A study of the epidemiology of Anaplasma marginale infections of cattle in southern Queensland: clinical disease and the prevalence of complement fixing antibodies

Epidemiology and genotyping of Anaplasma marginale and co-infection with piroplasms and other Anaplasmataceae in cattle and buffaloes from Egypt

BACKGROUND

Anaplasma marginale is an obligate intracellular bacterium and the main cause of bovine anaplasmosis in tropical and subtropical regions. In Egypt, data regarding the prevalence of A. marginale in ruminant hosts and of the circulating genotypes is lacking. This study therefore aimed to (i) investigate the presence, epidemiology and genotypes of A. marginale in cattle and buffaloes in Egypt, (ii) to evaluate suitable diagnostic tools and (iii) to identify co-infections of A. marginale with other selected tick-borne pathogens.

METHODS

Blood samples were collected from 394 animals (309 cattle and 85 buffaloes) from three different areas in Egypt. For the detection of A. marginale infection, several tests were compared for their sensitivity and specificity: blood smear analysis, enzyme-linked immunosorbent assay (ELISA), PCR, real-time PCR and reverse line blot (RLB) assay. Co-infections with A. marginale, piroplasms and other Anaplasmataceae were surveyed by RLB while A. marginale genotypes were identified by amplifying and sequencing the partial msp1α gene.

RESULTS

Anaplasma marginale DNA was amplified by qPCR in 68.3% of cattle and 29.4% of buffaloes. RLB showed infection with A. marginale in 50.2% of cattle and 42.5% of buffaloes. Blood smear analysis detected this agent in 16.2% of cattle and 2.4% of buffaloes. ELISA showed specific antibodies against A. marginale in 54.9% of cattle. Anaplasma marginale was associated, in cattle and buffaloes, with several tick-borne pathogens (Theileria annulata, Babesia bovis, Babesia bigemina, Babesia occultans and Anaplasma platys). A significant difference of A. marginale infection level was noticed in cattle, where animals between 3-5-years-old had a higher prevalence (79.2%) compared to those older than 5 years (36.4%) and younger than 3 years (59.7%) and one year (64.5%), respectively (P = 0.002281). Microsatellite analysis identified 15 different genotypes.

CONCLUSIONS

The epidemiological findings revealed high prevalence of A. marginale in cattle and buffaloes in all the investigated areas. The circulation of diverse genotypes was observed, most of these A. marginale genotypes being specific for Egypt. The qPCR assay was confirmed to be the most sensitive tool for detection of A. marginale in cattle and buffaloes even in the carrier state, highlighting the importance of using suitable diagnostic tests.

Productivity and health effects of anaplasmosis and babesiosis on Bos indicus cattle and their crosses, and the effects of differing intensity of tick control in Australia

Tick fever is an important disease of cattle where Rhipicephalus (Boophilus) microplus acts as a vector for the three causal organisms Babesia bovis, Babesia bigemina and Anaplasma marginale. Bos indicus cattle and their crosses are more resistant to the clinical effects of infection with B. bovis and B. bigemina than are Bos taurus cattle. Resistance is not complete, however, and herds of B. indicus-cross cattle are still at risk of babesiosis in environments where exposure to B. bovis is light in most years but occasionally high. The susceptibility of B. indicus cattle and their crosses to infection with A. marginale is similar to that of B. taurus cattle. In herds of B. indicus cattle and their crosses the infection rate of Babesia spp. and A. marginale is lowered because fewer ticks are likely to attach per day due to reduced numbers of ticks in the field (long-term effect on population, arising from high host resistance) and because a smaller proportion of ticks that do develop to feed on infected cattle will in turn be infected (due to lower parasitaemia). As a consequence, herds of B. indicus cattle are less likely than herds of B. taurus cattle to have high levels of population immunity to babesiosis or anaplasmosis. The effects of acaricide application on the probability of clinical disease due to anaplasmosis and babesiosis are unpredictable and dependent on the prevalence of infection in ticks and in cattle at the time of application. Attempting to manipulate population immunity through the toleration of specific threshold numbers of ticks with the aim of controlling tick fever is not reliable and the justification for acaricide application should be for the control of ticks rather than for tick fever. Vaccination of B. indicus cattle and their crosses is advisable in all areas where ticks exist, although vaccination against B. bigemina is probably not essential in pure B. indicus animals.

