Naegleriasis is an acute infectious disease caused by a free–living pathogenic amoeba, nongleria. It is a very rare fatal pathology. It is characterized by the presence of a general intoxication syndrome, symptoms of damage to the nervous system with the development of primary amoebic meningoencephalitis. Diagnostic measures provide for the detection of the parasite in the cerebrospinal fluid and biopsy material, serological methods, culture method and PCR are also used. Specific treatment has not been developed, amphotericin B is prescribed in combination with symptomatic agents.
For the first time this disease was registered in 1962 in Australia. The causative agent of Naegleria fowleri infection is named after the Australian scientist Malcolm Fowler, who presented a report on a previously unknown pathology. The infection is widespread everywhere, but it is more common in countries with tropical and subtropical climates, which is associated with the peculiarities of the development of pathogenic amoebas. During the period from 1962 to 2017, 143 cases of non-gleriosis were registered in the USA, of which only 4 ended in recovery, in other cases there was a fatal outcome. Seasonality is characteristic. The incidence rates increase from July to September, which is explained by the temperature regime of the existence of non-colonies. Young people and children who actively swim in lakes and pools are more often affected. Scientists cannot yet explain why only up to 8 people out of millions of bathers get sick a year.
The causative agent of the disease is a free–living pathogenic amoeba Naegleria fowleri. In the life cycle it has three stages: cyst, trophozoite, vegetative form. The pathogen can affect humans and animals only in the trophozoite stage. This stage is characterized by the presence of a contractile vacuole, the separation of the cytoplasm into ecto- and endoplasm, pseudopodia. With sharp fluctuations in temperature, trophozoites turn into vegetative forms, while acquiring two flagella and actively moving around the reservoir. A special feature is the ability to return to the trophozoite stage again. In the form of cysts, the pathogen tolerates unfavorable environmental conditions well.
Nongleria are thermophilic parasites. The most favorable temperature is considered to be 36-46 ° C, in such conditions, amoebas begin to multiply actively. An increase in temperature to 50-65 ° C kills microorganisms within a few hours. Pathogens and their cysts are sensitive to freezing. Of the chemical types of disinfection, chlorination is the most effective. The habitat consists of sources with warm fresh water, such as lakes, rivers, hot springs, water from industrial facilities, pools with poor maintenance and disinfection, soil. Microorganisms can live in humidifiers of air conditioners. Nongleria are not found in salt water. Infection occurs when diving, diving in polluted reservoirs, using contaminated liquid to flush the nose when water enters the nasopharynx. If swallowed, there is no infection, the disease does not spread between people.
Getting into the nasopharynx with infected water, amoebas penetrate through the mucous membrane, then through the olfactory nerve through the lattice plastic they enter the subarachnoid space, and from it into all parts of the central nervous system. In the brain, parasites are located around blood vessels, provoking the occurrence of hemorrhages and necrosis zones in gray and white matter. Meningoencephalitis develops. A pathoanatomic autopsy reveals swelling of the brain and its membranes, focal hemorrhages, melting of brain matter, fibrinous-purulent exudate on its surface. Multiple foci of demyelination are revealed. Trophozoites are detected in large quantities in biopsies and cerebrospinal fluid.
The incubation period is 2-3 days, less often up to two weeks. The disease belongs to the category of rapidly progressive, a detailed clinical picture is formed within about 5 days, patients usually die on 1-18 days. The initial symptoms are not strictly specific. The appearance of signs of general intoxication is characteristic: weakness, lethargy, drowsiness, headaches. There is a pronounced feverish reaction. Dyspeptic symptoms develop (nausea, vomiting).
During the peak period, there is an increase in manifestations indicating the involvement of the central nervous system in the pathological process. There is rigidity of the occipital muscles, general meningeal symptoms, signs of damage to the cranial nerves, especially olfactory (decreased or loss of sense of smell), hallucinations, convulsions. Neurological deficit increases up to coma. There are no data on the development of the immune response and the preservation of the immune status relative to naegleriasis.
Naegleriasis is a fatal disease, the diagnosis is most often made posthumously after examining the biopsy material. Patients die from edema of the brain and dislocation of its trunk, multiple hemorrhages with destruction of the brain substance. In addition, the cause of death may be the formation of pulmonary edema and the development of acute respiratory failure. During autopsy, signs of myocarditis and pneumonia are often detected, but there are no lifetime symptoms of these pathologies, and microscopy does not detect parasites in the lungs and heart. It is believed that in people with immunodeficiency, generalization of the process with the appearance of multiple organ lesions of a specific etiology is possible.
The diagnosis of naegleriasis is associated with significant difficulties due to the nonspecific nature of symptoms, the speed of development and the rarity of the disease. The examination is carried out by an infectious disease doctor. Upon examination, positive meningeal signs, signs of cranial nerve damage are determined. With the development of meningoencephalitis, focal neurological symptoms are revealed. Differential diagnosis is carried out with meningitis and meningoencephalitis of bacterial and viral etiology. The following clinical and laboratory methods are used in the diagnostic process:
- Detection of the pathogen. Many trophozoites are visualized in cerebrospinal fluid or brain biopsies under microscopy. Neutrophilic leukocytosis in the cerebrospinal fluid is characteristic. It is possible to use the cultural method by sowing the substrate on a nutrient medium, however, due to the considerable duration of the study, its practical significance is low.
- Identification of infectious markers. Currently, in the process of diagnostic search, serological methods are actively used to identify specific antigens using immunofluorescence reactions. A PCR technique has been developed to detect characteristic DNA sites.
Treatment of naegleriasis is carried out in a hospital in the intensive care unit. Specific drugs have not been developed. Positive results are noted when using amphotericin B, which is administered intravenously, subarachnoid or into the ventricles of the brain. In experiments, a positive effect was observed from the combined use of amphotericin B and azithromycin. A scheme of fluconazole + amphotericin B + rifampicin is being developed. In parallel, symptomatic treatment is prescribed: according to indications, detoxification, dehydration therapy is carried out, means for relieving seizures, antipyretic analgesics, glucocorticosteroids are used, artificial ventilation of the lungs is carried out.
Prognosis and prevention
The prognosis of naegleriasis is doubtful, the mortality rates reach 97%, but the improvement of diagnostic methods and the development of new treatment regimens increase the likelihood of a successful outcome. There is no specific prevention. Non–specific preventive measures include compliance with the rules of personal hygiene, prohibition of bathing in infected reservoirs (especially in hot weather), refusal to use questionable liquids for rinsing the nasal cavity. It is necessary to carry out sanitary control of water quality, carry out work on its purification and prevention of infection, observe the temperature and hygienic regime in swimming pools.