Describe the zoonotic diseases of public health importance.

Zoonotic Diseases

• The classification by the life cycle involved — direct zoonoses, needing only one vertebrate host (rabies, brucellosis, anthrax); cyclo-zoonoses, requiring more than one vertebrate host (hydatid disease, taeniasis); meta-zoonoses, requiring an invertebrate as well (plague, Japanese encephalitis, Kyasanur forest disease); and SAPRO-zoonoses, requiring a non-animal site such as soil or organic matter (histoplasmosis)
• Rabies is the most important in India, which accounts for a large share of global rabies deaths, mostly from dog bites
• It is a rhabdovirus reaching the central nervous system along peripheral nerves, and once symptoms appear it is essentially 100% fatal — which makes it the clearest example in medicine of a disease where prevention is everything and treatment is nothing
• Post-exposure prophylaxis has three components, and all three are examined:
• 1. Immediate wound washing with soap and running water for at least 15 minutes, followed by a virucidal agent
• This simple step alone substantially reduces the risk and is the single most effective measure, yet it is routinely skipped in favour of rushing to a hospital for injections
• DO not suture the wound, or suture only loosely after infiltrating immunoglobulin, since closing the wound drives virus into the tissue
• 2. Vaccine — modern cell-culture vaccine, given intramuscularly (Essen) or intradermally; the intradermal route uses a fraction of the dose and is far cheaper, which matters greatly at national scale
• 3. Rabies immunoglobulin, for category III exposures, infiltrated into and around the wound, which is where it does its work
• The categories of exposure — category I, touching or feeding an animal, or licks on intact skin — NO prophylaxis needed; category II, minor scratches or nibbling without bleeding — vaccine alone; category III, single or multiple transdermal bites, licks on broken skin, contamination of mucous membrane, or any bat exposure — vaccine plus immunoglobulin
• Control — mass dog vaccination, which is the only measure that eliminates the disease at source; animal birth control; pre-exposure prophylaxis for those at occupational risk; and public education about wound washing
• Other important zoonoses in India:
• Brucellosis — from unpasteurised milk and occupational contact, causing undulant fever; an occupational disease of veterinarians, abattoir workers and farmers
• Leptospirosis — from rodent urine contaminating water, with outbreaks after flooding, causing fever, jaundice, renal failure and conjunctival suffusion
• Anthrax — from spores in soil and in animal products, giving cutaneous, inhalational and intestinal forms; infected carcasses must not be opened, since exposure to air forms spores that persist in the soil for decades
• Plague — Yersinia pestis from rodents by the rat flea; a decline in rat population preceding human cases (rat fall) is the classic warning sign
• Kyasanur forest disease — a tick-borne haemorrhagic fever of the Western Ghats, notable as an Indian example
• NIPAH — from fruit bats, through date palm sap or intermediate hosts, with person-to-person spread and very high case fatality; outbreaks in Kerala
• Others — bovine tuberculosis, hydatid disease, taeniasis, toxoplasmosis, avian influenza and scrub typhus
• The "one health" approach is the conclusion this topic points to — human, animal and environmental health are inseparable, and require joint surveillance, shared laboratories and coordinated action between the health, animal husbandry, wildlife and environment sectors
• The drivers of emerging zoonoses — deforestation and encroachment on wildlife habitat, intensive livestock farming, the wildlife trade and live animal markets, climate change and international travel
• Wash the wound for fifteen minutes with soap and running water, which is the single most effective step and the most often skipped
• An animal reservoir makes eradication impossible, which is why rabies control means vaccinating dogs
• Do not suture a bite wound, since closing it drives virus into the tissue
• Infiltrate immunoglobulin into and around the wound, which is where it does its work rather than at a distant site
• Any bat exposure is category three, whatever it looked like, and needs both vaccine and immunoglobulin
• Rabies is essentially always fatal once symptomatic, which makes it the clearest case where prevention is everything
• The intradermal route uses a fraction of the dose, which matters greatly at national scale
• Never open an anthrax carcass, since exposure to air forms spores that persist in soil for decades
• Rat fall precedes human plague, and is the classical warning sign to act on
• Leptospirosis follows flooding, from rodent urine contaminating water, and should be suspected in post-flood fever
• Brucellosis comes from unpasteurised milk and occupational contact, and is an occupational disease of animal handlers
• Most emerging infections are zoonotic, which is the argument for One Health rather than a slogan
• Habitat encroachment drives emergence, alongside intensive farming, wildlife trade and international travel