“Bovine Sadness Complex” (piroplasmosis), a great problem for tropical and subtropical regions

In recent years, the farm-cattle production of Argentine field has gone through a process of geographical changes. Considering the competitiveness of growing soybean, traditional livestock was moved to deprived areas for agriculture such as the northeastern region of Argentina (NEA in Spanish), which includes Chaco, Corrientes and Formosa provinces. As a result, that area ranks second in terms of livestock production in the country.

Climate condition of NEA, such as humidity levels, rainfalls, and high temperatures facilitate the presence of ticks. One of these is the most common tick in bovines (Rhipicephalus (Boophilus) microplus), which transmits babesiosis –caused by protozoan Babesia bovis and Babesia bigemina- and anaplasmosis –caused by Anaplasma marginale-. These diseases cause “Bovine Sadness Complex” (piroplasmosis) (CTB in Spanish).

“This complex is known as “bovine sadness” due to of the weak state of the animals caused by anaemia and also because one of the Babesias stations in of the brain capillaries and leads to depression. The three diseases generally appear together, they are different pathogens but they all reproduce themselves in red blood cells. The main objective of the team is to develop diagnostic devices and vaccines to control these diseases transmitted by Rhipicephalus (Boophilus) microplus, which is endemic in the South America. In turn, this ectoparasite – a parasite outside the animal – also affects production because the cow losses weight, provides less milk, and causes discomfort in the animals”, Marisa Farber, CONICET independent at the “Veterinary and Agricultural Sciences Research Centre” (CICVYA) of INTA.

Veterinary and Agricultural Sciences Research Centre (CICVYA) of INTA
En este sentido Silvina Wilkowsky, investigadora independiente del CONICET en el mismo Instituto, explica que el CTB no es una enfermedad de denuncia obligatoria de los productores al Servicio Nacional de Sanidad y Calidad Agroalimentaria (SENASA). Sin embargo, este organismo es el que genera las normas para el control sanitario de estas parasitosis a nivel nacional y vigila el cumplimiento las mismas. Asimismo, tiene delimitadas zonas en la Argentina llamadas “de lucha” donde los productores deben controlar de manera obligatoria la garrapata en sus campos.

“In those regions where tick control is mandatory, the producers have to carry out the complete vector control using a tick-killing agent so as to keep low amounts and prevent their resistance to it. The aim of the programme is to stop the development of the ticks towards areas ecologically free of the vector”, Wilkowsky says.

There are different ways to control the disease: one of them is through the vector, that is to say the tick in which the producer has to put the tick-killing agent on his animals during several years and other applications that represent an extra cost and we have to repeat frequently. Another method would be to prevent the infection caused by the parasite through the vaccine against the three tick-borne haemoparasites. Finally, another method to control is to provide a diagnosis: a survey to see whether or not the animals have antibodies and on that basis provide a vaccine.

“The chemical substances that are used in tick-killing agents are very strong and affect the environment. The intensive and sometimes indiscriminate use of these substances make an impact because they are also effective against other arthropods that are not ticks. The best option is to find a vaccine either against the pathogens or the vector. In the countries where a vaccine against ticks is used, it has been proved that baths have to be less frequent, what reduces the possibilities of developing resistance and lessens the environmental impact”, Wilkowsky says.

For this reason, the team led by Farber and Wilkowsky studies the creation of diagnostic techniques and vaccines from the information on parasites, that is to say, the scientist look for the molecules that can contribute to the development of a control platform in the genomes.

“The veterinary diagnosis is different from the one in human health because the is not told whether the animal is ill or not. This kind of disease is assessed in terms of population and with that information experts establish levels of enzootic stability, in which the triad cattle-tick-pathogen is evaluated. Besides, scientists indirectly measure the antibody levels so as to see if these animals were in contact with the pathogens. From a few days before the animals are born till before they are one year old, if it is in contact with the tick and its pathogens, the animal develops natural immunity that lasts all its life, it is becomes immune naturally. For this reason, we can talk about stability in endemic areas”, Farber comments.

Currently, there are many vaccines for each of the three diseases that comprise the CTB. There is one for the Anaplasma marginale bacteria, which is based on another called Anaplasma centrale, which has lower pathogenicity and induces cross-immunity with A. marginale. The vaccines against the diseases caused by Babesia bovis and Babesia bigemina are based on experimentally attenuated strains of these same parasites. Although they are effective, these vaccines, which are called alive, have some drawbacks. As they have to do with living organisms, they are produced in animals or crops. For this reason, the logistics’ field application is difficult because they are more expensive, they have to be transported in cold, and they have short half lives.

One part of the research team is studying the development of vaccines with recombinant DNA technologies using proteins and non-replicating viruses. “The replacement of the attenuated vaccines for the ones called new generation, which are safer and more effective, is a worldwide trend. Some of the vaccines of the new generation are based on viral or attenuated bacterial vectors that do not develop the original disease they caused, and allowed researchers to insert genes that express the protein of interest in their genome. The development of a vaccine takes a long time and this is just the beginning, it is in the pre-clinical phase. For human use, there is only one vaccine and for veterinary use there are several that use these systems and everything seems to indicate that these are promising”, José Jaramillo Ortiz, CONICET postdoctoral fellow at the Biotechnology Institute, comments.

Furthermore, Valeria Montenegro, doctoral fellow at the same Institute, explains that in the same lines of recombinant vaccines development based on viral vectors, her objective is to design a double recombinant vaccine that protects the animals from Babesia bovis and Babesia bigemina.

The female researchers comment that apart from the development of platforms to select and present these antigens and induce one protective immune response, their challenge of this type of development is to choose the best candidates to do it. These type of vaccines are rationally designed, that is to say the scientists have to choose which are the proteins of the parasite first. Then, they need to take the DNA fragment encoding the protein, and after that insert it in one bacteria or virus to immunize the animal and manage to obtain the same protection achieved by the whole parasite.

The team led by Farber and Wilkowsky studies the development of molecular typing schemes that contribute to the epidemiology of the disease and aims to identify the level of variation of genotypes that were circulating in different regions of the country. This aspect is important to control the outbreaks, the living vaccines and design new ones.

Eliana Guillemi, CONICET postdoctoral fellow, comments that theses tools allow scientists to know which is the genotype and find if there is some geographical or distribution connections of those pathogens. This system of molecular typing helps us to study the population dynamics of microorganisms and these tools were used to identify cases of infection in wild animals (deer and anteater) and learn how similar they are to the ones present in cattle. From these very detailed molecular studies, it is possible to determine whether they went from wild animals to pet or if there is risk of infection of wildlife through the contact with livestock.

“We developed tools that somehow constitute a platform where one can then adapt and offer to address other problems. These diseases in particular involve all the variants: the environment, the host and vector. It highlights the concept of ‘One Health’ where animal, human and environmental health are integrated to lead a systemic approach which includes all variables involved, including the classic host-pathogen relationship.