by a spirochete, Borrelia burgdorferi.
Lyme disease has been reported in at least 24 states in the U.S., being most common in areas where certain Ixodes ticks occur. The highest incidence occur in Northeastern and upper midwestern states along with pacific northwestern states.
The life cycle involves several small mammals serving as reservoirs for the organism and a source of infection for the tick. Larval and nymphal Ixodes ticks become infected while feeding on these animals and transmit the infection to susceptible hosts transstadially during the next feeding cycle. Larger mammals, such as deer, often serve as important hosts for ticks and help maintain large tick numbers but appear to be of minimal importance in maintaining or amplifying the Borrelia organism.
The clinical features of infection with B. burgdorferi are typically flu-like in nature. A unique skin rash termed erythema migrans usually develops after several days from exposure at the site of tick attachment. This rash differs from that reported for RMSF in that the Lyme rash is "bulls-eye" in appearance. The disease itself is typically multi-focal involving numerous systems. Early symptoms are usually associated with the rash, expanding to many other systems including cardiac, and eventually resulting in arthritic signs.
Diagnosis is difficult. Serologic testing is often non-specific and organism culture is difficult and tedious. History of exposure and clinical signs often are important in a differential diagnosis.
Tetracycline hydrochloride is the treatment choice in uncomplicated cases with sodium and/or potassium penicillin being used in complicated and long term cases.
Prevention of tick infestations and early diagnosis is important in preventing disease in humans. Tick control is an important factor, especially in hyper-endemic areas.
Ehrlichia chaffeensis - human ehrlichiosis
Ehrlichia chaffeensis is the causative agent of human ehrlichiosis. Although other Ehrlichia species occur in a variety of animals including dogs, this appears to be the only organism that infects humans. It was first recognized in 1986 in North America with approximately 400 cases being confirmed since that time. The majority of cases are restricted to the Ozark Plateau region of the US. The E. chaffeensis organism has been shown to be experimentally infective for humans, dogs, and white-tailed deer although the role of these animals in the epizootology of human disease is unclear. The only confirmed (experimental) vector is Amblyomma americanum . A second species has recently been implicated in human cases in areas of the upper-midwest and perhaps the northeast U.S. First reported in 1994, this ehelichial organism was identified in neutrophils from a patient in Minnesota. Since the first reporting, about 170 human cases have been confirmed from patients in Minnesota, Wisconsin, Massachusetts, Connecticut, New York, Rhode Island, Pennsylvania, Maryland, Florida, Arkansas and California. Molecular analysis suggests that the Ehrlichia spp that causes this disease, referred to as human granulocytic ehrlichiosis (HGE) is the same agent that is responsible for granulocytotrophic ehrlichiosis of horses in California and elseware and in dogs in the Upper Midwest. Dogs in other areas have E. ewingii infections in which the organisms are in neutrophils, but this agent has not been incriminated as a human pathogen. The clinical diseaase in humans with HGE is vary similar to that seen with HME and is characterized by fever, chills, headache, nausea, cough, confusion, and arthraigia.
Clinical signs are typically flu-like in nature with symptoms of fever, headache, anorexia, myalgia, chills and weight loss being common. A RMSF-like rash occurs in about 20% of infected people.
Diagnosis is based on a history of exposure in an endemic area and can be confirmed by serologic tests (IFA) and/or identification of the organism in infected leukocytes and by culture methods.
Tetracycline appears to be the treatment of choice with remission of fever occurring as soon as 24 hours following treatment.
Minimizing tick exposure, early diagnosis and tick control measures are the only effective means of preventing infection
Tularemia - Francisella tularensis
The causative agent of tularemia (Francisella tularensis) is a small rod-shaped bacterium. There are several distinct types known that vary in virulence. The organism is worldwide in distribution and is capable of infecting a wide variety of animals. F. tularensis var tularensis is the most frequently isolated strain in the U.S. and is associated with tick-borne tularemia.
Symptoms include fever, chills, malaise and fatigue. Several clinical forms are reported including ulceroglandular, typhoidal, pharyngotonsillitis, and pleuropulmonary. The specific form is usually related to the initial route of infection. The agent can be transmitted by both direct and indirect methods with ticks being the most frequent source of infection in humans. Exposure to infected animals, especially rabbits is the second most common source of human infection.
