Anaplasma, Ehrlichia, Rickettsia infections
Edited November 1, 2016
Anaplasma spp., Ehrlichia spp. and Rickettsia spp. are vector-borne pathogens infecting many mammalian species, but causing disease in very few of them. Anaplasma phagocytophilum is the most important feline pathogen among them and co-infections are possible.
Some species (A. phagocytophilum, Ehrlichia chaffeensis, Ehrlichia ewingii, Rickettsia conorii, Rickettsia rickettsii, Rickettsia felis, Rickettsia typhi) are of zoonotic concern.
The geographical distribution of Anaplasma, Ehrlichia and Rickettsia pathogens overlaps with that of their competent vectors (ticks or fleas).
Little information is available on the pathogenesis of these agents in cats.
Clinical signs are usually reported soon after tick infestation. They are mostly non-specific and consist of fever, anorexia, lethargy. Joint pain may occur.
Blood or buffy-coat smear evaluation may be useful for cytological diagnosis of infections with Ehrlichia and Anaplasma spp.
Antibodies to rickettsial infections can be detected by immunofluorescence (IF) test and ELISA, but cross-reactions exist between organisms of the same genus.
Blood PCR analysis is a sensitive and specific method for confirming diagnosis at the onset of acute clinical signs before starting therapy when antibody testing is usually still negative.
Doxycycline is the first choice antibiotic for treating rickettsial infections.
Regular application of appropriate ectoparasiticide spot on or collars protects cats from infection.
In endemic areas blood donors should be tested for rickettsial blood-borne infections.
Infected cats are “sentinels” of the presence of rickettsial pathogens in ticks and fleas in a given geographical area and they signal a risk for people exposed to vectors.
Direct contact with cat saliva should be avoided because of the potential contamination by R. felis as well as by other zoonotic pathogens.
Agent properties and epidemiology
Obligate intracellular Gram negative coccoid organisms of the Anaplasma, Ehrlichia and Rickettsia genera are vector-borne members of the Rickettsiales order infecting humans and a wide variety of domestic and wild animals worldwide (Allison and Little, 2013). They generally have a wide host specificity, considering that many mammalian species can be infected. Importantly, some hosts might serve as reservoirs of infection; however, susceptibility to disease is usually more restricted.
Anaplasma, Ehrlichia and Rickettsia are difficult to culture in vitro; molecular genetics opened new avenues to study their infection biology (Allison and Little, 2013). Compared to dogs, these pathogens have been generally less studied in cats (Table 1).
|Ehrlichia genus||Countries in which the infection has been detected|
|E. canis||Canada USA Brazil Portugal|
|E. chaffeensis||USA Brazil|
|Ehrlichia spp.||Italy USA Kenia France|
|A. phagocytophilum||USA Sweden Finland Poland Switzerland Germany Italy Spain|
|A. platys||USA Brazil|
Anaplasma and Ehrlichia spp. are tick-borne pathogens of the Anaplasmataceae family and are pleomorphic intravacuolar organisms that replicate in haemopoietic cells. They give rise to cytoplasmic inclusion bodies: small elementary bodies (0.2-0.4 µm diameter), larger reticulate bodies and morulae (up to 2-6 µm).
Anaplasma phagocytophilum replicates in myeloid cells (mostly in neutrophils; Fig. 1) and is the agent of granulocytotropic anaplasmosis. It infects persons and a wide range of animal species worldwide, especially in the Northern hemisphere. It is the most important feline pathogen of the Anaplasma genus. Wild small mammals are the natural reservoirs. Antibody prevalence to A. phagocytophilum in cats has been reported as 4.5-33.3% in Italy (Ebani and Bertelloni, 2014; Persichetti et al., 2016), 2.0-8.0% in Spain (Solano-Gallego et al., 2006; Ayllón et al., 2012), 16.2% in Germany (Hamel et al., 2012), 22.1% in Sweden (Elfving et al., 2015) and 1.8-38.0% in the USA (Magnarelli et al., 2005; Billeter et al., 2007; Hegarty et al., 2015). Anaplasma phagocytophilum DNA was recently amplified in 0.4% of blood samples from cats admitted to veterinary clinics in South Germany (Bergmann et al., 2015).
