Epidemiology of bovine anaplasmosis and babesiosis in Latin America and the Caribbean

The various parameters which interact in the epizootiology of babesiosis and anaplasmosis and which it is necessary to obtain in a survey are analysed and the two diseases compared. Where no data are available from Latin America and the Caribbean, the references from Australia and the United States of America are discussed. The two principal objectives of a study on the epidemiology of babesiosis and anaplasmosis are: to determine the risk of occurrence to understand the relevant factors leading to outbreaks. The first objective is relatively simple to achieve for both diseases by calculating the animal inoculation rate (h) at a determined age and the critical value of h for enzootic stability. The second objective requires exhaustive and complex studies. For babesiosis epidemiology, studies of the tick infection rate, cattle infestation rate, genetic composition of cattle, acaricides, stocking rate, climatic data and other factors are necessary. Anaplasmosis epidemiology cannot be satisfactorily explained by considering it purely as a tick-borne disease. Difficulties to be overcome include the great diversity of haematophagous Diptera in Latin America, and the scarcity of data on the capacity of these insects as anaplasmosis vectors and their feed preferences on cattle.

Haemaphysalis juxtakochi, Ixodes pararicinus (Ixodidae) and Otobius megnini (Argasidae) in relation to the phytogeography of Argentina

The phytogeographical distributions of Haemaphysalis juxtakochi, Ixodes pararicinus and Otobius megnini in Argentina are described from material collected mainly from 1978 to the present. H. juxtakochi was found in the northwestern area of the Amazonian domain and in the Chaco, Espinal and Pampean provinces of the Chaco domain. It was detected on Mazama spp., Tapirus terrestris, dog, cattle and on the vegetation. Most findings of I. pararicinus were from mountain rangeland, where it was found on cattle and in a lesser extent on horses. Ticks from Argentina classified as Ixodes ricinus were probably I. pararicinus. O. megnini was detected on cattle an sheep in the Andean Patagonian domain and in the Monte, Chaco and Espinal provinces of the Chaco domain. This tick is considered typical of arid and semiarid conditions, however the findings from the Espinal province where from areas with an annual rainfall over 900 mm.

Ticks (Ixodidae) parasitizing humans in four provinces of north-western Argentina

In four provinces of north-western Argentina (Catamarca, Jujuy, Salta and Tucumán), between March 1976 and March 1990, 514 ticks were found on humans. They were identified as Rhipicephalus sanguineus group (1 male), Boophilus microplus (6 male, 1 female), Amblyomma parvum (9 male, 13 female), A. cajannense (35 male, 30 female, 81 nymphs), A. neumanni (33 male, 41 female, 144 nymphs) and Amblyomma spp. (10 nymphs, 110 larvae). Most of the ticks were from the phytogeographical region of Chaco, one (B. microplus) was from an ecotone between the Chaco and the Andean Patagonia region, and the remainder of the ticks were from the Amazon region.

Post-thawing viability of vaccines for bovine babesiosis and anaplasmosis cryopreserved with glycerol

Live frozen vaccines containing Babesia bovis, Babesia bigemina or Anaplasma centrale were prepared using glycerol as cryoprotectant and stored in liquid nitrogen. The viability of the vaccines was tested inoculating calves 1 h (n = 12), 2 h (n = 12), 12 h (n = 6) and 24 h (n = 6) after thawing. Babesia bovis and A. centrale were detected in thin and/or thick blood smears in all vaccinated calves; however, 1 of 12 calves inoculated 1 h after thawing and 3 of 6 calves inoculated 24 h after thawing did not develop a B. bigemina parasitaemia. The longer post-thawing durability of frozen vaccines cryoprotected with glycerol compared with those cryoprotected with dimethyl sulfoxide, presented by other authors, will extend their use under field conditions.

Estimation of the potential demand for a bovine babesiosis and anaplasmosis vaccine in Argentina

A survey to estimate the potential demand for a bovine babesiosis and anaplasmosis vaccine was carried out by a postal questionnaire sent to 4407 veterinarians in the north and centre of Argentina. Twenty-three percent of the questionnaires (1047) were answered; 317 (7.2% of the total, 30% of those answered) pointed out the occurrence of the diseases and/or probable demand for the vaccine. The minimum and maximum demands were 407,892 and 982,300 doses for anaplasmosis, and 272,496 and 631,400 doses for babesiosis, respectively. The results presented from here onwards are based on the minimum demand. Sixty-eight and 48% of the anaplasmosis and babesiosis vaccine demand, respectively, came from veterinarians living in the Boophilus microplus-free area, while the remainder came from the tick-infested area, reflecting the fact that many farm owners from the tick-infested area seek professional assistance from veterinarians living in the tick-free area. Most of the demand for both vaccines was aimed at breeding cattle (77.2%), 14.5% at dairy cattle and the rest at studs (8.3%). Veterinarians living in the tick-infested area demanded vaccine for breeding cattle in a higher proportion than veterinarians from the tick-free area, whose demand was greater for dairy cattle. In the tick-free area, the demand for anaplasmosis vaccine was twice that for babesiosis vaccine, whereas in the tick-infested area the demand was equal. This agrees with the fact that the anaplasmosis-stricken area extends beyond the tick-infested region. Sixty percent of the respondents preferred a vaccine frozen in liquid nitrogen, whilst the rest preferred a refrigerated one, the first group accounted for 73% of the total demand. Fifty-six percent of the demand occurred between March and June with the peak in April, which reflects the main weaning date. The elasticity of the demand is discussed in relation to the probable benefits to be accrued by the farmers who make use of it. The annual mortality rates due to both babesiosis and anaplasmosis were estimated at 1.5 and 3.5% in the milk herds of Salta and Tucumán, respectively. In the beef herds of these two provinces, the mortality rate due to both diseases has been estimated at 3.5%. Using these figures and current prices, the systematic application of the vaccine in calves would render a benefit-cost ratio between 4.6 and 9.0, which would warrant its use in the herds of the areas at risk, i.e. in enzootic instability.

Ecological aspects of four species of ticks found on cattle in Salta, northwest Argentina

The seasonal activity of Amblyomma cajennense, Amblyomma neumanni, Amblyomma parvum and Boophilus microplus on cattle was studied in a ranch located in the northern part of the phytogeographical district of the Chaco Serrano where the habitat had suffered minimal human disturbance. The female ticks on one side of 10-25 cows were counted at intervals of 20-50 days from 29 October 1985 to 5 November 1986. The percentage of cattle parasitized with larvae and nymphs of Amblyomma was recorded, along with the proportion corresponding to the different species. Collection of ticks from the ground cover vegetation in areas with and without forest was performed using the dragging technique. B. microplus was found all year round; peaks of abundance were observed in May (55 females per cow/2) and November 1986 (71 females per cow/2). The peak in November was unexpected and possibly due to a higher stocking rate around watering places and poor nutrition at the end of the dry season. A. cajennense appears to produce a generation a year. Larvae were more abundant from June to August, nymphs from August to November and females from November (34 per cow/2) to January (15 per cow/2). A. neumanni showed a cycle corresponding to a generation every 3 years regulated via diapause that involves, at least, all the summer months. The peak of abundance for larvae, nymphs and females occurred in late autumn-early winter. The highest number of females (44 per cow/2) was recorded in June.(ABSTRACT TRUNCATED AT 250 WORDS)