Transstadial and transovarial transmission of this organism is common in ticks. Most human cases occur in summer concomitant with peak tick activity while a second peak often occurs in winter as a result of contact with infected rabbits.
Symptoms generally occur in 3 to 5 days after exposure. The case fatality rate in the U.S. is about 5% to 7%.
Streptomycin is the antibiotic of choice but other antibiotics are also effective. Diagnosis is dependent on isolating the organism in culture or by detection of antibodies in sera by laboratory testing.
Infection of humans in the U.S. with Babesia organisms has been reported as early as 1957. Increased numbers of cases, however, have occurred since that time in Nantucket Island and Martha's Vineyard in Massachusetts, Shelter island, New York as well as in Wisconsin. The causative agent has been Babesia microti, a normal parasite of small mammals transmitted by Ixodes scapularis ticks. Recently, possible cases have been seen in the south-central states. Patients that have been splenectomized or are immunocompromized are especially susceptible to infection. Recent findings in the Pacific Northwest indicate that a species of Babesia that appears to be distinct from B. microti has been involved in human cases. The epidemiology of this parasite is still under investigation.
Clinical signs of human babesiosis mimic mild cases of malaria, appearing as a hemolytic anemia. Diagnosis is based on observing the organism in stained blood film.
Treatment with chloroquine has been reported effective although not completely tested. Tick control and prevention of infestation appears to be the best method of preventing infection.
TICK TRANSMITTED DISEASES OF ANIMALS
Rocky Mountain spotted fever.
As discussed above, RMSF is the most commonly reported tick-transmitted rickettsial infection of humans. The occurrence in dogs appears to be similar to that of humans. Most infected dogs are less than 3 years old and pure breed dogs appear to be more likely to suffer from clinical disease. Many infected dogs also have concomitant infections with other parasites such as Ehrlichia canis.
Clinical signs in dogs are similar to those in humans. Early signs are vague. Shortly afterward, signs include fever, chills, headache and abdominal pain. Dogs have a lower frequency of developing the typical rash than do people, Dogs often show hemorrhage of the mucus membranes rather than the skin. Neuralgic signs in dogs appear to be more common than in humans.
Diagnosis and treatment in dogs is similar to humans. Dogs that have recovered from infection appear to be immune to reinfection.
Minimizing tick exposure, tick control, and tick prevention are all important in reducing the possibility of infection.
Canines do not appear to play a role in increasing the prevalence of infection in humans.
Lyme disease - Borrelia burgdorferi
Lyme disease in animals appears to closely parallel that of human cases. Because of the difficulty in positive diagnosis of this organism, actual cases are often difficult to detect. Serologic reactivity often occurs in animals without any indication of clinical disease.
Cases in dogs appear to be the most common with the typical manifestations being arthritic -like symptoms. Although positive determination of infection is often impossible, treatment with tetracycline is frequently favorable, especially in more acute cases.
A commercial vaccine is available that is widely used in hyper-endemic areas of the U.S. Its true role in both preventing infection and eliminating clinical disease is still under investigation.
Babesia infections in dogs is caused by one of two species. B. canis and B. gibsoni. B. gibsoni is known primarily from northern Africa and the Far East while B. canis is endemic in the U.S. The primary vector for canine babesiosis is Rhipicephalus sanguineus. Both transovarial and transstadial transmission are known. Pathogenesis is determined primarily by the species of parasite involved. Host factors such as age are important. Two syndromes account for most of the clinical signs, hypertensive shock and hemolytic anemia. The hypertensive shock syndrome causes hypoxia and extensive tissue damage. Vascular stasis from slugging of parasitized cells within the capillary beds is the primary cause contributing to these signs. Erythrocyte parasites (piroplasms) that invade and destroy RBCs are the cause of the hemolysis (Iintravascular) and resulting anemia.