Anaplasma platys replicates in mature platelets and is the agent of thrombocytotropic anaplasmosis, a disease well documented worldwide in dogs (Sainz et al., 2015). In cats, it has been occasionally detected by PCR analysis (Lima et al., 2010; Qurollo et al., 2014; Hegarty et al., 2015). Anaplasma bovis has also been found by PCR in feline blood samples from Japan (Sasaki et al., 2012). Recently a novel, unclassified A. platys-like strain from cats was characterized in Sardinia (Italy). This strain, despite its tropism for platelets, is closely related to others identified in ruminants (Zobba et al., 2015).
Ehrlichia canis is the agent of canine monocytotropic ehrlichiosis. This disease was described in tropical and temperate areas worldwide, with the exception of Australia. Ehrlichia chaffeensis is the agent of human monocytotropic ehrlichiosis reported mainly from the USA. The granulocytotropic Ehrlichia ewingii has been evidenced in dogs and humans in the Midwestern and Southern United States. E. canis has been detected by PCR in blood samples from cats (Breitschwerdt et al., 2002; Oliveira et al., 2009; Ayllón et al., 2012; Braga et al., 2012, 2013, 2014; Maia et al., 2014; Hegarty et al., 2015; André et al., 2015). Less frequently, E. chaffeensis and E. ewingii were found (Braga et al., 2012; Hegarty et al., 2015). Cats seropositive for E. canis (6.0-18.0%) have been reported in Europe (Aguirre et al., 2004; Ortuño et al., 2005; Solano-Gallego et al., 2006; Ayllón et al., 2012; Ebani and Bertelloni, 2014; Persichetti et al., 2016), 5.5% in Brazil (Braga et al., 2012) and 0.7% in the USA (Hegarty et al., 2015).
Another member of the Anaplasmataceae family that leads to Neoehrlichiosis is ‘Candidatus Neoehrlichia mikurensis’ (genus ‘Candidatus Neoehrlichia’). This emerging tick-borne agent has been found mainly in immunocompromised patients, in ticks and rodents and recently also in two dogs (Diniz et al., 2011; Hofmann-Lehmann et al., 2016), but so far not in cats. The infection may be underdiagnosed because diagnostic assays are not yet widely available.
The Rickettsiaceae family includes the spotted fever group (SFG) and the typhus group agents (Allison and Little, 2013). More than 20 species are included in the SFG of the Rickettsia genus, some of them being important human pathogens. Historically, the most important zoonotic agents are R. conorii (the cause of Mediterranean spotted fever) in the Old World, and R. rickettsii (the agent of Rocky Mountains spotted fever) in the Americas. However, recent molecular studies have increasingly focused on other rickettsial species that may be involved in human clinical disease manifestations. Rickettsia massiliae for example is now recognised as the most widely distributed Rickettsia species that affects humans, being found worldwide (Brouqui et al., 2007).
Rickettsia rickettsii and R. conorii are both transmitted by ticks, infect dogs and may cause a clinical condition in dogs. Less information is available about the effect of these agents in cats. Feline infections caused by R. massiliae and R. conorii have been confirmed by both PCR and antibody testing in endemic areas of Spain and Portugal (Solano-Gallego et al., 2006; Alves et al., 2009; Vilhena et al., 2013; Segura et al., 2014), whereas cats seropositive for R. rickettsii have been reported in the USA (Case et al., 2006).
