Dengue fever was on the rise again in Sri Lanka and then along came Covid19

nb; updates in red

In 2017 a major dengue epidemic swept through Sri Lanka resulting in 186.000 cases and 302 deaths. Although the number of cases fell back, somewhat in 2018, the overall the trend of new cases is upwards. 2019 saw the second highest number of cases ever recorded, topping 100,000 and it is beginning to look like Dengue is running out of control once more. Already in January 2020 there have been over 9500 recorded cases, nearly double the figure for January 2019, and it looked like  new epidemics were emerging in Trincomalee and Batticaloa.

And then.. along came the COVID 19 pandemic and everything changed. The number of new cases dropped dramatically. In 2020 there were just 30,807 reported cases. and 2021 has started off at much lower levels than expected.

A closer look at the data

In 2015, the number of recorded cases of dengue fever dropped below 30,000. There was cautious optimism that Sri Lanka was beginning to win the war against dengue fever. That optimism was misplaced. 2016 saw the figures jump to over 55,000, a new high. Then came 2017,  with 186,101 recorded cases: an epidemic!

Leaving aside 2017, was 2018 any better? The simple answer is yes it was to a degree; 51,659 cases were recorded. However, in 2019 the situation has reversed. At the close of the year the number of cases had rocketed to 103,362

A measure of progress would be for the number of cases to fall for two consecutive years. The last time that happened was the period 2009 – 2011.

As the chart below shows

• good years (fewer cases) are usually followed by bad years
• confirmation that the overall trend is upwards

What no-one could predict was that there would be a pandemic the like of which we haven’t seen for around 100 years and that has really changed the picture. Just over 30,000 cases in 2020 and possibly similar in 2021. Does that mean dengue is under control? Why has the number of cases dropped so dramatically? Are we seeing the impact of curfew/lockdown working through? If people are staying indoors does that have an impact on the transmission of the virus? Or is it simply that given this new health threat cases of dengue fever are  under-reported?

Lots of questions and, as yet few answers given the problems in getting any kind of response to emails from medics. However, one of my Sri Lankan friends suggested that a key factor in the transmission of dengue may be that children may be important vectors. During the pandemic they have not been allowed out into garden areas play areas etc and with less mixing of children fewer children have become infected.. Worth a thought?

Old hotspots and new hotspots.

1. Repeat offenders. Colombo, Gampaha and Kalutara  (all in Western Province) Kurunegala, Kandy and Ratnapura always seem to have a high number of cases in comparison with the rest of the country.  The South West of the island regularly accounts for over 35% of cases, sometimes more. There are a number of reasons why.

• this is where the largest number of people live;  (5.8 million  or 27% of the population) more people = more cases)
• population densities are highest
• the province is the most urbanised
• the climate which is humid all year round is conducive to high mosquito populations

And since 2010  Jaffna has seen  an increasing number of cases culminating in over 8000 in 2019. This could be due to a number of reasons:

• water stored in uncovered containers during the dry season seems to have been the culprit, although this begs the question of why those inhabitants have restricted access to mains water.
• Since the end of the civil war in 2009 Jaffna has opened up to trade with increasing flows of people visiting the area especially to and from the south where dengue is endemic bringing with them the virus.
• Increasing re-development means more building sites which are ideal breeding grounds for mosquitos.

2.  Changing Hotspots

Other urban centres feature  as hotspots from time to time

1. Batticaloa in 2011 2015 and 2018 and now in 2020
2. Matara in 2012 and 2019
3. Galle in 2016 and 2019

The question is why is this  pattern  occurring? The answer is probably not simple one. For each town there are probably specific local circumstances that need to be taken into account.

In Batticaloa the building boom has been targeted as the source of the mini epidemics the town suffered. (Building sites are notorious breeding grounds for mosquitos)

In Galle and Matara the recent spikes in the number of cases has been blamed on a longer than average monsoon period and associated humid conditions.

