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THEILERIOSIS TODAY
A NATIONAL CRISIS
J.A.Lawrence
E.Waniwa
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THEILERIOSIS TODAY
• What is theileriosis?
• What is happening?
• Why is it happening?
• What can be done about it?
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WHAT IS THEILERIOSIS
• What is theileriosis?– Definition
– Distribution
– Variants
– Life cycle
– Clinical signs
– Post-mortem findings
– Diagnosis
• How is it transmitted?
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Theileriosis: Definition
• “A disease of animals caused by protozoa of the genus Theileria”
• Various species carried by various ticks cause heavy economic losses in cattle, sheep, goats and wildlife in Africa, southern Europe, Middle East, Asia and Australasia
• In Zimbabwe, specifically “a disease of cattle caused by Theileria parva”
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Theileria Parva: Distribution
COMOROS
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Theileria parva: Variants
• Three distinct epidemiological variants of disease caused by T. parva.
DISEASE TRANSMISSION SEASONALITY MORTALITY SPREAD
East Coast fever Cattle - cattle Non-seasonal High Rapid
Zimbabwe theileriosis
Cattle - cattle Rainy season Low Slow
Corridor disease Buffalo - cattle Non-seasonal High Self-limiting
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Theileria parva: Variants
East Coast fever + Corridor disease
Zimbabwe theileriosis + Corridor disease
Corridor disease
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Theileria parva: Historyin Zimbabwe
• 1901/2 East Coast fever introduced
• 1934 Corridor disease recognized
• 1936 Zimbabwe theileriosis (January disease) recognized
• 1954 East Coast fever eradicated, Corridor disease and Zimbabwe theileriosis persist
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Theileria parva: Life Cycle
Transformation
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Theileria parva: Clinical signs
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Theileria parva: Clinical signs
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Theileria parva: Post-mortem findings
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Theileria parva: Post-mortem findings
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Theileria parva: Post-mortem findings
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Theileria parva: Post-mortem findings
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Theileria parva: Post-mortem findings
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Theileria parva: Post-mortem findings
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Theileria parva: Post-mortem findings
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Theileria parva: Diagnosis
• Based on the detection of schizonts in blood, lymph node and spleen smears, in conjunction with history, clinical signs and post-mortem findings
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Theileria parva: Diagnosis
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Theileria parva: Diagnosis
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Theileria parva: Diagnosis
• Based on the detection of schizonts in blood, lymph node and spleen smears, in conjunction with history, clinical signs and post-mortem findings
• Piroplasms are non-specific
• Differentiation from other Theileria species is based on serological and molecular techniques
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Theileriosis in Zimbabwe
What Is Happening
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Theileriosis Confirmed At Central Veterinary Laboratory 2010-2019
Cas
es
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Theileriosis In 2018
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Districts With Theileriosis 2010-2019
Data missing
Dis
tric
ts
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Districts With Theileriosis 2019
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Seasonal Incidence Of TheileriosisC
ases
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Theileria parva is primarily a parasite of ticks
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The Brown Ear TickRhipicephalus appendiculatus
• The main vector of Theileria parva
• Three host tick
• Preferred hosts are cattle and large wild ungulates
• Adults feed preferentially on the ears
• Immatures feed on the head and neck
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The Brown Ear Tick
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The Brown Ear TickLife Cycle
Larvae
Nymphs
Adults
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The Brown Ear TickTransmission of Theileria
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The Brown Ear TickSeasonality in Southern Africa
January -March
April -June
July -September
October -December
Diapause Adults
LarvaeNymphs
No ticks
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East Coast FeverSeasonality in Zimbabwe
AdultsJanuary -March
LarvaeApril -June
NymphsJuly -September
No ticksOctober -December
Diapause
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Zimbabwe TheileriosisSeasonality
AdultsJanuary -March
LarvaeApril -June
NymphsJuly -September
No ticksOctober -December
Diapause
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Theileriosis In ZimbabweChange In Seasonality
AdultsJanuary -March
LarvaeApril -June
NymphsJuly -September
No ticksOctober -December
Diapause
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What Is Happening?
