Mosquitoes, ticks and other biting arthropods, and the pathogens associated with them, causing arthropod-borne diseases, have always been the most dangerous enemies of mankind. Watching the news and browsing the internet, it seems like the situation is getting worse. In Latin America, chikungunya arrived in the winter of 2013, and quickly spread in the footsteps of dengue, utilizing Aedes aegypti as it’s perfect vector. In 2014, it was followed by Zika virus, which in addition to non-specific symptoms, is responsible for causing microcephaly and other birth defects in infected newborns, as well as Guillen-Barre syndrome in adults. In North America, West Nile virus is firmly embedded in the ecosystem, the ticks that transmit Lyme disease are expanding their range, and other tick-borne pathogens such as anaplasmosis and babeosis are expanding. In the Balkans, we have a growing problem of Lumpy Skin Disease slowly creeping up towards Eastern Europe, while African Swine Fever is attempting to invade from Russia. In Southern Europe, and the Mediterranean, we have a growing number of arboviruses and other pathogens emerging, such as chikungunya and even Plasmodium vivax emerging in Greece. Finally in Africa, despite having a vaccine available, we have the largest yellow fever outbreak of the century, threatening to spill over to distant locations such as China.
One could argue that these current outbreaks fade in comparison to the carnage that these and similar diseases (e.g. the plague) caused throughout human history. Untold millions of people were killed by the black death in Europe, yellow fever during the construction of the Panama Canal, or throughout the United States, or by malaria across Africa, Asia, and even Europe and the United States. Modern medicine and availability of vaccines has saved and is saving countless lives from arthropod-borne diseases every day, and we had made great strides toward their control and potential elimination. A recent review paper by Benelli and Mehlhorn have summarized these achievements, the emerging technologies, and the challenges and difficulties that we’re still facing. In particular, malaria caused by Plasmodium falciparum can be efficiently treated by pharmaceuticals containing artemisinin, often in combination with other chemicals, in order to stave off emerging artemisinin resistance from spreading from SE Asia. The RTS’S vaccine provides partial protection against Plasmodium falciparum in younger children, and is already being used. These interventions, along with insecticide-treated nets (ITNs), and indoor residual spraying (IRS), resulted in a 42% drop in new cases of malaria in Africa, and a 71% drop in malaria mortality rates among children under five. In terms of controlling other vector-borne diseases, the first ever dengue vaccine was licensed, and has been already taken up by several countries. We know all about how to identify and eliminate mosquito breeding sites, aided by biological or chemical control. In addition, emerging technologies such as the release of genetically engineered mosquitoes to reduce populations of Aedes aegypti populations, and releasing mosquitoes to spread Wolbachia bacteria to make the same mosquito species unable to transmit dengue, are promising a future where we don’t have to worry about mosquitoes or at least the pathogens they transmit. We do have a well-tested, safe vaccine for yellow fever which is used to immunize hundreds of millions of people. We use short courses of the right antibiotics take care of most tick-borne bacterial infections such as Lyme disease and Rocky Mountain Spotted Fever. While we don’t have antiviral drugs or specific vaccines for a number of emerging arboviral diseases, most notably chikungunya and Zika virus in the Americas, we have the technology to develop such drugs and vaccines within a year, based on existing vaccines and platforms. So one could argue that we have nothing to worry about!
However, the nature of the dangers of emerging diseases today, including those transmitted by arthropods, is different than it was in the past. Globalization and the speed and frequency at which people, livestock and goods travel has made the world substantially smaller. Human-induced climate change contributes to a shift in the distribution of some vectors, making previously unsuitable locations suitable. Urbanization in the last several hundred years created the perfect habitat for anthropophilic vectors such as Aedes aegypti to flourish, combining with ever existing poverty to create pockets of impoverished, underserved populations even within nations traditionally considered “developed”. Unfortunately, current syndromic surveillance is insufficient to rapidly detect the introduction of novel pathogens, which is further exacerbated by the lack of economic and political power of these populations. Diseases that cause even a substantial burden, such as Chagas disease, become ‘neglected’, lacking affordable drugs, vaccines and other interventions. Populations in the revolving warzones of the World (e.g. Syria, Iraq, Afganistan, etc.) are mostly left to fend for themselves, except for NGOs such as Medicines sans Frontiers, the International Red Cross and the WHO, and become havens for reemerging diseases that were successfully controlled before. Even Lyme disease, which infects 300,000 people per year across all socioeconomic strata in the northeast US, struggles for funding, as it competes with other public health priorities. Many times, existing and simple solutions do not get implemented for lack of political will to provide funding. The failure of the US Congress to provide funding for the response against Zika virus in the United States before adjourning until the fall, leaving the federal agencies in a lurch to scrimp together what they can from other sources, is a case in point. In general, public health, and specifically mosquito control, is at the whim of political decisions, and is usually the first expense to be cut in a budget crunch. Citizens are generally unaware of the importance of mosquito and disease control, or are in opposition of mosquito control for environmental or mistaken health concerns. These concerns are further amplified for any novel control method involving genetic methods, lumping them together with concerns about GMOs. From this perspective, we could argue that a confluence of social factors combine to elevate the risk of the introduction and subsequent spread of emerging or re-emerging pathogens, while novel interventions are unnecessarily delayed. Some could even argue that we should feel lucky that we’re able to keep the level of funding and control that we currently have over these diseases.
Even though these two opposing perspectives offer fundamentally different viewpoints, both of them are supported by facts and are correct at the same time. They simply reflect our messy, complicated reality in which we need to navigate. The fate of vector-borne diseases, and the outcome of our war against them, depends then on our willingness and resolve to work together to make sure that we do everything we can to combat them, within and despite the constraints provided by the environment, both natural and man-made, including our fellow citizens. We don’t have any other choice.
Please comment, and share your opinion below, I would be very interested in your responses!