Fungi and disease

• Magnaporthe oryzae (rice blast)

  11-33% of rice harvest destroyed per annum 
• Blumeria (Erysiphe) graminis (powdery mildew of barley and wheat) 

  £400 million p.a. fungicide market
• Mycosphaerella graminicola (blotch disease of wheat)

  £250 million p.a. fungicide market
• Phytophthora infestans (late potato blight)

  £100 million p.a. fungicide market 
• rice

  • 150 M HA of rice cultivated per annum
  • 645 M tonnes per annum harvested
  • 23% of worlds calories supplied by rice
  • 90% of rice is grown and consumed in asia
  • world rice stock below 110M tonnes (2007/8)
  • 38% more rice is needed by 2030 to feed population growth
  • global population will be 9.2 billion in 2050, with 86% in underdeveloped countries
• Rice blast disease

  • annual losses of 11-18% yield (50% in Phillipines)
  • 10% loss is enough rice to feed 60 million people
  • occurs in more than 85 countries
  • china 2001-05 - 5.7 M HA rice destroyed
  • japan 1993 - 45% annual yield loss
  • recent epidemics - Korea, USA, China, Japan, Vietnam
  • most cultivar-specific resistance broken in 2-3 years
• M. oryzae symptoms

  • progression
  • initial symptoms white to grey-green lesions or spots with darker borders produced on all parts of the shoots
  • older lesions elliptical or spindle shaped and whitish to grey with necrotic borders
  • lesions wide in the centre and pointed toward either end that may enlarge and coalesce to kill the entire leaf
  • symptoms also observed on leaf collar, culm, culm nodes and the panicle neck node
  • nodal infection causes the culm to break at the infected node
  • outcome
  • few or no rice grains or whiteheads when neck is infected
• M. oryzae infection cycle

  1. conidia attach to host surface and germinate
  2. host cell death starts 4-5 days after infection
  3. conidia produce hyphal filament that adheres to host surface
  4. penetration peg employs turgor pressure to penetrate the plant cuticle and cell wall
• control measures - cultural practices

  • early sowing of seeds after rainy season
  • use fertiliser sparingly, with application of nitrogen in small increments
  • water management practices in rainfed areas lessens the likelihood of stress which aids disease
• control measures - breeding

  planting resistant varieties against the rice blast is currently the most practical and economical way of controlling rice blast
• control measures - chemicals

  systemic fungicides such as pyroquilon and tricyclazone are possible chemicals for controlling the disease
• pathogen associated structures

  • penetration via stomata or wounds
  • direct penetration
  • mechanical force
  • enzymatic penetration e.g. cutinase, pectinase
  • appressorium turgor pressure (80 Mpa) = breakdown of trehalose and glycogen
• what four criteria does fungi need to meet to cause disease in humans

  • the ability to grow at or above host body temperature
  • the ability to reach internal tissues by penetrating or evading host barriers
  • the ability to lyse tissues and absorb their components
  • the ability to evade host immune defences
• types of human mycoses

  • skin mycoses
  • superficial mycoses
  • cutaneous mycoses
  • subcutaneous mycoses
  • systemic mycoses
• systemic mycoses examples

  • C. albicans
  • A.fumigatus
  • C. neoformans
  • P. jiroveci
  • endemic species
  • H. capsulatum 
  • C. immitis
  • P. brasiliensis
  • B. dermatitidis
• C. albicans

  • pleiomorphic
  • thrush, skin and vaginal infection
  • blood-borne infection can be fatal
• A.fumigatus

  inhaled spores (~300 per day/person), ABPA aspergilloma, invasive aspergillosis
• C.neoformans

  • Cryptococcosis: lungs, meningitis
  • C. gattii primary pathogen
  • pigeon guano
• P.jiroveci

  pneumonia associated with HIV
• H.capsulatum 

  • most common fungal respiratory infection
  • bat guano
• C.immitis

  • San Joachim Valley Fever
  • most asymptomatic
• P.brasiliensis

  • dimorphic
  • inhilation
• B.dermatitidis

  mid west usa
• at risk groups

  • children/aging populations
  • immune suppressed patients
  • co-morbidities and fungal disease
  • immune competent patients
• diagnostic techniques for fungi

  • direct microscopic examination of clinical samples including histopathology
  • culture of the organism
  • serology/antigen detection tests
  • molecular diagnostics (DNA probe/sequence tests)
• drug discovery for fungal infection

  • new drugs in the pipeline
  • targeted screens based on identification of fungal specific components and pathways
  • combination techniques
  • synergy
  • reduced likelihood of resistance
  • interactions/contraindications e.g. flucytosine and AMB
  • other ideas
  • fungal viruses / better materials for implants
• what are aflatoxins

  naturally occuring mycotoxins that are produced by many species of Aspergillus, among the most carcinogenic substances known e.g. turkey X disease
• sir anthony's fire

  • caused by eating bread prepared from rye which is infected by ergot
  • symptoms - delirium, sensation of burning, vasoconstriction, limb numbness, cold, gangrene, limbs rot away
• Amanita muscaria - psychotropic drugs 

  • hallicinogenic properties caused by ibotenic acid and muscimol
  • fatalities have been associated with A.pantherina
  • nausea and vomiting are common. confusion, euphoria or sleepiness are possible. loss of muscular coordination, sweating, chills, visual distortions, a feeling of strength and delusions
  • symptoms appear after 30 minutes to 2 hours, lasting for hours