Rickettsia felis is worldwide an emerging flea-borne SFG human pathogen frequently detected in Ctenocephalides felis, less often in other flea species (Brouqui et al., 2007). C. felis is the vector and the recognised reservoir of R. felis, which is vertically transmitted to successive generations of fleas (Wedincamp and Foil, 2002). Recent studies carried out in some parts of Europe have shown that Ctenocephalides infection rates range from 2.8% in Albania (Silaghi et al., 2012) to 54.2% in Andalusia (Márquez et al., 2006). Cats are susceptible to R. felis infection and seroconvert after exposure to infected fleas. However, they are probably no reservoir hosts because of a short-term bacteraemia, with blood PCR testing usually negative in antibody positive cats (Wedincamp and Foil, 2000; Hawley et al., 2007; Segura et al., 2014; Persichetti et al., 2016). In rare cases, R. felis DNA can be amplified also from the skin or gingiva of cats, blood PCR testing being negative (Lappin and Hawley, 2009). It is unknown whether R. felis is present in other tissues of seropositive cats and whether it should be considered to be a feline pathogen.
Rickettsia typhi is a worldwide flea-borne rickettsia of the typhus group. It is the agent of murine or endemic typhus transmitted from rats by Xenopsylla fleas, or from cats to humans by C. felis, as well as to cats or wild animal reservoirs.
Just as in humans and dogs, co-infections with multiple vector-borne pathogens occur in cats; the consequences of such mixed infections are unknown (Maia et al., 2014; Qurollo et al., 2014; Hegarty et al., 2015; Lappin et al., 2015).
The geographical distribution of Anaplasma, Ehrlichia and Rickettsia pathogens overlaps with that of their competent vectors. In Europe, two tick species are mainly involved: Rhipicephalus sanguineus sensu lato, which is the main tick vector of E. canis and R. conorii (and suspected for A. platys); and Ixodes ricinus, the vector of A. phagocytophilum. Both species are found also on cats (Jameson and Medlock, 2011; Claerebout et al., 2013; Pennisi et al., 2015a).
Ixodes ricinus has a wide distribution, from the Mediterranean area to Scandinavian countries, and from Portugal to Ukraine (http://ecdc.europa.eu/en/healthtopics/vectors/vector-maps/Pages/VBORNET-maps-tick-species.aspx). In the Eastern part of Europe a closely related species, Ixodes persulcatus is found (Sainz et al., 2015). Rhipicephalus sanguineus sensu lato (the brown dog tick or kennel tick) is common in the Mediterranean basin; in northern countries, R. sanguineus is not indigenous but it can hibernate sheltered in cracks of kennel structures so that the area of its distribution is expanding northward.
In summary, E. canis and A. platys are considered endemic in Mediterranean countries but are spreading northward, whereas A. phagocytophilum is reported mainly in Northern and Central Europe (Sainz et al., 2015). In stray cats in Northern Italy, blood PCR for A. phagocytophilum, Ehrlichia spp. and Rickettsia spp. tested positive in 17.7%, 5.4% and 31.9%, respectively (Spada et al., 2014). Similar rates were found in healthy cats as compared to those showing clinical signs. Blood transfusion consequently may be a nonvectorial mode of transmission for rickettsial agents in cats, as it is well known in dogs (Sainz et al., 2015).
Pathogenesis and clinical signs
Little information is available on the pathogenesis of these agents in cats. A limited number of studies on experimental infections or exposure with A. phagocytophilum or R. felis in cats exist. Intraperitoneal experimental infection with A. phagocytophilum infected blood in a small number of cats resulted in a mild disease with transient fever not associated with changes in appetite or general appearance. However, mild reduction in total leukocyte, neutrophil and lymphocyte counts, remarkable reduction in PCV values, and transient increase of ALT and AST values were detected (Foley et al., 2003). Anti-nuclear antibodies and increased expression of γIFN mRNA were also found in infected cats but they had normal antibody responses to FHV and FeLV vaccination two weeks post infection (p.i.). When experimental infection with A. phagocytophilum was performed in FIV-infected cats, upregulation of IL-10 expression was observed instead of γIFN, but the clinical course of disease was similar (Foley et al., 2003). The recent experimental exposure of four cats with wild-caught adult Ixodes scapularis induced a quite subclinical dual infection with A. phagocytophilum and Borrelia burgdorferi (Lappin et al., 2015). In fact, a transient lymphopenia was the only abnormality detected during 13 weeks of observation after tick infestation, concerning general appearance, appetite, body temperature and cell blood count of the experimental cats (Lappin et al., 2015).
