Cytauxzoonosis
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''Cytauxzoon felis'' is a
protozoal Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically, ...
organism transmitted to domestic
cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...
s by
tick bite Ticks are parasitic arachnids of the order Ixodida. They are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, and species, but can become larger when engorged. Ticks ar ...
s, and whose
natural reservoir In Infection, infectious disease ecology and epidemiology, a natural reservoir, also known as a disease reservoir or a reservoir of infection, is the population of organisms or the specific environment in which an infectious pathogen naturally li ...
host is the
bobcat The bobcat (''Lynx rufus''), also known as the wildcat, bay lynx, or red lynx, is one of the four extant species within the medium-sized wild cat genus '' Lynx''. Native to North America, it ranges from southern Canada through most of the c ...
. ''C. felis'' has been found in other wild
felid Felidae ( ) is the Family (biology), family of mammals in the Order (biology), order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ). The 41 extant taxon, extant Felidae species exhibit the gre ...
species such as the
cougar The cougar (''Puma concolor'') (, ''Help:Pronunciation respelling key, KOO-gər''), also called puma, mountain lion, catamount and panther is a large small cat native to the Americas. It inhabits North America, North, Central America, Cent ...
, as well as a
white tiger The white tiger (ashy tiger) is a leucistic morph of the tiger, typically the Bengal tiger. It is occasionally reported in the Indian wilderness. It has the typical black stripes of a tiger, but its coat is otherwise white or near-white, and ...
in captivity. ''C. felis'' infection is limited to the family
Felidae Felidae ( ) is the Family (biology), family of mammals in the Order (biology), order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ). The 41 extant taxon, extant Felidae species exhibit the gre ...
which means that ''C. felis'' poses no
zoonotic A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a virus, bacterium, parasite, fungi, or prion) that can jump from a non-human vertebrate to a human. When h ...
(transmission to humans) risk or agricultural (transmission to farm animals) risk. Until recently it was believed that after infection with ''C. felis'', pet cats almost always died. As awareness of ''C. felis'' has increased it has been found that treatment is not always futile. More cats have been shown to survive the infection than was previously thought. New treatments offer as much as 60% survival rate.


Terminology

''Cytauxzoon felis'' belongs to the order
Piroplasmida Piroplasmida is an order of parasites in the phylum Apicomplexa. They divide by binary fission and as sporozoan parasites they possess sexual and asexual phases (sexual reproduction occurs in the tick gut). They include the tick parasites ''Ba ...
and the family
Theileriidae Theileriidae is a family of parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it s ...
. ''C. felis'' is related to ''
Theileria ''Theileria'' is a genus of parasites that belongs to the phylum Apicomplexa, and is closely related to ''Plasmodium''. Two ''Theileria'' species, ''T. annulata'' and ''T. parva'', are important cattle parasites. ''T. annulata'' causes tropical ...
spp''. of African
ungulate Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with Hoof, hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined ...
s. It is not a
bacterium Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...
, not a
virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...
, and not a
fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
, but is instead a
protozoan Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...
that infects the blood cells of cats.


Epidemiology

The first case of ''C. felis'' was documented in
Missouri Missouri (''see #Etymology and pronunciation, pronunciation'') is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it border ...
in 1976, and in the past it was believed to be limited to south central and southeastern
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
. There have been more cases popping up in the
mid-Atlantic region The Mid-Atlantic is a region of the United States located in the overlap between the nation's Northeastern and Southeastern states. Traditional definitions include seven U.S. states: New York, New Jersey, Pennsylvania, Delaware, Maryland, Virgi ...
in the United States, and even as far north as
Pennsylvania Pennsylvania, officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appalachian, and Great Lakes region, Great Lakes regions o ...
and
North Dakota North Dakota ( ) is a U.S. state in the Upper Midwest, named after the indigenous Dakota people, Dakota and Sioux peoples. It is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minneso ...
in bobcats. There has not been any age or sex predilection made, but intact animals have shown more prevalence in some studies; in particular intact males. In studies it is unclear if the sex predilection is due to the increased roaming of intact animals or another reason. The most common seasons for the disease to become apparent are spring and summer and appear to affect outdoor cats the most often. The reason that outdoor cats get infected more is due to the increased exposure to ticks. Ticks are also active in spring and summer.


