VPAR 131: Hepatozoon spp. and Hemogregarines

Hepatozoon spp.

• Apicomplexan protozoa under the Family Hepatozoidae, commonly referred to as hemogregarines
• Vertebrates (birds, mammals, and reptiles) are intermediate hosts, while invertebrates (ticks, mites, tsetse fly, sand fly, lice, fleas, triatomine bugs, mosquitoes, and leeches) are definitive hosts
• Sexual development and sporogony occur in invertebrates, while merogony and gametogony occur in vertebrates

Hepatozoon of dogs

• Two species affecting dogs: Hepatozoon canis and H. americanum
• Infection occurs through ingestion of infected ticks
• Intrauterine transmission of H. canis and transmission by predation in H. americanum have been reported
• Tick vectors: Rhipicephalus sanguineus for H. canis and Amblyomma maculatum for H. americanum
• Cats can also be infected with H. canis

Life cycle of Hepatozoon in dogs

• H. canis primarily affects hemolymphoid organs, while H. americanum affects skeletal and cardiac muscles
• Sporozoites penetrate the gut wall, invade mononuclear cells, and disseminate to hemolymphoid organs through blood or lymph
• Schizonts occur in endothelial cells of spleen, bone marrow, and liver
• Gamonts occur in leukocytes

H. americanum infection

• Sporozoites may be taken up by macrophages and carried to skeletal or cardiac muscles
• Infected macrophages form the nidus for muscle cyst, with concentric layers of mucopolysaccharide material produced and deposited around the infected cell
• Merozoites are released when the cyst ruptures and are taken up by leukocytes

Clinical signs and diagnosis of Hepatozoon in dogs

• H. canis infection can be subclinical to life-threatening, while H. americanum infection is frequently severe and debilitating
• Anemia is the most common hematological abnormality in H. canis infection
• Leukocytosis occurs in high parasitemia, and neutrophilia is a consistent finding in H. americanum infection
• Clinical signs include fever, muscular pain, and mucopurulent ocular discharge
• H. canis is diagnosed by microscopic detection of gamonts in blood smears, while H. americanum is confirmed by muscle biopsy

Treatment of Hepatozoon in dogs

• Imidocarb dipropionate is the drug for H. canis, given every 14 days until gamonts are no longer observed in the blood smear
• For H. americanum, a combination of trimethoprim-sulfadiazine, pyrimethamine, and clindamycin can be given orally for 14 days

Hepatozoon spp. of other animals

• Hepatozoon felis was first reported in India, affecting skeletal muscle, lungs, and myocarcium
• H. muris affects rats, with its vector being the mite Laelaps echidninus

Characteristics of Hepatozoon spp.

• All members possess cilia for locomotion, which may be simple or compound
• Most have two sets of nuclei: a micronucleus containing a normal set of chromosomes concerned with reproductive process, and a macronucleus responsible for cytoplasmic activities
• Reproduction is by binary fission or conjugation, without true sexual reproduction involving gametes

Phylum Ciliophora: Ciliates

• Three orders of veterinary importance: Prostomatidorida, Oligohymeophorasida, and Polyhemenophorasida
• Balantidium coli is the most commonly known ciliate that can cause disease in pigs, cattle, primates, rodents, and other animals, occurring in the lumen of the large intestine

Balantidium coli

• Cilia are arranged in longitudinal rows all over the body
• Two forms: trophozoite and cyst form
• Can produce superficial to deep ulcers associated with dysentery, resembling those of Entamoeba histolytica
• Pulmonary infection and peritonitis have been reported in immunocompromised individuals
• Diagnosis is through clinical signs, ulcerative lesions, and presence of very large numbers of B. coli
• Acute infections may be treated with tetracyclines or carbasone

Quiz on Hepatozoon spp., apicomplexan protozoa, and their role as hemogregarines in vertebrates such as birds, mammals, and reptiles.