Clinical signs in dogs with Babesia infections are hyperacute, acute, chronic or subclinical. Most dogs in he U.S. are subclinical. Dogs with hyperacute babesiosis may present in shock , comatose or dead after less than a one day history of anorexia and lethargy. Shock and metabolic acidosis are the result of severe anemia. In the U.S. the most common presentation for B. canis in puppies is acute characterized by lethargy, anorexia, fever, and hemolytic anemia. Hematuria and vomiting are common. Other signs include fever, hemoglobinemia, hemoglobinuria, icterus and splenomegaly. Chronic infections in canines are characterized by intermittent fever, depressed appetite and loss of body condition. The primary hemotologic abnormalities seen in dogs include anemia, thrombocytopenia and lymphocytosis. A mild normocytic, normochromic anemia is seen the first day after infection followed by a macrocytic, hypochromic anemia
Diagnosis is dependent on microscopic observation of piroplasms in Giemsa stained blood films. Serology (IFA) is useful in detecting occult infections. Treatment includes both supportive and babesiacidal measures. The most effective drugs are diminazene aceturate, phenamidine isethionate, and imidocarb dipropionate, none of which are approved in the U.S.
Babesia felis and B. cati are species infecting cats. Felines with babesiosis are usually younger than 2 yeas of age and present with lethargy, anorexia, weakness, rough coat and diarrhea.
Babesia odocoilei was first reported from white-tailed deer in New Mexico in 1958 and was later detected in Texas, Oklahoma and Virginia. Ixodes scapularis appears to be the primary vector based on experimental transstadial studies.
Deer appear to suffer little or no clinical problems as a result of infection. There is no indication that this organism has any impact on deer health or survival.
Diagnosis is based on finding the piroplasms in Giemsa stained blood films or by in vitro cultivation techniques. Most natural infections are characterized by low level parasitemia and often occur with concomitant Theileria cervi infections.
Ehrlichia species infections occur in a variety of animals. Ehrlichia canis, E. platys, E. ewingii, E. equi and E. risticii are obligate intracellular organism parasitizing circulating leukocytes or thrombocytes of the host. Several species in this genus cause both clinical and subclinical disease in canids. Although disease caused by these organisms was once thought to be rare, improved diagnostic capabilities and an awareness of the presence of the organisms along with a probable increase in incidence has resulted in more frequent reporting. Presently, E. canis is one of the most commonly reported canine infectious disease in the U.S. occurring any place the vector, the brown dog tick, occurs.
Three phases of the disease are recognized in canids: acute, subclinical and chronic. The chronic phase is often divided into mild chronic and severe chronic for a better clinical presentation. Pathogenicity often varies from species to species. As a result, making a clear differentiation between the acute and chronic phase of infection is often difficult.
The incubation period for E. canis lasts 8 to 20 days. The progression of infection consists of an acute phase of 2 to 4 weeks during which the organism multiplies. Nonspecific signs such as fever, ocularnasal discharge, anorexia, depression, weight loss and mild anemia may occur. The acute phase usually resolves spontaneously and is followed by a subclinical phase. During this phase, the body weight normalized and the dog appears clinically normal. Laboratory abnormalities such as a mild thrombocytopenia and hyperglobinemia often occur. Serum antibodies usually begin to rise 7 to 28 days after infection and continue to rise during the subclinical phase. The subclinical phase may last 40 to 129 days but may persist for years.
Infections with E. platys (a parasite infecting platylids) result after an incubation period of 8 to 15 days. Infected dogs usually are not clinically ill and rarely show signs of hemorrhage even with a thrombocytoperia. Duel infections with E. canis are common. Infection with E. equi, usually seen as infections of circulating neutrophils in horses, are reported from dogs. In dogs, it usually results in a mild or inapparent infection. E. risticii, the agent of Potomac horse fever, can also occur in dogs under experimental conditions.
Diagnosis requires microscopic identification of the morluae in circulating cells of Giemsa stained blood films. Serology, using E. canis antigen is routinely used.
Treatment usually involves tetracycline therapy. Supportive care is usually necessary in chronically incepted animals.
Recently, an yet unnamed Ehrlichia organism has been identified from white-tailed deer that cross reacts serologically with E. canis and E. chaffeensis. However, recent studies have shown the organism to be a distance species.