Symptoms and signs

Most infected cats have been healthy before a very sudden onset of severe disease. The course of clinical disease is often swift with clinical signs of
lethargy Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness, or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overw ...
and inappetence within 5 to 20 days after the tick bite. Cats develop a high fever, but the temperature may become low before death. Other clinical findings can be:
dehydration In physiology, dehydration is a lack of total body water that disrupts metabolic processes. It occurs when free water loss exceeds intake, often resulting from excessive sweating, health conditions, or inadequate consumption of water. Mild deh ...
, icterus (
jaundice Jaundice, also known as icterus, is a yellowish or, less frequently, greenish pigmentation of the skin and sclera due to high bilirubin levels. Jaundice in adults is typically a sign indicating the presence of underlying diseases involving ...
),
enlarged liver Hepatomegaly is enlargement of the liver. It is a non-specific medical sign, having many causes, which can broadly be broken down into infection, hepatic tumours, and metabolic disorder. Often, hepatomegaly presents as an abdominal mass. Dependi ...
and spleen,
lymphadenopathy Lymphadenopathy or adenopathy is a disease of the lymph nodes, in which they are abnormal in size or consistency. Lymphadenopathy of an inflammatory type (the most common type) is lymphadenitis, producing swollen or enlarged lymph nodes. In c ...
, pale mucous membranes,
respiratory distress Shortness of breath (SOB), known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing discomfort that c ...
,
tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal ...
or
bradycardia Bradycardia, also called bradyarrhythmia, is a resting heart rate under 60 beats per minute (BPM). While bradycardia can result from various pathological processes, it is commonly a physiological response to cardiovascular conditioning or due ...
, and tick infestation (although ticks are not often found on infected cats since cats typically groom ticks off their fur). Signs of disease seen on blood work include
hemolytic anemia Hemolytic anemia or haemolytic anaemia is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells (RBCs), either in the blood vessels (intravascular hemolysis) or elsewhere in the human body (extravascular). This most commonl ...
,
thrombocytopenia In hematology, thrombocytopenia is a condition characterized by abnormally low levels of platelets (also known as thrombocytes) in the blood. Low levels of platelets in turn may lead to prolonged or excessive bleeding. It is the most common coag ...
, increased or decreased
white blood cell White blood cells (scientific name leukocytes), also called immune cells or immunocytes, are cells of the immune system that are involved in protecting the body against both infectious disease and foreign entities. White blood cells are genera ...
numbers, icterus, and elevated
liver enzymes Liver function tests (LFTs or LFs), also referred to as a hepatic panel or liver panel, are groups of blood tests that provide information about the state of a patient's liver. These tests include prothrombin time (PT/INR), activated partial t ...
. Death usually follows the onset of clinical signs within a few days. However, more recent studies show not all cats develop clinical signs after infection, and some cats survive the infection.


Life cycle and transmission

The life cycle for ''Cytauxzoon felis'' has not been completely described. Bobcats become persistent carriers of the organism after they develop mild or subclinical infection and then serve as the reservoir host. ''C. felis'' is transmitted by the Lone star tick (''
Amblyomma americanum ''Amblyomma americanum'', also known as the lone star tick, northeastern water tick, turkey tick, and cricker tick, is a type of tick indigenous to much of the eastern United States and Mexico that bites painlessly and commonly goes unnoticed, r ...
'') that feeds on an infected bobcat then transmits the organism to another bobcat, or to a pet cat. Many other types of ticks may feed on the cats, but the only other tick that has been shown to transmit the organism is the American dog tick (''
Dermacentor variabilis ''Dermacentor variabilis'', also known as the American dog tick or wood tick, is a species of tick that is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever and tularemia (''Francisella tul ...
'') but only in a research setting. In the past, domestic cats were thought to always die from infection so they were considered terminal hosts or "dead end hosts". Now there have been documented cases of cats that get sick and survive the infection and even those that never show clinical signs at all. Cats cannot catch the infection from another cat directly without being bitten by a tick. The life cycle of the protozoa has a tissue phase and an
erythrocytic Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...
(red blood cell) phase. The organism goes through
asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...
phase that is called
schizogony Fission, in biology, is the division of a single entity into two or more parts and the regeneration of those parts to separate entities resembling the original. The object experiencing fission is usually a cell, but the term may also refer to ho ...
which occurs in the mononuclear phagocytic cells. In the tissue phase, the macrophage cells that are infected often clog
venules A venule is a very small vein in the microcirculation that allows blood to return from the capillary beds to drain into the venous system via increasingly larger veins. Post-capillary venules are the smallest of the veins with a diameter of bet ...
in organs such as the liver, spleen, lungs, and lymph nodes. It is this phase that is associated with clinical disease if the schizonts are numerous. Schizonts next form merozoites that break out of the
macrophage Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...
cells and infect the red blood cells (erythrocytes). The erythrocytic disease is not as important for clinical disease, but is often used to diagnose ''C. felis'' because
piroplasm Piroplasmida is an order of parasites in the phylum Apicomplexa. They divide by binary fission and as sporozoan parasites they possess sexual and asexual phases (sexual reproduction occurs in the tick gut). They include the tick parasites ''B ...
s (erythrocytes that have phagocytized
merozoite Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism i ...
s) can be seen on a
peripheral blood smear A blood smear, peripheral blood smear or blood film is a thin layer of blood smeared on a glass microscope slide and then stained in such a way as to allow the various blood cells to be examined microscopically. Blood smears are examined in the i ...
under the microscope. It is not clear why some cats become clinically affected with ''C. felis'' while others never show any signs. There are speculations about resistance in some cats, and speculations about different strains of ''C. felis'' with differing virulence. There is not enough information to prove any of these theories, but cats in the same household or same regions can have drastically different clinical presentations. Some studies even show multi-cat households have had one cat die and another be persistently infected. When cats survive infection they have persistent
parasitemia Parasitemia is the quantitative content of parasites in the blood. It is used as a measurement of parasite load in the organism and an indication of the degree of an active parasitic infection. Systematic measurement of parasitemia is important in ...
which shows up in the blood as piroplasms, but these cats do not have the tissue phase again and therefore do not again show the clinical illness.


