Which of the following is a vector of infection?
A- A contaminated ball
B- A contaminated thermometer
C- An infected person
D- An infectious fly
Correct Response: D
An infectious fly is an example of a vector that can transmit infection. Other vectors, or nonhuman living beings that can transmit infections to humans, include mice, vermin and mosquitoes. Inanimate items that can spread infection by contact are referred to as fomites. Examples of fomites include a contaminated thermometer, balls and door knobs. An infected human being is a host according to the chain of infection and not a vector.
In recent years, the number of travelers to tropical countries has experienced great growth. These are exotic places where you can get diseases such as malaria, yellow fever or dengue, transmitted by insects that act as vectors. The adoption of some preventive measures, such as vaccination or chemoprophylaxis and the follow-up of some basic hygiene standards, is intended to ensure a happy stay for the traveler.
Tropical diseases are those predominantly infectious pathologies prevalent in countries located in the intertropical zone with poor hygienic, socio-economic and environmental conditions. These conditions allow the creation of a suitable habitat for a large number of microorganisms, vectors and reservoirs and house a large population with a great diversity of racial, genetic and cultural characteristics.
Depending on their destination, travelers may be exposed to various infectious diseases depending on the pathogens present in the area. The risk of becoming infected will depend on several factors, such as the purpose of the trip, the itinerary, the quality of accommodation, hygiene, sanitation and the behavior of the traveler. The main routes of transmission of tropical diseases are:
- Food and water: typhoid fever, cholera.
- Vectors: malaria, yellow fever.
- Animals: zoonosis (rabies, brucellosis).
It is also possible that transmission occurs through air, soil, blood or sexual contacts. However, this time we will focus on tropical vector-borne diseases and related preventive measures.
Transmitters of tropical diseases:
A vector is an organism that transmits a parasite or microorganism from one host to another. Vectors play a fundamental role in the transmission of a large number of tropical diseases. Many insects are hematophagous vectors that ingest the disease-causing microorganism while feeding on the blood of an infected host (human or animal) and subsequently injecting it into a new host at the time of another blood draw. Table 1 shows the main vectors of the diseases and the parasites that cause them.
Water plays a fundamental role in the life cycle of most vectors and the transmission of vector diseases depends on the season, as there is a direct relationship between rainfall and the presence of breeding sites. Temperature also influences, since it limits the distribution of vectors according to altitude and latitude.
Vector protection:
The best protection against tropical diseases is to prevent vectors with:
Insect repellents They are substances that are applied in the exposed areas of the skin or in clothing to avoid human contact / vector. The repellent does not kill insects. You can find natural repellents (citronella, garlic); ultrasound (pencils that emit ultra-sounds at a frequency that mimics the male mosquito's signals), of little use, since they usually emit a narrow band of frequencies that can disturb certain species, but not all. We have, finally, chemical repellents, which are the most effective. It is convenient to use those whose composition contains DEET (N, N-diethyl-m-toluamide), 3- (N-butyl-N-acetyl) -amino-ethyl propionate, permethrin or icaridin. Repellents should be applied especially during periods of the day when a bite is more likely to occur since mosquitoes, for example, are more active between dusk and dawn, while other vectors, such as ticks, are active any time. Care must be taken in the application of repellents to avoid contact with mucous membranes, they should not be applied to the face, sensitive sunburned or damaged skin or deep skin folds. In hot and humid climates it may be advisable to repeat the applications every 3-4 h. When the product is used on clothing, its effect is more lasting. In any case, it is important to strictly follow the instructions for use on the package and avoid overdosing.
Spirals against mosquitoes. They are insecticidal vaporizers that contain as an active ingredient a synthetic pyrethroid.
Aerosol sprays. They are effective in killing and killing insects and can be applied in the bedrooms before bedtime. They have a short duration effect, so it is convenient to combine them with vaporizers or mosquito nets.
Yellow fever:
Etiology. Disease caused by the yellow fever virus, an arbovirus belonging to the genus Flavivirus.
Transmission. The disease is transmitted by the bite, among others, of the Aedes aegypti mosquito during daylight hours. The vectors that cause this disease can be found in the forests of South America. The yellow fever virus infects both humans and monkeys. In jungle and forested areas, monkeys are the main reservoir of the infection and transmit the disease from monkey to monkey. Infective mosquitoes can bite humans who enter forested areas resulting in sporadic cases or small outbreaks. In urban areas, infection among humans is transmitted by mosquitoes, which leads, in nuclei with high population density, to large epidemics of yellow fever. In Africa it is common, in humid savanna areas, that mosquitoes infect both humans and monkeys, causing localized outbreaks.