Parasites belonging to the genus Theileria infect a variety of domestic and wild ruminants in many parts of the world. The only known species in the U.S. is T. cervi infecting white-tailed deer. First reported in 1961, recent studies have documented its development in both the deer host and the tick vector. Amblyomma americanum is the only known vector with transstadial transmission being the only means of infection.
T. cervi occurs in white-tailed deer any place that the lone-star tick also occurs. Infection usually occurs by transmission to newly born fawns by unfed overwintering, infected flat adult ticks. Fawns typically develop parastiemias sufficient to serve as a source of infection for both larval and nymphal ticks, thus perpetuating the cycle. Adult deer typically maintain a parasitemia below 1%.
Clinical signs rarely occur in healthy deer and the parasite appears to play little role in either mortalities or morbidity.
The genus Cytauxzoon is reported in numerous animals throughout Africa. C. felis was first reported in the U.S. in 1976 and is now known to occur throughout the south and south-central region of the U.S. Dermacentor variabilis is the only confirmed vector (experimental) with only transstadial transmission occurring.
The normal life cycle appears to involve free-ranging bobcats as a natural host for this parasite. Infections in health bobcats appear to result in little disease but the infected animal serves as a asymptotic carrier for life.
Infections in domestic cats is uniformly fatal with only two cases of recovery being recorded. Necropsy findings in domestic cats include splenic hemorrhages with pallor and icterus (above left). Most organs showed petechial hemorrhages. Microscopic lesions include numerous large parasitized mononuclear phagocytes filled with schizonts within the lumen of veins and venus channels of the lungs, liver, lymph nodes and spleen and to a lesser extent in vessels of other organs.
Piroplasms in circulating erythrocytes occur at about 0.5% to 5% parasetemia in bobcats (above middle). Piroplasms may or may not be present in infected domestic cats at the time of presentation. Clinical signs of depression, mild anemia elevated temperature (followed by sub-normal), and lethargy are the most common signs at presentation. Clinical signs occur between 7 and 12 days following exposure.
Diagnosis is by detecting piroplasms in circulating erythrocytes in stained blood films or by detection of schizonts in the lumen of vessels in stained impression smears or histologic preparations (above right).
No serologic test is presently available and no treatment has proven effective in either preventing infection or eliminating clinical signs. Tick control and prevention of infestations is important as well as minimizing exposure of domestic animals to free-ranging cats and their ticks.
Recent reports have also documented that mountain lions (including the Florida panther) are susceptible to infection.
Members of the genus Hepatozoon are parasites in white blood cells of a variety of animals. Transmission to dogs is by the brown dog tick which transmits the infection when the dog ingests the infected tick.
Most naturally infected dogs do not develop clinical signs unless concurrently infected, immunosurpressed, have a defective neutrophil function or are under 4 months of age. Clinical signs include pain in the lumbar region, reluctance to move, ocular-nasal discharge, diarrhea, anorexia and periosteal bone proliferation.
Diagnosis is based on identifying the gametocytes in leukocytes in stained peripheral blood films or radiographaphically.
No treatment is effective in eliminating the organism but palliative treatment with non-steroid anti-inflammatory drugs is helpful in relieving discomfort.
Haemobartonella species are parasites of canines, felines and rodents. H. canis is an epierythrocytic rickettsial parasite . The organism occurs on RBCs with latent infections being common. The organism appears as chains across the surface of the infected cell or as small dots, rods or rings. Transmission is mainly by the brown dog tick with both transstadial and transovarial transmission occurring. Most natural infections in dogs do not develop into clinical problems but when they do occur they are usually associated with a developing anemia. Diagnosis is based on microscopic identification of peripheral blood smears. Treatments similar to that used for canine ehrlichiolsis involving tetracycline, oxytetracycline, etc. Antibiotic therapy probably does not eliminate the organism completely form infected dogs.
