Medical Entomology: Zoonoses & Arthropod-borne Diseases

• Medical Entomology studies insects, insect-borne diseases, and related issues affecting human and public health
• The field focuses on understanding, preventing, and controlling arthropod-borne diseases, classified as "Zoonoses" ("Zoon" means animals, and "nosos/noson" means illness/diseases)
• Zoonosis is a disease or infection transmitted from animals to humans ('anthropozoonosis') or vice versa ('zooanthroponosis')

Medical Entomology Subdivisions

• Public health entomology studies arthropods and human health
• Veterinary entomology studies arthropods and their impact on pets, livestock, and wildlife

Arthropods Role in Human & Animal Health: Direct causes of diseases

• Arthropods act as parasites, organisms living at the expense of their hosts (e.g., protozoans, helminths, arthropods)
• Pathogens are organisms whose presence can potentially cause disease (e.g., viruses, fungi, bacteria)
• Ectoparasitoses are diseases caused by contact, like bloodfeeding/bloodsucking, burrowing, crawling, or scraping between arthropods and host body surfaces
• Examples of ectoparasites: bloodsucking (ticks, fleas, lice), burrowing (mites)
• Ectoparasites cause dermatoses, allergic reactions, loss of efficiency/productivity, weight loss, and lowered milk production in animals
• Endoparasitoses involve arthropods that invade vertebrate hosts' tissues or body cavities
• "Chigoe" or "chigger" fleas embed as the host's tissues swell around the feeding site
• Myiasis is caused by Diptera fly larvae (maggots) infesting tissues

Arthropods Role in Human & Animal Health: Envenomization

• Envenomization is the introduction of venom (for defense or prey) or toxins (proteins causing poisonous reactions) via arthropod bites or stings
• Wasps (mastoparan), bees (melittin), and spiders (e.g., neurotoxin) produce venom

Arthropods Role in Human & Animal Health: Allergic Reactions

• Allergic reactions involve physiological mechanisms defending against foreign substances
• Antigens are foreign substances that trigger antibody production
• Allergens are antigens causing strong defensive reactions, resulting in allergies
• Hypersensitive reactions cause itching, redness, swelling, and rash
• Arthropod venoms can act as allergens, leading to anaphylaxis (fatal shock, low BP, blocked airways, nausea and vomiting)
• Examples of anaphylaxis causes include house dust mites, cockroaches, and mosquitos

Arthropods Role in Human & Animal Health: Other symptoms

• Delusory parasitosis is a psychopathic state marked by a strong sense of arthropod infestation, even if none exists
• Results of delusory parasitosis include self-inflicted scratching or treatment causing skin rash, redness, and abrasions
• Annoyance caused by abundance, small size, or flying into eyes, ears, and nose causes annoyance
• Fear of arthropods can occur such as Entomophobia (fear of insects), Arachnophobia (fear of spiders and arachnids), Acarophobia (fear of mites and ticks)
• Intense fear can result in excessive measures such as overtreatment with insecticides
• Formicophilia involves arousal when ants, cockroaches, or similar are allowed on the genitalia, perianal area, or nipples
• Food contamination occurs when house flies regurgitate or defecate pathogen-contaminated fluids on food, transmitting pathogens to humans or animals
• Integument can also transfer pathogens to food items

Arthropods Role in Human & Animal Health: Vectors

• Vectors transmit pathogens from one host to another
• Arthropods carry infections from animals to humans, or from human to human
• Mosquitoes and tsetse flies transmit infections through biting

Arthropods Role in Human & Animal Health: Intermediate Hosts

• Larval fleas in bedding ingest tapeworm eggs, becoming infected and infecting adult fleas

Brief History of Medical Entomology

• Patrick Manson showed Culex pipiens fatigans mosquitoes transmit Wuchereria bancrofti, causing filariasis
• Theobald Smith & Frederick L. Kilbourne showed cattle tick Rhipicephalus annulatus transmits Babesia bigemina, causing Texas cattle fever (bovine babesiosis)
• Ronald Ross demonstrated mosquitoes transmit avian malarial parasites from diseased to healthy sparrows
• Giovani Battista Grassi described cyclical development of malarial parasites in anopheline mosquitoes
• Paul Louis Simond showed fleas transmit Yersinia pestis bacteria, causing plague
• Josiah Nott cited circumstantial evidence mosquitoes transmit yellow fever virus
• Carlos Finlay cited Aedes aegypti mosquitoes vector the yellow fever virus
• Walter Reed proved A. aegypti is principle yellow fever vector
• David Bruce demonstrated tsetse fly Glossina palpalis transmits trypanosomes, causing African trypanosomiasis
• Howard Taylor Ricketts showed Rocky Mountain wood tick Dermacentor andersoni vectors Rickettsia rickettsii, causing Rocky Mountain spotted fever
• F. Percival Mackie showed human body lice vector Borrelia recurrentis spirochetes, causing louse-borne relapsing fever
• Carlos Chagas demonstrated the bug Panstrongylus megistus transmits the agent that causes American trypanosomiasis (Chagas disease)

Explore medical entomology, focusing on insects, insect-borne diseases, and their impact on human health. Understand arthropod-borne diseases classified as Zoonoses, and the roles of public health and veterinary entomology. Learn how arthropods directly cause diseases as parasites and vectors of pathogens.