Concomitant feline immunodeficiency virus (FIV) and Mycoplasma haemofelis in a barn cat

Abstract

A 5-year-old male barn cat was presented with lethargy and excessive bleeding following castration. The patient developed hemolytic anemia and diagnostic tests revealed infection with feline immunodeficiency virus and Mycoplasma haemofelis. This case serves as a reminder of the importance of testing for infectious diseases and educating owners on feline infectious disease prevention and management.

On June 6th, 2017, a 6.4 kg, 5-year-old intact domestic shorthair cat was presented at Troy Veterinary Services for elective castration as part of a barn cat sterilization program to provide surgical experience during the student externship. The patient had been vaccinated for rabies in April 2016 and had no history of previous medical illnesses. Physical examination completed before surgery revealed tachychardia, multiple old scars on the face/neck area, and 4 broken canine teeth with significant inflammation around the base of the teeth. Respiratory rate was not obtained due to excessive purring; all other vital signs and the rest of the physical examination were within normal limits. An open castration was performed and there were no complications associated with anesthesia or surgery. There were no signs of complications after surgery, the patient recovered well and was discharged in the afternoon later that day.

The following day the patient was presented by the owner for lethargy and excessive bleeding from the surgery site. On presentation the cat was bright, alert, and responsive and some minor bleeding was observed from the right scrotal incision; no inflammation was noted. The patient was tachycardic and tachypnic, but the rest of the physical examination did not identify any other abnormalities. Blood was collected from the medial saphenous vein for in-house determination of packed cell volume (PCV) and total solids (TS). A PCV of 26% was below the reference interval (RI) (30% to 45%) for cats, while TS of 68 g/L was within the RI (55 to 75 g/L). No plasma discoloration was observed in the capillary tube. The patient was kept overnight for monitoring. On June 8th, 2017 PCV and TS were measured again and both values (22% and 50 g/L, respectively) were below the reference intervals; moderate hemolysis was observed in the plasma. The patient was less active and a mild cough was noted; however, he continued to eat and drink well. Slight bleeding was observed from the right scrotal incision.

A complete blood (cell) count (CBC) revealed a regenerative anemia [hematocrit (HCT) was 30.1% (RI: 30.3% to 52.3%), hemoglobin (HGB) was 95 g/L (RI: 98 to 162 g/L), reticulocytes 105 × 10⁹/L (RI: 30.0 to 50.0 × 10⁹/L)] and monocytosis, 0.9 × 10⁹/L (RI: 0.05 to 0.67 × 10⁹/L). Red cell distribution width was 24.7%, the high end of normal, (RI: 15.0% to 27%) suggesting a shift to macrocytic anemia. Cytological examination of erythrocytes on a blood smear stained with Diff-Quik revealed moderate anisocytosis, 1 to 2 reticulocytes per high power field, and occasional hypochromic erythrocytes. Monocytosis and occasional band neutrophils were observed, while eosinophils and lymphocytes appeared normal. Small cellular inclusions consistent with Mycoplasma haemofelis were observed on erythrocytes (Figure 1). From the clinical presentation and blood analysis differential diagnoses included opportunistic infection with Mycoplasma spp. secondary to feline immunodeficiency virus (FIV) or feline leukemia virus (FeLV) immunosuppression or idiopathic hemolytic anemia plus possible chronic respiratory infection.

Figure 1.

Blood smear showing the presence of small cellular bodies. Peripheral blood stained with Diff-Quick at 100× magnification. The dotted area has been zoomed in the rectangle. Arrows point to blue epi-cellular bodies.

Blood from the jugular vein was collected and sent to the Animal Health Laboratory (AHL) (Guelph, Ontario) for FIV/FeLV ELISA and Mycoplasma spp. polymerase chain reaction (PCR). Fecal flotation was negative for parasites. Lateral and dorso-ventral radiographs revealed a cranio-ventral and caudo-dorsal interstitial to alveolar pattern and pneumonia was suspected. Also, an irregularly marginated soft tissue structure in the right caudal lung lobe was observed (Figure 2). The patient was started on amoxicillin/clavulanic acid (Clavaseptin; Vétoquinol, Lavaltrie, Quebec), 62.5 mg, PO, q12h for 10 d. The cat remained in the hospital pending results of the tests for FIV, FeLV and Mycoplasma. Results from the AHL indicated seropositivity for FIV antibodies and seronegativity for FeLV antigen. The PCR for Mycoplasma spp. was positive for M. haemofelis, negative for M. haemominutum, and inconclusive for M. turicensis. The patient was started on doxycycline (doxycycline hyclate capsules; Apotex, Toronto, Ontario), 100 mg, PO, q24h for 14 d. Although the patient continued to maintain a good demeanor, good appetite, and no other clinical signs while in the hospital, by the 7th day of hospitalization the PCV had dropped to 15% while TS remained within normal range. Also, the cat’s weight dropped from the initial 6.4 kg to 5.9 kg. Due to owner’s circumstances the cat was discharged on that day. The owner was informed about management of FIV and the importance of compliance with antibiotic treatment.

Figure 2.

Lateral and ventro-dorsal radiographs showing cranio-ventral and caudo-dorsal interstitial to alveolar pattern. Also, an irregularly marginated soft tissue structure (white arrow) was observed in the right caudal lung lobe.

Telephone communication with the cat’s caretaker the following week indicated that the cat had improved activity and was eating and drinking well; however, coughing persisted. At last communication with the owners, 22 d after discharge, the patient was doing well. There was no further follow-up.

