Babesia bigemina- Agent of Texas Cattle fever.
This important parasite of cattle has a similar life cycle to Plasmodium only no tissue stages occur in the vertebrate animal. Infection involves only RBCs. Babesiosis is a tick transmitted disease with transovarial and transstadial transmission occurring. Clinical signs in the bovine are related to RBC loss due to parasite multiplication. Occasional complications occur with cerebral forms. Hemoglobinuria (blood int he urin) is common, resulting from massive cell distruction. Diagnosis is dependent on identifying piroplasms in infected erythrocytes (above) in Giemsa stained blood films. Infections are often more pathogenic for adult animal than young. Texas cattle fever is eradicated from the U.S. but constant surveillance of our southern border is necessary. There are many species of Babesia which infect other animals including horses, dogs, cats wildlife, and humans.
Babesia sp. infections in canines are caused by one of two species, B. canis and B. gibsoni. B. canis infections are endemic to the U.S. while B. gibsoni is known primarily from northern Africa and the Far East. B. felis and B. cati are both species infecting cats.
The primary vector for canine babesiosis is Rhipicephalus sanguineus . Pathogenesis is determined primarily by the species of parasite involved (and/or strain). Host factors such as the age of the host are also important. Two syndromes account for most of the clinical signs observed in animals with babesiosis, hypotensive shock and hemolytic anemia. The hypotensive shock syndrome causes hypoxia and extensive tissue damage. Vascular stasis from slugging of parasitized cells within the capillary beds are the primary cause contributing to these signs. Erythrocyte parasitemia results in hemolysis (intravascular) that is the cause of the anemia.
Clinical signs of dogs with babesiosis may be hyperacute, acute, chronic or subclinical. Most dogs in the U.S. are subclinical. Dogs with hyperacute babesiosis may present in shock or are comatose or dead after less than one day history of anorexia and lethargy. Shock and metabolic acidosis are the result of severe anemia. Acute presentations (more common in Africa, Asia and southern Europe) are characterized by lethargy, anorexia, fever, and hemolytic anemia. In the U.S this is the most common presentation for B. canis infected puppies. Dogs with acute presentations usually have a 2 to 3 day history of anorexia and lethargy. Hematuria and vomiting are common. Other signs include fever, hemoglobinemia, hemoglobinuria, icterus and splenomegaly. Chronic infections in canines are characterized by intermittent fever, decreased appetite loss of body condition. Recent findings have indicated that B. gibsoni may also be endemic in the U.S. with reports from dogs in both Connecticut and California with no history of foreign travel. The most common clinical signs for B. gibsoni infectionss are lethargy, anorexia, and anemia. See a report by Conrad, P., et. al.,1991. JAVMA 199: 601-605 for details.
Cats with babesiosis are usually younger than 2 years and present with lethargy, anorexia, weakness, rough hair coat and diarrhea.
The primary hematologic abnormalities seen in animals with beabesiosis include anemia, thrombocytopenia and lymphocytosis. A mild normocytic, normochromic anemia is seen in the first few days 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.
Human babesiosis is now more common than in previous years. Most cases are documented species known to infect rodents (B. microti) and/or cattle (B. divergens). The vector for most human cases in the U.S. is Ixodes scapularis Recently, an apparently new species of Babesia has been identified in splenecttomized patients in Washington state.
Theileria parva parva- Agent of East-Coast Fever (ECF) in east and south Africa.
Members of this genus are similar to Babesia except that sporozoites enter lymphocytes (Koch's blue bodies) (above) where schizogony occurs prior to RBC invasion. Piroplasms occur in RBCs (below). ECF is a serious disease of cattle with a high mortality rate. The disease is characterised by lymphoid hyperplasia followed by lymphoid depletion and leucopenia. The incubation period for the disease averages 13 days following exposure. The acute form of the disease (most common) lasts between 1 and 3 weeks and is characterised by a rising temperature (105 - 107 F). Associated with the fever are lymph node swelling, nasal discharge and swelling of the eye lids and ears. Pulmonary oedema usually occurs, often leading to death. East Coast Fever is another tick transmitted disease without transovarial transmission. Rhipicephalus appendiculatus is the primary vector although other genera and numerous species are capable of transmission. This or similar piroplasms are present in many wild species in Africa few, of which show any clinical disease.
Treatment with parvoquine or buparvoquine is effective after initial exposure to sporozoites. Continuous tick control is important in prevention.
Theileria parva lawrenci- This species of Theileria is similar to T. parva parva but thought to be originally a parasite of cape buffalo. This disease is often encountered in an area known as the "corridor", an area of over 100 square miles between Hluhluwe and Umfolozi game reserves in Zululand. The Aftican cape buffalo is susceptible to infection with this organism but developes only mild clinical signs while transmission to cattle results in high mortalities. Some researchers believe this to be a transformed or mutated formof T. parva parva while most consider it a distinct species.
T. annulata is another species in this genus occuring in bovines in North Africa, the Middle and Far East, and southern Europe and is vectored by species of Hyalomma ticks.
T. mutans occurs in bovines in Africa. Asia, and Australia. The disease caused by this organism is generally benign and mortalities are rare. Several genera of ticks can transmit this organism. A single reporting exists of this parasite in cattle in the U.S.
T. taurotragi, originally described from an eland, also occurs in bovines in Africa.
Other species of Theileria occur in sheep (T. hirci in East Africa, Iraq, Turkey and Greece and T. ovis in Africa, Asia, India and Europe).
Theileria cervi- This is a non-pathogenic parasite of deer in North America. It is the only member of this genus in the U.S. and appears to occur only in white-tailed deer. Infections are transmitted by Amblyomma americanum and occur throughout the southwestern and south-central states..
Cytauxzoon felis- Agent of feline cytauxzoonosis.
This organism is a uniformly fatal parasite of domestic felines in North America. Infections are reported throughout most of the south and south-central states. Other members of this genus are present in a variety of African animals but this is the only memebr of this genus known to occur in the U.S.. The life cycle involves a wildlife reservoir, the bobcat that serves as an asymptomatic carrier. . Dermacentor variabilus is the only known tick vector. The life cycle for the parasite is similar to that of Theileria spp except schizogony occurs in endothelial macrophages of blood vessels. Only transstadial transmission is known.
Clinical signs in infected cats are typical of any infection that results in a hemolytic crisis such as anorexia, labored breathing, lethargy, dehydration, depression, icterus, and fever. Cats usually die 2 to 3 days after the body temperature peaks (103-107F) ; usually being sub-normal at death. The entire course of the clinical infection lasts less than 7 days.
Diagnosis is by the detection of pyroplasms in circulating erytrhocytes. Infection levels are usually below 2% and often death occurs prior to the presence of an erythroparasitemia. Diagnosis at necropsy can be accomplished by detection of schizont laden macrophages in the intima of blood vessels of all organs (above). Giemsa stained impression smears of lung, liver, spleen, etc. are the best tissues.
No treatment has proven effective against this organism. Supportive care may extend the clinical period but only 2 confirmed cases of recovery are documented.
Tick control is important in preventing exposure. Recent changes in both demographics and living preferences have influenced both animal and human tick-transmitted disease prevelance. Exposure of domestic cats to ticks normally infesting bobcats has increased the prevelance of this disease in many regions of the U.S.