This important disease of cattle is a tick and/or fly transmitted disease with a complicated life cycle. Many cases may be the result of mechanical or accidental transmission by humans. Anaplasmosis is a disease of adult cattle as severe clinical signs do not occur until the animal is over 18 months of age. Younger animals are susceptible to infection but do not exhibit clinical disease. In mature cattle, the incubation period is 15-36 days averaging 26. There is an increase in body temperature during this period and mature animals may die during this time. Organisms (initial bodies) appear in the blood several days after the fever. Anorexia develops along with an anemia. In severe cases, the anemia may make the animal susceptible to other problems. Pathogenesis is related to RBC loss and the resultant anemia. Treatment is with tetracycline although it is not known if the animals totally eliminate the organism. Carriers, either treated animals or animals infected while young, are the source of infection. A vaccine is available but is not of value in the face of an outbreak. White-tailed deer appear to be susceptible to infection but do not play a role in either transmission or maintenance of the parasite.
Diagnosis is dependent on identification of the initial bodies in stained blood films or by serologic testing. Tick control and prevention is important in preventing infection. Prophylactic use of tetracycline is effective in preventing infections in endemic areas.
Tick paralysis is a disease caused by numerous species of ticks from several genera and is characterized by an acute, ascending flaccid motor paralysis. The paralysis affects the myoneural junction particularly the conduction rate of slower conducting terminal fibers of small diameter. The paralysis acts on motor nerves by diminishing the liberation of acetycholine and by causing damage to receptor sites. Although detected worldwide, there are notable differences in paralytic responses. Localized toxic reactions have also been described. A yet uncharacterized toxin is believed to be responsible for the paralysis. Paralysis in both humans and animals has been reported from infestations involving numerous ticks and as few as a single tick.
Prevention of infestation appears to be the only sure means of avoiding paralysis. Recovery, if diagnosed in time, is usually complete following tick removal.
Tick control on the host can be accomplished by the direct application of acaricide to the animal's hair or skin (sprays or dips) or by bathing the animal with acaracide. Many products are available for this purpose including Pyrethrums, Carboryl, marathon, Lindane, Amitraz, permethrins and chlorfenvinphos. Most are effective for 1 to 2 weeks.
Control off the host can be accomplished by using Chlorphyrifos (Dursban) or tetrachlorvinphos (Rabon, Stirophos). These are USDA approved products designed for application in parks, recreational areas, etc. and should be timed to coincide with tick activities.
Collars that effect both fleas and ticks are available for both dogs and cats. There are many active ingredients impregnated into the resin or plastic of the collar that allows the acaracide to be released slowly over time. The effectiveness of the acaracide in the collar is related tot he toxicity or the ingredient and to the speed of release. Collars containing propoxur and dichlorvos provide rapid control of ticks with most ticks that are attached being killed by 72 hours after application. Collars with chlorfenvinphos provide the greatest and longest protection against reinfestation.
Zoonosis Updates. 1990. American Veterinary Medical Association. pp139.
Kocan, A. and K.M. Kocan. 1991. Tick-transmitted protozoan diseases of wildlife in North America. Bulletin of the Society of Vector Ecology. 16: 94-108.
Ewing, S.A., J. Dawson, A. Kocan, et al. 1995. Experimental transmission of Ehrlichia chaffeensis among white-tailed deer by Amblyomma americanum. Journal of Medical Entomology 32: 368-374.
Laird, J. A. Kocan, K. Kocan, et al. 1988. Susceptibility of Amblyomma americanum to natural and experimental infections with Theileria cervi. Journal of wildlife Diseases. 24: 679-683.
Blouin, E., A. Kocan, B. Glenn, K. Kocan, et al. 1984. Transmission of Cytauxzoon felis from bobcats to domestic cats by Dermacentor variabilis. Journal of Wildlife Diseases 20: 241-242.
Lane, J., and A. Kocan. 1983. Hepatozoon sp infection in bobcats. Journal of the American Veterinary Medical Association. 183: 1323-1324.
Waldrup, K., A. Kocan, R. Barker, et al. 1990. Transmission of Babesia odocoilei in white-tailed deer by Ixodes scapularis. Journal of Wildlife Diseases 26: 390-391.
Dawson, J., C. Warner, V. Baker, S. Ewing, D. Stalknecht, W. Davidson, A. Kocan, J. Lockhart, and J. Olson. 1996. Ehrlichia-like 16S rDNA sequence from wild white-tailed deer (Odocoiles virginianus). J. Parasitol. 82: 52-58.
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