Important Rickettsial Diseases of animals

Pashu Sandesh, 19th July 2018

Sonali Mishra, Kunal Pandit, Gaytri Kashyap

RICKETTSIAL DISEASES

These are Gram negative, non-spore forming, non-motile, small obligate intracellular highly pleomorphic bacteria. Their cell wall is bigger than virus but smaller than bacteria. They have DNA and RNA and also have an ATP transport system that allows them to use host ATP, so replication within the cytoplasm of eukaryotic host cells. Arthropod acts as reservoirs and vectors (e.g., ticks, mites, lice or fleas) for the disease. These are sensitive to antibiotics.       

Need for studying animal Rickettsioses-

1. Economic losses to livestock industries
2. Mental and emotional distress to the owners
3. Financial costs to owners- via veterinary treatments, tick-prevention programs

BOVINE ANAPLASMOSIS/ GALLSICKNESS

1. Anaplasma phagocytophilum – Zoonotic
2. A. marginale - Clinical outbreaks
3. A. centrale - limited pathogenicity

Prevalence- All six continents, especially in tropical areas

Physical Vectors-

Flies, Horse Flies, Stable Flies, Dear Flies, Mosquitoes

Instruments

Surgical Instruments, Dehorning Instruments, Castration Instruments, Hypodermic Needles

Biological Vector

Ticks

PATHOGENESIS

1. RBCs Phagocytosis
2. Anemia
3. Lack of O₂& Nutrients in tissues
4. Animal remains carrier
5. Calves Under 6 Months- Show no Signs or Symptoms
6. Up to 18 months old- Show only Symptoms

GROSS LESIONS

• Severe anemia with pale mucous membrane and icterus.
• Spleen is greatly enlarged and reddish in colour.
• Liver and the gall bladder is distended with granular bile.
• Petechiae of epicardium and catarrhal gastroenteritis are evident.
• Liver is also enlarged with rounded edges.

MICROSCOPICAL LESIONS

• Hyperplasia of bone marrow.
• Extramedullary haematopoiesis in spleen and liver is observed.

DIFFERENTIAL DIAGNOSIS

Other haemolytic diseases- Babesia, Post parturient bovine haemoglobinuria

Heart water disease

Causative agent: Ehrlichia ruminantium

Animal Transmission

Vector-borne – Amblyomma ticks.

Larvae and nymphs infected from infected animals.

Clinical Signs

Incubation period: 14 to 28 days

Four forms of disease

        I.            Peracute (rare)

     II.            Acute (most common)

   III.            Subacute (rare)

  IV.            Mild or subclinical

Acute form:Most common form

1. Sudden fever (107^oF)
2. Inappetence, depression
3. Tachypnea, respiratory distress
4. Nervous signs

     V.            Chewing movements, eyelid twitching, tongue protrusion, circling, paddling

6. Death  within 1 week

Post Mortem Lesions

Hydropericardium, Hydrothorax, Ascites, Pulmonary & mediastinal edema, Lymphadenopathy, Congestion and edema in the brain.

MICROSCOPIC LESIONS- Edematous and generalized luecocytic infiltration in tissues, demonstration of organism in vascular endothelium.

Diagnosis:

1. Clinical signs

Fever, respiratory distress, sudden death

1. Presence of Amblyomma ticks
2. Laboratory Tests
3. Microscopic identification organism
4. PCR, IFA, ELISA

Canine Monocytic Ehrlichiosis (Tracker dog disease, Canine haemorrhagic fever, Tropical canine pancytopaenia)

Causative agent- Ehrlichia canis

Vector:The Brown Dog Tick (Rhipicephalus sanguineus) usually spreads Ehrlichia canis

Clinical signs

Nonspecific signs –

Fever, Anorexia & lethargy, lymphadenopathy, splenomegaly & weight loss, vomiting, diarrhea, lameness, edema in the hind legs, dyspnea & purulent oculo-nasal discharge.

Bleeding disorders - Anemia, mild epistaxis, petechiae and ecchymoses, death - Consequence of hemorrhages or secondary infections.

Ocular signs:

Anterior uveitis, corneal opacity and tortuous retinal vessels, corneal opacity, bleeding haemorrhages on gums.

POSTMORTEM LEISONS

Hemorrhage in mucosa of GI tract, urogenital tract, kidneys, edematous and haemorrhagic lymph node, and edema of limbs.

MICROSCOPIC LESIONS

Perivascular accumulation of RE cells, plasma cells in meninges, liver, kidney and lymph reticular organs, bone marrow hypo plastic, degeneration and centrilobular necrosis in liver

Diagnosis

Dog with fever, enlarged lymph nodes, bleeding, or arthritis in multiple joints.Low platelet numbers, high globulin levels, and mild anemia on blood testing, canine thrombocytopaenia, pancytopenia. Ehrlichia canis seen in membrane-bound inclusions (morulae) within the cytoplasm of a monocyte (buffy coat smear, Wright stain).

 Sonali Mishra¹, Kunal Pandit², Gaytri Kashyap¹

¹Division of Veterinary Pathology, ICAR-Indian Veterinary Research Institute, Izatnagar – 243 122, Bareilly, U.P, India

²Department of Veterinary Anatomy, C.V.A.Sc., GBPUAT, Pantnagar – 263 145, Uttarakhand, India