In naturally exposed cats, clinical signs of feline granulocytotropic anaplasmosis are usually reported soon after tick infestation. They are mostly non-specific and consist of fever, anorexia, lethargy and dehydration. Clinico-pathological abnormalities include mild or moderate thrombocytopenia, anaemia and lymphopenia (Bjöersdorff et al., 1999; Lappin et al., 2004; Schaarschmidt-Kiener et al., 2009; Heikkilä et al., 2010; Adaszek et al., 2013; Savidge et al., 2015). Lameness and swollen joints, epistaxis or pain on abdominal palpation were less frequently reported (Bjöersdorff et al., 1999; Tarello, 2005; Adaszek et al., 2013). The clinical course is usually short and not severe and abnormalities resolve quickly, particularly when antibiotic treatment is given.
Natural infection with A. platys in a cat in Brazil was associated with anorexia, lethargy, concurrent urinary infection and thrombocytopenia (Lima et al., 2010). In another cat persistent A. platys infection was found concurrently with Bartonella henselae, B. koehlerae and Candidatus Mycoplasma haemominutum infections and the cat was also affected by multiple myeloma (Qurollo et al., 2014). In both cases, the pathogenic role of A. platys was not clearly established. In the cat with multiple myeloma, immunosuppression due to a severe monoclonal gammopathy could have been responsible for increased susceptibility to the co-infections.
Experimental subcutaneous inoculation of cats with a canine strain of E. canis was not successful and the pathogenesis of feline monocytotropic ehrlichiosis in cats is not known (Lappin and Breitschwerdt, 2012). The natural disease has been confirmed by molecular testing only in a few cases and mainly manifests as non-specific signs such as fever, anorexia and lethargy, but more rarely hyperesthesia, joint pain, pale mucous membranes, lymph node and spleen enlargement, and haemorrhagic diathesis (petechiae, vitreous haemorrhage) have also been reported (Lappin and Breitschwerdt, 2012). Haematology can reveal non-regenerative anaemia, thrombocytopenia, pancytopenia and increased or decreased white cell counts (Lappin and Breitschwerdt, 2012). Bone marrow hypoplasia is found in cats with pancytopenia or anaemia and thrombocytopenia on haematology (Breitschwerdt et al., 2002). The most consistent biochemical abnormality seen with feline monocytotropic ehrlichiosis was hyperproteinaemia and polyclonal or monoclonal gammopathy, which is also typical of the chronic course of canine monocytotropic ehrlichiosis (Lappin and Breidtschwerdt, 2012). Anti-nuclear antibodies were found in some cats and neutrophilic polyarthritis was diagnosed in a cat with joint signs (Breitschwerdt et al., 2002).
Rickettsia felis infection was evaluated in clinically ill cats, but no association was found between antibody positivity and fever and no febrile cat was found to be PCR positive for R. felis or R. rickettsii (Bayliss et al., 2009).
Another study has explored the associations between Ehrlichia spp. or A. phagocytophilum infections and anaemia, but no significant associations were detected (Ishak et al., 2006).
The main indication for diagnostic investigations for Rickettsial diseases is a febrile syndrome affecting cats exposed to ticks in endemic areas, especially stray or outdoor pet cats not protected by the regular use of appropriate ectoparasiticides.