Nature of the disease It is difficult to recognize in the early stages of the disease. The diagnosis is made by a blood test. Most infections cause an acute disease that develops in 2 phases: fever, muscle pain, headaches, chills, anorexia, nausea and / or vomiting, often with bradycardia. This stage evolves, after several days, to a second phase with a recurrence of fever, jaundice, abdominal pain, vomiting and hemorrhagic manifestations. Yellow fever is a disease of mandatory international declaration.
Geographical distribution. The yellow fever virus is endemic in some tropical areas of Africa and Central and South America.
Risk for the traveler. Travelers are exposed in all areas where yellow fever is endemic. The highest danger occurs in jungle and forested areas.
Prophylaxis. Vaccination is mandatory to enter some countries. Regardless of this requirement, vaccination is recommended for all travelers heading to endemic areas. It is only administered in authorized vaccination centers, where the International Certificate of Vaccination is issued. Its legal validity is 10 years after 10 days of the first dose, and immediate revaccination. When vaccination against yellow fever is contraindicated for medical reasons, it is necessary to carry a medical certificate of exemption issued in international vaccination centers.
Precautions: Avoid mosquito bites during the day and night.
Filariasis:
Etiology. This term encompasses parasitic diseases caused by nematodes of the Filarioidea family, which includes lymphatic filariasis and onchocerciasis (river blindness).
Transmission. Lymphatic filariasis is transmitted by the bite of mosquitoes of the genus Anopheles, Culex, Aedes and Mansonia, which inject larvae of the Wuchereria bancrofti nematode while "sucking blood." Onchocerciasis is transmitted by the bite of flies of the Simulium genus that inject Onchocerca volvulus.
Nature of the disease Lymphatic filariasis is a chronic parasitic disease in which adult filarias lodge in the lymphatic vessels, throwing microfilariae into the bloodstream. Symptoms include fever, lymphadenitis and retrograde lymphangitis. Lymphatic filariasis, also known as elephantiasis, is the most peculiar symptomatic form. It consists of the thickening of the skin and the underlying areas and is triggered when the parasite hinders the lymphatic system mainly affecting the lower extremities.
Onchocerciasis is a chronic parasitic disease that occurs with adult worms in fibrous nodules under the skin. These discharge microfilariae, which migrate through the skin, causing dermatitis, and reach the eye where they cause damage that leads to blindness.
Geographical distribution. Lymphatic filariasis is located in sub-Saharan Africa and in Southeast Asia. Onchocerciasis is mainly concentrated in Central West Africa and in Central and South America.
Risk for the traveler. It is low, unless there is great exposure to vectors in endemic areas.
Prophylaxis. Any.
Precautions: Avoid exposure to mosquito bites and flies.
A- A contaminated ball
B- A contaminated thermometer
C- An infected person
D- An infectious fly
Correct Response: D
An infectious fly is an example of a vector that can transmit infection. Other vectors, or nonhuman living beings that can transmit infections to humans, include mice, vermin and mosquitoes. Inanimate items that can spread infection by contact are referred to as fomites. Examples of fomites include a contaminated thermometer, balls and door knobs. An infected human being is a host according to the chain of infection and not a vector.
In recent years, the number of travelers to tropical countries has experienced great growth. These are exotic places where you can get diseases such as malaria, yellow fever or dengue, transmitted by insects that act as vectors. The adoption of some preventive measures, such as vaccination or chemoprophylaxis and the follow-up of some basic hygiene standards, is intended to ensure a happy stay for the traveler.
Tropical diseases are those predominantly infectious pathologies prevalent in countries located in the intertropical zone with poor hygienic, socio-economic and environmental conditions. These conditions allow the creation of a suitable habitat for a large number of microorganisms, vectors and reservoirs and house a large population with a great diversity of racial, genetic and cultural characteristics.
Depending on their destination, travelers may be exposed to various infectious diseases depending on the pathogens present in the area. The risk of becoming infected will depend on several factors, such as the purpose of the trip, the itinerary, the quality of accommodation, hygiene, sanitation and the behavior of the traveler. The main routes of transmission of tropical diseases are:
- Food and water: typhoid fever, cholera.
