Jabbar S. Ahmed

Status of tick distribution in Bangladesh, India and Pakistan

On a global basis, ticks transmit a greater variety of pathogenic microorganisms, protozoa, rickettsiae, spirochaets, and viruses than any other arthropods and are among the most important vectors of diseases affecting livestock, humans, and companion animals. Ticks and tick-borne diseases (TTBDs) affect 80% of the world cattle population and are widely distributed throughout the world, particularly in tropical and subtropical countries including India, Pakistan, and Bangladesh. Ticks and tick-transmitted infections have coevolved with various wild animal hosts, which constitute the reservoir hosts for ticks and tick-borne pathogens of livestock, pets, and humans. In this region, the livestock sector is suffering from a number of disease problems caused by bacteria, viruses, fungi, and parasites. Among the parasitological problems, the damage caused by TTBDs is considered very high, and the control of TTBDs has been given priority.

Ovine theileriosis in China : a new look at an old story

A fatal disease of sheep and goats in the northwestern part of China has in the past been reported to be due to Theileria lestoquardi. However, some characteristics of the causative agent are not in accordance with attributes ascribed to this parasite. We therefore determined the nucleotide sequence of the 18 small subunit ribosomal RNA (18S rRNA) gene of T. lestoquardi and the parasite identified in China and compared it with that of other Theileria and Babesia species. In the inferred phylogenetic tree, the 18S rRNA sequence of the Chinese parasite falls inside the clade consisting of Theileria species evidencing that it belongs to this genus. The 18S rRNA sequence of the Chinese parasite was found to be most closely related to Theileria buffeli and clearly divergent to T. lestoquardi, suggesting that it was a yet unrecognized Theileria species. The phylogenetic relationship of Theileria species infecting sheep and goats on the basis of their 18S rRNA gene structure was addressed. We report on the existence of at least two additional ovine and caprine piroplasm species, designated T. luwenshuni and T. uilenbergi.

Characterization of a polymorphic Theileria annulata surface protein (TaSP) closely related to PIM of Theileria parva: implications for use in diagnostic tests and subunit vaccines.

Theileria annulata is a tick-transmitted protozoan that causes tropical theileriosis, an often fatal leukoproliferative disorder of cattle. To characterize and identify parasite proteins suitable as diagnostic antigens and/or vaccine candidates, a cDNA clone encoding a macroschizont stage protein was isolated and characterized (here designated TaSP). The gene, present as a single copy within the parasite genome, is transcribed in the sporozoite and schizont stage and codes for a protein of about 315 amino acids, having a predicted molecular weight of 36 kDa. Allelic variants were found within single parasite isolates and between isolates originating from different geographical regions. The N-terminal part contains a predicted signal peptide and the C-terminal section encodes membrane-spanning regions. Comparison of a number of cDNA clones showed that both these sequence regions are conserved while the central region shows both size and amino acid sequence polymorphism. High identity of the N- and C-terminal regions with the polymorphic immunodominant molecule (PIM) of Theileria parva (identity of 93%), the existence of a central polymorphic region and two short introns within genomic clones suggest that the presented gene/protein may be the T. annulata homologue of PIM. However, the central region of TaSP has no significant identity with PIM, contains no repetitive peptide motifs and is shorter, resulting in a lower molecular weight. The existence of the predicted secretion signal peptide and membrane spanning regions suggest that TaSP is located at the parasite membrane.

Innate and Adaptive Immune Responses Co-operate to Protect Cattle against Theileria annulata

For many years it was assumed that Theileria annulata resembled T. parva, parasitizing lymphocytes and causing lymphoproliferative disease, with the two species being controlled by similar protective immune responses. Patricia Preston et al. here review the evidence that has led to a different view of T. annulata. It is now thought that the schizonts of T. annulata inhabit macrophages and B cells, and that tropical theileriosis is not a lymphoproliferative disease. Both innate and adaptive responses contribute to recovery from infection and resistance to challenge and cytokines produced by infected and uninfected cells influence the outcome of infection. Partial protection has been stimulated recently by defined recombinant antigens; efficacy depended upon the delivery system.

