Nonhuman Reservoirs Chapter 27

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Nonhuman ReservoirsChapter 27
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Nonhuman Reservoirs

• Zoonoses
• Vector-borne
• Soil-borne

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Zoonoses

• Direct contact, aerosols or bites
• Immunization veterinary care preventative
• Not feasible for feral animals
• Ex.
• Rabies
• Hantavirus pulmonary syndrome

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Rabies

• Reservoir primarily in saliva of feral animals,
  i.e. raccoons, skunks, coyotes, foxes, bats and
  stray cats and dogs
• 52,000 fatal cases per year worldwide
• 1 million receive treatment for bites
• Rhabdoviridae RNA virus that infects CNS cells
• Incubation time variable 9 month avg.
• Virus proliferates in thalamus and hypothalamus
  leading to onset of fever, excitation, dilation
  of pupils, excessive salivation, anxiety,
  uncontrollable spasms of throat muscles leading
  to respiratory paralysis and death
• Diagnosis
• tissue samples screened using monoclonal Ab
• Viral inclusion bodies i.e. Negri bodies in nerve
  cells
• Suspected cases can be immunized with Abs 100
  effective

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Hantavirus Pulmonary Syndrome

• Bunyaviridae
• Enveloped single stranded RNA virus
• Reservoir
• Rodents
• Virus contaminated excreta
• Aerosol
• Symptoms
• fever, myalgia, thrombocytopenia, leukocytosis
  and pulmonary capillary leakage
• Death due to asphyxiation
• Virulence and symptoms differ based on viral
  strain
• No specific treatment or vaccine available

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Vector-borne Illnesses

• Arthropod-borne
• Rickettsial diseases
• Lyme disease
• Malaria
• West Nile
• Plague

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Rickettsias

• Strictly intracellular bacteria that inhabit
  fleas, ticks, lice
• Typhus group
• Spotted fever group
• Ehrlichiosis group

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i. Typhus Rickettesia prowazekii

• Transmitted via bite of head louse
• Cells of R.prowazekii are introduced into skin
  via bite contaminated with louse feces
• Incubation 1-3 weeks
• Multiplies in lining of RBCs
• Symptoms
• fever, headache, malaise, characteristic rash
• Can cause damage to CNS, lungs, kidneys and heart
  
• Tetracycline and Chloramphenicol

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ii. The Spotted Fever group Rickettsia rickettsii

• Prevalent in southeastern states
• Transmitted via dog and wood tick fecal matter
• R.rickettsii grows within host cell cytoplasm and
  nucleus
• Incubation 3-12 days
• Symptoms
• fever and severe headache, rash all over body,
  vomiting and diarrhea
• Tetracyline and Chloramphenicol

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iii.Ehrlichiosis Group Ehrlichia

• Emerging tick borne diseases in US
• Deer and humans also serve as reservoirs
• Human monocytic ehrlichiosis (HME)
• Human granulocyte ehrlichiosis (HGE)
• Symptoms
• Fever, headache, malaise, leukocytopenia and
  thrombocytopenia, changes in liver function
• Blood leukocytes have visible inclusions of
  Ehrlichia cells
• Golfers and hikers prone
• Prevention protective clothing, DEET
• Treatment Doxycycline

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Lyme Disease

• Emerging tick borne disease
• Spirochete Borrelia burgdorferi
• Deer tick Ixodes scapularis
• Symptoms
• fever, headache, backache, chills, fatigue
• Additionally, in 75 of cases large rash erythema
  migrans appears at site of tick bite
• Tetracycline and penicillin
• Chronic Lyme disease arthritis, neurological
  involvement, cardiac damage, seizures
• Latent symptoms resemble Syphilis
• ELISA and PCR

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Malaria

• Protozoan P.vivax, P.falciparum
• Part of life cycle carried out in humans and
  mosquito vector (female Anopheles)
• Dramatic impact on human genetics and evolution
• Anopheles found in warmer climates i.e. tropics
• Symptoms chills and fever (104F)
• Loss of RBCs leads to anemia and enlargement of
  spleen
• Chloroquine can be used to treat intracellular
  stage
• Primaquine
• Survive in liver and reinitiate infection
• Drug-resistance expensive
• Control of mosquito population

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Malaria (Contd.)

• Dramatic impact on human genetics and evolution
• Endemic in Africa for several thousand years
• West Africans developed resistance to malaria
  cause by P.falciparum
• Altered RBC protein hemoglobin S instead of A
  (single amino acid)
• Hemoglobin S binds oxygen less efficiently
• Low oxygen concentrations change shape of cell
  from biconcave to elongated C shape i.e. sickle
  cell
• Homozygous for this trait sickle cell anemia
• Heterozygous resistance to malaria (P.falciparum
  cannot grow in low-potassium environment)
• Mediterranean regions resistance related to
  deficiency of RBCs in enzyme G6PD reducing
  compound
• Higher levels of oxidants such as hydrogen
  peroxide due to growth of P.falciparum normally
  removed by G6PD causes damage to parasite
  membranes

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West Nile Virus

• WNV member of Flavivirus
• Invades nervous system of warm-blooded hosts
• Horses, humans and birds
• 1999 U.S
• Several mosquito species
• Symptoms fever, headache, nausea,
  lymphadenopathy
• Rarely fatal
• Life-long immunity
• Antiviral drugs currently unavailable

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Soil-Borne

• Fungi, bacteria
• Fungi opportunistic pathogens
• Trigger allergic reactions Ex. Aspergillus causes
  asthma
• Fungal exotoxins
• Infections mycoses Ex. Atheletes foot
  Histoplasmosis (spores)
• Control of infections is challenging
• Tetanus Clostridium tetani
• Tetanus toxin paralysis and respiratory failure