Knowing the total number of cases per district is useful from a planning point of view for the authorities healthcare professionals. However, it is obvious that the bigger the population, in all likelihood, the greater the number of cases.

For a more accurate comparison of districts, and to get a clearer picture of the prevalence of dengue across Sri Lanka we can use a different measure; number of cases per thousand of the population. When we do this we see a slightly different picture.

 

Area	Population	2017	2018	2019	2020
Colombo	2324,349	14.9	4.41	8.7	1.82
Gampaha	2304833	13.7	2.49	6.8	1.1
Kalutara	1221948	9	2.53	6.5	1.4
Kandy	1375382	10.7	2.78	6.4	2.48
Matale	484531	6.5	1.87	4.8	1,22
Nuwara Eliya	711644	1.3	0.29	0.6	0.24
Galle	1063334	6	0.90	6.5	1.56
Hambantota	599903	6	1.82	3.3	0.61
Matara	814048	7.8	1.40	4.9	0.67
Jaffna	583882	10.4	6.95	13.5	3.69
Kilinochchi	113510	5	3.02	3.3	1.19
Mannar	99570	5.4	2.20	2.4	1.38
Vavuniya	172115	6.2	3.42	4.7	1.46
Mulativu	92238	4.2	1.23	2.6	0.94
Batticaloa	526,567	10.6	9.19	4.8	6.78
Ampara	649402	1.4	0.36	0.6	0.49
Trincomalee	379541	13.2	2.94	6.9	6.02
Kurunegala	1818465	6.2	1.34	1.7	0.53
Puttalam	762396	10.3	2.64	2.8	0.65
Anuradhapura	860575	3.4	1.00	1.3	0.5
Polonnaruwa	406088	3.5	0.79	1.3	0.6
Badulla	815405	4.5	0.75	2.3	0.61
Moneragala	451058	7.2	1.89	0.7	0
Ratnapura	1088007	10.4	2.04	3.6	1.81
Kegalle	840648	11.4	1.82	3.2	1.03
Kalmunai	106780	28.4	16.47	12.9	9.18
average		8.5	0.64		1.4

Prevalance of cases per 000 of the population

Patterns

1. The expected pattern of highest prevalence in Western Province is not quite as strong as one might suppose although prevalence is still on the high side as might be expected, given the high population density and  relatively high level of urbanisation.
   • Colombo is falling down the order; so in 2020 it was 6th highest 
   • Gamapaha is way down at 15th on the list in 2020
2. The hotspots in 2019 were, Jaffna, Kalmunai, Colombo Trincomalee and Gampaha in that order
3. In 2020 only three places stand out; Kalmunai, Trincomalee and Batticaloa. Early in there year it looked like there was a problem in Jaffna but cases declined in the second half of the year.

note: Already in January 2021, Batticaloa has had around 700 cases. No other centre has anywhere near that number. So someone needs to ask why the number of dengue cases remaining high in Batticaloa when they are way down everywhere else except Kalmunai?

Kalmunai is an interesting one because it is so different from Ampara where it is located. Prevalence is always high it seems. Again it is worth asking the question why.

Dengue had been on the rise again but who or what was to blame?

The Monsoon

Generally speaking, the longer and wetter the monsoon periods in Sri Lanka lead to increased numbers of cases. Mosquitos breed most rapidly in wet conditions which are found particularly in Western Province during both the May – June monsoon and the the inter-monsoon (October/November). As NDCU Director, Anura Jayasekara pointed out recently, this year the monsoon gone on a month longer.

Whilst that works for Western province and Kandy it doesn’t explain the spike in cases in Jaffna. So wetter weather is one factor.

Virus Mutation

Another factor is the virus itself

There are 4 strains of dengue each of which can mutate.. so every few years a new strain emerges to which people have no immunity to.. and this has a major impact

According to National Dengue Control Unit’s Director, Dr Anura Jayasekara, a new dengue strain a previously latent serotype 3 (DENV3) becoming active.is circulating this year in Sri Lanka. This is a different strain than during the 2017 outbreak which was caused by the emergence of serotype2 (DENV2).

