Diagnostics of Domestic Animal Infectious Diseases

 Postmortem Diagnosis

When Negri bodies were detected or animal tests were positive, it could be confirmed as rabies.

However, even if the Negri bodies were not detected or could not be determined by animal tests, rabies could not be ruled out, and a comprehensive judgment was made in conjunction with other diagnoses.

◎Detection of Negri bodies

At that time, the detection rate of Negri bodies in rabies-positive dogs was approximately 90%. The detection of Negri bodies was the same as in 1917, with sections made from Ammon’s horn by the Bohne method and stained using the Mann, Lents, Stutsel, and Ban Gieson staining methods.

◎Animal Study

The most reliable diagnostic method at the time was animal study.

Rabbits, guinea pigs, and mice were used for the study. Guinea pigs were often used because they were believed to have a shorter incubation period of 2 to 3 days compared to rabbits. An emulsion is prepared from specimens taken from the Ammon’s horn or medulla oblongata and inoculated into the brain. If the specimen is positive for rabies, symptoms develop after an incubation period of 8 days at the earliest, generally 14 to 20 days, and the animal dies within 1 to 2 days.

If specimens are potentially contaminated, inoculate with phenol-glycerin for 24 hours before preparing an emulsion or by intramuscular injection.

◎Serum Reaction

Diagnosis by complement binding reaction has been considered, but no practical method has yet been found.

 Pathologic Anatomical Diagnosis

Few lesions are characteristic of rabies.

The cadaver has bite wounds and lacerations. The oral mucosa is reddish in color and edematous. There is a lot of tongue coating, and edema and hemorrhagic plaques on the vocal cords. The salivary glands are hyperemic and there is serous infiltration between connective tissues. The stomach is often empty, but foreign bodies may be present. The gastric mucosa may also be hemorrhagic plaques the size of a small nut.

Hyperemia and edema may occur in the brain and spinal cord, but the gross changes are not apparent. Histologically, there is non-purulent cerebrospinal gray matter inflammation, infiltration of small round cells around capillaries, degeneration of ganglion cells, and proliferation of collagen cells. Changes are particularly prominent in the cerebrum, midbrain, medulla oblongata, and the 7th, 10th, and 12th paired ganglia. It should be noted, however, that these lesions are not unique to rabies, as they also occur in other viral diseases.

 Clinical Symptoms

◎Furious rabies

・Prodromal phase：Lasts from half a day to one day.

Behavior changes drastically, showing anxiety and becoming angry easily. The animal has a good appetite but prefers to eat foreign objects such as straw, grass, and feces.

They do not actively bite their owners but may bite unknown objects under unusual stimuli.

The most noticeable symptoms during this period are a drastic change in the animal’s behavior, hyperreflexia, and increased aggression.

・Stimulating phase or fastigium：Lasts 2 to 3 days.

The animal becomes frantic, becoming agitated at the slightest provocation, and bites not only the owner but also any living or inanimate object, and may even bite itself.

During this period, its vocalization changed completely, and its fearless aggression toward anything and everything made people feel insane.

However, from this period to the paralyzed period, they sometimes go through a period of decline. In other words, after having gone to the limits of their frenzy, they may lie down on the ground as if exhausted, or they may stay in one place and stare blankly at the other side, only to suddenly go berserk again.

They also become paralyzed in parts of their bodies, suffering from vocal cord paralysis and difficulty swallowing, which causes their hoarse bark and makes it difficult for them to eat. Salivation increases and there is significant drooling.

・Paralysis Phase

During this period, the animal reaches a point of extreme prostration, with paralysis of the mandible, tongue, eyes, and hind limbs.

The animal opens its mouth, hangs its tongue, drools, and has strabismus and pupils that are dilated or constricted. Hindlimb paralysis results in a staggering gait and finally in the inability to get up, leading to death.

◎Dysmorphic, atypical, and depressed

There are three types of paraplegia: the prodromal type, which progresses from the prodromal phase to the paralytic phase immediately; the paralytic type, which begins with sedation and paralytic symptoms and leads to death in a relatively short time; and the long-sedative type, which shows sedative symptoms.

In very rare cases, transient agitation is followed by recovery.