Rickettsiosis: a neglected one health threat
Among the vector-borne diseases, the 2nd most important vector after mosquitoes in transmitting the diseases in animals is tick. Ticks transmit a number a diseases in animals through biting and blood feeding e.g. babesiosis, theileriosis, anaplasmosis, rickettsiosis, CCHF etc. Last year, tick borne CCHF was epidemic in some districts of Punjab, Pakistan.
Pakistan is the 4th largest milk producing country of the world. Total annual milk production of Pakistan is 34 million tons. A big portion (58%) of this production is obtained from buffaloes. So, the livestock is considered as an asset for the people of Pakistan. Healthy livestock means more production, prosperous farmers and ultimately progressing Pakistan.
Livestock animals are threatened by a number of diseases of varying origin; bacterial, viral and protozoal. Many of these diseases directly affect the production performance of the animals like decrease in milk and beef production. These diseases may be transmitted to the animals either by direct contact or through vectors. Arthropod diseases which are transmitted by any vector are called vector-borne diseases.
Among livestock, there is a wide variety of vectors which transmit diseases in them e.g. flies, ticks, fleas, mosquitoes etc. Among the vector-borne diseases, the 2nd most important vector after mosquitoes in transmitting the diseases in animals is tick.
Ticks are basically hematophagous ectoparasites which belong to phylum arthropoda and class arachnida. Tick infestation is a very alarming issue of the dairy industry. Economic losses due to tick infestation per buffalo and cow are estimated as 3763 and 4538 rupees/year respectively.
Ticks also transmit a number a diseases in animals through biting and blood feeding e.g. babesiosis, theileriosis, anaplasmosis, rickettsiosis, CCHF etc. Last year, tick borne CCHF was epidemic in some districts of Punjab, Pakistan.
Rickettsiosis is a bacterial disease, caused by R.rickettsii which is a gram negative, intracellular bacteria. The disease is transmitted by ticks to the animals. Various species of ticks are responsible for the causation of rickettsiosis e.g. Hyalomma spp, dermacentor spp, Rhiphicephalus spp, heamaphysalius spp etc.
It also has public health significance and in humans is known as Rocky Mountain Spotted Fever (RMSF). This disease is most common in African countries and in people of those areas who are fond of travelling.
This bacteria was first identified in ticks in 1991 in China. Later, it was diagnosed in Central Africa in 1994. There are some reports about the presence of rickettsiosis in Pakistan too, but very little data is available.
However, it is prescribed that diversified fauna of ticks in Pakistan increases chances of this disease in animals and humans. Hence, screening the vector population may help in identifying the risk.
Ticks become infected when they bite any infected animal during taking blood meal to complete their life cycle. Bacteria along with the blood get entry into the tick. Inside the tick, pathogens move towards hemocoel and then to salivary glands where they multiply.
When this infected tick bites another healthy animal, bacteria also enter into the healthy host animal. In the blood of infected animal it proliferates and show clinical signs of the disease.
Both trans-stadial and trans-ovarian transmissions are possible in case of rickettsiosis. In transovarial transmission, the eggs of the infected tick are also infected during all of its development stages. While in transstadial transmission, pathogen is transmitted from one developmental stage to the successive stage.
Tick bites are usually painless and are mostly on those areas which are not easy to observe like inguinal region, axilla etc.
After entry into the host, the pathogen multiplies inside the lymph nodes and causes septicemia showing clinical signs of the disease as pyrexia, anorexia, vomiting, abdominal spasm, decreased blood pressure, splenomegaly, hepatomegaly and nervous incoordination.
It also lead into the formation of rashes on the body at later stage of the disease which change into the petechial hemorrhages. The incubation period of the pathogen is between 2-14 days.
The diagnosis of rickettsiosis is done by using conventional staining of blood smear to see the bacteria inside blood cells under the microscope and by using molecular tools e.g. PCR. Clinical signs of disease may also help in tentative diagnosis but disease is confirmed by molecular detection of pathogen.
Antibiotics are recommended for the treatment of rickettsiosis. Teteracycline and chloramphenicol shows better efficacy against this pathogen. Specific antibiotic used for the disease is Tetracycline. Because it can kill the bacteria intracellularly.
Prevention and control
For the prevention and control of ticks and tick-borne diseases animals should be examined after regular interval for the presence of ticks, if ticks are present on animals then promptly contact with a registered veterinarian for effective treatment, as a prophylactic measure anti-tick spray can be used for small animals, the environment of the animals should be kept clean to avoid the growth of ticks and all the crevices in the farm or around the surroundings of animals should be filled as these are the hiding place for ticks.
Purpose of this article is awareness to the community about tick-borne rickettsiosis so that they can protect the animals from the adverse effects of this disease and can promptly contact a veterinarian upon the presence of similar clinical signs in their animals for proper diagnosis.
Currently the experts of the Department of Parasitology, Faculty of Veterinary Science, University of Agriculture Faisalabad are conducting research on this disease in order to control this pathogen and to cut-off its life cycle.
Recently, a project has been initiated through financial support of the Higher Education Commission, Islamabad to screen the host and vector population of some selected districts of Punjab, Pakistan for molecular identification of rickettsial pathogen for risk assessment.
This article is jointly written by Adil Ejaz1, Dr. Muhammad Sohail Sajid1,2, Prof. Dr. Zafar Iqbal1. The authors are associated with Molecular Parasitology Lab, Department of Parasitology, UAF. 1Department of Parasitology, 2One Health Laboratory, US-Pakistan Center for Advanced Studies in Agriculture and Food Security (USPCAS-AFS), University of Agriculture, Faisalabad, Pakistan.
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