I. Safety in Handling Ticks
A. Field-Collected TicksConsideration should be given to the possible hazard to people from pathogens present in field-collected ticks. The most important pathogen recognized is Crimean Congo haemorrhagic fever virus, usually associated with ticks of the genus Hyalomma and widely prevalent within the geographic distribution of Rhipicephalus appendiculatus.
1. Persons handling field tick collections should be made aware of potential hazards.2. Ticks of the Hyalomma species generally should not be removed from hosts; engorged or partially engorged ticks should not be crushed in the fingers.
3. If they must be removed, ticks should be handled with forceps.
B. Tick Handling Facilities
The handling of field-collected ticks in the laboratory must be controlled to avoid accidental attachment to personnel.
1. Field-collected ticks should be fed on rabbits and cattle in isolation facilities.2. Animals on which ticks have fed should be destroyed following transmission and pick-up.
3. Following engorgement of field-collected ticks on laboratory animals, aliquots should be homogenized and tested for extraneous human pathogens by inoculation in neonatal mice and BHK and Vero cells. The effects of these inoculations should be studied through three passages.
4. Any unused ticks should be destroyed by chemical means or by incineration.
C. Stabilate Preparation
Care should be taken in the preparation of sporozoite stabilates to avoid aerosol infection of personnel with extraneous pathogens during the grinding of ticks.
1. Personnel grinding ticks should be educated in the potential hazards involved.2. Access to areas where ticks are homogenized should be restricted to specified and informed personnel.
3. Personnel should wear protective clothing, including gloves and masks.
4. Tick grinding should be carried out under a big-hazard hood with a negative air pressure.
D. Improving Awareness of Tick-Transmitted Zoonotic Pathogens
Safety for laboratory personnel can be improved if information is made more widely available and greater care is taken with identification of pathogens and diagnosis if personnel become ill.
1. Lists of potential human pathogens such as Rickettsia conori, Borrelia sp. (Lime disease), Babesia divergens, B. microti, Ehrlichia sennetsu and E. cants should be prepared, and known tick associations, distribution and human disease syndromes should be documented.2. Methods for identifying extraneous pathogens in stabilates should be employed where possible.
3. Improved methods for identifying zoonotic viruses, rickettsia and bacteria in ticks should be developed.
4. Any suspected occurrence of human infection from ticks should be fully investigated and documented.
II. Safety for Cattle
A. Safety and Purity of StabilatesBoth ticks and experimental mammals are potential sources of contamination of stabilates with extraneous pathogens. In both cases, potential contaminants include Ehrlichia bovis, Borrelia sp., Oribi viruses, Bunya viruses and others.
1. Field ticks should not be used for the preparation of bulk stabilates. Well-characterized and pathogen-free laboratory colonies of ticks should be Used for this purpose.2. Only clean and healthy cattle and rabbits should be used for tick feeding.
3. Stabilates should be prepared in as sterile a manner as possible. Under some conditions, the use of antibiotics at concentrations appropriate for tissue culture may be indicated.
4. Prepared stabilates should be subjected to routine tests for safety by inoculation into neonatal mice and BHK and Vero cells, followed by three passages in these systems.
5. Stabilates should be subjected to routine characterizations in vivo, which should involve infectivity testing in splenectomized and intact susceptible cattle, sensitivity to tetracyclines and other antitheilerial drugs and cross-immunity in vivo.
B. Contamination of Stabilates with other Theileria parva Parasites
Care must be taken to avoid contamination of the infection being used for preparation of stabilate in the laboratory with other T. parva stocks.
1. A set of rules should be established for handling infected ticks and the rules adhered to rigidly.2. Tick unit facilities should allow for the strict separation of infected and uninfected ticks.
3. Tick unit personnel should use separate overalls for each batch of ticks used in stabilate preparation and the overalls should be sterilized daily.
4. Work should not be carried out on many different stocks simultaneously.
5. Stabilate storage systems should incorporate clear labelling of each stabilate tube.
III. Effect of an Immunizing Stock
The introduction of an immunizing stock that does not originate from that area may result in that parasite or a component parasite(s) of that stock becoming established through a carrier state in cattle and ticks. The long-term effect of the introduction of new (and potentially lethal) parasites on the disease epidemiology should be monitored.The characterization of parasites in target populations should be carried out before immunization and at intervals following immunization.