- Vectors: malaria, yellow fever.
- Animals: zoonosis (rabies, brucellosis).
It is also possible that transmission occurs through air, soil, blood or sexual contacts. However, this time we will focus on tropical vector-borne diseases and related preventive measures.
Transmitters of tropical diseases:
A vector is an organism that transmits a parasite or microorganism from one host to another. Vectors play a fundamental role in the transmission of a large number of tropical diseases. Many insects are hematophagous vectors that ingest the disease-causing microorganism while feeding on the blood of an infected host (human or animal) and subsequently injecting it into a new host at the time of another blood draw. Table 1 shows the main vectors of the diseases and the parasites that cause them.
Water plays a fundamental role in the life cycle of most vectors and the transmission of vector diseases depends on the season, as there is a direct relationship between rainfall and the presence of breeding sites. Temperature also influences, since it limits the distribution of vectors according to altitude and latitude.
Vector protection:
The best protection against tropical diseases is to prevent vectors with:
Insect repellents They are substances that are applied in the exposed areas of the skin or in clothing to avoid human contact / vector. The repellent does not kill insects. You can find natural repellents (citronella, garlic); ultrasound (pencils that emit ultra-sounds at a frequency that mimics the male mosquito's signals), of little use, since they usually emit a narrow band of frequencies that can disturb certain species, but not all. We have, finally, chemical repellents, which are the most effective. It is convenient to use those whose composition contains DEET (N, N-diethyl-m-toluamide), 3- (N-butyl-N-acetyl) -amino-ethyl propionate, permethrin or icaridin. Repellents should be applied especially during periods of the day when a bite is more likely to occur since mosquitoes, for example, are more active between dusk and dawn, while other vectors, such as ticks, are active any time. Care must be taken in the application of repellents to avoid contact with mucous membranes, they should not be applied to the face, sensitive sunburned or damaged skin or deep skin folds. In hot and humid climates it may be advisable to repeat the applications every 3-4 h. When the product is used on clothing, its effect is more lasting. In any case, it is important to strictly follow the instructions for use on the package and avoid overdosing.
Spirals against mosquitoes. They are insecticidal vaporizers that contain as an active ingredient a synthetic pyrethroid.
Aerosol sprays. They are effective in killing and killing insects and can be applied in the bedrooms before bedtime. They have a short duration effect, so it is convenient to combine them with vaporizers or mosquito nets.
Protective clothing They can be useful during the hours of the day when vectors are active.
Mosquito nets They are extraordinarily useful as a protection system while sleeping. They can be used with or without insecticide application. It is recommended to use strong nets with a mesh size of less than 1.5 mm.
Tropical vector-borne diseases:
Vector-borne diseases are considered "neglected" as they tend to mainly affect the poorest populations, residents in remote rural areas, marginal suburban neighborhoods or conflict zones in developing countries. Neglected tropical diseases affect about 1 billion people, particularly poor populations living in tropical and subtropical climate zones.
Dengue:
Etiology. Disease caused by dengue virus, a flavivirus, of which there are 4 related serotypes: Den-1, Den-2, Den-3 and Den-4.
Transmission. Through the Aedes aegypti mosquito, which bites during daytime hours.
Nature of the disease It can occur in 3 clinical forms: - Dengue fever: an acute febrile illness that manifests itself with the sudden onset of fever, followed by generalized symptoms and, sometimes, macular skin rash. Patients recover within a few days.
- Dengue hemorrhagic fever: it is characterized by the acute appearance of fever followed by other symptoms such as thrombocytopenia, an increase in vascular permeability and hemorrhagic manifestations.
- Dengue shock syndrome: it is very rare, but it has severe hypotension that requires urgent treatment to correct hypovolemia.
Geographical distribution. It extends through tropical and subtropical regions of Central and South America, Southeast and South Asia, as well as in Africa.
Risk for the traveler. The risk is high in endemic areas and in those affected by dengue epidemics.
Prophylaxis. Any.
Precautions Travelers have to take protective measures to avoid mosquito bites both during the day and at night.
Schistosomiasis (bilharziasis):
Etiology. Disease caused by several species of schistosomes, blood parasites (trematodes) among which Schistosoma mansoni, S. aponicum and S. haematobium.
Transmission. The infection is caused by contact with fresh water contaminated by larvae (cercariae) of schistosomes, which develop in snails that, in turn, become infected with the excretion of eggs in the urine or in the feces of man. The larvae penetrate the skin of people who swim in those waters.
