Difference between revisions of "Feline Infectious Anaemia"

Revision as of 20:31, 24 March 2012

Previously known as: Haemobartonellosis

Caused by: Mycoplasma haemofelis , previously known as Haemobartonella felis

Introduction

Feline Infectious Anaemia, caused by Mycoplasma haemofelis (Mhf), is a regenerative anaemia of cats. The disease occurs worldwide and should be considered as a differential diagnosis for any cat presenting with anaemia.

Aetiology

Mhf is one of a group of organisms known as haemotropic mycoplasmas which infect several other domestic animal species. The causative organism was previously called Haemobartonella felis and thus the disease was known as haemobartonellosis. Polymerase chain reaction (PCR) assays allowing DNA analysis resulted in the reclassification of the organism in 2001¹. Two other haemotropic mycoplasmas (Candidatus M. haemominutum and Candidatus M. turicensis) have been identified in cats but appear to be less pathogenic².

Mhf can vary in shape from cocci to rods and are sometimes present in chains on the cell surface.

The mode of transmission of Mhf is poorly understood.

Signalment

The major group at risk for Mhf infection are male cats who spend time outdoors. In many areas of the world an association has been shown between Mhf and retroviral infections². It has been demonstrated that cats infected with Mhf and feline leukaemia virus (FeLV) are likely to develop more severe anaemia that cats infected only with Mhf³.

Pathogenesis

The pathogenesis of Mhf is not fully understood. It is thought that the presence of the parasite on the surface of the red blood cells may induce antibody production⁴. The anaemia, which is primarily extravascular, may be due to direct damage of erythrocytes by the organism or as a result of the antibodies produced by the infected animal ².

Clinical signs

Infected cats most commonly present for lethargy and decreased appetite. Physical examination findings can include signs of anaemia, such as mucous membrane pallor, tachypnoea and tachycardia, elevated temperature and occasionally jaundice. The anaemia can be severe and rapidly fatal in some cases.

Diagnosis

The most commmon findings from complete blood counts from cats with Mhf infections are a marcocytic, hypochromic regenerative anaemia. Reticulocytes and Howell-Jolly bodies may be identified on cytologic examination.

Mhf infection can be definitvely diagnosed by identification of organisms on a blood smear, appearing as cocci or rods and sometimes forming short chains of organisms. However, the test is less than 50% sensitive ⁵ as the animal's immune response causes organisms to disappear from the blood stream for several days, often to reappear a few days later.

Treatment

Infected cats should be treated with doxycycline for 3 weeks twice daily. Enrofloxacin is also a good treatment choice especially in refractory cases when combined with doxycycline.

A blood transfusion may also be required in cases of severe anaemia.

As blood sucking endoparasites, such as Fleas, are thought to spread disease the animal should also receive flea treatment.

Prednisolone is also advised to treat the immune mediated mechanisms and to prevent further erythrophagocytosis.

Prognosis

Varied prognosis depending on the severity of the anaemia at presentation. If not treated 1/3 of affected animals will die. Antibiotics do not clear the infection so many cats become carriers of the organism however relapses are uncommon.

Feline Infectious Anaemia Learning Resources
Flashcards Test your knowledge using flashcard type questions	Small Animal Emergency and Critical Care Medicine Q&A 12
Literature Search Search for recent publications via CAB Abstract (CABI log in required)	Mycoplasma haemofelis publications Feline Infectious Anaemia publications
Full Text Articles Full text articles available from CAB Abstract (CABI log in required)	Diagnosis and management of Hemoplasma infections. Lappin, M. R.; The North American Veterinary Conference, Gainesville, USA, Small animal and exotics. Proceedings of the North American Veterinary Conference, Orlando, Florida, USA, 17-21 January, 2009, 2009, pp 655-656, 23 ref. Bartonellosis and hemoplasmosis in dogs and cats: emerging issues. Lappin, M. R.; The North American Veterinary Conference, Gainesville, USA, Small animal and exotics. Proceedings of the North American Veterinary Conference, Volume 21, Orlando, Florida, USA, 2007, 2007, pp 629-631

References

Niemark
Sykes, JE (2010) Feline Hemotropic Mycoplasmas Vet Clinics of North America Small Animal pp. 1157-1170
Hagiwara, MK (2009) Anemia in Cats: Is It Mycoplasma? Proceedings of the 34th World Small Animal Veterinary Congress
Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2)W.B. Saunders Company

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

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 ==Clinical signs==
-The peracute disease is associated with severe anaemia and immunosuppression, and can be rapidly fatal.
-Fever, anaemia, depression, weakness and [[Icterus|jaundice]] occur in the acute form. In the chronic form animals present with [[Regenerative and Non-Regenerative Anaemias|anaemia]], lethargy and weight loss.
+Infected cats most commonly present for lethargy and decreased appetite. Physical examination findings can include signs of anaemia, such as mucous membrane pallor, tachypnoea and tachycardia, elevated temperature and occasionally [[Icterus|jaundice]]. The anaemia can be severe and rapidly fatal in some cases.
-Cyclic fever may also occur during the transient period of parasitaemia.
-Recovery can occur with a regenerative bone marrow response, however severe anaemia may occur in the presence of [[Feline Leukaemia Virus|feline leukaemia virus]] (FeLV).
 ==Diagnosis==
-The best diagnostic test is a PCR, which is very sensitive and enables differentiation of the different species.
-The organism can also be diagnosed on blood smears.
-The organism can be intermittently seen microscopically on the surface of red blood cells on Giemsa-stained blood smears. The organism stains blue and can look like rings or rods.
-Erythrophagocytosis may be evident and parasitised erythrocytes will become spherical.
-The organism must be differentiated from [[Regenerative and Non-Regenerative Anaemias|Howell-Jolly bodies]] and other parasites. Due to the cyclic parasitaemia the organism causes, negative blood smears will not rule out the disease.
-Additionally [[Immunofluorescence]] of blood smears can demonstrate the organism.
+The most commmon findings from complete blood counts from cats with Mhf infections are a marcocytic, hypochromic regenerative anaemia. Reticulocytes and Howell-Jolly bodies may be identified on cytologic examination.
-Haematology will show a decreased packed cell volume and a low red blood cell count. The anaemia is usually regenerative. FeLV infection is associated with macrocytosis.
+Mhf infection can be definitvely diagnosed by identification of organisms on a blood smear, appearing as cocci or rods and sometimes forming short chains of organisms. However, the test is less than 50% sensitive <sup>5</sup> as the animal's immune response causes organisms to disappear from the blood stream for several days, often to reappear a few days later.
 ==Treatment==