Zoonotic diseases are diseases that can be transmitted between animals and humans. These diseases can be caused by bacteria, viruses, fungi, parasites or other infectious agents. Transmission of these diseases can occur through direct contact with infected animals, ingestion of contaminated food, inhalation of aerosols or respiratory droplets, or via vectors such as mosquitoes or ticks.
Beyond the serious implications for human and animal health, it is important to understand the wider impact of zoonotic diseases and other infectious diseases on global health. According to the World Health Organization (WHO), almost 16 per cent of deaths worldwide are attributed to infectious diseases. This highlights the importance of addressing these diseases comprehensively and taking proactive measures to prevent their spread and control their impact on public health.
Some of the diseases we encounter are:
· Dengue: Dengue is a viral disease transmitted mainly by mosquitoes of the genus Aedes, such as Aedes aegypti or Aedes albopictus (tiger mosquito). The disease is endemic in tropical and subtropical areas of the world, where the mosquitoes that transmit it can be found in abundance.
In more severe cases, known as severe dengue or dengue haemorrhagic fever, the disease can cause potentially fatal complications such as severe bleeding and shock. It is therefore crucial to seek medical attention if you experience dengue symptoms and live in an area where the disease is common.
The Southern Cone of America is currently facing one of the worst dengue epidemics in recent history, with more than 4.2 million cases reported in the first three months of 2024 and, sadly, more than 1,200 related deaths. Faced with this public health challenge, scientists and health experts are working hard to find new tools and strategies to help prevent and combat the spread of this devastating disease.
In Brazil, public researchers have devised a revolutionary technique that uses the dengue-transmitting mosquito itself, Aedes aegypti, as a "Trojan horse" to exterminate larvae and thus reduce the population of infected mosquitoes. This innovative strategy, developed by the Fiocruz Institute and led by Professor Rodrigo Gurgel of the University of Brasilia, is based on the concept of "Larvicide Dissemination Stations (EDL)".
How does this strategy work? EDLs are traps designed with a special attractant for Aedes aegypti mosquitoes. These traps, which resemble black buckets, contain a cloth impregnated with pyriproxyfen, a highly effective larvicide. The mosquitoes, attracted by the water and the black colour of the container, come to the traps and land on the impregnated cloth. In doing so, they become contaminated with the larvicide, which adheres to their bodies.
Herein lies the genius of the strategy: as the mosquitoes move to other areas in search of new larval breeding sites, they carry the larvicide with them. On contact with the water at these new sites, the pyriproxyfen dissolves, acting as a lethal agent for Aedes aegypti larvae without harming other non-target organisms. Essentially, the mosquitoes themselves become carriers of the larvicide, taking the solution to the places where it is most needed.
This approach represents a significant step in the fight against dengue and other mosquito-borne diseases. By harnessing the natural behaviour of mosquitoes, an effective reduction in the Aedes aegypti population can be achieved and, consequently, in the spread of the dengue virus. Moreover, this strategy is environmentally friendly and offers a promising alternative to traditional vector control methods.
· Avian influenza: Avian influenza, also called bird flu, is a viral disease that mainly affects birds but can be transmitted to humans and other mammals. It is highly contagious and can have serious consequences for the poultry industry and public health.
Transmission occurs mainly through direct contact with contaminated secretions or faeces, as well as through contact with contaminated surfaces. In humans, symptoms range from mild to severe respiratory complications and even death. Although bird-to-human transmission is rare, there is a risk that the virus could mutate and become more transmissible between humans, triggering a pandemic.
To prevent its spread, biosecurity measures are applied on poultry farms, along with vaccination campaigns in high-risk birds and active surveillance to detect outbreaks and respond quickly. It is also crucial to educate the population about proper hygiene and to promote early detection of suspected cases.
- Recently, the World Health Organization (WHO) confirmed a case of avian influenza (H5N1) in a man in Texas, United States. This individual had been exposed to dairy cattle presumed to be infected with the virus. The young man, who is recovering, experienced eye redness, suggesting conjunctivitis, as his only symptom.
Human infections with avian influenza A viruses, including A(H5N1) viruses, are uncommon but can occur sporadically around the world. However, this case is particularly notable, as it appears to be the first human A(H5N1) infection acquired through contact with an infected mammal. Although human infections with other influenza subtypes acquired via mammals have been recorded, this situation is unique.
To date, no additional cases of human infection associated with this particular event have been identified. The WHO stresses that this is the first time a human A(H5N1) infection acquired through contact with infected cattle has been confirmed.
- The National Veterinary Services Laboratory has identified a new case of avian influenza in a dairy herd in North Carolina, marking a milestone in an outbreak that has already affected six states of the United States. This incident, which adds to a series of earlier positives, raises concerns about animal health and food safety, as well as about possible transmission to humans.
The first cases were identified through unpasteurised clinical milk samples from sick cattle on farms in Kansas and Texas, where dead wild birds were also found, suggesting a possible transmission route. Since then, up to twenty cases have been confirmed, with Texas being the worst-affected state.
Federal agencies are working closely with the industry to encourage rapid reporting of livestock illnesses, thereby minimising the impact on farmers, consumers and other animals. Although only 10% of the cattle on the affected farms show symptoms, such as reduced production and loss of appetite, the authorities state that the loss of milk will not have a significant impact on supply or prices.