By Prof Dr Abdullah G Arijo
In Pakistan, more than 75% of the rural population practices livestock husbandry, and most of these people depend upon livestock for their subsistence.
Crimean-Congo Hemorrhagic Fever virus (CCHFV) and other significant tick-transmitted pathogens of humans and animals are endemic to certain geographic regions of Pakistan. Called the “Asian Ebola virus”, CCHFV can emerge from rural areas where people are exposed to infected ticks and be transmitted person-to-person resulting in mini-epidemics, especially in hospital settings and urban centers, with significant human morbidity and mortality. Other tick-borne diseases, including Anaplasmosis and Babesiosis can cause significant losses in animal production systems, directly and indirectly impacting growth in Pakistan’s agricultural economy and in the livelihood of rural Pakistanis. Because of the high level of biological containment needs to conduct assessment, diagnostic assays, and infection control studies of CCHFV, and the risk of CCHFV being used as a bioterrorism weapon, alternative solutions are critically needed to protect the health and economic well-being of normal Pakistanis from this and other dangerous tick-transmitted pathogens
Ticks are found in almost every region of the world and are second only to mosquitoes in their public health and veterinary importance [Sonenshine, 1991]. However, ticks transmit the greatest variety of pathogens to humans and animals of any arthropod vector (Balashov, 1972), and diseases transmitted by ticks are global medical and veterinary public health problems (Sonenshine, 1991). Importantly, especially in developing countries, tick-borne diseases affect 80% of the world’s cattle population and are widely distributed (de Castro, 1997). Moreover, ticks represent an important proportion of all animal diseases affecting the livelihood of poor farmers in countries like Pakistan. Blood feeding ixodid (hard) ticks transmit a wide variety of bacterial, rickettsial, viral and protozoan diseases of veterinary and human health significance including Anaplasmosis, Cowdriosis, East Coast Fever, Babesiosis, Lyme borreliosis, tick-borne relapsing fever, ehrlichiosis, Rocky Mountain spotted fever, Boutonneuse fever, Queensland tick typhus, Q fever and numerous arboviral haemorrhagic fevers and encephalopathies [Sonenshine, 1993]. Due to their efficiency as vectors of a wide variety of pathogens, broad vertebrate host range and worldwide distribution, ixodid ticks also are recognized as potential vectors of a number of pathogens of bio- or agro-terrorism significance including Crimean-Congo haemorrhagic fever virus (CCHFV), Rickettsia rickettsii (Rocky Mountain Spotted Fever) the tick-borne encephalitis (TBE) complex of flaviviruses (Central European tick-borne encephalitis, Far Eastern tick-borne encephalitis, Russian spring and summer encephalitis, Kyasanur forest disease and Omsk hemorrhagic fever), Coxiella burnetii (Q fever), and Francisella tularensis (tularemia) (CDC, NIH).
Tick-transmitted Infections in Pakistan
Animal diseases, in general and tick-borne diseases (TBD) are high among the factors directly and indirectly hampering growth in livestock production and the whole agricultural sector of Pakistan’s economy due to the many roles of livestock as sources of food and income, by generating employment, delivery of energy (dung, biomass), fertilizer, weed control, use of marginal lands, investment, and savings as well as transport (Sansoucy, 1995). Tick-borne diseases also are a significant human public health problem in Pakistan.
Being a sub-tropical country, Pakistan has a rich fauna of disease vectors, including mosquitoes, soft and hard ticks, the latter of which transmit several significant vector-borne diseases. However, active research on vector-borne disease is scarce. Major tick-borne diseases in Pakistan include Crimean-Congo hemorrhagic fever (CCHF), as well as human and animal anaplasmosis caused, by the agents Anaplasma phagocytophilum and Anaplasma marginale, respectively. Crimean-Congo hemorrhagic fever virus (CCHFV) causes a highly lethal tick-borne viral disease, and outbreaks occur mainly in the cold, arid regions of Pakistan. Humans appear to be the only hosts of CCHFV that manifest disease, while infection in other hosts is largely inapparent. The virus replicates in its natural hosts, which include ticks as well as a variety of domestic and wild vertebrates including sheep, goats, cattle, camels, and dogs. Tick-transmitted A. marginale infects cattle, negatively impacting animal health and production while A. phagocytophilum causes both human and animal disease. The direct and indirect implications of tick infestations on the condition of life in rural Pakistan are inextricably linked to human and animal health.
Several groups of individuals are at-risk of contracting CCHF, including people who
work outdoors, and especially those that work with large domestic animals. high risk occupations
include herders, farmers, slaughterhouse workers and veterinarians. Exposures such as from crushing infected ticks and butchering infected animals are frequent sources of CCHFV infection. Disease among health care workers attending CCHFV infected patients also is common, and risk can be extremely high especially during the hemorrhagic period of disease (Smego, et al, 2004). This high degree of transmissibility among people is the main reason that the US Centers for Disease Control and Prevention has classified CCHFV as a biosafety level-4 pathogen (www.cdc.gov) which consequently has significantly limited research investigations. Moreover, the highly pathogenic nature of CCHFV has led to concerns over its use as an agent of bioterrorism. Referred to as “Asian Ebola Virus” (Smego et al., 2004), CCHFV is readily transmitted from person to person, and has a high case-fatality rate (>30%) (Athar et al., 2003; Flick and Whitehouse, 2005; Ergonul, 2006). The virus also is transmissible by small-particle aerosol. Table IV gives data on major outbreaks and mortality due to CCHF in Pakistan from 1976-2005.
Tick infestation has great effect on productivity potential in livestock and poultry. Therefore, mass eradication control approaches are required to embark upon both with short term and long term planning.