Treatment of dogs infected with Hepatozoon americanum: 53 cases (1989-1998)

Chemical and Pharmacological Properties of Decoquinate: A Review of Its Pharmaceutical Potential and Future Perspectives

Decoquinate (DQ) is an antimicrobial agent commonly used as a feed additive for birds for human consumption. Its use as an additive is well established, but DQ has the potential for therapy as an antimicrobial drug for veterinary treatment and its optimized derivatives and/or formulations, mainly nanoformulations, have antimicrobial activity against pathogens that infect humans. However, DQ has a high partition coefficient and low solubility in aqueous fluids, and these biopharmaceutical properties have limited its use in humans. In this review, we highlight the antimicrobial activity and pharmacokinetic properties of DQ and highlight the solutions currently under investigation to overcome these drawbacks. A literature search was conducted focusing on the use of decoquinate against various infectious diseases in humans and animals. The search was conducted in several databases, including scientific and patent databases. Pharmaceutical nanotechnology and medicinal chemistry are the tools of choice to achieve human applications, and most of these applications have been able to improve the biopharmaceutical properties and pharmacokinetic profile of DQ. Based on the results presented here, DQ prototypes could be tested in clinical trials for human application in the coming years.

Case Report: Persistent Moderate-to-Severe Creatine Kinase Enzyme Activity Elevation in a Subclinical Dog

A 4-year-old, male-castrated, mixed breed dog was presented for a routine wellness examination at which time a moderate increase in serum creatine kinase (CK) enzyme activity (hyperCKemia) (15,137 IU/L; reference interval 10–200 IU/L), and moderate increases in alanine transaminase and aspartate aminotransferase enzyme activities were first identified. There was no history of clinical abnormalities (e.g., lethargy, lameness, anorexia, dysphagia, weakness, gait abnormalities, or exercise intolerance) and the physical examination was unremarkable. The dog was screened for several relevant potential infectious diseases known to cause inflammatory myopathies and was treated empirically with clindamycin. The serum total CK enzyme activity remained increased, which prompted recommendations for an echocardiogram, electromyogram (EMG), and muscle biopsy acquisition. The echocardiogram and electrocardiographic monitoring were unremarkable. The EMG and muscle biopsies were declined by the owner. The dog was evaluated several times in the subsequent 5 years and remained subclinical with unremarkable physical examinations despite a persistent moderate-to-severe hyperCKemia. Differential diagnoses considered most likely in this dog were an occult/latent hereditary muscular dystrophic disorder or idiopathic hyperCKemia, a phenomenon not yet reported in the veterinary literature. This report describes for the first time, clinical and diagnostic features of a subclinical dog with persistent moderate-to-severe hyperCKemia.

Severe myositis associated with Sarcocystis spp. infection in 2 dogs

BACKGROUND

Dogs are definitive hosts for numerous species of the intracellular protozoan parasite Sarcocystis. Reports of sarcocysts in muscles of dogs most often represent incidental findings.

HYPOTHESIS/OBJECTIVES

To report the clinicopathologic, ultrastructural, and molecular findings in 2 dogs with myositis associated with Sarcocystis spp. infection, as well as the response to treatment with antiprotozoal drugs.

ANIMALS

Two dogs with severe myositis in association with massive sarcocystosis.

METHODS

Retrospective case review. Affected dogs were identified by a diagnostic laboratory. Attending clinicians were contacted, and the medical records reviewed. Immunostaining and electron microscopy were performed on muscle biopsies. Biopsies also were subjected to 18S rRNA gene PCR.

RESULTS

Both dogs had fever, lymphopenia, thrombocytopenia, and increased serum alanine aminotransferase (ALT) activity when first evaluated. One dog developed hyperbilirubinemia. Subsequently, both dogs had increased serum creatine kinase activity and clinical signs of myositis, with reluctance to move, generalized pain, and muscle wasting. Histopathology of muscle biopsies showed severe inflammatory and necrotizing myopathy with numerous sarcocysts. Ultrastructural studies and 18S rRNA gene sequence results were consistent with infection with a Sarcocystis spp. other than Sarcocystis neurona. Both dogs initially were treated unsuccessfully with clindamycin and anti-inflammatory drugs. One dog died. The other dog subsequently responded to treatment with decoquinate.

CONCLUSIONS AND CLINICAL IMPORTANCE

Sarcocystis spp. infection should be included in the differential diagnosis for dogs that develop fever, thrombocytopenia, increased liver enzyme activities, and clinical and biochemical evidence of myositis. Although additional studies are required, decoquinate holds promise as an effective treatment for the disease.

