Babesiois is a tick-borne disease caused by a parasite, Babesia, which is similar to malaria in presentation and is often a common co-infection with Lyme disease.
There is a long history of infection with a form of Babesia or Bovine Tick Fever in cattle throughout Australia. As early as 1897, cattle were vaccinated for Babesia. (1,2)
Currently it is believed that Bovine Babesiosis is caused by two organisms in Australia: Babesia bovis and Babesia bigemina. Of the two species, B bovis is by far the most important, causing about 80% of outbreaks and an even higher percentage of deaths. Both Babesia species are single cell organisms that develop in the red blood cells of cattle and are transmitted in Australia by the cattle tick Boophilus microplus. So far there is evidence showing different forms of Babesia can be transmitted by different kinds of ticks to other mammals in Australia such as dogs and horses.
While more than 100 species of Babesia have been reported worldwide, so far only a few have been identified as causing human infections. Babesia microti and Babesia divergens have been identified in most human cases, but other variants (considered different species) have been recently identified, such as Babesia duncani (also known as WA-1, originally found on the west coast of the United States) and MO-1 (found in Missouri, USA). There is some speculation that Babesia rodhaini (found in rodents in Asia and Australia) may be capable of infecting human red blood cells. (3)
More research is needed to determine if some form of Babesia is present in ticks in Australia which bite and infect human hosts. Up to present only research into canine and bovine babesia has been conducted in Australia – the Lyme Disease Association of Australia is keen for research into human babesia infections to begin as soon as possible.
In absence of that research, it is important to be mindful of the symptoms of Babesiosis if you are bitten by a tick in Australia or abroad in order to help seek out early diagnosis.
Babesia infection often is asymptomatic and can be associated with mild, nonspecific symptoms. The infection also can be severe and life threatening, particularly in people who are asplenic, immunocompromised, or elderly.
In general, babesiosis, like malaria, in its acute stage is characterized by:
- Fever, typically 40-41 C
- Hemolytic anaemia
Infected people may instead have a gradual onset of the following symptoms:
- Anorexia (loss of appetite or depressed appetite can be present)
- Fever and other influenza-like symptoms:
- Myalgia (muscle aches)
- Arthralgia (joint aches)
Some patients have reported chest pressure and shortness of breath or a sensation of the inability to take in full, deep breaths. Less common findings include hyperesthesia, sore throat, abdominal pain, conjunctival injection, photophobia, weight loss, and non-productive cough.
Clinical signs generally are minimal, often consisting only of fever and tachycardia (rapid heartbeat), although mild hepatosplenomegaly (enlargement of liver and spleen) may be noted. Thrombocytopenia and a normal or low white blood cell count are common.
If untreated, illness can last for several weeks or months; even asymptomatic people can have persistent low-level parasitemia, sometimes for longer than 1 year.
Infections caused by B. divergens tend to be more severe (frequently fatal if not appropriately treated) than those due to B. microti, where clinical recovery is possible with correct timely treatment.
In general, if a more severe flu-like illness accompanies a tick bite, research has indicated that it is more likely both Lyme Borreliosis (Lyme disease or Borrelia infection of another kind) and a co-infection such as Babesia is present.
The diagnosis of a Babesia infection is primarily a clinical diagnosis – blood tests are used to support diagnosis (false negative results are common). Current testing in Australia is unreliable, and blood will need to be sent overseas (ie to IgeneX in the USA) in order to get a more accurate result. The result of blood testing will depend on the immune response of the patient to the Babesia infection, and so more severely affected patients have commonly tested less positive than those whose immune system has more effectively fought the parasite, and therefor have less severe symptoms. Blood smears may be examined under a microscope to try to identify the parasite inside red blood cells, however this method is most reliable within the first two weeks of the infection. Commercial tests currently work for only three species of Babesia, and there are likely many species yet to be discovered. PCR polymerase chain reaction) test can detect Babesia DNA in blood. A FISH (Fluorescent In-Situ Hybridization) assay can detect the ribosomal RNA of Babesia in thin blood smears. Also, a patient’s blood can also be tested for antibodies to Babesia. It may be necessary to run several different tests and negative results should not be used to rule out treatment. The rationale for this is that it can take weeks to months for Babesia to incubate and show a positive test result.
Babesiosis is most often treated with a combination of two types of anti-parasite drugs, atovaquone (Mepron/Wellvone & Malarone) plus an erythromycin-type drug (azithromycin, clarithromycin, or telithromycin). A combination of Clindamycin and quinine have been used to treat Babesiosis in the past -- but also if the patient cannot tolerate or is allergic to atovaquone and/or an erythromycin-type drug. Currently atovaquone & azithromycin are not on the PBS list for Babesiosis, and are therefor only available on a private prescription, which may make them prohibitively expensive for some people.
The anti-parasite drugs used to treat Babesiosis are the same as those used to treat Malaria -- if one has had to take anti-malarials for an overseas trip, then you may have had one of these medications already. Long-standing infections may need to be treated for several years, and relapses sometimes occur and must be retreated.
Since Bovine Babesiois can lead to serious fatality in cattle, studies continue in Australia to determine how best to diagnose and treat this condition. (4)
The haemoprotozoan Babesia canis has been recognized in Australia for many years, and a second, smaller species has recently been discovered. Genetic studies of samples collected in southeastern Australia were genetically identical to Babesia gibsoni, a species not previously known in Australia. (5,6) Horses in Australia have been known to be infected with Babesia equi, and in neighbouring New Zealand, a new form of Babesia, Babesia kiwiensis, has been found in kiwis on the North Island. (7)
- Encyclopedic Reference of Parasitology: Diseases, treatment, therapy (2001) By Heinz Mehlhorn, Philip M. Armstrong.
- Encyclopedia of Parasitology, Volume 1 (2008) edited by Heinz Mehlhorn.
- J Vet Med Sci. 2005 Sep;67(9):901-7. Isolation of a human erythrocyte-adapted substrain of Babesia rodhaini and analysis of the merozoite surface protein gene sequences. Kawabuchi T, Tsuji M, Kuwahara S, Nishida A, Shimofurutachi T, Oka H, Ishihara C. School of Veterinary Medicine, Rakuno-Gakuen University,Ebetsu, Japan.
- Trends Parasitol. (2010) Dec;26(12):591-9. Epub 2010 Jul 2. Recent insights into alteration of red blood cells by Babesia bovis: moovin' forward. Gohil S, Kats LM, Sturm A, Cooke BM. Department of Microbiology, Monash University, Victoria, Australia.
- J Parasitol. 2003 Apr;89(2):409-12. Two species of canine Babesia in Australia: detection and characterization by PCR. By Jefferies R, Ryan UM, Muhlnickel CJ, Irwin PJ.
- Vet Clin North Am Small Anim Pract. (2010) Nov;40(6):1141-56. Canine babesiosis. By Irwin PJ.
- J Parasitol. (2008) Apr;94(2):557-60. Molecular characterization of Babesia kiwiensis from the brown kiwi (Apteryx mantelli). Jefferies R, Down J, McInnes L, Ryan U, Robertson H, Jakob-Hoff R, Irwin P. School of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, 6150 Western Australia, Australia.