Chapter 5 Zoonotic and Vector-borne Diseases

Objectives Define what is meant by a vector-borne disease and a zoonotic disease Discuss three human diseases transmitted by each Discuss methods used to control vector-borne and zoonotic disease

Zoonosis Refers to “an infection or infectious disease transmissible under natural conditions from vertebrate animals to humans.”

Vector “. . . an insect or any living carrier that transports an infectious agent from an infected individual or its wastes to a susceptible individual or its food or immediate surroundings.”

Examples of Vectors Various species of rodents (rats and mice) Arthropods (mosquitoes, ticks, sand flies, biting midges – “no-see-ums”)

Methods of Transmission Contact with the skin A bite or scratch from an animal Direct inhalation or ingestion The bite of an arthropod vector

Vector-Borne Diseases Malaria Leishmaniasis Plague Lyme Disease Rocky Mountain Spotted Fever

Malaria Found in more than 100 countries (USA) > 40% of the world’s population at risk Endemic regions: Central and South America Africa India Southeast Asia Middle East Oceania Annual death toll more than 1 million persons

Malaria Transmission By mosquitoes that carry a parasite known as a plasmodium. Transmission involves the complex life cycle of mosquitoes (the vector) and human hosts.

Infectious Agents of Malaria Plasmodium falciparum Most deadly Plasmodium vivax Plasmodium ovale Plasmodium malariae

Symptoms of Malaria Fever and flu-like signs Vomiting and diarrhea Jaundice (due to anemia) Kidney failure Seizures and coma Death

The Cost of Malaria Lost productivity, lost earnings, and negative impacts upon tourism The direct costs include treatment and prevention of the disease (medicine, hospitalization, and pesticide use).

Figure 5-3 Female Anopheles gambiae mosquito feeding. Source: Reprinted courtesy of the CDC Public Health Image Library. ID# 1662. Jim Gathany Content Provider. Available at: http://phil.cdc.gov/ phil/details.asp. Accessed March 1, 2010.

Control of Malaria Spraying with DDT and administering synthetic anti-malaria drugs. Dicholor-diphenyl-tricholorethane (DDT) Thought to be harmful to wildlife; use of DDT was opposed by many. South Africa has used annual spraying of DDT inside of homes.

Leishmaniasis (Protozoa) Cutaneous leishmaniasis is transmitted by the bite of an infected sand fly. Source: Reprinted from CDC Public Health Image Library, ID# 352. Available at: http://phil.cdc.gov/phil/details.asp. Accessed May 28, 2005.

Leishmaniasis (2) The reservoir are rodents, humans and carnivores (dogs). Transmitted from the reservoir to the human host by a sand fly. Endemic in a total of 82 countries (including Mediterranean and Middle East) – US Military

Factors Associated with Leishmaniasis Movement of the human population into endemic areas Increasing urbanization Extension of agricultural projects into endemic areas Climate change due to warming

Control of Leishmaniasis Apply insecticides in dwelling areas Use of screens on houses Eliminate breeding areas Destroy rodent burrows Control domestic dogs

Plague The bacterium Yersinia pestis is the infectious agent, harbored by rodents Treated with antibiotics Transmitted by the bite of a flea Infects both animals and humans May have caused the plague epidemic during the Middle Ages (the “black death”)

Signs of the Plague Fever and chills Headaches Infections of lymph glands Pneumonic plague (secondary infection)

Control of the Plague Keep rodents in check. Remove food sources. Wear gloves if handling wildlife. 50-60% case fatality, if not treated.

Source: Reprinted from Centers for Disease Control and Prevention, Plague: CDC Plague Home Page. Available at: http://www.cdc.gov/ncidod/dvbid/plague/index.htm. Accessed June 8, 2005.

Lyme Disease Identified in 1977 - Lyme, Connecticut Arthritis cases among children Caused by a bacterium Borrelia burgdorferi Treated with antibiotics Transmitted when humans are bitten by black-legged ticks (deer) ticks Wear light color clothing

(Top) From left to right: The black-legged tick (Ixodes scapularis) adult female, adult male, nymph, and larva. Source: Reprinted from Centers for Disease Control and Prevention. Lyme Disease. Available at: http://www.cdc.gov/ncidod/dvbid/lyme/ld_transmission.htm. Accessed December 9, 2005.

