HUMAN BABESIOSIS: A THREAT TO PUBLIC HEALTH

Human Babesiosis is a parasitic, vector-borne disease that is becoming more and more significant for public health.

By Nida Naazir, Muhammad Kasib Khan, Muhammad Adnan Sabir Mughal, Zaheer Abbas

BABESIOSIS:

Babesia, an intraerythrocytic protozoan, causes the tick-borne, malaria-like disease known as Babesiosis which is an obligate intracellular apicomplexan protozoan and largely by members of the Genus Ixodes of Ticks. Anemia is brought on by Babesia’s invasion of mammalian red blood cells. Babesiosis mostly affects animals but can occasionally infect people.

ZOONOTIC IMPORTANCE OF BABESIOSIS:

BOVINE BABESIOSIS:

Numerous domestic and wild animals, as well as humans occasionally are afflicted Babesiosis. Babesiosis infections in other domestic animals such as horses, sheep, goats and dogs assume varied degrees of importance around the world while having a substantial economic impact on the cattle business due to the loss of meat and beef output of affected animals and death. In tropical and subtropical areas the two main species in cattle B. bigemina and B. bovis are prevalent.

HUMAN BABESIOSIS:

Zoonotic species have been observed on almost every continent since the first case was reported in human in 1957 in a farmer who had his spleen removed in Croatia. The genus Ixodes of the ticks transmits zoonotic Babesia species. Babesia infections in humans can be contracted through tick bites, contaminated blood from infected transfusion donors or placental transmission from an infected mother to foetus. In healthy people, infections are typically asymptomatic and self-limiting. Babesia species differ in terms of their contagiosity to infect humans, virulence and pathogenicity. Various factors (e.g. increased immunosuppression, altered landscapes and climatic conditions as well as changes in the quantity and community structures of host and vector species have all contributed to an increase in tick-borne diseases in humans including Babesiosis. The four Babesia species that have been recognized as infecting humans are B. microti, B. divergens, B. duncani and B. venatorum. It has been proven beyond a doubt that these species infect the human beings.

 

 

DISEASE TRANSMISSION:

Babesiosis is a disorder in which tiny parasites infect the red blood cells of vertebrates. To complete their life cycle, the parasites need both a vertebrate and a non-vertebrate host. Ixodid ticks in the nymphal stage are responsible for transmitting them to vertebrate hosts. Ticks that are adults may take part in this transmission as well. These ticks are typically present in grassy regions, pastures and woodland areas throughout the warm spring and summer months. Babesia microti is spread to human hosts in North America by deer ticks, Ixodes scapularis.  Ixodes persulcatus is the vector for the spread of Babesia venatorum in China. The Babesial parasites are spread throughout Europe by Ixodes ricinus ticks.

LIFE CYCLE:

Two hosts, including a rodent, primarily the white-footed mouse, Peromyscus leucopus, are necessary for the Babesia microti life cycle. A tick carrying Babesia transmits sporozoites into the mouse host during a blood meal. Sporozoites migrate inside erythrocytes and reproduce asexually (budding). Some parasites in the blood can separated into male and female gametes, albeit they cannot be seen under a light microscope. The definitive host is a tick, in this case the deer tick, Ixodes dammini (I. scapularis). Gametes combine after being consumed by the proper tick, go through a sporogonic cycle, and produce sporozoites. Transovarial transmission has been documented for “big” Babesia spp. but not for the “small” Babesiae, such as B. microti. When infected ticks bitten it and the humans become part of the cycle. A Babesia-infected tick transfers sporozoites into the human host during a blood meal. Upon entering erythrocytes, sporozoites engage in asexual reproduction (budding). The clinical symptoms of the illness are caused by the blood stage parasites multiplying. For all intents and purposes, humans are considered to be dead-end hosts, and ticks feeding on infected people are most likely to cause very little, if any, additional transmission. Blood transfusions are known to be a common method of human-to-human transfer.

Figure 1: Life cycle of Human Babesiosis.

SIGNS AND SYMPTOMS:

Patients may experience different disease severity and have three distinct syndromes are:

 (1). Mild to moderate viral-like Illness. 

  • . Severe disease with a fulminant course resulting in death / persistent relapsing course.
  • . Asymptomatic infection.

MILD TO MODERATE VIRAL-LIKE ILLNESS:

It is distinguished by the slow onset of fatigue and malaise, which is followed by sporadic fever and one or more of the following symptoms: chills, sweats, headache, anorexia and myalgia. Rarely, mild hepatomegaly or splenomegaly is also reported. For several weeks to months, the sickness persists.

SEVERE DISEASE WITH A FULMINANT COURSE:

It happens in persons who have immunosuppressive illnesses like HIV that are also coinfected, cancer malignancy and splenectomy. These immunosuppressive illnesses experience a prolonged or recurrent course of illness. Babesiosis complications, such as acute respiratory failure, congestive heart failure and splenic infarction are frequently linked to severe disease.

ASYMPTOMATIC INFECTION:

After being bitten by an infected tick, patients who go on to develop symptoms of Babesiosis initially have a subclinical infection. Asymptomatic parasitemia may last for months or years after symptoms have subsided. Asymptomatic infection that lasts for a long time in natural hosts increases the likelihood that the virus will spread to arthropod vectors and new hosts, ensuring its pathogen survival.

DIAGNOSIS:

On a physical examination, there are no pathognomonic symptoms. When people have viral-like symptoms and have recently been outside in a region where Babesiosis is endemic in the summer or early fall, they should be tested for Babesiosis. Babesiosis non-specific laboratory results show erythrocyte lysis. Thrombocytopenia, a normocytic hemolytic anaemia, and an increased reticulocyte count are frequently seen. Babesia infection is typically definitively diagnosed by microscopic examination of the organism on thick and thin blood smears stained with Giemsa or Wright. Round, oval, or pear-shaped forms with red chromatin and blue cytoplasm are possible for several Babesia species.

Babesial DNA can be amplified from blood samples by using the Polymerase Chain Reaction (PCR). For detecting Babesial DNA in blood, PCR provides a highly sensitive and specific, albeit expensive test is used. To prevent false-positive PCR results, certain safety measures must be taken. Serology is also helpful in verifying the diagnosis of Babesiosis. By using an indirect immunofluorescence assay (IFA), anti-Babesial IgM and IgG antibodies can be found.

TREATMENT:

Babesiosis typically recovers on its own and has little to no symptoms in the majority of healthy persons but people with weakened immune systems may need to be treated with highly efficient antibacterial medication combinations: the mixtures of atovaquone and azithromycin as well as the combination of clindamycin and quinine. Blood transfusions may be used to treat people with severe cases of Babesiosis who have their spleens removed.

CONTROL MEASURES:

Utilizing many methods of illness prevention, such as preventive measures that are personal, residential or community approaches. Avoiding areas where ticks, mice, and deer are known to thrive is one personal protection approach, especially from May through October. Avoiding brushy regions where ticks may be abundant is especially important for those who are at heightened risk, such as asplenic or other immunocompromised people who reside or travel in endemic areas. Such steps should include wearing long-sleeved shirts, long pants, and hats; wearing light-colored clothing to make ticks more visible and clothing should be sprayed or impregnated with permethrin and using appropriate Tick repellents. DEET-containing products should be applied to the skin in the event that the legs remain exposed. Attached ticks should be removed as soon as possible by use of tweezers.

Residential land should be sprayed with acarcidial drugs. The danger of infection can be significantly reduced by community initiatives to minimize the local deer population. Currently the Red Cross and other blood donation agencies prohibit people with a history of Babesiosis from donating blood in order to prevent transfusion-related cases.