So, a variance in the monsoon pattern and the emergence of a previously latent strain of the dengue virus are two factors which can explain why the number of cases is on the rise. However, the monsoon does not cause dengue fever and neither is the virus itself the main cause of the rise in cases, although it is obviously a contributory factor.

Viruses spread by some form of vector and in this case it is the mosquito. Blaming the weather and pointing to the emergence of new virus strains ignores the fact that if there were no mosquitos to spread the virus there would be no dengue fever.

Failure to deal with the mosquito; the vector

The dengue mosquito is an urban creature. It breeds where there are sites which store or trap even small amounts of water; see below.

Construction sites industrial premises, school yards and gardens all provide ideal breeding grounds for the aedes mosquito. So do the piles of discarded trash that are simply dumped and left to slowly rot on the streets of urban areas like Colombo.

A major problem is the apathetic public attitude towards dengue fever. Individuals, businesses and institutions simply do not do enough to keep areas clear of potential breeding sites. Fogging is a useful tool in controlling mosquito populations but reliance on this one means of defence has shown to be not enough.

Part of the reason for public apathy is that existing laws are not strictly enforced. However, would it make much difference when piles of rubbish are left unattended and uncleared in the streets of many towns?

Control programmes appear to have been scaled down. Between 2014 and 2016 there was a programme in place to identify and remove mosquito breeding sites. This was a public health, police and military partnership which it is claimed led to a 50% reduction in dengue cases.

( see https://www.sciencedaily.com/releases/2019/06/190605134854.htm ) for a review of the report in Science Daily)

However, this was discontinued and we can see what has happened to the number of dengue cases since. Reducing the number of dengue cases should be at the top of the government’s priority list.

• It would  save lives.
• It would reduce costs on an already over burdened health service
• It would reduce the number of days lost to work through illness.

A concerted programme of mosquito control makes sense on every level. But whilst it can be argued that the authorities can and should be doing more it is fundamentally down to the general public, to the schools, construction companies to recognise their role and take greater responsibility for tackling the mosquito menace

In country which has eradicated malaria (also a mosquito vector disease) it seems hard to understand why the same is not happening where dengue fever is concerned.

Conclusion

Maybe the problem lies in a  general public acceptance of dengue fever. It is convenient to last all of the blame at the door of municipal councils, health authorities and the government. However, there is a limit to what the authorities can achieve if the general public do not adopt a responsible attitude to the control of mosquito breeding sites. In short it isn’t the government’s problem it is everyone’s problem. The re-establishment of a centrally directed task force is probably necessary. A strict enforcement of existing laws, ensuring no individuals or organisations can get around those laws would also help. Education at all levels, and a continued repetition of key messages, might have an impact on the public.

And it is down to local communities to engage and take control of the clearance of mosquito breeding sites, not to wait around got the authorities to do it for them

Dengue can’t in all probability be eradicated BUT it can be held in check. Dengue is present in Singapore, but even though urban population densities are high, higher than in Sri Lanka, overall the incidence is much lower. In 2091 there were around 17,000 cases. The reason?

• Dengue awareness is much higher; check out this website for example

https://www.nea.gov.sg/dengue-zika/dengue/dengue-community-alert-system

• Construction sites which are shown to be negligent are issued with stop work orders and the companies are publicly named
• Households are regularly inspected and enforcement actions are taken against individual households whee breeding sites are found
• fogging is routine and takes place twice weekly
• people take the threat of dengue seriously; anti mosquito messages are everywhere and vigilance is much higher see below

1. 

• organisations and individuals are publicly accountable

Something needs to change in Sri Lanka. For now the Covid pandemic is giving Sri Lanka a respite (of sorts) from the misery of dengue, but at sown point the effects of the pandemic will begin to wane and when they do there is a very real possibility that dengue fever will re-emerge.