Discussion

Feline immunodeficiency virus (FIV), a common infectious agent of cats, is a retrovirus that resembles human immunodeficiency virus (HIV) (1). Experimental infection of naïve cats with FIV has shown the disease has a similar progression as infection of humans with HIV: following initial acquisition there is an acute phase, then an asymptomatic phase, and lastly a terminal phase, which has been named “feline acquired immunodeficiency syndrome — FAIDS” (2). During the acute phase cats can present with transient fever, leukopenia, and lymphadenopathy; but often these clinical signs go unnoticed (3). It may be difficult for owners to recognize these clinical signs, particularly if the animal lives outdoors and is not under constant supervision, such as in this case of a barn cat. Cats may be asymptomatic for years following the initial response of the immune system; therefore, it is impossible to determine a timeline for infection. Cats infected with FIV have an impaired immune system due to reduced CD4⁺ helper T-cells, making them more susceptible to opportunistic infections (2,4). Life expectancy in FIV positive (FIV + ve) cats has been reported to be not significantly less than for FIV negative (FIV – ve) cats (2,4); but this could be due to lack of exposure to opportunistic agents or highly virulent pathogens (4). Infection with FIV persists for life (2–4) and death within 2 y of positive testing has been reported in 18% of positive cats (2).

Prevalence of FIV infection in cats in North America (4–11) ranges from 0.9% in healthy indoor cats (5) to 23% in stray cats (6); however, all studies found males are over-represented. For example, in a 2006 survey, 71.7% of all FIV positive cats were males (5); furthermore, intact males had a higher prevalence than castrated males (5,6). Transmission of the virus is commonly a result of bite wounds, although vertical transmission has also been described (4,12,13), so it is not surprising that intact males are overrepresented as they are more likely to be involved in fights with other males. The patient described here had multiple scars, so there is a high possibility that he had been involved in cat-to-cat aggression. In North America, it is not possible to differentiate positive FIV results because of natural infection from those due to vaccination (3,5).

Mycoplasma haemofelis is one of the 3 known species of hemotropic mycoplasmas or hemoplasmas, Gram-negative bacteria that attach to the outer surface of erythrocytes. Mycoplasma haemofelis is the most pathogenic of the 3; the other 2, Candidatus Mycoplasma haemominutum and Candidatus Mycoplasma turicensis are less pathogenic (14,15). Although M. haemofelis is one of the most common infectious causes of regenerative anemia in cats (16) and one of the causative agents of immune-mediated hemolytic anemia (IMHA) (16,17), it is also the least prevalent of the 3 (18). The frequency of cats presenting with anemia due to hemotropic Mycoplasma infection has been reported at 14% (19). Immune-mediated hemolytic anemia in cats is not commonly a primary disorder, but rather a secondary disease. In cats infected with M. haemofelis, the damage to the red blood cells is not directly caused by the bacteria, but is a result of the immune response to the infection (16,17).

Clinical signs of hemoplasmosis can vary depending on factors such as stage of infection and concurrent diseases; however, acutely ill cats often present with anorexia, weight loss, depression, lethargy, pallor, and dehydration (14). Anemia and bacteremia are observed following the acute phase which can last 3 to 4 wk (18). On the day following castration, one of the owner’s presenting complaints was lethargy; anorexia, pyrexia, dehydration, and pallor were not observed. Weight loss was observed towards the end of the hospitalization period, and could have been due to an unidentified cause. It is impossible to determine the exact timeline for hemoplasma infection, and it is possible that the patient had been an asymptomatic carrier and that stress caused reactivation of the infection as has been reported (16,18). Removing a barn cat from his territory, taking him into a new and stressful environment such as a veterinary clinic, in addition to the stress associated with castration, may have been enough for the disease to recur.

Feline hemoplasma infection is more common in males (18), and while there is controversy as to whether or not there is an association with retroviral infection (18,20), 1 study reported that cats infected with M. haemofelis are 6 times more likely to be FIV positive (21). Despite the lack of direct relationship between retroviral and M. haemofelis infections, infections with intracellular organisms are common in FIV positive cats. In the present case we could not determine if this patient was infected by FIV first, which made him more susceptible to M. haemofelis.

Transmission of hemoplasmas has been attributed to arthropod vectors (i.e., fleas) (22,23), but transmission in the absence of vectors has also been observed (14), and may be due to cat aggression (23). The patient had a significant amount of old scars and scratches that could be an indication of previous fights, which could have resulted in acquiring FIV and/or M. haemofelis. The treatment of choice for cats infected with feline hemoplasma is doxycycline, but only partial clearance has been observed despite appropriate dosage and duration (14,16,18). Long-term clearance (6 mo) was demonstrated in 1 case with treatment for 6 wk (24). The patient in this report was treated with a higher dose than recommended, due to his clinical condition and our knowledge of poor response of hemoplasmas. Whether this treatment resulted in clearance is not known as the patient was lost to follow-up.

It is important to isolate and segregate cats known to be positive for retroviruses to avoid the spread of FIV and other infectious diseases among feral, stray, and owned free-roaming cats. Since 2013 there have been no studies on the seroprevalence of FIV in Canadian cat populations. Knowledge of seroprevalence of infectious diseases such as FIV and FeLV is important to monitor frequency and distribution of this and other diseases in cats. In 2008, the American Association of Feline Practitioners recommended a partnership between pet owners and veterinarians, with the intention of educating people, and increasing testing and vaccination to maximize prevention (3). We need to emphasize to owners that although FIV and FeLV on their own might not result in disease, predisposing cats to other infectious diseases can not only reduce cat life-expectancy and quality of life, but can also result in diseases with zoonotic potential. The potential for zoonosis with hemoplasma infection has been described (14,18). Furthermore, preventing transmission can help in preventing mutations that might facilitate crossing into new host species (6).

This case serves as a reminder of the importance of improving testing for infectious diseases and educating owners on feline infectious disease prevention and management.