Ticks and tick-borne diseases in Asia with special emphasis on China

Abstract. An international conference on the control of ticks and tick-borne diseases sponsored by the European Commission was held in Shanghai between 11 and 15 September 2000. Participants from China, Europe, Australia, India, Iran, Israel, Japan and Thailand attended the meeting. The main objectives were: (1) determining the current situation concerning the epidemiology, economics, diagnosis and integrated control measures of ticks and tick-borne diseases caused by protozoan and rickettsial pathogens; (2) the creation of regional and international research networks and priority settings; (3) the creation of training possibilities for young scientists; (4) the identification of new research directions and priority settings in relation to vaccine development and diagnostics. The papers presented during this meeting focused on parasite characterisation and the description of yet unidentified Theileria and Babesia species pathogenic for large and small ruminants in China. In addition, progress made in immunity and vaccine development against the pathogens mentioned above and their vector ticks was also discussed.

Phylogenetic Position of Small‐Ruminant Infecting Piroplasms

Abstract:  Theileria and Babesia are tick‐transmitted protozoa that cause great economical losses in livestock. Recently, interest has risen in sheep‐infecting piroplasms and a number of previously unidentified pathogens were described, particularly in China. To address the phylogenetic relationship of Theileria and Babesia species infecting sheep, the complete sequences of the 18 S small subunit ribosomal RNA genes of a panel of piroplasm isolates, including T. lestoquardi, T. ovis, T. separata, B. ovis, B. motasi, B. crassa, and several novel species, were compared. The classification based on the established phylogenetic tree corresponded with traditional systematics and revealed that sheep/goat piroplasm species are of a polyphyletic origin. In addition, these studies revealed the existence of at least two novel sheep/goat piroplasm species, designated Theileria sp. (China 1) and Theileria sp. (China 2).

Application of the recombinant Theileria annulata surface protein in an indirect ELISA for the diagnosis of tropical theileriosis

The recombinant surface protein of Theileria annulata (TaSP) was used in the standardization and validation of an enzyme linked immunosorbent assay (ELISA) for the detection of circulating antibodies against tropical theileriosis. ELISA data were expressed as the percentage positivity (PP) of the reactivity of an internal positive control. A total of 50 sera samples from a disease-free area were used for the calculation of the cut-off value which served as a threshold between the positive and the negative sera samples. This was determined as the mean PP plus two standard deviations or the twice the mean PP of the results obtained with these negative samples. The obtained thresholds were 17.8% and 18.3%, respectively. Accordingly, the reactivity of 140 field sera samples collected at random from an area known to be endemic for tropical theileriosis in Sudan was determined as PP values which were then compared to the results obtained using the indirect fluorescence antibody test (IFAT) from the same samples. Both tests showed a high degree of correlation. The TaSP-ELISA had a sensitivity of 99.1% and specificity of 90.47% when taking the IFAT as a reference test. Our test has proved its suitability for the diagnosis of tropical theileriosis and could be used in serological surveys to map out the prevalence of the disease or to monitor vaccination efficiencies in disease-free populations.

Transmission of an unidentified Theileria species to small ruminants by Haemaphysalis qinghaiensis ticks collected in the field

Abstract. The transmission of a recently identified Theileria species pathogenic for sheep and goats in northern China is described. Haemaphysalis qinghaiensis nymphs which had been collected from grass in epidemic areas were able to transmit this Theileria species to sheep. The pathogen was also transmitted to sheep and goats by three batches of adult ticks collected from grass, ticks collected when moving about on sheep and ticks which were found partially engorged on sheep or goats.

Current status of ticks in Asia

Ticks and tick-borne diseases (TTBD) pose a major constraint for the development and improvement of the livestock industry. They cause economical losses by decreasing milk production, effecting weight loss, and increasing risk for bacterial, viral, and fungal infections. It has been reported that 80% of 1,200 million cattle are at risk for TTBDs causing a global annual loss of US

Validation of the indirect TaSP enzyme-linked immunosorbent assay for diagnosis of Theileria annulata infection in cattle

7,000 million. Ticks are currently considered to be second only to mosquitoes as vectors of human infectious diseases in the world. There are more than 850 species recognized with approximately 180 in the family Argasidae (soft ticks) and the others in the family Ixodidae (hard ticks). In Asia, the economical losses due to TTBDs is great; however, the knowledge on Asian ticks is scarce and needs intensive studies regarding their geographical distribution, ecology, and diseases transmission. To close this gap, the Asian component of the Integrated Consortium on Ticks and Tick-Borne Diseases (ICTTD-3) organized a meeting held from 26th–28th April 2006 in Pendik, Istanbul, Turkey on the characterization of Asian ticks. Besides the knowledge dissemination, this meeting resulted in a number of achievements such as the establishment of working groups for epidemiological studies and distribution of tick differentiation protocols and diagnostic tools.