JPC SYSTEMIC PATHOLOGY

NERVOUS SYSTEM

February 2023

N-P07 (NP)

 

Signalment (JPC #4085377): 15-day-old, male, Angus x Nellore cross, ox (Bos taurus)

 

HISTORY: In September, on a farm in midwestern Brazil, eight out of 100, 15-day-old cross bred (Angus x Nelore) calves got sick. Affected calves were lethargic, ataxic, and unable to follow their mothers. They were unsuccessfully treated with florfenicol and sodium dipyrone. 5/8 sick calves died; the remaining 3/8 were referred to the Veterinary Teaching Hospital where they were examined and given supportive therapy. Two of those calves died within 24 hours of the onset of clinical signs and were necropsied. The remaining calf recovered with treatment. Clinical signs included fever, apathy, icterus, stiffness of the neck, and difficulty standing due to incoordination that rapidly progressed to sternal decubitus, lateral decubitus, muscle tremors, paddling movements, nystagmus, tachycardia, and tachypnea. One calf had lost of menace reflex and another one had opisthotonus. All calves were parasitized by Rhipicephalus (Boophilus) microplus ticks.

 

HISTOPATHOLOGIC DESCRIPTION: Cerebrum: Diffusely within the gray matter and multifocally within the white matter and meninges, there is mild congestion of capillaries, arterioles, and venules. Diffusely within all blood vessels, many erythrocytes contain one or two basophilic, 1 µm diameter, round to pyriform protozoal apicomplexan trophozoites (piroplasms). There is mild perivascular and perineuronal edema in the gray matter.

 

MORPHOLOGIC DIAGNOSIS: Cerebrum, erythrocytes: Intracytoplasmic apicomplexan parasites, morphology compatible with Babesia bovis, Angus x Nelore cross, bovine.

 

ETIOLOGIC DIAGNOSIS: Cerebral babesiosis

 

CAUSE: Babesia bovis

 

SYNONYMS:Texas fever, tick fever, piroplasmosis, red water

 

GENERAL DISCUSSION:  

Babesia sp. in general:

• Phylum Apicomplexa; class Piroplasmidia; family Babesiidae; a tick transmitted, intraerythrocytic protozoal parasite that causes anemia and hemoglobinuria
• Classified as large and small form
• There are numerous species of Babesia affect a wide range of domestic and wild animal hosts in a host species-specific manner
• Transmitted by hard ticks (definitive host) of the family Ixodidae (Rhipicephalus, Ixodes, Boophilus, Haemaphysalis, Hyalomma, and Dermacentor)
• Tick populations increase when severe droughts are followed by heavy rains thus increasing the prevalence of Babesia spp.

Babesia sp. in cattle:

• Calves are less susceptible than adults
• Acquired immunity occurs for at least four years after infection
• Babesia bovis (small) and Babesia bigemina (large) occur in cattle worldwide but have been eradicated from North America

 

PATHOGENESIS:  

• Severity of disease depends more on the species of infecting Babesia than on the number of organisms inoculated
• Suspected penetration of organism into erythrocytes is via activation of the alternate pathway; the organism achieves adherence and later invasion by C3b
• Erythrocytes are lysed as parasites emerge; acute infection may result in death within a few days

• Hemolysis due to direct damage to erythrocytes by protozoal proteases, immune-mediated destruction, or oxidative damage

• Sludging of infected erythrocytes within the microvasculature of the brain, liver, and kidney leads to hypoxic injury
• Hemoglobinuric nephrosis
• Release of vasoactive peptides that can result in circulatory shock and failure

• Intense visceral congestion and pulmonary edema
• Parasite is source of proteases which activate plasma kallikrein, a hypotensive agent, and activator of bradykinin, a potent vasodilator
• Contributes to severe anemia

• Metabolic acidosis (severe B. canis) or alkalosis (B. bovis) due to circulatory failure from extensive plugging of microvasculature by sequestered erythrocytes
• Animal may die suddenly due to myocardial failure as a result of severe anemia

 

LIFE CYCLE: 

• Inoculation of intermediate host (wide range of domestic and wild animals) by tick vector > within erythrocytes, organisms multiply asexually by binary fission and form two to four piroplasms > ticks infected by ingestion of infected blood
• Proposed life cycle within tick (definitive host):