Blood or buffy-coat smear evaluation may be useful for cytological diagnosis of infections with Ehrlichia and Anaplasma spp. In general, intracytoplasmic inclusion bodies are more frequently found in granulocytotropic anaplasmosis than in monocytotropic ehrlichiosis. Anaplasma phagocytophylum inclusion bodies are found in 1-24% of circulating neutrophils in cats with natural granulocytotropic anaplasmosis. In experimentally infected cats they appear 7-9 days p.i. (Foley et al., 2003) or over the first 10 weeks after tick infestation (Lappin et al., 2015). After antibiotic therapy they are no longer visible (Bjöersdorff et al., 1999; Heikkilä et al., 2010; Lappin et al., 2015). With A. platys, bacteraemia is cyclical at 1 to 2-week intervals, with a higher percentage of circulating infected platelets occurring during the first cycles (Harvey et al., 1978).
Antibodies to rickettsial infections can be detected by immunofluorescence (IF) test and ELISA. Cross-reaction is possible between A. phagocytophilum and A. platys but not with E. canis, although E. canis can cross react with other Ehrlichia spp. Antibodies against A. phagocytophilum were detected in an experimental study within 14 days p.i. and seroconversion occurs in natural infections even in antibiotic treated cats (Foley et al., 2003). In cats experimentally exposed to infected ticks, antibodies against A. phagocytophilum appeared 2-6 weeks after infestation (Lappin et al., 2015). In the case of a positive IF test at first sampling, a 4-fold increase of the titre over four weeks may confirm the acute course of the infection (Bjöersdorff et al., 1999; Foley et al., 2003; Lappin et al., 2004; Heikkilä et al., 2010). Some cats testing positive to E. canis by PCR were found to be antibody negative despite the chronic course of their disease suggesting that a negative antibody test does not exclude the diagnosis in cats with compatible clinical signs (Breitschwerdt et al., 2002).
Blood PCR analysis is a sensitive and specific method for confirming diagnosis at the onset of acute clinical signs when antibody testing is usually still negative (Foley et al., 2003; Lappin et al., 2015). Because of overlapping clinical signs, the use of genus-inclusive primers for Ehrlichia–Anaplasma and Rickettsia spp. genera in PCRs has been suggested followed by sequencing of any resulting PCR products to determine the infecting species (Allison and Little, 2013). However, a recent study demonstrated that some genus-specific PCRs also detect Pseudomonas sequences and may lead to false positive results that may only be recognized after sequencing analysis (Hofmann-Lehmann et al., 2016). Alternatively, the use of species-specific real-time TaqMan assays may be faster and more sensitive options for the molecular detection of rickettsaemia. Samples for microscopic detection or PCR should be collected prior to the initiation of antibiotic treatment.
Doxycycline is the first choice antibiotic for treating rickettsial infections. It is administered at 10 mg/kg orally q24 for 28 days. Clinical improvement is seen in the first 24-48 hours unless co-infections not susceptible to doxycycline are present such as protozoal vector-borne agents, or if other complications develop such as severe bleeding. Animals generally respond well to treatment but may remain persistently infected.
In cases testing negative by microscopy, PCR or antibody test, or if results are not yet available, but where there is a strong clinical suspicion of rickettsial infections, treatment should be initiated to prevent the potential of rapid progression of clinical disease.
As vectors are the main routes of transmission of rickettsial infections, regular application of appropriate ectoparasiticide spot on or collars may protect cats from becoming infected, as it is well recognised in dogs.
In endemic areas, blood donors should be tested for rickettsial blood-borne infections to confirm they are negative before being used as donors (Pennisi et al., 2015b).
Recommendations to avoid zoonotic transmission
Rickettsial pathogens are transmitted to humans by competent vectors. Infected cats, as well as dogs, are “sentinels” of the presence of rickettsial pathogens in ticks and fleas in a given geographical area and they signal a risk for people exposed to vectors. Regular application of ectoparasiticides to pets reduces the risk of exposure of humans to vectors of rickettsial agents. Direct contact with cat saliva should be avoided because of the potential contamination by R. felis as well as by other zoonotic pathogens.
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