Natural infection of calves by Anaplasma marginale in dairy herds of the Metalúrgica Region, Minas Gerais

The dynamic of natural infections by Anaplasma marginale in calves was evaluated during a period of one year on two farms located in the Metalúrgica Region, State of Minas Gerais, Brazil. Blood samples were collected weekly for rickettsemia and packed cell volume (PCV) determination. The animals born from March to July suffered the infection in October and November, independently of their age, whilst calves born from September to December acquired the infection during the first days of life. These animals presented patent rickettsemia from 30 days of life. During the patent period PCV decreased after one week of infection, ranging from 20 to 23%. It was concluded, that in the region studied, the transmission of A. marginale is influenced by climatic conditions, and that calves born during the dry season are more likely to acquire the infection when they are exposed to high transmission levels during the subsequent raining season.

Soroprevalência de Anaplasma marginale em bovinos na mesorregião Norte Fluminense

Avaliou-se a soroprevalência de Anaplasma marginale em bovinos de nove municípios na mesorregião Norte Fluminense do estado do Rio de Janeiro através do ensaio de imunoadsorção enzimática (ELISA) indireto. 532 amostras de soro de bovinos foram analisadas; dos quais, 497 eram fêmeas e 35 eram machos; e destes, 444 animais com aptidão zootécnica para corte e 88 com aptidão para leite. A avaliação sorológica revelou que 485 (91,16%) foram positivas, dos quais: 55,45% com título de 1:500, 22,18% com título de 1:1000, 6,77% com título de 1:2000, 3,01% com título de 1:4000, 1,50% com título de 1:8000, 0,94% com título de 1:16000, 0,75% com título de 1:32000, 0,56% com título de 1:64000 e 8,84% foram negativos. A análise da prevalência segundo a faixa etária foi realizada dividindo-se em três grupos etários: 1 a 3 anos (n= 110), 3 a 6 anos (n= 241) e > 6 anos (n= 181), onde 91,82%, 92,95% e 88,95% dos animais foram positivos, respectivamente. Segundo a aptidão zootécnica, 91,22% dos bovinos com aptidão para corte e 90,91% dos bovinos com aptidão para leite foram positivos. Em relação ao sexo, 91,35% das fêmeas e 88,57% dos machos foram positivos. Não houve diferença significativa (P>0,05) entre os grupos etários, entre os sexos e entre as aptidões zootécnicas. A prevalência entre os municípios não diferiu significativamente (P>0,000), demonstrando que a infecção por A. marginale em bovinos é alta e homogênea entre os municípios. A mesorregião estudada foi caracterizada como uma área de estabilidade enzoótica.

Seroprevalence survey for Anaplasma marginale-infection of Austrian cattle

A serologic survey study of 5,076 Austrian cattle farming herds was carried out in the period of December 1988 till March 1990. One animal was randomly selected from each herd and the antibody titer against Anaplasma marginale in blood serum samples was evaluated by means of the complement fixation test. The number of these tested blood samples was 3.6% of 140,081 cattle herd farms of Austria. 109 (2.1%) of the tested animals showed positive titers (1:10) against Anaplasma marginale, in relation to the 140,081 cattle herds 0.08%, 4,786 (94.3%) blood serum samples were sero-negative, 188 (3.8%) reacted anticomplementary. The highest number of antibody-positive animals of 8 tested Austrian districts could be found in Carinthia (46 = 5.7%). In Burgenland all tested sera turned out to be negative. Concerning the distribution of sero-positive animals in Austria it can be stated that a decrease of positive reactors from southern to northern region is evident. A connection between the occurrence of anaplasmosis in Italy, Yugoslavia, Switzerland and Hungary, is postulated as a result of the different systems of keeping cattle in the provinces and the regional increase of tick invasion. Possibly an intensive animal transportation is of importance due to the introduction of the disease mentioned before. The results obtained show that anaplasmosis does occur in different areas of Austria. For control of this disease in Austria it is proposed that all imported cattle should be tested serologically for antibodies against Anaplasma marginale. Other diseases in connection with anemia should be excluded by clinical, serological, blood-, as well as pathological examinations.