• Sexual phase within the tick’s gastrointestinal tract > schizogony resulting in large motile vermicules > vermicules migrate to tissues, especially the ovary and invade the eggs (transovarial transmission) > vermicules continue to multiply within the eggs and larval tissues > when larvae feed, vermicules enter the salivary gland, develop into infective sporozoites, and are inoculated into the new mammalian host

 

TYPICAL CLINICAL FINDINGS:

• High fever, weakness/lethargy, anemia (severity increases with splenectomy), hemoglobinuria, hemoglobinemia, and icterus
• Intravascular and extravascular hemolysis
• CNS signs terminally due to sludging of parasitized erythrocytes in brain capillaries
• Photosensitization due to overload of the phylloerythrin-conjugating sequence resulting from excess bilirubin secondary to hemolysis
• Macrocytic erythrocytes, reticulocytosis, thrombocytopenia

 

TYPICAL GROSS FINDINGS:  

• Uniform congestion of the cerebral gray matter that imparts a striking, deep pink color (cerebral flush) and contrasts strongly with the white matter 

• Note: The presence or absence of cerebral flush is the most reliable gross feature for differentiating B. bovis infections (cerebral flush present) from B. bigemina infections (cerebral flush and neuro signs absent) in cattle. 

• Anemia, variably severe icterus, and hemoglobinuria
• Severe splenomegaly, lymphadenopathy, pulmonary edema, and hemorrhage
• Dark, congested, and swollen liver and kidneys; the liver may be heavily stained with bile and the kidneys are stained with hemoglobin 
• Ascites; pericardial and thoracic effusions; subepicardial and subendocardial petechiation and ecchymoses; red-tinged plasma and urine
• Subcutaneous, subserous, and intramuscular connective tissue and fat is edematous

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Intraerythrocytic, 1-2 µm, basophilic, round to pyriform protozoa
• Capillaries within the brain, kidney, skeletal muscle, and heart contain parasitized erythrocytes
• Characteristic of severe hemolytic anemia:

• Variably severe hemoglobinuric nephrosis (U-T10) with severe congestion, focal hemorrhage, hemoglobin casts, interstitial mononuclear cell infiltrates, varying degrees of proximal tubular necrosis, and tubular epithelial cell swelling and engorgement with hemosiderin or hemoglobin (droplets or crystals)
• Centrilobular and midzonal hepatocellular degeneration with fatty infiltration and necrosis, centrilobular congestion, portal and centrilobular lymphoplasmacytic infiltrates, Kupffer cell hypertrophy and hemosiderosis
• Spleen and lymph nodes: Necrosis of germinal centers, congestion, erythrophagocytosis and hemosiderosis; histiocytosis of lymph node medullary sinuses
• Bone marrow: Erythroid hyperplasia, mild hemosiderosis

 

ULTRASTRUCTURAL FINDINGS:

• Limited by a plasma membrane, contain ER, Golgi and food vacuoles
• An electron dense apical complex consisting of polar rings, micronemes and rhoptries located at the blunt end of the parasite

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Examination of Giemsa stained peripheral blood smears
• Detection of antibodies by hemagglutination, complement fixation, or fluorescent antibody
• PCR 

 

DIFFERENTIAL DIAGNOSIS:

• Anaplasma: 1 µm intraerythrocytic spheres
• Ehrlichia: Found individually or as clusters in circulating monocytes or granulocytes
• Theileria (N-P08): Koch’s blue body (macroschizont) in lymphocytes and in erythrocytes as micromerozoites, gamonts, and gametes

 

COMPARATIVE PATHOLOGY:  

• Canine: B. canis (large) and B. gibsoni, B. conradae, B. microti-like, Theileria annae, and an unnamed Theileria sp. (small; used to be thought that all small Babesia of dogs were B. gibsoni); young dogs more susceptible

1. The subspecies B. canis vogeli is the main agent in Brazil

• Equine: Theileria equi (formerly B. equi; small), or B. caballi (large), occurs worldwide

1. Equine piroplasmosis may cause an inflammatory myopathy, likely due to increase in IFN-, IL-12, and TNF- (Pasolini, Vet Pathol 2018)