Perspectives on canine and feline hepatozoonosis

Two species of Hepatozoon are currently known to infect dogs and cause distinct diseases. Hepatozoon canis prevalent in Africa, Asia, southern Europe, South America and recently shown to be present also in the USA causes infection mainly of hemolymphoid organs, whereas Hepatozoon americanum prevalent in the southeastern USA causes myositis and severe lameness. H. americanum is transmitted by ingestion of the Gulf Coast tick Amblyomma maculatum and also by predation on infected prey. H. canis is transmitted by Rhipicephalus sanguineus, in South America also by Amblyomma ovale, and has also been shown to be transmitted transplacentally. Hepatozoonosis of domestic cats has been described mostly from the same areas where canine infection is present and the exact identity of the species which infect cats, their pathogenicity and vectors have not been elucidated. The diagnosis of hepatozoonosis is made by observation of gamonts in blood smears, histopathology, PCR or serology. The main treatment for H. canis is with imidocarb dipropionate whereas H. americanum infection is treated with an initial combination of trimethoprim-sulfadiazine, pyrimethamine and clindamycin followed by maintenance with decoquinate. Treatment for both diseases has not been reported to facilitate complete parasite elimination and new effective drugs are needed for the management of these infections. Prevention of hepatozoonosis should be based on avoidance of oral ingestion of infected tick vectors and infected prey.

Failure of imidocarb dipropionate to eliminate Hepatozoon canis in naturally infected dogs based on parasitological and molecular evaluation methods

The efficacy of imidocarb dipropionate for the treatment of Hepatozoon canis infection was studied in three naturally infected asymptomatic dogs followed longitudinally over 8 months. Response to treatment was followed by monitoring blood counts, parasitemia levels in blood, parasite in concentrated buffy-coat smears and by PCR. The dogs were initially treated with a low dose of 3 mg/kg imidocarb dipropionate twice a month and when parasitemia persisted after five treatments, with the regular dose of 6 mg/kg. In one dog, H. canis gamonts were no longer detectable by blood and buffy-coat microscopy after 2 months of therapy with 6 mg/kg while in the two other dogs gamonts were intermittently found in blood but persistently detectable in buffy-coat smears during the whole study period. Furthermore, combined therapy with doxycycline monohydrate administered at 10 mg/kg/day PO for 4 weeks also failed to eliminate H. canis. PCR revealed that parasite DNA was present in the blood of all dogs at all sampling dates regardless of treatment refuting the effectiveness of treatment suggested by negative blood microscopy. Detection of H. canis in buffy coat was found to be twice as sensitive than by blood smear and detection by PCR was even more sensitive revealing infection in eight samples (16% of total samples) negative by blood and buffy-coat microscopy. In conclusion, imidocarb dipropionate was not effective in eliminating H. canis from dogs treated repeatedly over 8 months. Microscopical detection is not sufficient for the evaluation of treatment response in H. canis infection and follow up by molecular techniques is recommended.

Vacuolar myopathy in a dog resembling human sporadic inclusion body myositis

Sporadic inclusion body myositis (sIBM) is the most common myopathy in people over the age of 50 years. While immune-mediated inflammatory myopathies are well documented in dogs, sIBM has not been described. An 11-year-old dog with chronic and progressive neuromuscular dysfunction was evaluated for evidence of sIBM using current pathologic, immunohistochemical and electron microscopic diagnostic criteria. Vacuoles and congophilic intracellular inclusions were identified in cryostat sections of multiple muscle biopsies and immunostained with antibodies against amyloid-β peptide, amyloid-β precursor protein, and proteosome 20S of the ubiquitin–proteosome system. Cellular infiltration and increased expression of MHC Class I antigen were observed. Cytoplasmic filamentous inclusions, membranous structures, and myeloid bodies were identified ultrastructurally. These observations constitute the first evidence that both the inflammatory and degenerative features of human sIBM can occur in a non-human species.

Infectious hepatopathies in dogs and cats

This article serves to review the various infectious diseases that affect the liver primarily or as a part of systemic infection. Although bacterial infections are probably the most common cause of infectious hepatitis, the clinician should be aware of other potential organisms and other commonly involved systems. Therefore, this article includes a description of common bacterial, mycobacterial, viral, fungal, protozoal, parasitic, and rickettsial diseases in dogs and cats.

Molecular epizootiology of canine hepatozoonosis in Croatia

An epizootiological survey was conducted to investigate the prevalence of hepatozoonosis in a population of 924 apparently asymptomatic dogs from different regions of Croatia. DNA was isolated from canine blood and screening PCR on the 666 bp fragment of 18S rRNA revealed that 108 (11.8%) of dogs were infected. Positive samples were confirmed by partial sequencing of the 18S rRNA gene. The consensus sequences, derived from various sequence data sets, were compared with sequences of 18S ssrRNA of Hepatozoon spp. available in GenBank. The alignments revealed 106 Hepatozoon canis and two Hepatozoon sp. sequences. Among H. canis isolates, we found a certain amount of heterogeneity, while both Hepatozoon sp. isolates were identical to the Spanish isolate (Accession No. AY600625) from Clethrionomys glareolus. On the basis of eight commonly mutated nucleotide positions in the partial 18S rRNA gene sequence, we divided the H. canis isolates into five groups. The results obtained indicate a higher prevalence and significance of hepatozoonosis in Croatia than previously believed and demonstrate that the organisms belonging to H. canis that infect European dogs are genetically very heterogeneous.

