Malaria is a group of human diseases transmitted by mosquitoes of the genus Anopheles (malaria mosquito).
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Malaria mosquito
Adult mosquitoes are dipterous with an elongated body 6-7 mm long, gray, gray-brown color, small head, long thin proboscis. The wings, covered with scales along the veins, at rest are folded horizontally over the abdomen, overlapping one another, the abdomen is narrow. The body is fragile and does not differ in mechanical strength.
The main differences between malaria mosquitoes and “ordinary” ones:
- in the malaria mosquito, the back pair of limbs is long, so the malaria mosquito sits with its butt raised and its head lowered, other mosquitoes sit straight or lower their abdomen slightly,
- This mosquito has a pair of antennae located next to the mouthparts that are the same length as the “sting”; ordinary mosquitoes have short antennae.
There are about 420 species known in the world, and only 40 species are capable of transmitting malaria. Many people are afraid of the common malaria mosquito, the centipede, but it is absolutely safe.
The infection is transmitted by female mosquitoes. They need living blood to develop their offspring. When bitten, they inject their saliva into the wound to prevent the blood from clotting. This saliva may contain various microbes.
Recent studies by European and American scientists have shown that infected mosquitoes are more persistent in their search for live blood and are more aggressive. It has been suggested that it is the malaria virus that influences their behavior in order to continue to exist.
In addition, it has been established that malaria mosquitoes more often attack people indoors and are especially active with even a slight increase in carbon dioxide concentration.
The “long-legged malarial mosquito,” which is not at all dangerous, is often mistaken for malaria.
Malarial plasmodia
They belong to the simplest (single-celled) animals.
There are 4 types of plasmodia:
- causative agent of tertian malaria,
- causative agent of malaria such as tertian malaria or oval malaria,
- causative agent of tropical malaria,
- the causative agent of four-day malaria.
The development of malarial plasmodia occurs sexually in the body of the definitive host, the malaria mosquito (Anopheles), and asexually in the body of the intermediate host, humans.
The causative agents of malaria enter the human body in the form of a sporosite - a spindle-shaped cell with one nucleus. After 15-45 minutes, they enter the liver with the blood and actively penetrate into its cells. The stage of tissue development begins, during which cells rapidly divide.
This period corresponds to the incubation period, is asymptomatic and can last from 7 days to several months and even years.
After the destruction of liver cells, the parasites enter the blood and actively penetrate into erythrocytes (red blood cells), where they grow and reproduce.
After the destruction of the erythrocyte membrane, a new form of the parasite (merozoites) enters the bloodstream. A significant part of them are killed by antibodies produced by the human immune system.
The duration of this period depends on the type of plasmoid:
- for three-day and tropical malaria is 48 hours,
- for four days - 72 hours.
The completion of each parasite development cycle leads to a progressive increase in their number circulating in the blood.
Malaria
This disease has been known since ancient times. Basically, the distribution zone was in tropical countries, but this year many larvae of malaria mosquitoes were also found in water bodies in the middle zone.
In temperate climates, the incidence is clearly seasonal, occurring in the summer and autumn months. In countries with tropical climates, malaria infection occurs all year round.
Immunity to malaria is unstable, short-lived, and specific to each type of malaria. Most types of malaria are benign, but tropical malaria often has complications that can be fatal.
Routes of infection
The main carrier of the disease is mosquitoes. However, there are other ways of transmitting infection.
Sometimes plasmoids are transmitted through blood transfusions if the donor blood contains parasites.
Infection through undisinfected medical instruments is possible. This route of transmission is especially relevant in people who inject drugs.
During pregnancy, intrauterine infection, as a rule, does not occur. This happens in rare cases when the mother is completely immune.
The source of infection is a sick person or a parasite carrier whose blood contains mature sexual forms of plasmoids.
Patients with tropical malaria in the first days of the disease are not a source of infection, since parasites begin to be detected in the peripheral blood only on the 9-10th day of the disease. At 2-3 weeks their number increases significantly.
In areas with high incidence rates, the main source of infection is children from 6 months to 5 years. Their lack of specific immunity contributes to a high level of parasites in the blood and they intensively infect carriers. However, their disease is asymptomatic and therefore diagnosed late.
In areas with temperate climates, the source of infection is often people who have vacationed in tropical countries.
Parasites in the salivary glands of female malaria mosquitoes remain viable for up to a month. Therefore, overwintered females are not infectious.
Symptoms
The incubation period depends on the type of pathogen. With tropical malaria it is 8-16 days, with three-day and oval malaria it can be short (10-20 days) and long (7-14 months or more), with four-day malaria - 3-6 weeks.
Usually the disease begins acutely, but before the attack there may be a period (3-4 days) when malaise, chilling, and dry mouth are observed.
Malaria can be distinguished from other diseases due to its characteristic paroxysmal onset.
A malarial attack can last from 1 hour to 12 hours and develops in three stages with the following symptoms:
- chills last 1-3 hours,
- fever - from 6 to 8 hours,
- sweating from 2 to 5 hours.
With three-day and oval malaria, attacks are repeated every other day, with four-day malaria - after 2 days. Between attacks the patients feel satisfactory.
After 2-4 attacks, the liver and spleen enlarge.
During the acute period of fever, herpetic rashes appear on the lips and wings of the nose.
With tropical malaria, anemia develops after the first attacks; with other types, it develops in the 2-3rd week.
Diagnostics
To make a diagnosis, three conditions must be met:
- regularly alternating typical febrile attacks,
- enlargement of the spleen and liver,
- detection of malarial plasmoids in the blood.
A blood test is recommended for patients with fever for 5 days or more.
If the patient has typical symptoms, and the first test is negative, then it is repeated 2-3 times with an interval of several days.
The results obtained are often assessed on the following scale:
“+” – 1-10 parasites in 100 fields of view (5-50 parasites in 1 µl of blood),
“++” – 10-100 parasites in 100 fields of view (50-500 parasites in 1 µl of blood),
“+++” – 1-10 parasites in each field of view (500-5000 parasites in 1 µl of blood),
“++++” – more than 10 parasites in each field of view (more than 5000 parasites in 1 µl of blood).
There are rapid diagnostic methods for tropical malaria, which are based on the detection of malarial antigen. These methods are reliable, easy to perform, make it possible to detect malaria from the first hours of the disease, their time is 10 minutes.
Treatment
Benign forms of malaria (three-day, four-day and oval malaria) are treated quite easily. Chloroquine (Delagid) is recommended for their treatment.
The course of treatment for three-day and oval malaria is 3 days, for four-day malaria - 4 days.
During treatment, it is necessary to monitor the level of parasites and if after 48 hours it does not decrease, the drug or treatment regimen should be changed.
Difficulties arise in the treatment of tropical malaria.
The World Health Organization (WHO) recommends the following treatment regimens for uncomplicated malaria:
- artemether + lumefantrine,
- artesunate + amodiaquine,
- artesunate + pyrimethamine (Fansidar).
In case of severe tropical malaria and there is no effect from taking the tablets, a quinine solution is administered intravenously.
Prevention
The main measure to prevent the disease is the timely identification of a sick person.
It is also important to destroy the carriers of malaria—mosquitoes. Physical, chemical and biological methods are used to treat residential premises, areas and bodies of water. To protect against mosquito attacks, take measures to prevent insects from entering the room and use repellents.
Before visiting the sites of the disease, it is necessary to undergo a preventive course of treatment with pyrimethamine .
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