Diagnosis

One way to diagnose ''C. felis'' is by taking blood and performing a peripheral blood smear to look for the erythrocytic piroplasms. The erythrocytic piroplasms are usually shaped like signet rings and are 1 to 1.5 μm. Not all cats that are infected will have the piroplasms on their blood smear, especially if they are early in disease course. Another method of diagnosing infection in sick cats is to take needle aspirates of affected organs and find the schizonts inside mononuclear cells in the tissues; examination of tissue is also useful for the diagnosis after cats have died. Blood samples can be sent away for
polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to make millions to billions of copies of a specific DNA sample rapidly, allowing scientists to amplify a very small sample of DNA (or a part of it) sufficiently to enable detailed st ...
(PCR) testing to confirm infection. Other diseases that might resemble cytauxzoonosis should be ruled out. A major rule-out for ''C. felis'' is ''
Mycoplasma haemofelis ''Mycoplasma haemofelis'' is an epierythrocytic parasitic bacterium. It often appears in bloodsmears as small (0.6 μm) coccoid bodies, sometimes forming short chains of three to eight organisms. It is usually the causative agent of feline ...
'' (formerly known as ''Haemobartonella felis''); clinical signs can be similar to cytauxzoonosis and the organism may be confused on the peripheral smear. Because it causes similar signs in outdoor cats during the spring and summer,
tularemia Tularemia, also known as rabbit fever, is an infectious disease caused by the bacterium '' Francisella tularensis''. Symptoms may include fever, skin ulcers, and enlarged lymph nodes. Occasionally, a form that results in pneumonia or a throat ...
is another disease the veterinarian may want to rule out. Other laboratory tests are often abnormal in sick cats. The
CBC CBC may refer to: Media * Cadena Baja California or Grupo Cadena, a radio and television broadcaster in Mexico * Canadian Broadcasting Corporation, Canada's radio and television public broadcaster ** CBC Television ** CBC Radio One ** CBC Music ** ...
of an infected cat often shows a
pancytopenia Pancytopenia is a medical condition in which there is significant reduction in the number of almost all blood cells (red blood cells, white blood cells, platelets, monocytes, lymphocytes, etc.). If only two parameters from the complete blood cou ...
, or a decrease in red blood cells, white blood cells, and
platelet Platelets or thrombocytes () are a part of blood whose function (along with the coagulation#Coagulation factors, coagulation factors) is to react to bleeding from blood vessel injury by clumping to form a thrombus, blood clot. Platelets have no ...
s; in some cases there is not a decrease in all three values. Clotting tests may be prolonged. Increased liver enzymes are common, and
electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...
disturbances,
hyperglycemia Hyperglycemia is a condition where unusually high amount of glucose is present in blood. It is defined as blood glucose level exceeding 6.9 mmol/L (125 mg/dL) after fasting for 8 hours or 10 mmol/L (180 mg/dL) 2 hours after eating. Blood gluc ...
, and acid-base disturbances can also be observed.


Treatment and prevention

The preventative measure of keeping cats inside in areas with high infection rates can prevent infection. Approved tick treatments for cats can be used but have been shown not to fully prevent tick bites. The most often used treatments for cytauxzoonosis are imidocarb dipropionate and a combination of
atovaquone Atovaquone, sold under the brand name Mepron, is an antimicrobial medication for the prevention and treatment of ''Pneumocystis jirovecii'' pneumonia (PCP). Atovaquone is a chemical compound that belongs to the class of naphthoquinones. Atova ...
and
azithromycin Azithromycin, sold under the brand names Zithromax (in oral form) and Azasite (as an eye drop), is an antibiotic medication used for the treatment of several bacterial infections. This includes otitis media, middle ear infections, strep throa ...
. Although imidocarb has been used for years, it is not particularly effective. In a large study, only 25% of cats treated with this drug and supportive care survived. 60% of sick cats treated with supportive care and the combination of the
anti-malarial drug Antimalarial medications or simply antimalarials are a type of antiparasitic chemical agent, often naturally derived, that can be used to treat or to prevent malaria, in the latter case, most often aiming at two susceptible target groups, young c ...
atovaquone and the antibiotic azithromycin survived infection. Quick referral to a veterinarian equipped to treat the disease may be beneficial. All infected cats require supportive care, including careful fluids, nutritional support, treatment for complications, and often
blood transfusion Blood transfusion is the process of transferring blood products into a person's Circulatory system, circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used ...
. Cats that survive the infection should be kept indoors as they can be persistent carriers after surviving infection and might indirectly infect other cats after being themselves bitten by a vector tick.


References


External links


Cytauxzoonosis - The Merck Veterinary Manual





Cytauxzoonosis - WSAVA 2002
{{Taxonbar, from=Q779053 Parasites of cats Zoonoses Veterinary protozoology