Write the salient features (aetiology, non human principal host, mode of infection, symptoms and class of zoonoses) for the following zoonotic diseases: Brucellosis

Brucellosis: A Detailed Overview

Etiology

Brucellosis is caused by bacteria belonging to the genus Brucella. Several species are implicated in human infections, with the most common being:

• Brucella abortus (primarily from cattle)
• Brucella melitensis (primarily from goats and sheep)
• Brucella suis (primarily from pigs)
• Brucella canis (primarily from dogs)
• Brucella ovis (primarily from sheep)
• Brucella neotomae (primarily from desert cottontail rabbits)

These bacteria are Gram-negative, facultative intracellular bacteria, meaning they can survive and multiply within host cells.

Non-Human Principal Host

The non-human principal hosts vary depending on the Brucella species. This variation is crucial in understanding transmission routes:

• Brucella abortus: Cattle (Bovines) are the primary reservoir.
• Brucella melitensis: Goats and Sheep are the primary reservoirs. Historically, this has been the most common species causing human infections.
• Brucella suis: Wild boars and domestic pigs.
• Brucella canis: Dogs.

The bacteria often cause reproductive losses (abortion, infertility) in these animals, which contributes to their spread.

Mode of Infection

Transmission typically occurs through direct or indirect contact with infected animals or their products:

• Ingestion: Consumption of unpasteurized milk or dairy products is a common route.
• Inhalation: Inhaling contaminated dust or aerosols, especially in slaughterhouses and farms.
• Skin Contact: Contact with infected animal tissues, placentas, or vaginal discharge through cuts or abrasions.
• Insect Vectors: Ticks and other insects can mechanically transmit the bacteria in some regions.

Brucellae are relatively fragile outside the host and are susceptible to drying, heat, and sunlight. However, they can persist for long periods in cool, moist environments.

Symptoms

Brucellosis presents with a wide range of clinical manifestations, making diagnosis challenging. Common symptoms include:

• Fever: Often intermittent and undulating.
• Arthralgia/Arthritis: Joint pain and inflammation.
• Headache: Severe and persistent.
• Fatigue: Profound exhaustion.
• Loss of Appetite: Weight loss.
• Back Pain: Musculoskeletal pain.
• Endocarditis: Infection of the heart valves (a rare but serious complication).
• Orchitis: Inflammation of the testicles (in males).

The incubation period can range from a few days to several weeks or even months.

Class of Zoonoses

Brucellosis is classified as a Contact Zoonosis. This means it's transmitted through direct contact with infected animals or their tissues/products, rather than through airborne transmission or vector-borne mechanisms. It can also be considered an Anthropozoonotic disease, where transmission occurs between animals and humans.

Brucella Species	Primary Animal Host	Human Infection Prevalence	Geographic Distribution
B. abortus	Cattle	Lower	Historically significant in areas with cattle farming.
B. melitensis	Goats/Sheep	Higher	Mediterranean region, Middle East, parts of Asia and Africa.
B. suis	Wild/Domestic Pigs	Variable	Europe, North America