A sensitive ELISA technique for the diagnosis of Anaplasma marginale infections

A sensitive enzyme-linked immunosorbent assay (ELISA) technique using a horse radish peroxidase conjugate is described for measuring Anaplasma marginale antibodies in bovine serum. This technique utilizes two antigen preparations, a 'negative' antigen derived from an animal prior to infection and a 'positive' antigen derived from A. marginale-infected red cells from the same animal following infection. This markedly reduces cross-reactions which are a result of isoantigens. Absorbance values obtained using the 'negative' antigen are subtracted from those obtained using the 'positive' antigen to give a net figure. Of 100 A. marginale-positive sera tested no false negative results were obtained. All 11 animals maintained tick-free after initial diagnosis of naturally transmitted anaplasmosis were positive 3 years later, 15 A. marginale-infected animals maintained with ticks were positive 27 months after initial infection and a further 26 animals infected with A. marginale by blood inoculation were positive 3 months later. Three per cent of negative sera, 2% of B. bovis and 4% of B. bigemina-positive sera gave positive reactions.

Susceptibility of Bos indicus and Bos taurus to Anaplasma marginale and Babesia bigemina infections

The reaction of Bos taurus and pure-bred Bos indicus heifers to infection with the intraerythrocytic parasites Anaplasma marginale and Babesia bigemina was studied. B. bigemina infection at 18 months and A. marginale infection at 13 or 24 months resulted in slightly less severe reactions in pure-bred Bos indicus cattle than in Bos taurus. In both breeds, the reaction to A. marginale infection was more severe in older cattle. The severity of B. bigemina infection was not affected by a previous infection with A. marginale.

Observations on anaplasmosis following field exposure to heavy and light infestations with Boophilus microplus

Two groups of Normandy calves were exposed to heavy (mean half body count = greater than 300) or light (mean half body count = 9) natural infestations with Boophilus microplus. All of the calves became infected with Anaplasma marginale. Despite the difference in tick challenge level, there was no significant difference in the incubation period, increase in body temperature, level or duration of Anaplasma parasitemia, decrease in packed cell volume, or complement-fixing antibody response, between the heavily and lightly infected calves. Neither the incubation period nor the clinical severity of anaplasmosis was significantly influenced by the number of infested tick vectors.

A comparative study of experimental anaplasmosis in Bos indicus and Bos taurus cattle

Comparative studies were carried out on the susceptibility of 8 Bos taurus and 10 predominantly Bos indicus cross cows aged 48 months to Anaplasma marginale infection. Measurements were carried out on bodyweight, parasitaemia, haematological factors, humoral antibody response and serum transaminase levels. Except for minor differences in reaction Bos indicus and Bos taurus animals were equally susceptible to infecton with the strain of A. marginale employed. Such differences observed were not significant.

Susceptibility of Bos indicus crossbred and Bos taurus cattle to Anaplasma marginale infection

The effects of infection with Anaplasma marginale in groups of Bos indicus-Brahman crossbred and Bos taurus cattle aged 27 and 48 months were studied using the parameters of body weight change, packed cell volume, parasitaemia and humoral antibody. Twenty-six animals (8 Bos taurus and 18 Bos indicus crosses) of each age group were infected. No significant differences between any of the groups were observed.