Nature of the disease It causes chronic conditions in which adult schistosomes remain for years in the host's veins, where they produce eggs that damage those organs where they are deposited. Thus S. mansoni and S. japonicum cause liver and intestinal signs and symptoms, and S. haematobium causes urinary dysfunction.
Geographical distribution. S. mansoni is present in countries in sub-Saharan Africa, Brazil, Suriname and Venezuela. S. haematobium is found in sub-Saharan Africa and in areas of the eastern Mediterranean.
Risk for the traveler. In endemic areas, travelers are exposed when swimming or wading in freshwater.
Prophylaxis. Any.
Precautions Avoid direct contact with potentially contaminated fresh water in endemic areas. If accidental exposure occurs, the skin should be dried vigorously to reduce penetration of the cercariae.
Yellow fever:
Etiology. Disease caused by the yellow fever virus, an arbovirus belonging to the genus Flavivirus.
Transmission. The disease is transmitted by the bite, among others, of the Aedes aegypti mosquito during daylight hours. The vectors that cause this disease can be found in the forests of South America. The yellow fever virus infects both humans and monkeys. In jungle and forested areas, monkeys are the main reservoir of the infection and transmit the disease from monkey to monkey. Infective mosquitoes can bite humans who enter forested areas resulting in sporadic cases or small outbreaks. In urban areas, infection among humans is transmitted by mosquitoes, which leads, in nuclei with high population density, to large epidemics of yellow fever. In Africa it is common, in humid savanna areas, that mosquitoes infect both humans and monkeys, causing localized outbreaks.
Nature of the disease It is difficult to recognize in the early stages of the disease. The diagnosis is made by a blood test. Most infections cause an acute disease that develops in 2 phases: fever, muscle pain, headaches, chills, anorexia, nausea and / or vomiting, often with bradycardia. This stage evolves, after several days, to a second phase with a recurrence of fever, jaundice, abdominal pain, vomiting and hemorrhagic manifestations. Yellow fever is a disease of mandatory international declaration.
Geographical distribution. The yellow fever virus is endemic in some tropical areas of Africa and Central and South America.
Risk for the traveler. Travelers are exposed in all areas where yellow fever is endemic. The highest danger occurs in jungle and forested areas.
Prophylaxis. Vaccination is mandatory to enter some countries. Regardless of this requirement, vaccination is recommended for all travelers heading to endemic areas. It is only administered in authorized vaccination centers, where the International Certificate of Vaccination is issued. Its legal validity is 10 years after 10 days of the first dose, and immediate revaccination. When vaccination against yellow fever is contraindicated for medical reasons, it is necessary to carry a medical certificate of exemption issued in international vaccination centers.
Precautions: Avoid mosquito bites during the day and night.
Filariasis:
Etiology. This term encompasses parasitic diseases caused by nematodes of the Filarioidea family, which includes lymphatic filariasis and onchocerciasis (river blindness).
Transmission. Lymphatic filariasis is transmitted by the bite of mosquitoes of the genus Anopheles, Culex, Aedes and Mansonia, which inject larvae of the Wuchereria bancrofti nematode while "sucking blood." Onchocerciasis is transmitted by the bite of flies of the Simulium genus that inject Onchocerca volvulus.
Nature of the disease Lymphatic filariasis is a chronic parasitic disease in which adult filarias lodge in the lymphatic vessels, throwing microfilariae into the bloodstream. Symptoms include fever, lymphadenitis and retrograde lymphangitis. Lymphatic filariasis, also known as elephantiasis, is the most peculiar symptomatic form. It consists of the thickening of the skin and the underlying areas and is triggered when the parasite hinders the lymphatic system mainly affecting the lower extremities.
Onchocerciasis is a chronic parasitic disease that occurs with adult worms in fibrous nodules under the skin. These discharge microfilariae, which migrate through the skin, causing dermatitis, and reach the eye where they cause damage that leads to blindness.
Geographical distribution. Lymphatic filariasis is located in sub-Saharan Africa and in Southeast Asia. Onchocerciasis is mainly concentrated in Central West Africa and in Central and South America.
Risk for the traveler. It is low, unless there is great exposure to vectors in endemic areas.
Prophylaxis. Any.
Precautions: Avoid exposure to mosquito bites and flies.
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