Rocky Mountain Spotted Fever Rickettsial agent is Rickettsia rickettsii A febrile disease (fever) Treated with antibiotics Case fatality rate up to 25% if untreated Transmitted by an infected tick

Viral Hemorrhagic Fever (VHF) Viruses require animal host or insect host as a natural reservoir Limited to geographic areas where host survives Animal host reservoirs include: rodents like the cotton rat, deer mouse, and house mouse.

Arthropod-Borne Viral Diseases Also known as arboviral diseases. A group of viral diseases caused by blood-feeding arthropod vectors Vectors that transmit arboviruses: Ticks, sand flies, biting midges, and mosquitoes.

Arboviral Encephalitides Caused by a virus that produces an acute inflammation of: Sections of the brain Spinal cord Meninges Many forms of encephalitis: St. Louis encephalitis Western equine encephalitis

Arboviral Encephalitides (continued) Transmitted by the bite of mosquitoes from the reservoir to a human host. The reservoir may be wild birds and small animals. Cost of arboviral encephalitides -$150 million/year, including: vector control surveillance activities

Symptoms of Arboviral Disease Acute CNS [central nervous system] illness Acute fevers of short duration, with and without an exanthum [rash] Hemorrhagic fevers Polyarthritis and rash of variable duration

West Nile Virus Classified as a mosquito-borne arboviral disease, the agent is a Flavivirus. Mosquitoes become infected when they feed on infected birds. Health effects vary from no symptoms to very severe symptoms.

Emerging Zoonoses Zoonotic diseases caused by: new agents. known agents that occur in locales or species that previously did not appear to be affected by these known agents.

Factors Affecting Emerging Zoonoses Ecological changes: deforestation conversion of grasslands irrigation Other factors include: migration and urbanization of humans changes in human behavior (wars)

Examples of Emerging Zoonoses Bacterial: Escherichia coli O157:H7 (hemolytic-uremic syndrome) Mass food processing technology allowing contamination of meat Parasitic: Cryptosporidium and other pathogens Contaminated surface water, faulty water purification

Examples of Emerging Zoonoses Non-conventional agent: Bovine spongiform encephalopathy (Mad Cow Disease) Changes in rendering process Viral: Hantaviruses Ecological/environmental changes Increasing rodent contacts

Hantavirus Pulmonary Syndrome (HPS) – Rare The causative agent is the hantavirus family of Bunyaviridae. Transmitted when aerosolized (airborne) by rodent urine and droppings Primary vectors are species of rodents: cotton rat, rice rat, white-footed mouse, and deer mouse.

Hantavirus Carrier The main host for the hantavirus is the deer mouse--Peromyscus maniculatus, which is found throughout North America. Source: Reprinted from CDC Public Health Image Library, ID# 1183. Photo credit: James Gathany. Available at: http://phil.cdc.gov/Phil/details.asp. Accessed September 26, 2005.

Dengue Fever Caused by flaviviruses The vector for transmission: the Aedes aegypti mosquito. Occurs primarily in tropical areas: Southeast Asia, Tropical Africa, and South America. The proportion of deaths as high as 40 to 50% if untreated.

Symptoms of Dengue Fever Acute fever Headache Muscle and joint pain Appetite loss Stomach problems Rash Hemorrhaging (shock)

Dengue Fever in the U.S. Dengue fever has occurred in the continental U.S. Southern Texas and the southeastern states at theoretical risk. May be imported by travelers who returning from endemic tropical areas

Other Zoonotic Diseases Rabies – Virus that affect CNS Receive treatment if bitten Anthrax - Bacterium Inspired (breathing) is most deadly

Control of Mosquito-Borne Diseases Use sentinel chickens. Drain standing water. Use mosquito-eating fish in ponds. Repair window screens. Wear repellents and protective clothing. Spray in populated areas.

Travel Advisories www.cdc.gov/travel