4 nights’ catch, 1917 Lascelles, Victoria, Australia
Impact of rodents Agriculture Field damage/reduced yield of staple crops Loss, damage, contamination to stored crops Health Zoonosis – lassa fever, plague, leptospirosis Yield of vegetable crops, marketability Contamination – dysentery (Salmonella etc.) Property Buildings, furniture, utensils, roads, wires, clothes, blankets, fishing nets …..
>750 million poor in rice-producing Asia! >750 million poor in rice-producing Asia! 70% of the world’s poor live in Asia
Nutrition from rice (selected Asian countries, 1999) Sources: FAO online database (2001); World Development Report (2002); World Bank 0 10 20 30 40 50 60 70 80 Myanmar Laos Vietnam Bangladesh Cambodia Indonesia Thailand Philippines Korea China Malaysia India Japan World Calories Protein
Region and population Rice produced (tonne) Loss to rodents (%) Rice eaten (kg/year) People fed per year if no rat losses Indonesia 210 million 50,000,00017249 33 million (52% calories) Vietnam 80 million 31,000,00030280 8 million (67% calories) Asia 3.6 billion 540,000,0005150 180 million (32% calories) 10 360 million Rice field losses to rats
Losses to rats in Bangladesh Field losses 10 – 20 % (up to 100% in some years) Storage losses 5 – 10 % (can be > 200kg per house) Foregone production ? Other crop losses
Damage crops, stored grain, clothes, houses Loss of production increases crop area Environmental risks from poisons Disease impacts Rats are the No. 1 pest affecting rice production in many Asian countries
Rodents and Disease Rodents are vectors and reservoirs for more than 60 different diseases. Hantavirus The Plague Leptospirosis Rat Typhus (rickettsia) Neuro-angiostrongyliasis (rat lungworm) are five of the major rodent-borne diseases that commonly affect human populations in Asia
Why rodents? Why are rodents important reservoirs and vectors of human disease? Mammals with common physiology Commensality with long “co-evolution” living in close proximity to humans Generalist feeders exploiting waste and human/livestock food Rodents can pick up and transmit more than 60 different diseases
Morbidity rate of Leptospirosis by province, Northeastern region, Thailand 1996 - 2002 Morbidity rate of Leptospirosis by province, Northeastern region, Thailand 1996 - 2002 0- 2.4 2.41 -15 199619971998 1999 15.01 - 50 > 50 Morbidity rate/100,000 20002001 2002
W. Tangkanakul et al. 2005. SE Asian J Trop Med Public Health 36, YearCasesIncidence(/100,000)Deaths 1996 398 398 1997 2331 23313.4 1999 6080 60809.8266 20001428523.7362 20011021716.4171 2002 6864 6864 95 95
Leptospirosis human epidemiology in Thailand 7 to 9 times more males affected 71-84% farmers; most 25-54 years Peak incidence in Aug to Nov (rains) Serotypes: australis, sejroe, pyrogenes Higher incidence if villages had pot holes in roads
Information on leptospirosis in Asian countries is extremely limited. Information on leptospirosis in Asian countries is extremely limited. Little is known about: The status of rodent diseases in Asia that affect humans and/or their livestock Which rodents are key reservoir species The persistence of the infective parts of the disease life cycle in rice agro- ecosystems Leptospirosis human epidemiology in Thailand
Leptospirosis & Typhus in Lao PDR In 2001-2003 at Mahosot Hospital in Vientiane, of 427 adults with unexplained fever, from serological evidence: 10% leptospirosis 10% leptospirosis 10% murine typhus 10% murine typhus 15% scrub typhus 15% scrub typhus
Main risk factor – time spent in flooded paddies
Health impacts of rodent diseases Epidemics of rodent-borne diseases can have a significant impact on a local rural economy. Zoonosis can cause disability at key times and lead to no crop, a late crop, or reduced crop yield. In poorer communities, disability for a month at a key time may lead to no crop, a late crop, or reduced crop yield. Rodent diseases can lead to a debt treadmill!
The Plague Etiologic agent Yersinia pestis - bacillus Bubonic Plague: enlarged, tender lymph nodes, fever, chills and prostration. Septicemic Plague: fever, chills, prostration, abdominal pain, shock and bleeding into skin and other organs Pneumonic Plague: fever, chills, cough and difficulty breathing; rapid shock and death if not treated early Pharyngeal and Meningitic Plague also documented
Stenseth, N.C, Aikimbayev, A., Atshabar, B.B., Begon, M., Belmain, S.R., Bertherat, B., Carniel, E., Gage, K.L., Leirs, H. and Rahalison, L. (in press) Plague: Past, Present and Future. PLoS Medicine.
Squalid high-density slum conditions and poor sanitation promote transmission Confusion fuelled by poor levels of information in government press statements Media reports unconfirmed/suspected cases, exaggerating death tolls Agricultural exports and cargo embargoed, export loss of more than $420 million Investor confidence plummets, $600 million to $3 billion loss to Indian economy 45,000 people cancelled flights to India International migrant workers stranded Divali [Festival of Lights] cancelled Official death toll was 56 Approx. 700 suspected cases Speculation that it was not plague continues to this day Surat
Urban outbreaks of plague will happen again Can we learn from the past? Economic non- disease costs can be very high