From dog to man: the broad spectrum of inflammatory myopathies

The purpose of this review is to describe the various forms of inflammatory myopathy that occur spontaneously in dogs, and discuss the similarities and differences between inflammatory myopathy in dogs and humans. Some interesting muscle-specific autoantigens have recently been discovered in canine autoimmune myositis, and they are associated with specific forms of inflammatory myopathy. These autoantigens may now be investigated in humans. Furthermore, the association of distinct inflammatory myopathies with certain breeds of dogs point to important genetic components of inflammatory myopathy that can now be studied using dogs as both parallel disorders and animal models. Other canine myositides, associated with infectious and histiocytic diseases, may also be relevant to similar human disorders.

Characterization of stages of Hepatozoon americanum and of parasitized canine host cells

American canine hepatozoonosis is caused by Hepatozoon americanum, a protozoan parasite, the definitive host of which is the tick, Amblyomma maculatum. Infection of the dog follows ingestion of ticks that harbor sporulated H. americanum oocysts. Following penetration of the intestinal mucosa, sporozoites are disseminated systemically and give rise to extensive asexual multiplication in cells located predominantly in striated muscle. The parasitized canine cells in "onion skin" cysts and in granulomas situated within skeletal muscle, as well as those in peripheral blood leukocytes (PBL), were identified as macrophages by use of fine structure morphology and/or immunohistochemical reactivity with macrophage markers. Additionally, two basic morphologic forms of the parasite were observed in macrophages of granulomas and PBLs. The forms were presumptively identified as merozoites and gamonts. The presence of a "tail" in some gamonts in PBLs indicated differentiation toward microgametes. Recognition of merozoites in PBLs supports the contention that hematogenously redistributed merozoites initiate repeated asexual cycles and could explain persistence of infection for long periods in the vertebrate host. Failure to clearly demonstrate a host cell membrane defining a parasitophorous vacuole may indicate that the parasite actively penetrates the host cell membrane rather than being engulfed by the host cell, as is characteristic of some protozoans.

Hepatozoon spp.: pathological and partial 18S rRNA sequence analysis from three Brazilian dogs

Molecular and histopathological studies were carried out on samples from three Brazilian dogs with persistent hepatozoonosis parasitemia. Canine hepatozoonosis was confirmed by finding gametocytes in blood smears. Histopathological examination of skeletal muscle biopsy revealed muscle degeneration and atrophy, and degenerating/regenerating myofibers, similar to the muscle degeneration caused by Hepatozoon americanum . However, the large cystic structures typical of H. americanum were not observed in muscle biopsies from these dogs. Partial 18S rRNA sequences amplified by PCR from the three Brazilian samples demonstrated closest similarity to the Hepatozoon sp. Fukuoka described in Japan (>99% identity). These results indicate that both additional clinical cases and genes need examination in order to determine the phylogenetic relatedness among canid Hepatozoon species.

American canine hepatozoonosis

American canine hepatozoonosis (ACH) is a tick-borne disease that is spreading in the southeastern and south-central United States. Characterized by marked leukocytosis and periosteal bone proliferation, ACH is very debilitating and often fatal. Dogs acquire infection by ingesting nymphal or adult Gulf Coast ticks (Amblyomma maculatum) that, in a previous life stage, ingested the parasite in a blood meal taken from some vertebrate intermediate host. ACH is caused by the apicomplexan Hepatozoon americanum and has been differentiated from Old World canine hepatozoonosis caused by H. canis. Unlike H. canis, which is transmitted by the ubiquitous brown dog tick (Rhipicephalus sanguineus), H. americanum is essentially an accidental parasite of dogs, for which Gulf Coast ticks are not favored hosts. The geographic portrait of the disease parallels the known distribution of the Gulf Coast tick, which has expanded in recent years. Thus, the endemic cycle of H. americanum involves A. maculatum as definitive host and some vertebrate intermediate host(s) yet to be identified. Although coyotes (Canis latrans) are known to be infected, it is not known how important this host is in maintaining the endemic cycle. This review covers the biology of the parasite and of the tick that transmits it and contrasts ACH with classical canine hepatozoonosis. Clinical aspects of the disease are discussed, including diagnosis and treatment, and puzzling epidemiologic issues are examined. Brief consideration is given to the potential for ACH to be used as a model for study of angiogenesis and of hypertrophic osteoarthropathy.