• Swine: B. trautmanni, B. perroncitoi
• Domestic and wild cats (South America, Africa and India): B. cati, B. felis, B. herpailuri and B. pantherae (all small)

1. The 16S-like rRNA subunits of B. microti and Cytauxzoon sp. share 91% identity

• Sheep: B. ovis and B. motasi
• Mice: B. rodhaini, B. hylomysci, B. divergens
• White-tailed deer, elk, caribou, reindeer, desert bighorn sheep, and musk oxen:  B. odocoilei 
• Man

1. Usually B. microti, a Babesia of mice and rodents
2. Infections with Theileria equi, B. bovis, and B. divergens have been reported

• NHPs: 

1. B. pitheci in both OWMs and NWMs. Restricted to Africa. Only slightly pathogenic in normal monkeys, but can result in severe anemia and death after splenectomy.
2. Entopolypoides macaci in OWMs (cynos, rhesus, babboons, and guenons) and chimpanzees; phylogenetic evidence showed the synonymy of Entopolypoides and Babesia with a 97.9% sequence similarity; no true piriform stage.

• Babesia spp. has been reported in numerous wildlife and zoo animal species 

1. B. macropi in kangaroos and wallabies
2. B. thomasi in hyraxes
3. B. caballus in Przewalksi horses
4. B. bicornis in black rhinoceros
5. B. trautmanni and B. perroncitoi in wild boars, warthogs, and bushpigs
6. B. kiwiensis in North Island brown kiwi chicks

 

References:  

1. Abee CR, Mansfield K, Tardif S, Morris T. Nonhuman Primates in Biomedical Research: Volume 2: Diseases. 2nd ed. San Diego, CA: Elsevier; 2012: 220.
2. Agnew D, Nofs S, Delaney MA, Rothenburger JL. Xenartha, Erinacoemorpha, Some Afrotheria, and Phloidota. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 530.
3. Boes KM, Durham AC. Bone marrow, blood cells, and the lymphoid/lymphatic system. In: Zachary JF ed. Pathologic Basis of Veterinary Disease. 7th ed., St. Louis, MO: Mosby Inc.; 2022:832-833.
4. Cheville NF. Ultrastructural Pathology. 2nd ed. Ames, IA: Wiley-Blackwell; 2009:538-540. 
5. Church ME, Terio KA, Keep MK. Procyonidae, Viverridae, Hyenidae, Herpestidae, Eupleridae, and Prionodontidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 315.
6. Duncan M. Perissodactyls. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 2018; 450.
7. Farina LL, Lankton JS. Chiroptera. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 626.
8. Higgins D, Rose K, Spratt D. Monotremes and Marsupials. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 474-475.
9. Howerth EW, Nemeth NM, Ryser-Degiorgis MP. Cervidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 170-171.
10. Jones MEB, Gasper DJ, Mitchell E. Bovidae, Antilocapridae, Giraffidae, Tragulidae, Hippopotamidaw. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 139.
11. Keel MK, Terio KA, McAloose D. Canidae, Ursidae, and Ailuridae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018:  250-251.
12. Martinez MAJ, Gasper DJ, Mucino MCC, Terio KA. Suidae and Tayassuidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 221.
13. Pasolini MP, Pagano TB, Costagliola A, et. al. Inflammatory myopathy in horses with chronic piroplasmosis. Vet Pathol. 2018; 55(1): 133-143.
14. Smith DA. Palaeognathae: Apterygiformes, Casuariiformes, Rheiformes, Struthioniformes; Tinamiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 647.
15. Stockham SL, Scott MA. Fundamentals of Veterinary Clinical Pathology. 2nd ed. Hoboken, NJ: Wiley; 2008: 81, 86, 139, 171-172, 177, 184, 234, 242. 
16. Valli VEO, Kiupel M, Bienzle D. Hematopoietic system. In: Maxie MD, ed. Jubb, Kennedy & Palmer Pathology of Domestic Animals. 6th ed. vol. 3. St. Louis, MO: Elsevier; 2016:117-120.
17. Zablotsky SM, Walker DB. Peripheral Blood Smears. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier Mosby; 2014:455. 

 

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