Japanese B virus infectionClinical signs, differential diagnosis, treatment and prevention in cattle, goats, sheep, pigs, poultry and horses.

Overview

A mosquito-borne viral disease causing reproductive losses in pigs and encephalitis in horses. Japanese encephalitis virus (JEV), a Flavivirus maintained in nature between mosquitoes, pigs and wild birds; pigs are efficient amplifying hosts, horses are dead-end hosts.

Clinical signs

Swine (Reproductive Failure): Infection in nonpregnant pigs is usually subclinical, occasionally causing a mild transient fever.
In pregnant sows, it causes severe reproductive failure characterized by fetal death, mummified fetuses, stillborn pigs, and weak piglets.
In boars, it causes sudden unilateral or bilateral orchitis (testicular swelling or subsequent atrophy) and reproductive failure/reduced fertility.
In young piglets under 6 months, it can cause a nonsuppurative encephalitis.
Horses (Neurologic form): Causes a variable encephalitis.
Mild/subacute form: fever (up to 39.5°C), anorexia, sluggish movements, and transient jaundice (2–3 days).
Severe form: high fever (up to 41°C or higher), profound lethargy, stupor, somnolence, bruxism/chewing motions, dysphagia (pharyngeal paralysis), petechiation of nasal and oral mucosa, incoordination, staggering…
Cattle, Sheep, Goats: Infection is almost entirely clinically inapparent and of little significance.

Predisposing factors

Bites of vector mosquitoes of the genus Culex (particularly Culex tritaeniorhynchus, and potentially Aedes koreicus or Ochlerotatus detritus).
Prevalence is increased during the monsoonal/wet season.
Proximity to rice fields where nitrogenous fertilizers and phytoplankton enhance mosquito larval survival.
Overwintering of the virus occurs in pigs and birds when mosquitoes are absent.

Look-alikes to rule out

African horse sickness Hepatic Encephalopathy (HE) Menangle virus infection Bovine Brucellosis Pseudorabies Babesiosis Botulism Tetanus

Treatment

There is no specific treatment available for the disease.
Symptomatic and supportive treatment includes antipyretics, anticonvulsants, maintaining hydration and nutrition, and treating secondary bacterial infections 183 image text,.

Prevention

1. Control mosquito vectors (spraying of insecticides inside housing, cattle sheds, pig sites, and vegetation; water management in rice fields; use of larvicides or biological agents like Azolla microphylla) 183 image text, 676, 1087. 2.

Source

A Textbook of the Diseases of Cattle, Horses, Sheep, Pigs and Goat by ELSEVIER (Pages 2136–2137); A Textbook of the Diseases of Cattle, Horses, Sheep, Pigs and Goat by ELSEVIER (Pages 1263–1271); Preventive Veterinary Medicine by ICAR (Pages 181–183).

MSD Veterinary Manual — Equine Arboviral Encephalomyelitis (accessed 2026-08-11)

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