American canine hepatozoonosis

Hepatozoon americanum infection is an emerging tickborne disease in the southern United States. This organism causes a very different and much more severe disease than does Hepatozoon canis, the etiologic agent of canine hepatozoonosis in the rest of the world. H americanum is transmitted through ingestion of the definitive host, Amblyomma maculatum (the Gulf Coast tick). Clinical signs of American canine hepatozoonosis tend to wax and wane over time and may include lameness, weakness, pain, muscle atrophy, fever, and mucopurulent ocular discharge. Radiographs typically reveal periosteal proliferation of various bones. Extreme leukocytosis is the most common laboratory finding, along with a mild elevation of serum alkaline phosphatase. Diagnosis is made by visualization of gamont-containing neutrophils or monocytes on examination of blood smears; observation of typical cysts, meronts or pyogranulomas on muscle biopsy; or detection of serum antibodies against H americanum sporozoites. Common complications of chronic infection include glomerulopathies, amyloidosis, and vasculitis. Although the prognosis for this disease in the past was guarded to poor, recent advances in treatment have increased the long-term survival rate of infected dogs.

American canine hepatozoonosis

American canine hepatozoonosis is an emerging, tick-transmitted infection of domestic dogs caused by a recently recognized species of apicomplexan parasite, Hepatozoon americanum. The known definitive host of the protozoan is the Gulf Coast tick, Amblyomma maculatum. Presently recognized intermediate hosts include the domestic dog and the coyote, Canis latrans. Laboratory-reared larval or nymphal A. maculatum can be infected readily by feeding to repletion on a parasitemic intermediate host; sporogony requires 35-40 days. Transmission of infection to the dog has been produced experimentally by oral administration of mature oocysts or oocyst-containing ticks. Canine disease follows experimental exposure in 4-6 weeks and is characterized by systemic illness, extreme neutrophilic leukocytosis, muscle and bone pain, and proliferation of periosteal bone. Histopathological findings include multifocal skeletal and cardiac myositis associated with escape of mature merozoites from within the host-cell environment. There is also rapid onset of periosteal activation and osteogenesis and, less frequently, glomerulopathy and amyloidosis. Sequential stages of development of H. americanum in both the dog and the tick have been elucidated. Gamonts potentially infectious to ticks have been observed in peripheral blood leukocytes of the dog in as few as 28 days after exposure to oocysts. Young coyotes experimentally exposed to a canine strain of H. americanum acquired disease indistinguishable from that of similarly exposed young dogs.

Analysis of the 18S rRNA gene sequence of a Hepatozoon detected in two Japanese dogs

Partial sequences of the 18S rRNA gene (625 bp) from a Hepatozoon detected in two canine hepatozoonosis cases, one clinical and one subclinical, in Japan were analyzed. Both sequences were identical to each other and they were closely related to the Hepatozoon canis strain found in Israel with 99% (617/625) nucleotide identity. Both Hepatozoon americanum and Hepatozoon catasbianae were distantly related to the Japanese Hepatozoon with 94% (586/625) and 91% (566/625) identities, respectively. In a phylogenetic tree, the Japanese Hepatozoon was most closely related to H. canis from Israel but was significantly different than H. americanum and H. catasbianae. These results suggest that the Hepatozoon detected in the Japanese dogs might be a strain variant of H. canis, but is apparently a different species than H. americanum.

Inflammatory myopathies

Inflammatory myopathies are the result of infiltration of inflammatory cells into striated muscle, with or without an association with an underlying cause. Two broad classifications are IIMs and secondary inflammatory myopathies associated with other diseases. Standard diagnostic criteria for inflammatory myopathy include the presence of weakness or loss of specific muscle group function, an increase in CK, EMG changes associated with muscle membrane instability, and histologic evidence of inflammation. Not all these criteria, however, must be present. Fresh-frozen biopsy from two proximal muscles is recommended for biopsy confirmation. IIM can either focally affect head or neck muscles or be more diffuse. MMM is an immune-mediated disease characterized by a humoral antibody produced against the unique type IIM and type I variant mvofibers of masticatory muscles of dogs, which causes inflammation and loss of function of the muscles of mastication. Idiopathic polymyositis can affect focal muscle groups (extraocular, laryngeal) or present as multifocal or diffuse involvement of skeletal muscle in the cat and dog. Familial canine DM is an inflammatory disease of the striated muscle, skin, and vasculature in young Collies, Shetland Sheepdogs (Shelties), and, rarely, Collie-crossbred dogs. Immunosuppressive therapy is the key to successful treatment. Protozoal parasitic myopathies are the most common cause of clinically relevant secondary inflammatory myopathies. The degree of systemic involvement is often the limiting factor to successful treatment. Early recognition of the clinical signs for proper diagnostic testing and institution of appropriate therapy can result in a rewarding outcome in treating inflammatory myopathies in the cat and dog.