• Theileria parva is changing from seasonal to non-seasonal, with rapid spread and high mortality
1930’s todayDISEASE SEASONALITY MORTALITY SPREAD
East Coast fever Non-seasonal High Rapid
Zimbabwe theileriosis
Rainy season Low Slow
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Why Is It Happening?
• Change in cattle?
• Change in the Theileria?
• Change in the tick?
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Change In The Theileria
• Has the Theileria that was present in Zimbabwe for 80 years suddenly changed its character?
• Has an East African type of Theileria been reintroduced?
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Change In The Tick?
• Has the Brown Ear Tick increased in numbers to overwhelm the seasonal effect? Are nymphs so numerous that they can transmit fatal disease?
• Has the Brown Ear Tick changed its character? Can nymphs now transmit T. parva more efficiently than before?
• Has another species of tick become involved in transmission?
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Lowveld Brown Ear Tick
• Brown Ear Tick (Rhipicephalus appendiculatus) was identified in 1901
• Lowveld Brown Ear Tick (Rhipicephalus zambeziensis) was not identified until 1981
• Differences– Adults almost identical – feed on ears
– Lowveld Tick larvae and nymphs more easily differentiated – feed on legs
– Lowveld Tick more tolerant of dry conditions
– Lowveld Tick nymphs efficient vectors of T. parva
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Distribution of Lowveld Brown Ear Tick in Zimbabwe
1982 2014
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Lowveld Brown Ear Tick: Distribution In Zimbabwe
• Why has the distribution changed?
– Failure of dipping
– Lack of movement control
– Climate change?
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Lowveld Brown Ear Tick: Transmission of Theileriosis
• The Lowveld Brown Ear Tick is known to be a major vector of East Coast fever, especially in winter, in the Southern Province of Zambia
• It is likely that it is the tick responsible for transmission of theileriosis in Zimbabwe in winter
• Transmission throughout the year favours the appearance of strains of Theileria parva that are more virulent, spread more easily and cause higher mortality
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What Can Be Done To Control Theileriosis?
National level
• National control/eradication programme
– Intensive dipping
– Movement control
– Quarantine of infected properties
– Destocking
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What Can Be Done To Control Theileriosis?
Farm level
• Effective fencing (double along public roads/vulnerable boundaries)
• Effective dipping, throughout the year
• Prevention of introduction of tick-infested or Theileria-infected cattle (including vaccinated animals)
• Prevention of introduction of tick-infested hay
• Surveillance – disease and ticks (NB legs)
• Early treatment of clinical cases
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What Can Be Done To Control Theileriosis?
Immunization
• Live parasites in blood and spleen - ineffective
• Molecular vaccine – no vaccine yet developed
• Cell culture vaccine – not effective with Theileria parva
• Infection and treatment
• Block treatment with tetracyclines – unreliable
• NB Infection and treatment and block treatment create carriers
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Infection and Treatment
• Bulk up selected isolate of Theileria in cattle, infect ticks, prepare deep-frozen stabilate, establish safe/effective dose, and inoculate simultaneously with long-acting tetracycline
• Shortcomings
– Immunization is generally most effective with a local isolate
– Immunized cattle are likely to be carriers
– Logistical difficulties
– Expense – up to USD7/head (2019)
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Immunization In Zimbabwe
• A local isolate, Boleni, was developed and tested in the mid-1990’s by an FAO project
• It proved to be effective against all isolates tested, except those originating from buffalo
• It could be administered without tetracyline coverage
• No vaccine available since 2005
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Conclusions
• Theileriosis has re-emerged as a serious constraint to cattle production
• The major reason may be the reintroduction of the Lowveld Brown Ear Tick to the highveld
• There is little prospect of an effective national control programme
• Cattle owners must accept responsibility for control in their herds
• Immunization may play a role in control programmes